Etabs Concrete Frame Design

Computers and Structures, Inc.Berkeley, California, USA

Version 8January 2002

ETABS®

Integrated Building Design Software

Concrete Frame Design Manual

Copyright Computers and Structures, Inc., 1978-2002.The CSI Logo is a trademark of Computers and Structures, Inc.

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The computer program ETABS and all associated documentation are proprietary andcopyrighted products. Worldwide rights of ownership rest with Computers andStructures, Inc. Unlicensed use of the program or reproduction of the documentation inany form, without prior written authorization from Computers and Structures, Inc., isexplicitly prohibited.

Further information and copies of this documentation may be obtained from:

Computers and Structures, Inc.1995 University Avenue

Berkeley, California 94704 USA

Phone: (510) 845-2177FAX: (510) 845-4096

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DISCLAIMER

CONSIDERABLE TIME, EFFORT AND EXPENSE HAVE GONE INTO THEDEVELOPMENT AND DOCUMENTATION OF ETABS. THE PROGRAM HASBEEN THOROUGHLY TESTED AND USED. IN USING THE PROGRAM,HOWEVER, THE USER ACCEPTS AND UNDERSTANDS THAT NO WARRANTYIS EXPRESSED OR IMPLIED BY THE DEVELOPERS OR THE DISTRIBUTORSON THE ACCURACY OR THE RELIABILITY OF THE PROGRAM.

THIS PROGRAM IS A VERY PRACTICAL TOOL FOR THE DESIGN/CHECK OFCONCRETE STRUCTURES. HOWEVER, THE USER MUST THOROUGHLY READTHE MANUAL AND CLEARLY RECOGNIZE THE ASPECTS OF CONCRETEDESIGN THAT THE PROGRAM ALGORITHMS DO NOT ADDRESS.

THE USER MUST EXPLICITLY UNDERSTAND THE ASSUMPTIONS OF THEPROGRAM AND MUST INDEPENDENTLY VERIFY THE RESULTS.

i

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA DECEMBER 2001

CONCRETE FRAME DESIGN

Contents

General Concrete Frame Design Information

1 General Design InformationDesign Codes 1-1Units 1-1Overwriting the Frame Design Procedure for a Con-

crete Frame1-1

Design Load Combinations 1-2Design of Beams 1-2Design of Columns 1-3Beam/Column Flexural Capacity Ratios 1-4Second Order P-Delta Effects 1-4Element Unsupported Lengths 1-6Analysis Sections and Design Sections 1-7

2 Concrete Frame Design ProcessConcrete Frame Design Procedure 2-1

3 Interactive Concrete Frame DesignGeneral 3-1Concrete Design Information Form 3-1

4 Output Data Plotted Directly on the ModelOverview 4-1Using the Print Design Tables Form 4-1Design Input 4-2Design Output 4-2


ii

Concrete Frame Design Specific to UBC97

5 General and NotationIntroduction to the UBC 97 Series of Technical Notes 5-1Notation 5-2

6 PreferencesGeneral 6-1Using the Preferences Form 6-1Preferences 6-2

7 OverwritesGeneral 7-1Overwrites 7-1Making Changes in the Overwrites Form 7-3Resetting Concrete Frame Overwrites to Default

Values7-4

8 Design Load Combinations

9 Strength Reduction Factors

10 Column DesignOverview 10-1Generation of Biaxial Interaction Surfaces 10-2Calculate Column Capacity Ratio 10-5

Determine Factored Moments and Forces 10-6Determine Moment Magnification Factors 10-6Determine Capacity Ratio 10-8

Required Reinforcing Area 10-10Design Column Shear Reinforcement 10-10

Determine Required Shear Reinforcement 10-14Reference 10-15

11 Beam DesignOverview 11-1Design Beam Flexural Reinforcement 11-1

Determine Factored Moments 11-2Determine Required Flexural Reinforcement 11-2

Contents

iii

Design Beam Shear Reinforcement 11-10

12 Joint DesignOverview 12-1Determine the Panel Zone Shear Force 12-1Determine the Effective Area of Joint 12-5Check Panel Zone Shear Stress 12-5Beam/Column Flexural Capacity Ratios 12-6

13 Input DataInput data 13-1Using the Print Design Tables Form 13-3

14 Output DetailsUsing the Print Design Tables Form 14-3

Concrete Frame Design Specific to ACI-318-99

15 General and NotationIntroduction to the ACI318-99 Series of Technical

Notes15-1

Notation 15-2

16 PreferencesGeneral 16-1Using the Preferences Form 16-1Preferences 16-2

17 OverwritesGeneral 17-1Overwrites 17-1Making Changes in the Overwrites Form 17-3Resetting Concrete Frame Overwrites to Default

Values17-4

18 Design Load Combinations

19 Strength Reduction Factors


iv

20 Column DesignOverview 20-1Generation of Biaxial Interaction Surfaces 20-2Calculate Column Capacity Ratio 20-5

Determine Factored Moments and Forces 20-6Determine Moment Magnification Factors 20-6Determine Capacity Ratio 20-9

Required Reinforcing Area 20-10Design Column Shear Reinforcement 20-10

Determine Section Forces 20-11Determine Concrete Shear Capacity 20-12Determine Required Shear Reinforcement 20-13

References 20-15

21 Beam DesignOverview 21-1Design Beam Flexural Reinforcement 21-1

Determine Factored Moments 21-2Determine Required Flexural Reinforcement 21-2Design for T-Beam 21-5Minimum Tensile Reinforcement 21-8Special Consideration for Seismic Design 21-8

Design Beam Shear Reinforcement 21-9Determine Shear Force and Moment 21-11Determine Concrete Shear Capacity 21-12Determine Required Shear Reinforcement 21-13

22 Joint DesignOverview 22-1Determine the Panel Zone Shear Force 22-1Determine the Effective Area of Joint 22-4

Check Panel Zone Shear Stress 22-4Beam/Column Flexural Capacity Ratios 22-6

23 Input DataInput Data 23-1Using the Print Design Tables Form 23-3

Contents

v

24 Output DetailsUsing the Print Design Tables Form 24-3

Design Codes Technical Note 1 - 1

©COMPUTERS AND STRUCTURES, INC., BERKELEY, CALIFORNIA JANUARY 2002


Technical Note 1General Design Information

This Technical Note presents some basic information and concepts helpfulwhen performing concrete frame design using this program.

Design CodesThe design code is set using the Options menu > Preferences > ConcreteFrame Design command. You can choose to design for any one design codein any one design run. You cannot design some elements for one code andothers for a different code in the same design run. You can, however, performdifferent design runs using different design codes without rerunning theanalysis.

UnitsFor concrete frame design in this program, any set of consistent units can beused for input. You can change the system of units at any time. Typically, de-sign codes are based on one specific set of units.

Overwriting the Frame Design Procedure for a ConcreteFrameThe two design procedures possible for concrete beam design are:

Concrete frame design

No design

If a line object is assigned a frame section property that has a concrete ma-terial property, its default design procedure is Concrete Frame Design. A con-crete frame element can be switched between the Concrete Frame Design andthe "None" design procedure. Assign a concrete frame element the "None"design procedure if you do not want it designed by the Concrete Frame De-sign postprocessor.

General Design Information Concrete Frame Design

Technical Note 1 - 2 Design Load Combinations

Change the default design procedure used for concrete frame elements byselecting the element(s) and clicking Design menu > Overwrite FrameDesign Procedure. This change is only successful if the design procedureassigned to an element is valid for that element. For example, if you select aconcrete element and attempt to change the design procedure to Steel FrameDesign, the program will not allow the change because a concrete elementcannot be changed to a steel frame element.

Design Load CombinationsThe program creates a number of default design load combinations for con-crete frame design. You can add in your own design load combinations. Youcan also modify or delete the program default load combinations. An unlim-ited number of design load combinations can be specified.

To define a design load combination, simply specify one or more load cases,each with its own scale factor. For more information see Concrete Frame De-sign UBC97 Technical Note 8 Design Load Combination and Concrete FrameDesign ACI 318-99 Technical Note 18 Design Load Combination.

Design of BeamsThe program designs all concrete frame elements designated as beam sec-tions in their Frame Section Properties as beams (see Define menu >FrameSections command and click the Reinforcement button). In the design ofconcrete beams, in general, the program calculates and reports the requiredareas of steel for flexure and shear based on the beam moments, shears, loadcombination factors, and other criteria, which are described in detail in Con-crete Frame UBC97 Technical Note Beam Design 11 and Concrete Frame ACI318-99 Technical Note 21 Beam Design. The reinforcement requirements arecalculated at each output station along the beam span.

All the beams are designed for major direction flexure and shear only.Effects resulting from any axial forces, minor direction bending, andtorsion that may exist in the beams must be investigated independ-ently by the user.

In designing the flexural reinforcement for the major moment at a particularsection of a particular beam, the steps involve the determination of themaximum factored moments and the determination of the reinforcing steel.

Concrete Frame Design General Design Information

Design of Beams Technical Note 1 - 3

The beam section is designed for the maximum positive and maximum nega-tive factored moment envelopes obtained from all of the load combinations.Negative beam moments produce top steel. In such cases, the beam is al-ways designed as a rectangular section. Positive beam moments producebottom steel. In such cases, the beam may be designed as a rectangular- orT-beam. For the design of flexural reinforcement, the beam is first designedas a singly reinforced beam. If the beam section is not adequate, the requiredcompression reinforcement is calculated.

In designing the shear reinforcement for a particular beam for a particular setof loading combinations at a particular station resulting from the beam majorshear, the steps involve the determination of the factored shear force, thedetermination of the shear force that can be resisted by concrete, and thedetermination of the reinforcement steel required to carry the balance.

Design of ColumnsThe program designs all concrete frame elements designated as column sec-tions in their Frame Section Properties as columns (see Define menu>Frame Sections command and click the Reinforcement button). In thedesign of the columns, the program calculates the required longitudinal steel,or if the longitudinal steel is specified, the column stress condition is reportedin terms of a column capacity ratio. The capacity ratio is a factor that gives anindication of the stress condition of the column with respect to the capacity ofthe column. The design procedure for reinforced concrete columns involvesthe following steps:

Generate axial force-biaxial moment interaction surfaces for all of the dif-ferent concrete section types of the model.

Check the capacity of each column for the factored axial force and bendingmoments obtained from each load combination at each end of the column.This step is also used to calculate the required reinforcement (if none wasspecified) that will produce a capacity ratio of 1.0.

Design the column shear reinforcement.

The shear reinforcement design procedure for columns is very similar to thatfor beams, except that the effect of the axial force on the concrete shear ca-pacity needs to be considered. See Concrete Frame UBC97 Technical Note 10


Technical Note 1 - 4 Second Order P-Delta Effects

Column Design and Concrete Frame ACI 318-99 Technical Note 20 ColumnDesign for more information.

Beam/Column Flexural Capacity RatiosWhen the ACI 318-99 or UBC97 code is selected, the program calculates theratio of the sum of the beam moment capacities to the sum of the columnmoment capacities at a particular joint for a particular column direction, ma-jor or minor. The capacities are calculated with no reinforcing overstrengthfactor, α, and including ϕ factors. The beam capacities are calculated for re-versed situations and the maximum summation obtained is used.

The moment capacities of beams that frame into the joint in a direction that isnot parallel to the major or minor direction of the column are resolved alongthe direction that is being investigated and the resolved components areadded to the summation.

The column capacity summation includes the column above and the columnbelow the joint. For each load combination, the axial force, Pu, in each of thecolumns is calculated from the program analysis load combinations. For eachload combination, the moment capacity of each column under the influence ofthe corresponding axial load Pu is then determined separately for the majorand minor directions of the column, using the uniaxial column interaction dia-gram. The moment capacities of the two columns are added to give the ca-pacity summation for the corresponding load combination. The maximum ca-pacity summations obtained from all of the load combinations is used for thebeam/column capacity ratio.

The beam/column flexural capacity ratios are only reported for Special Mo-ment-Resisting Frames involving seismic design load combinations.

See Beam/Column Flexural Capacity Ratios in Concrete Frame UBC97 Techni-cal Note 12 Joint Design or in Concrete Frame ACI 318-99 Technical Note 22Joint Design for more information.

Second Order P-Delta EffectsTypically, design codes require that second order P-Delta effects be consid-ered when designing concrete frames. The P-Delta effects come from twosources. They are the global lateral translation of the frame and the local de-formation of elements within the frame.


Second Order P-Delta Effects Technical Note 1 - 5

Consider the frame element shown in Figure 1, which is extracted from astory level of a larger structure. The overall global translation of this frameelement is indicated by ∆. The local deformation of the element is shown as δ.The total second order P-Delta effects on this frame element are those causedby both ∆ and δ.

The program has an option to consider P-Delta effects in the analysis. Con-trols for considering this effect are found using the Analyze menu > SetAnalysis Options command and then clicking the Set P-Delta Parametersbutton. When you consider P-Delta effects in the analysis, the program does agood job of capturing the effect due to the ∆ deformation shown in Figure 1,but it does not typically capture the effect of the δ deformation (unless, in themodel, the frame element is broken into multiple pieces over its length).

In design codes, consideration of the second order P-Delta effects is generallyachieved by computing the flexural design capacity using a formula similar tothat shown in Equation. 1.

MCAP = aMnt + bMlt Eqn. 1

where,

MCAP = Flexural design capacity

∆

δ

Original position of frameelement shown by verticalline

Position of frame elementas a result of global lateraltranslation, ∆, shown bydashed line

Final deflected position offrame element thatincludes the global lateraltranslation, ∆, and thelocal deformation of theelement, δ

Figure 1: The Total Second Order P-Delta Effects on a Frame ElementCaused by Both ∆∆∆∆ and δδδδ


Technical Note 1 - 6 Element Unsupported Lengths

Mnt = Required flexural capacity of the member assuming there isno translation of the frame (i.e., associated with the δ defor-mation in Figure 1)

Mlt = Required flexural capacity of the member as a result of lateraltranslation of the frame only (i.e., associated with the ∆ de-formation in Figure 1)

a = Unitless factor multiplying Mnt

b = Unitless factor multiplying Mlt (assumed equal to 1 by theprogram; see below)

When the program performs concrete frame design, it assumes that the factorb is equal to 1 and it uses code-specific formulas to calculate the factor a.That b = 1 assumes that you have considered P-Delta effects in the analysis,as previously described. Thus, in general, if you are performing concreteframe design in this program, you should consider P-Delta effects in theanalysis before running the design.

Element Unsupported LengthsThe column unsupported lengths are required to account for column slender-ness effects. The program automatically determines these unsupportedlengths. They can also be overwritten by the user on an element-by-elementbasis, if desired, using the Design menu > Concrete Frame Design >View/Revise Overwrites command.

There are two unsupported lengths to consider. They are L33 and L22, asshown in Figure 2. These are the lengths between support points of the ele-ment in the corresponding directions. The length L33 corresponds to instabilityabout the 3-3 axis (major axis), and L22 corresponds to instability about the2-2 axis (minor axis). The length L22 is also used for lateral-torsional bucklingcaused by major direction bending (i.e., about the 3-3 axis).

In determining the values for L22 and L33 of the elements, the program recog-nizes various aspects of the structure that have an effect on these lengths,such as member connectivity, diaphragm constraints and support points. Theprogram automatically locates the element support points and evaluates thecorresponding unsupported length.


Analysis Sections and

Figure 2: Major

It is possible foby the programple, assume a cother, at a floorone direction ondirection will ex

Analysis SeAnalysis sectionwhen you click section is whatenated the curren

Tip:

It is important to utions.

Design Sections Technical Note 1 - 7

and Minor Axes of Bending

r the unsupported length of a frame element to be evaluated as greater than the corresponding element length. For exam-olumn has a beam framing into it in one direction, but not the level. In this case, the column is assumed to be supported inly at that story level, and its unsupported length in the other

ceed the story height.

ctions and Design Sectionss are those section properties used to analyze the modelthe Analyze menu > Run Analysis command. The designver section has most currently been designed and thus desig-t design section.

nderstand the difference between analysis sections and design sec-


Technical Note 1 - 8 Analysis Sections and Design Sections

It is possible for the last used analysis section and the current design sectionto be different. For example, you may have run your analysis using a W18X35beam and then found in the design that a W16X31 beam worked. In thatcase, the last used analysis section is the W18X35 and the current designsection is the W16X31. Before you complete the design process, verify thatthe last used analysis section and the current design section are the same.The Design menu > Concrete Frame Design > Verify Analysis vs De-sign Section command is useful for this task.

The program keeps track of the analysis section and the design sectionseparately. Note the following about analysis and design sections:

Assigning a beam a frame section property using the Assign menu >Frame/Line > Frame Section command assigns the section as both theanalysis section and the design section.

Running an analysis using the Analyze menu > Run Analysis command(or its associated toolbar button) always sets the analysis section to be thesame as the current design section.

Assigning an auto select list to a frame section using the Assign menu >Frame/Line > Frame Section command initially sets the design sectionto be the beam with the median weight in the auto select list.

Unlocking a model deletes the design results, but it does not delete orchange the design section.

Using the Design menu > Concrete Frame Design > Select DesignCombo command to change a design load combination deletes the designresults, but it does not delete or change the design section.

Using the Define menu > Load Combinations command to change a de-sign load combination deletes the design results, but it does not delete orchange the design section.

Using the Options menu > Preferences > Concrete Frame Designcommand to change any of the composite beam design preferences deletesthe design results, but it does not delete or change the design section.

Deleting the static nonlinear analysis results also deletes the design resultsfor any load combination that includes static nonlinear forces. Typically,


Analysis Sections and Design Sections Technical Note 1 - 9

static nonlinear analysis and design results are deleted when one of thefollowing actions is taken:

Use the Define menu > Frame Nonlinear Hinge Properties com-mand to redefine existing or define new hinges.

Use the Define menu > Static Nonlinear/Pushover Cases com-mand to redefine existing or define new static nonlinear load cases.

Use the Assign menu > Frame/Line > Frame Nonlinear Hingescommand to add or delete hinges.

Again, note that these actions delete only results for load combinations thatinclude static nonlinear forces.

Concrete Frame Design Procedure Technical Note 2 - 1



Technical Note 2Concrete Frame Design Process

This Technical Note describes a basic concrete frame design process usingthis program. Although the exact steps you follow may vary, the basic designprocess should be similar to that described herein. Other Technical Notes inthe Concrete Frame Design series provide additional information, includingthe distinction between analysis sections and design sections (see AnalysisSections and Design Sections in Concrete Frame Design Technical Note 1General Design Information).

The concrete frame design postprocessor can design or check concrete col-umns and can design concrete beams.

Important note: A concrete frame element is designed as a beam or a col-umn, depending on how its frame section property was designated when itwas defined using the Define menu > Frame Sections command. Note thatwhen using this command, after you have specified that a section has a con-crete material property, you can click on the Reinforcement button andspecify whether it is a beam or a column.

Concrete Frame Design ProcedureThe following sequence describes a typical concrete frame design process fora new building. Note that although the sequence of steps you follow mayvary, the basic process probably will be essentially the same.

1. Use the Options menu > Preferences > Concrete Frame Designcommand to choose the concrete frame design code and to review otherconcrete frame design preferences and revise them if necessary. Notethat default values are provided for all concrete frame design prefer-ences, so it is unnecessary to define any preferences unless you want tochange some of the default values. See Concrete Frame Design ACIUBC97 Technical Notes 6 Preferences and Concrete Frame Design ACI318-99 Technical Notes 16 Preferences for more information.

Concrete Frame Design Process Concrete Frame Design

Technical Note 2 - 2 Concrete Frame Design Procedure

2. Create the building model.

3. Run the building analysis using the Analyze menu > Run Analysiscommand.

4. Assign concrete frame overwrites, if needed, using the Design menu >Concrete Frame Design > View/Revise Overwrites command. Notethat you must select frame elements before using this command. Alsonote that default values are provided for all concrete frame design over-writes, so it is unnecessary to define any overwrites unless you want tochange some of the default values. Note that the overwrites can be as-signed before or after the analysis is run. See Concrete Frame DesignUBC97 Technical Note 7 Overwrites and Concrete Frame Design ACI318-99 Technical Note 17 Overwrites for more information.

5. To use any design load combinations other than the defaults created bythe program for your concrete frame design, click the Design menu >Concrete Frame Design > Select Design Combo command. Notethat you must have already created your own design combos by clickingthe Define menu > Load Combinations command. See ConcreteFrame Design UBC97 Technical Note 8 Design Load Combinations andConcrete Frame Design ACI 318-99 Technical Note 18 Design LoadCombinations for more information.

6. Click the Design menu > Concrete Frame Design > Start De-sign/Check of Structure command to run the concrete frame design.

7. Review the concrete frame design results by doing one of the following:

a. Click the Design menu > Concrete Frame Design > Display De-sign Info command to display design input and output information onthe model. See Concrete Frame Design Technical Note 4 Output DataPlotted Directly on the Model for more information.

b. Right click on a frame element while the design results are displayedon it to enter the interactive design mode and interactively design theframe element. Note that while you are in this mode, you can reviseoverwrites and immediately see the results of the new design. SeeConcrete Frame Design Technical Note 3 Interactive Concrete FrameDesign for more information.

Concrete Frame Design Concrete Frame Design Process

Concrete Frame Design Procedure Technical Note 2 - 3

If design results are not currently displayed (and the design has beenrun), click the Design menu > Concrete Frame Design > Interac-tive Concrete Frame Design command and then right click a frameelement to enter the interactive design mode for that element.

8. Use the File menu > Print Tables > Concrete Frame Design com-mand to print concrete frame design data. If you select frame elementsbefore using this command, data is printed only for the selected ele-ments. See Concrete Frame Design UBC97 Technical Note 14 OutputDetails and Concrete Frame Design ACI 318-99 Technical Note 24 Out-put Details for more information.

9. Use the Design menu > Concrete Frame Design > Change DesignSection command to change the design section properties for selectedframe elements.

10. Click the Design menu > Concrete Frame Design > Start De-sign/Check of Structure command to rerun the concrete frame designwith the new section properties. Review the results using the proceduresdescribed in Item 7.

11. Rerun the building analysis using the Analyze menu > Run Analysiscommand. Note that the section properties used for the analysis are thelast specified design section properties.

12. Click the Design menu > Concrete Frame Design > Start De-sign/Check of Structure command to rerun the concrete frame designwith the new analysis results and new section properties. Review the re-sults using the procedures described above.

13. Again use the Design menu > Concrete Frame Design > ChangeDesign Section command to change the design section properties forselected frame elements, if necessary.

14. Repeat the processes in steps 10, 11 and 12 as many times as neces-sary.

15. Rerun the building analysis using the Analyze menu > Run Analysiscommand. Note that the section properties used for the analysis are thelast specified design section properties.

Concrete Frame Design Process Concrete Frame Design

Technical Note 2 - 4 Concrete Frame Design Procedure

Note:

Concrete frame design is an iterative process. Typically, the analysis and design will bererun multiple times to complete a design.

16. Click the Design menu > Concrete Frame Design > Start De-sign/Check of Structure command to rerun the concrete frame designwith the new section properties. Review the results using the proceduresdescribed in Item 7.

17. Click the Design menu > Concrete Frame Design > Verify Analysisvs Design Section command to verify that all of the final design sec-tions are the same as the last used analysis sections.

18. Use the File menu > Print Tables > Concrete Frame Design com-mand to print selected concrete frame design results, if desired.

It is important to note that design is an iterative process. The sections used inthe original analysis are not typically the same as those obtained at the endof the design process. Always run the building analysis using the final framesection sizes and then run a design check using the forces obtained from thatanalysis. Use the Design menu > Concrete Frame Design > VerifyAnalysis vs Design Section command to verify that the design sections arethe same as the analysis sections.

General Technical Note 3 - 1



Technical Note 3Interactive Concrete Frame Design

This Technical Note describes interactive concrete frame design and review,which is a powerful mode that allows the user to review the design results forany concrete frame design and interactively revise the design assumptionsand immediately review the revised results.

GeneralNote that a design must have been run for the interactive design mode to beavailable. To run a design, click the Design menu > Concrete Frame De-sign > Start Design/Check of Structure command.

Right click on a frame element while the design results are displayed on it toenter the interactive design mode and interactively design the element in theConcrete Design Information form. If design results are not currently dis-played (and a design has been run), click the Design menu > ConcreteFrame Design > Interactive Concrete Frame Design command and thenright click a frame element to enter the interactive design mode for that ele-ment.

Important note: A concrete frame element is designed as a beam or a col-umn, depending on how its frame section property was designated when itwas defined using the Define menu > Frame Sections command and theReinforcement button, which is only available if it is a concrete section.

Concrete Design Information FormTable 1 describe the features that are included in the Concrete Design Infor-mation form.

Interactive Concrete Frame Design Concrete Frame Design

Technical Note 3 - 2 Table 1 Concrete Design Information Form

Table 1 Concrete Design Information FormItem DESCRIPTION

Story This is the story level ID associated with the frame element.

Beam This is the label associated with a frame element that has beenassigned a concrete frame section property that is designatedas a beam. See the important note previously in this TechnicalNote for more information.

Column This is the label associated with a frame element that has beenassigned a concrete frame section property that is designatedas a column. See the important note previously in this Techni-cal Note for more information.

Section Name This is the label associated with a frame element that has beenassigned a concrete frame section property.

Reinforcement Information

The reinforcement information table on the Concrete Design Information form shows theoutput information obtained for each design load combination at each output stationalong the frame element. For columns that are designed by this program, the item withthe largest required amount of longitudinal reinforcing is initially highlighted. For columnsthat are checked by this program, the item with the largest capacity ratio is initially high-lighted. For beams, the item with the largest required amount of bottom steel is initiallyhighlighted. Following are the possible headings in the table:

Combo ID This is the name of the design load combination considered.

Station location This is the location of the station considered, measured fromthe i-end of the frame element.

Longitudinalreinforcement

This item applies to columns only. It also only applies to col-umns for which the program designs the longitudinal reinforc-ing. It is the total required area of longitudinal reinforcing steel.

Capacity ratio This item applies to columns only. It also only applies to col-umns for which you have specified the location and size of re-inforcing bars and thus the program checks the design. Thisitem is the capacity ratio.

Concrete Frame Design Interactive Concrete Frame Design

Table 1 Concrete Design Information Form Technical Note 3 - 3


The capacity ratio is determined by first extending a line fromthe origin of the PMM interaction surface to the point repre-senting the P, M2 and M3 values for the designated load com-bination. Assume the length of this first line is designated L1.Next, a second line is extended from the origin of the PMM in-teraction surface through the point representing the P, M2 andM3 values for the designated load combination until it intersectsthe interaction surface. Assume the length of this line from theorigin to the interaction surface is designated L2. The capacityratio is equal to L1/L2.

Major shearreinforcement

This item applies to columns only. It is the total required area ofshear reinforcing per unit length for shear acting in the columnmajor direction.

Minor shearreinforcement

This item applies to columns only. It is the total required area ofshear reinforcing per unit length for shear acting in the columnminor direction.

Top steel This item applies to beams only. It is the total required area oflongitudinal top steel at the specified station.

Bottom steel This item applies to beams only. It is the total required area oflongitudinal bottom steel at the specified station.

Shear steel This item applies to beams only. It is the total required area ofshear reinforcing per unit length at the specified station forloads acting in the local 2-axis direction of the beam.

Overwrites Button Click this button to access and make revisions to the concreteframe overwrites and then immediately see the new design re-sults. If you modify some overwrites in this mode and you exitboth the Concrete Frame Design Overwrites form and the Con-crete Design Information form by clicking their respective OKbuttons, the changes to the overwrites are saved permanently.

When you exit the Concrete Frame Design Overwrites form byclicking the OK button the changes are temporarily saved. Ifyou then exit the Concrete Design Information form by clickingthe Cancel button the changes you made to the concrete frameoverwrites are considered temporary only and are not perma-nently saved. Permanent saving of the overwrites does not ac-tually occur until you click the OK button in the Concrete DesignInformation form as well as the Concrete Frame Design Over-writes form.

Interactive Concrete Frame Design Concrete Frame Design

Technical Note 3 - 4 Table 1 Concrete Design Information Form


Details Button Clicking this button displays design details for the frame ele-ment. Print this information by selecting Print from the Filemenu that appears at the top of the window displaying the de-sign details.

Interaction Button Clicking this button displays the biaxial interaction curve for theconcrete section at the location in the element that is high-lighted in the table.

Overview Technical Note 4 - 1



Technical Note 4Output Data Plotted Directly on the Model

This Technical Note describes the input and output data that can be plotteddirectly on the model.

OverviewUse the Design menu > Concrete Frame Design > Display Design Infocommand to display on-screen output plotted directly on the program model.If desired, the screen graphics can then be printed using the File menu >Print Graphics command. The on-screen display data presents input andoutput data.

Using the Print Design Tables FormTo print the concrete frame input summary directly to a printer, use the Filemenu > Print Tables > Concrete Frame Design command and click thecheck box on the Print Design Tables form. Click the OK button to send theprint to your printer. Click the Cancel button rather than the OK button tocancel the print. Use the File menu > Print Setup command and theSetup>> button to change printers, if necessary.

To print the concrete frame input summary to a file, click the Print to Filecheck box on the Print Design Tables form. Click the Filename>> button tochange the path or filename. Use the appropriate file extension for the de-sired format (e.g., .txt, .xls, .doc). Click the OK buttons on the Open File forPrinting Tables form and the Print Design Tables form to complete the re-quest.

Note:

The File menu > Display Input/Output Text Files command is useful for displaying out-put that is printed to a text file.

The Append check box allows you to add data to an existing file. The path andfilename of the current file is displayed in the box near the bottom of the PrintDesign Tables form. Data will be added to this file. Or use the Filename

Output Data Plotted Directly on the Model Concrete Frame Design

Technical Note 4 - 2 Design Input

button to locate another file, and when the Open File for Printing Tables cau-tion box appears, click Yes to replace the existing file.

If you select a specific concrete frame element(s) before using the File menu> Print Tables > concrete Frame Design command, the Selection Onlycheck box will be checked. The print will be for the selected steel frame ele-ment(s) only.

Design InputThe following types of data can be displayed directly on the model by select-ing the data type (shown in bold type) from the drop-down list on the DisplayDesign Results form. Display this form by selecting he Design menu > Con-crete Frame Design > Display Design Info command.

Design Sections

Design Type

Live Load Red Factors

Unbraced L_Ratios

Eff Length K-Factors

Cm Factors

DNS Factors

DS Factors

Each of these items is described in the code-specific Concrete Frame DesignUBC97 Technical Note 13 Input Data and Concrete Frame Design ACI 318-99Technical Note 23 Input Data.

Design OutputThe following types of data can be displayed directly on the model by select-ing the data type (shown in bold type) from the drop-down list on the DisplayDesign Results form. Display this form by selecting he Design menu > Con-crete Frame Design > Display Design Info command.

Concrete Frame Design Output Data Plotted Directly on the Model

Design Output Technical Note 4 - 3

Longitudinal Reinforcing

Shear Reinforcing

Column Capacity Ratios

Joint Shear Capacity Ratios

Beam/Column Capacity Ratios

Each of these items is described in the code-specific Concrete Frame DesignACI 318-99 Technical Note 24 Output Details and Concrete Frame DesignUBC97 Technical Note 14 Output Details.

General and Notation Technical Note 5 - 1


CONCRETE FRAME DESIGN UBC97

Technical Note 5General and Notation

Introduction to the UBC97 Series of Technical NotesThe Concrete Frame Design UBC97 series of Technical Notes describes in de-tail the various aspects of the concrete design procedure that is used by thisprogram when the user selects the UBC97 Design Code (ICBO 1997). Thevarious notations used in this series are listed herein.

The design is based on user-specified loading combinations. The programprovides a set of default load combinations that should satisfy requirementsfor the design of most building type structures. See Concrete Frame DesignUBC97 Technical Note 8 Design Load Combinations for more information.

When using the UBC 97 option, a frame is assigned to one of the followingfive Seismic Zones (UBC 2213, 2214):

Zone 0

Zone 1

Zone 2

Zone 3

Zone 4

By default the Seismic Zone is taken as Zone 4 in the program. However, theSeismic Zone can be overwritten in the Preference form to change the de-fault. See Concrete Frame Design UBC97 Technical Note 6 Preferences formore information.

When using the UBC 97 option, the following Framing Systems are recognizedand designed according to the UBC design provisions (UBC 1627, 1921):

Ordinary Moment-Resisting Frame (OMF)

General and Notation Concrete Frame Design UBC97

Technical Note 5 - 2 General and Notation

Intermediate Moment-Resisting Frame (IMRF)

Special Moment-Resisting Frame (SMRF)

The Ordinary Moment-Resisting Frame (OMF) is appropriate in minimal seis-mic risk areas, especially in Seismic Zones 0 and 1. The Intermediate Mo-ment-Resisting Frame (IMRF) is appropriate in moderate seismic risk areas,specially in Seismic Zone 2. The Special Moment-Resisting Frame (SMRF) isappropriate in high seismic risk areas, specially in Seismic Zones 3 and 4. TheUBC seismic design provisions are considered in the program. The details ofthe design criteria used for the different framing systems are described inConcrete Frame Design UBC97 Technical Note 9 Strength Reduction Factors,Concrete Frame Design UBC97 Technical Note 10 Column Design, ConcreteFrame Design UBC97 Technical Note 11 Beam Design, and Concrete FrameDesign UBC97 Technical Note 12 Joint Design.

By default the frame type is taken in the program as OMRF in Seismic Zone 0and 1, as IMRF in Seismic Zone 2, and as SMRF in Seismic Zone 3 and 4.However, the frame type can be overwritten in the Overwrites form on amember-by-member basis. See Concrete Frame Design UBC97 Technical Note7 Overwrites for more information. If any member is assigned with a frametype, the change of the Seismic Zone in the Preferences will not modify theframe type of an individual member that has been assigned a frame type.

The program also provides input and output data summaries, which are de-scribed in Concrete Frame Design UBC97 Technical Note 13 Input Data andConcrete Frame Design UBC97 Technical Note 14 Output Details.

English as well as SI and MKS metric units can be used for input. The code isbased on Inch-Pound-Second units. For simplicity, all equations and descrip-tions presented in this Technical Note correspond to Inch-Pound-Secondunits unless otherwise noted.

NotationAcv Area of concrete used to determine shear stress, sq-in

Ag Gross area of concrete, sq-in

As Area of tension reinforcement, sq-in

Concrete Frame Design UBC97 General and Notation


'sA Area of compression reinforcement, sq-in

As(required) Area of steel required for tension reinforcement, sq-in

Ast Total area of column longitudinal reinforcement, sq-in

Av Area of shear reinforcement, sq-in

Cm Coefficient, dependent upon column curvature, used to calculatemoment magnification factor

D' Diameter of hoop, in

Ec Modulus of elasticity of concrete, psi

Es Modulus of elasticity of reinforcement, assumed as 29,000,000 psi(UBC 1980.5.2)

Ig Moment of inertia of gross concrete section about centroidal axis,neglecting reinforcement, in4

Ise Moment of inertia of reinforcement about centroidal axis of mem-ber cross section, in4

L Clear unsupported length, in

M1 Smaller factored end moment in a column, lb-in

M2 Larger factored end moment in a column, lb-in

Mc Factored moment to be used in design, lb-in

Mns Nonsway component of factored end moment, lb-in

Ms Sway component of factored end moment, lb-in

Mu Factored moment at section, lb-in

Mux Factored moment at section about X-axis, lb-in

Muy Factored moment at section about Y-axis, lb-in

Pb Axial load capacity at balanced strain conditions, lb

General and Notation Concrete Frame Design UBC97

Technical Note 5 - 4 General and Notation

Pc Critical buckling strength of column, lb

Pmax Maximum axial load strength allowed, lb

P0 Acial load capacity at zero eccentricity, lb

Pu Factored axial load at section, lb

Vc Shear resisted by concrete, lb

VE Shear force caused by earthquake loads, lb

VD+L Shear force from span loading, lb

Vu Factored shear force at a section, lb

Vp Shear force computed from probable moment capacity, lb

a Depth of compression block, in

ab Depth of compression block at balanced condition, in

b Width of member, in

bf Effective width of flange (T-Beam section), in

bw Width of web (T-Beam section), in

c Depth to neutral axis, in

cb Depth to neutral axis at balanced conditions, in

d Distance from compression face to tension reinforcement, in

d' Concrete cover to center of reinforcing, in

ds Thickness of slab (T-Beam section), in

'cf Specified compressive strength of concrete, psi

fy Specified yield strength of flexural reinforcement, psify ≤ 80,000 psi (UBC 1909.4)

Concrete Frame Design UBC97 General and Notation


fys Specified yield strength of flexural reinforcement, psi

h Dimension of column, in

k Effective length factor

r Radius of gyration of column section, in

α Reinforcing steel overstrength factor

β1 Factor for obtaining depth of compression block in concrete

βd Absolute value of ratio of maximum factored axial dead load tomaximum factored axial total load

δs Moment magnification factor for sway moments

δns Moment magnification factor for nonsway moments

εc Strain in concrete

εs Strain in reinforcing steel

ϕ Strength reduction factor




Technical Note 6Preferences

This Technical Note describes the items in the Preferences form.

GeneralThe concrete frame design preferences in this program are basic assignmentsthat apply to all concrete frame elements. Use the Options menu > Prefer-ences > Concrete Frame Design command to access the Preferences formwhere you can view and revise the concrete frame design preferences.

Default values are provided for all concrete frame design preference items.Thus, it is not required that you specify or change any of the preferences. Youshould, however, at least review the default values for the preference itemsto make sure they are acceptable to you.

Using the Preferences FormTo view preferences, select the Options menu > Preferences > ConcreteFrame Design. The Preferences form will display. The preference optionsare displayed in a two-column spreadsheet. The left column of the spread-sheet displays the preference item name. The right column of the spreadsheetdisplays the preference item value.

To change a preference item, left click the desired preference item in eitherthe left or right column of the spreadsheet. This activates a drop-down box orhighlights the current preference value. If the drop-down box appears, selecta new value. If the cell is highlighted, type in the desired value. The prefer-ence value will update accordingly. You cannot overwrite values in the drop-down boxes.

When you have finished making changes to the concrete frame preferences,click the OK button to close the form. You must click the OK button for thechanges to be accepted by the program. If you click the Cancel button to exit

Preferences Concrete Frame Design UBC97

Technical Note 6 - 2 Preferences

the form, any changes made to the preferences are ignored and the form isclosed.

PreferencesFor purposes of explanation in this Technical Note, the preference items arepresented in Table 1. The column headings in the table are described as fol-lows:

Item: The name of the preference item as it appears in the cells at theleft side of the Preferences form.

Possible Values: The possible values that the associated preference itemcan have.

Default Value: The built-in default value that the program assumes forthe associated preference item.

Description: A description of the associated preference item.

Table 1: Concrete Frame Preferences

ItemPossibleValues

DefaultValue Description

Design Code Any code inthe program

UBC97 Design code used for design ofconcrete frame elements.

Phi BendingTension

>0 0.9 Unitless strength reduction factor perUBC 1909.

Phi Compres-sion Tied


Phi Compres-sion Spiral


Phi Shear >0 0.85 Unitless strength reduction factor perUBC 1909.

Number Inter-action Curves

≥4.0 24 Number of equally spaced interactioncurves used to create a full 360-degreeinteraction surface (this item should bea multiple of four). We recommend thatyou use 24 for this item.

Concrete Frame Design UBC97 Preferences

Preferences Technical Note 6 - 3


ItemPossibleValues


Number Inter-action Points

Any odd value≥1.0

11 Number of points used for defining asingle curve in a concrete frameinteraction surface (this item should beodd).

Time HistoryDesign

Envelopes orStep-by-Step

Envelopes Toggle for design load combinationsthat include a time history designed forthe envelope of the time history, ordesigned step-by-step for the entiretime history. If a single design loadcombination has more than one timehistory case in it, that design loadcombination is designed for theenvelopes of the time histories,regardless of what is specified here.

Overwrites Technical Note 7 - 1



Technical Note 7Overwrites

GeneralThe concrete frame design overwrites are basic assignments that apply onlyto those elements to which they are assigned. This Technical Note describesconcrete frame design overwrites for UBC97. To access the overwrites, selectan element and click the Design menu > Concrete Frame Design >View/Revise Overwrites command.

Default values are provided for all overwrite items. Thus, you do not need tospecify or change any of the overwrites. However, at least review the defaultvalues for the overwrite items to make sure they are acceptable. Whenchanges are made to overwrite items, the program applies the changes onlyto the elements to which they are specifically assigned; that is, to the ele-ments that are selected when the overwrites are changed.

OverwritesFor explanation purposes in this Technical Note, the overwrites are presentedin Table 1. The column headings in the table are described as follows.

Item: The name of the overwrite item as it appears in the program. Tosave space in the formes, these names are generally short.

Possible Values: The possible values that the associated overwrite itemcan have.

Default Value: The default value that the program assumes for the asso-ciated overwrite item.

Description: A description of the associated overwrite item.

An explanation of how to change an overwrite is provided at the end of thisTechnical Note.

Overwrites Concrete Frame Design UBC97

Technical Note 7 - 2 Overwrites

Table 1 Concrete Frame Design Overwrites

ItemPossibleValues


ElementSection

ElementType

Sway Special,Sway Interme-

diate,Sway

OrdinaryNonSway

Sway Special Frame type; see UBC 1910.11 to1910.13.

Live LoadReduction

Factor

>0

≤1.0

1. Used to reduce the live load contribu-tion to the factored loading.

HorizontalEarthquake

Factor

>0

≤1.0

1.

UnbracedLength Ratio

(Major)

>0

≤1.0

1.0


(Minor)

>0

≤1.0

1.0

EffectiveLength Factor

(K Major)

>0

≤1.0

1 See UBC 1910.12.1.


(K Minor)

>0

≤1.0

1 See UBC 1910.12.1.

MomentCoefficient(Cm Major)

>0

≤1.0

1 See UBC 1910.12.3.1 relates actualmoment diagram to an equivalent uni-form moment diagram.

MomentCoefficient(Cm Minor)

>0

≤1.0

1 See UBC 1910.12.3.1 relates actualmoment diagram to an equivalent uni-form moment diagram.

NonSwayMoment Factor

(Dns Major)

>0

≤1.0

1 See UBC 1910.12.

Concrete Frame Design UBC97 Overwrites



ItemPossibleValues



(Dns Minor)

1 See UBC 1910.12.

Sway MomentFactor

(Ds Major)

1 See UBC 1910.12.

Sway MomentFactor

(Ds Minor)

1 See UBC 1910.12.

Making Changes in the Overwrites FormTo access the concrete frame overwrites, select an element and click the De-sign menu > Concrete Frame Design > View/Revise Overwrites com-mand.

The overwrites are displayed in the form with a column of check boxes and atwo-column spreadsheet. The left column of the spreadsheet contains thename of the overwrite item. The right column of the spreadsheet contains theoverwrites values.

Initially, the check boxes in the Concrete Frame Design Overwrites form areall unchecked and all of the cells in the spreadsheet have a gray backgroundto indicate that they are inactive and the items in the cells cannot bechanged. The names of the overwrite items are displayed in the first columnof the spreadsheet. The values of the overwrite items are visible in the secondcolumn of the spreadsheet if only one element was selected before the over-writes form was accessed. If multiple elements were selected, no values showfor the overwrite items in the second column of the spreadsheet.

After selecting one or multiple elements, check the box to the left of an over-write item to change it. Then left click in either column of the spreadsheet toactivate a drop-down box or highlight the contents in the cell in the right col-umn of the spreadsheet. If the drop-down box appears, select a value from

Overwrites Concrete Frame Design UBC97


the box. If the cell contents is highlighted, type in the desired value. Theoverwrite will reflect the change. You cannot change the values of the drop-down boxes.

When changes to the overwrites have been completed, click the OK button toclose the form. The program then changes all of the overwrite items whoseassociated check boxes are checked for the selected members. You must clickthe OK button for the changes to be accepted by the program. If you click theCancel button to exit the form, any changes made to the overwrites are ig-nored and the form is closed.

Resetting Concrete Frame Overwrites to Default ValuesUse the Design menu > Concrete Frame Design > Reset All Overwritescommand to reset all of the steel frame overwrites. All current design resultswill be deleted when this command is executed.

Important note about resetting overwrites: The program defaults for theoverwrite items are built into the program. The concrete frame overwrite val-ues that were in a .edb file that you used to initialize your model may be dif-ferent from the built-in program default values. When you reset overwrites,the program resets the overwrite values to its built-in values, not to the val-ues that were in the .edb file used to initialize the model.

Design Load Combinations Technical Note 8 - 1



Technical Note 8Design Load Combinations

The design load combinations are the various combinations of the prescribedload cases for which the structure needs to be checked. For the UBC 97 code,if a structure is subjected to dead load (DL) and live load (LL) only, the stresscheck may need only one load combination, namely 1.4 DL + 1.7 LL (UBC1909.2.1). However, in addition to the dead and live loads, if the structure issubjected to wind (WL) and earthquake (EL) loads, and considering that windand earthquake forces are reversible, the following load combinations mayneed to be considered (UBC 1909.2).

1.4 DL (UBC 1909.2.1)1.4 DL + 1.7 LL (UBC 1909.2.1)

0.9 DL ± 1.3 WL (UBC 1909.2.2)0.75 (1.4 DL + 1.7 LL ± 1.7 WL) (UBC 1909.2.2)

0.9 DL ± 1.0 EL (UBC 1909.2.3, 1612.2.1)1.2 DL + 0.5 LL ± 1.0 EL) (UBC 1909.2.3, 1612.2.1)

These are also the default design load combinations in the program wheneverthe UBC97 code is used.

Live load reduction factors can be applied to the member forces of the liveload condition on an element-by-element basis to reduce the contribution ofthe live load to the factored loading. See Concrete Frame Design UBC97Technical Note 7 Overwrites for more information.

Strength Reduction Factors Technical Note 9 - 1



Technical Note 9Strength Reduction Factors

The strength reduction factors, ϕ, are applied on the nominal strength to ob-tain the design strength provided by a member. The ϕ factors for flexure, ax-ial force, shear, and torsion are as follows:

ϕ = 0.90 for flexure (UBC 1909.3.2.1)

ϕ = 0.90 for axial tension (UBC 1909.3.2.2)

ϕ = 0.90 for axial tension and flexure (UBC 1909.3.2.2)

ϕ = 0.75 for axial compression, and axial compressionand flexure (spirally reinforced column) (UBC 1909.3.2.2)

ϕ = 0.70 for axial compression, and axial compressionand flexure (tied column) (UBC 1909.3.2.2)

ϕ = 0.85 for shear and torsion (non-seismic design) (UBC 1909.3.2.3)

ϕ = 0.60 for shear and torsion (UBC 1909.3.2.3)




Technical Note 10Column Design

This Technical Note describes how the program checks column capacity or de-signs reinforced concrete columns when the UBC97 code is selected.

OverviewThe program can be used to check column capacity or to design columns. Ifyou define the geometry of the reinforcing bar configuration of each concretecolumn section, the program will check the column capacity. Alternatively, theprogram can calculate the amount of reinforcing required to design the col-umn. The design procedure for the reinforced concrete columns of the struc-ture involves the following steps:

Generate axial force/biaxial moment interaction surfaces for all of the dif-ferent concrete section types of the model. A typical biaxial interactionsurface is shown in Figure 1. When the steel is undefined, the programgenerates the interaction surfaces for the range of allowable reinforce-ment1 to 8 percent for Ordinary and Intermediate moment resistingframes (UBC 1910.9.1) and 1 to 6 percent for Special moment resistingframes (UBC 1921.4.3.1).

Calculate the capacity ratio or the required reinforcing area for the fac-tored axial force and biaxial (or uniaxial) bending moments obtained fromeach loading combination at each station of the column. The target capac-ity ratio is taken as 1 when calculating the required reinforcing area.


The following four subsections describe in detail the algorithms associatedwith this process.

Column Design Concrete Frame Design UBC97

Technic

Figur

GenThe cof disfailuremulatintera

al Note 10 - 2 Generation of Biaxial Interaction Surfaces

e 1 A Typical Column Interaction Surface

eration of Biaxial Interaction Surfacesolumn capacity interaction volume is numerically described by a seriescrete points that are generated on the three-dimensional interaction surface. In addition to axial compression and biaxial bending, the for-ion allows for axial tension and biaxial bending considerations. A typicalction diagram is shown in Figure 1.

Concrete Frame Design UBC97 Column Design

Generation of Biaxial Interaction Surfaces Technical Note 10 - 3

The coordinates of these points are determined by rotating a plane of linearstrain in three dimensions on the section of the column. See Figure 2. Thelinear strain diagram limits the maximum concrete strain, εc, at the extremityof the section, to 0.003 (UBC 1910.2.3).

The formulation is based consistently upon the general principles of ultimatestrength design (UBC 1910.3), and allows for any doubly symmetric rectan-gular, square, or circular column section.

The stress in the steel is given by the product of the steel strain and the steelmodulus of elasticity, εsEs, and is limited to the yield stress of the steel, fy(UBC 1910.2.4). The area associated with each reinforcing bar is assumed tobe placed at the actual location of the center of the bar and the algorithmdoes not assume any further simplifications with respect to distributing thearea of steel over the cross section of the column, such as an equivalent steeltube or cylinder. See Figure 3.

The concrete compression stress block is assumed to be rectangular, with a

stress value of 0.85 'cf (UBC 1910.2.7.1). See Figure 3. The interaction algo-

rithm provides correction to account for the concrete area that is displaced bythe reinforcement in the compression zone.

The effects of the strength reduction factor, ϕ, are included in the generationof the interaction surfaces. The maximum compressive axial load is limited toϕPn(max), where

ϕPn(max) = 0.85ϕ[0.85 'cf (Ag-Ast)+fyAst] (spiral) (UBC 1910.3.5.1)

ϕPn(max) = 0.85ϕ[0.85 'cf (Ag-Ast)+fyAst] (tied) (UBC 1910.3.5.2)

ϕ = 0.70 for tied columns (UBC 1909.3.2.2)

ϕ = 0.75 for spirally reinforced columns (UBC 1909.3.2.2)

The value of ϕ used in the interaction diagram varies from ϕmin to 0.9 basedon the axial load. For low values of axial load, ϕ is increased linearly from ϕmin

to 0.9 as the nominal capacity ϕPn decreases from the smaller of ϕPb or

0.1 'cf Ag to zero, where Pb is the axial force at the balanced condition. In

cases involving axial tension, ϕ is always 0.9 (UBC 1909.3.2.2).


Technica

Figure

l Note 10 - 4 Generation of Biaxial Interaction Surfaces

2 Idealized Strain Distribution for Generation of Interaction Surfaces


Calculate Column Capacity Ratio Technical Note 10 - 5

Figure 3 Idealization of Stress and Strain Distribution in a Column Section

Calculate Column Capacity RatioThe column capacity ratio is calculated for each loading combination at eachoutput station of each column. The following steps are involved in calculatingthe capacity ratio of a particular column for a particular loading combinationat a particular location:

Determine the factored moments and forces from the analysis load casesand the specified load combination factors to give Pu, Mux, and Muy.

Determine the moment magnification factors for the column moments.

Apply the moment magnification factors to the factored moments. Deter-mine whether the point, defined by the resulting axial load and biaxialmoment set, lies within the interaction volume.

The factored moments and corresponding magnification factors depend on theidentification of the individual column as either “sway” or “non-sway.”


Technical Note 10 - 6 Calculate Column Capacity Ratio

The following three sections describe in detail the algorithms associated withthis process.

Determine Factored Moments and ForcesThe factored loads for a particular load combination are obtained by applyingthe corresponding load factors to all the load cases, giving Pu, Mux, and Muy.The factored moments are further increased for non-sway columns, if re-quired, to obtain minimum eccentricities of (0.6 + 0.03h) inches, where h isthe dimension of the column in the corresponding direction (UBC1910.12.3.2).

Determine Moment Magnification FactorsThe moment magnification factors are calculated separately for sway (overallstability effect), δs, and for non-sway (individual column stability effect), δns.Also the moment magnification factors in the major and minor directions arein general different.

The program assumes that it performs a P-delta analysis and, therefore, mo-ment magnification factors for moments causing sidesway are taken as unity(UBC 1910.10.2). For the P-delta analysis, the load should correspond to aload combination of 0.75 (1.4 dead load + 1.7 live load)/ϕ if wind load gov-erns, or (1.2 dead load + 0.50 live load)/ϕ if seismic load governs, where ϕ isthe understrength factor for stability, which is taken as 0.75 (UBC1910.12.3). See also White and Hajjar (1991).

The moment obtained from analysis is separated into two components: thesway (Ms) and the non-sway (Ms) components. The non-sway componentswhich are identified by “ns” subscripts are predominantly caused by gravityload. The sway components are identified by the “s” subscripts. The swaymoments are predominantly caused by lateral loads, and are related to thecause of side-sway.

For individual columns or column-members in a floor, the magnified momentsabout two axes at any station of a column can be obtained as

M = Mns + δsMs. (UBC 1910.13.3)The factor δs is the moment magnification factor for moments causing sidesway. The moment magnification factors for sway moments, δs, is taken as 1because the component moments Ms and Mns are obtained from a “second or-der elastic (P-delta) analysis.”



The computed moments are further amplified for individual column stabilityeffect (UBC 1910.12.3, 1910.13.5) by the nonsway moment magnificationfactor, δns, as follows:

Mc = δnsM2 , where (UBC 1910.12.3)

Mc is the factored moment to be used in design, and

M2 is the larger factored and amplified end moment.

The non-sway moment magnification factor, δns, associated with the major orminor direction of the column is given by (UBC 1910.12.3)

δns =

c

u

m

PP

C

75.01 −

≥ 1.0, where (UBC 1910.12.3)

Pc = 2

2

)( ukl

EIπ, (UBC 1910.12.3)

k is conservatively taken as 1; however, the program allows the user tooverride this value.

EI is associated with a particular column direction given by:

EI =d

gc IE

β+1

4.0 , (UBC 1910.12.3)

maximum factored axial dead loadβd = maximum factored axial total load and (UBC 1910.12.3)

Cm = 0.6 + 0.4b

a

MM

≥ 0.4. (UBC 1910.12.3.1)

Ma and Mb are the moments at the ends of the column, and Mb is numericallylarger than Ma. Ma / Mb is positive for single curvature bending and negativefor double curvature bending. The above expression of Cm is valid if there isno transverse load applied between the supports. If transverse load is presenton the span, or the length is overwritten, Cm = 1. Cm can be overwritten bythe user on an element-by-element basis.


Technica

The magnification factor, δns, must be a positive number and greater than 1.Therefore, Pu must be less than 0.75Pc. If Pu is found to be greater than orequal to 0.75Pc, a failure condition is declared.

The above calculations use the unsupported length of the column. The twounsupported lengths are l22 and l33, corresponding to instability in the minorand major directions of the element, respectively. See Figure 4. These are thelengths between the support points of the element in the corresponding di-rections.

Figure

If the puser ca

DetermThe prof the

l Note 10 - 8 Calculate Column Capacity Ratio

4 Axes of Bending and Unsupported Length

rogram assumptions are not satisfactory for a particular member, then explicitly specify values of δs and δns.

ine Capacity Ratioogram calculates a capacity ratio as a measure of the stress conditioncolumn. The capacity ratio is basically a factor that gives an indication


Calculate Colum

of the stress condition of the column with respect to the capacity of the col-umn.

Before entering the interaction diagram to check the column capacity, themoment magnification factors are applied to the factored loads to obtain Pu,Mux, and Muy. The point (Pu, Mux, Muy.) is then placed in the interaction spaceshown as point L in Figure 5. If the point lies within the interaction volume,the column capacity is adequate; however, if the point lies outside the inter-action volume, the column is overstressed.

Figure 5 G

This capacitcation of pextended oby three-di

n Capacity Ratio Technical Note 10 - 9

eometric Representation of Column Capacity Ratios

y ratio is achieved by plotting the point L and determining the lo-oint C. The point C is defined as the point where the line OL (ifutwards) will intersect the failure surface. This point is determinedmensional linear interpolation between the points that define the


Technical Note 10 - 10 Required Reinforcing Area

failure surface. See Figure 5. The capacity ratio, CR, is given by the ratio

OCOL

.

If OL = OC (or CR=1), the point lies on the interaction surface and thecolumn is stressed to capacity.

If OL < OC (or CR<1), the point lies within the interaction volume and thecolumn capacity is adequate.

If OL > OC (or CR>1), the point lies outside the interaction volume and thecolumn is overstressed.

The maximum of all the values of CR calculated from each load combination isreported for each check station of the column, along with the controlling Pu,Mux, and Muy set and associated load combination number.

Required Reinforcing AreaIf the reinforcing area is not defined, the program computes the reinforce-ment that will give a column capacity ratio of one, calculated as described inthe previous section entitled "Calculate Column Capacity Ratio."

Design Column Shear ReinforcementThe shear reinforcement is designed for each loading combination in the ma-jor and minor directions of the column. The following steps are involved indesigning the shear reinforcing for a particular column for a particular loadcombination caused by shear forces in a particular direction:

Determine the factored forces acting on the section, Pu and Vu. Note thatPu is needed for the calculation of Vc.

Determine the shear force, Vc, that can be resisted by concrete alone.

Calculate the reinforcement steel required to carry the balance.

For Special and Intermediate moment resisting frames (Ductile frames), theshear design of the columns is also based on the probable and nominal mo-ment capacities of the members, respectively, in addition to the factored


Design Column Shear Reinforcement Technical Note 10 - 11

moments. Effects of the axial forces on the column moment capacities areincluded in the formulation.


Determine Section Forces In the design of the column shear reinforcement of an Ordinary moment

resisting concrete frame, the forces for a particular load combination,namely, the column axial force, Pu, and the column shear force, Vu, in aparticular direction are obtained by factoring the program analysis loadcases with the corresponding load combination factors.

In the shear design of Special moment resisting frames (i.e., seismicdesign) the column is checked for capacity-shear in addition to the re-quirement for the Ordinary moment resisting frames. The capacity-shearforce in a column, Vp, in a particular direction is calculated from the prob-able moment capacities of the column associated with the factored axialforce acting on the column.

For each load combination, the factored axial load, Pu, is calculated. Then,

the positive and negative moment capacities, +uM and −

uM , of the column

in a particular direction under the influence of the axial force Pu is calcu-lated using the uniaxial interaction diagram in the corresponding direction.The design shear force, Vu, is then given by (UBC 1921.4.5.1)

Vu = Vp + VD+L (UBC 1921.4.5.1)

where, Vp is the capacity-shear force obtained by applying the calculatedprobable ultimate moment capacities at the two ends of the column actingin two opposite directions. Therefore, Vp is the maximum of

1PV and 2PV ,

where

1PV =L

MM JI+− +

, and

2PV =L

MM JI−+ +

, where


Technical Note 10 - 12 Design Column Shear Reinforcement

−+II MM , , = Positive and negative moment capacities at end I of the

column using a steel yield stress value of αfy and no ϕfactors (ϕ = 1.0),

−+JJ MM , , = Positive and negative moment capacities at end J of the

column using a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0), and

L = Clear span of column.

For Special moment resisting frames, α is taken as 1.25 (UBC 1921.0).VD+L is the contribution of shear force from the in-span distribution ofgravity loads. For most of the columns, it is zero.

For Intermediate moment resisting frames, the shear capacity of thecolumn is also checked for the capacity-shear based on the nominal mo-ment capacities at the ends and the factored gravity loads, in addition tothe check required for Ordinary moment resisting frames. The designshear force is taken to be the minimum of that based on the nominal (ϕ =1.0) moment capacity and factored shear force. The procedure for calcu-lating nominal moment capacity is the same as that for computing theprobable moment capacity for special moment resisting frames, exceptthat α is taken equal to 1 rather than 1.25 (UBC 1921.0, 1921.8.3). Thefactored shear forces are based on the specified load factors, except theearthquake load factors are doubled (UBC 1921.8.3).

Determine Concrete Shear CapacityGiven the design force set Pu and Vu, the shear force carried by the concrete,Vc, is calculated as follows:

If the column is subjected to axial compression, i.e., Pu is positive,

Vc = 2 cvg

uc A

AP

f

+

000,21' , (UBC 1911.3.1.2)

where,

'cf ≤ 100 psi, and (UBC 1911.1.2)


Design Column Shear Reinfo

Vc ≤ 3.5 'cf cv

g

u AA

P

+

5001 . (UBC 1911.3.2.2)

The term g

u

AP

must have psi units. Acv is the effective shear area which is

shown shaded in Figure 6. For circular columns, Acv is not taken to begreater than 0.8 times the gross area (UBC 1911.5.6.2).

Figure 6 Shear Stres

rcement Technical Note 10 - 13

s Area, Acv



If the column is subjected to axial tension, Pu is negative, (UBC1911.3.2.3)

Vc = 2 'cf

+

g

u

AP

5001 Acv ≥ 0 (UBC 1911.3.2.3)

For Special moment resisting concrete frame design, Vc is set to zeroif the factored axial compressive force, Pu, including the earthquake effect

is small (Pu < 'cf Ag / 20) and if the shear force contribution from earth-

quake, VE, is more than half of the total factored maximum shear forceover the length of the member Vu(VE ≥ 0.5Vu) (UBC 1921.4.5.2).

Determine Required Shear ReinforcementGiven Vu and Vc, the required shear reinforcement in the form of stirrups orties within a spacing, s, is given for rectangular and circular columns by thefollowing:

Av = df

sVV

ys

cu )/( −ϕ, for rectangular columns (UBC 1911.5.6.1, 1911.5.6.2)

Av = '

)/(2Df

sVV

ys

cu −ϕπ

, for circular columns (UBC 1911.5.6.1, 1911.5.6.2)

Vu is limited by the following relationship.

(Vu / ϕ-Vc) ≤ 8 'cf Acv (UBC 1911.5.6.8)

Otherwise redimensioning of the concrete section is required. Here ϕ, thestrength reduction factor, is 0.85 for nonseismic design or for seismic designin Seismic Zones 0, 1, and 2 (UBC 1909.3.2.3) and is 0.60 for seismic designin Seismic Zones 3 and 4 (UBC 1909.3.4.1). The maximum of all the calcu-lated values obtained from each load combination are reported for the majorand minor directions of the column, along with the controlling shear force andassociated load combination label.

The column shear reinforcement requirements reported by the program arebased purely on shear strength consideration. Any minimum stirrup require-ments to satisfy spacing considerations or transverse reinforcement volumet-


Reference Technical Note 10 - 15

ric considerations must be investigated independently of the program by theuser.

ReferenceWhite. D. W., and J.F., Hajjar. 1991. Application of Second-Order Elastic

Analysis in LRFD: Research in Practice. Engineering Journal. AmericanInstitute of Steel Construction, Inc. Vol. 28, No. 4.




Technical Note 11Beam Design

This Technical Note describes how this program completes beam design whenthe UBC97 code is selected. The program calculates and reports the requiredareas of steel for flexure and shear based on the beam moments, shears, loadcombination factors and other criteria described herein.

OverviewIn the design of concrete beams, the program calculates and reports the re-quired areas of steel for flexure and shear based upon the beam moments,shears, load combination factors, and other criteria described below. The re-inforcement requirements are calculated at a user-defined number ofcheck/design stations along the beam span.

All beams are designed for major direction flexure and shear only.Effects caused by axial forces, minor direction bending, and torsionthat may exist in the beams must be investigated independently bythe user.

The beam design procedure involves the following steps:

Design beam flexural reinforcement

Design beam shear reinforcement

Design Beam Flexural ReinforcementThe beam top and bottom flexural steel is designed at check/design stationsalong the beam span. The following steps are involved in designing the flex-ural reinforcement for the major moment for a particular beam for a particu-lar section:

Determine the maximum factored moments

Determine the reinforcing steel

Beam Design Concrete Frame Design UBC97

Technical Note 11 - 2 Design Beam Flexural Reinforcement

Determine Factored MomentsIn the design of flexural reinforcement of Special, Intermediate, or Ordinarymoment resisting concrete frame beams, the factored moments for each loadcombination at a particular beam section are obtained by factoring the corre-sponding moments for different load cases with the corresponding load fac-tors.

The beam section is then designed for the maximum positive +uM and maxi-

mum negative −uM factored moments obtained from all of the load combina-

tions.

Negative beam moments produce top steel. In such cases, the beam is al-ways designed as a rectangular section. Positive beam moments producebottom steel. In such cases, the beam may be designed as a Rectangular- ora T-beam.

Determine Required Flexural ReinforcementIn the flexural reinforcement design process, the program calculates both thetension and compression reinforcement. Compression reinforcement is addedwhen the applied design moment exceeds the maximum moment capacity ofa singly reinforced section. The user has the option of avoiding the compres-sion reinforcement by increasing the effective depth, the width, or the gradeof concrete.

The design procedure is based on the simplified rectangular stress block asshown in Figure 1 (UBC 1910.2). It is assumed that the compression carriedby concrete is less than 0.75 times that which can be carried at the balancedcondition (UBC 1910.3.3). When the applied moment exceeds the momentcapacity at this designed balanced condition, the area of compression rein-forcement is calculated assuming that the additional moment will be carriedby compression and additional tension reinforcement.

The design procedure used by the program for both rectangular and flangedsections (L- and T-beams) is summarized below. It is assumed that the de-

sign ultimate axial force does not exceed 0.1 'cf Ag (UBC 1910.3.3); hence, all

the beams are designed for major direction flexure and shear only.

Concrete Frame Design UBC97 Beam Design

Des

Fig

DeIn topFig

wheq

ign Beam Flexural Reinforcement Technical Note 11 - 3

ure 1 Design of a Rectangular Beam Section

sign for Rectangular Beamdesigning for a factored negative or positive moment, Mu (i.e., designing or bottom steel), the depth of the compression block is given by a (seeure 1), where,

a = d - bf

Md

c

u

ϕ−

'2

85.0

2,

ere the value of ϕ is 0.90 (UBC 1909.3.2.1) in the above and the followinguations. Also β1 and cb are calculated as follows:

β1 = 0.85 - 0.05

−000,1

000,4'cf , 0.65 ≤ β1 ≤ 0.85, (UBC 1910.2.7.3)

cb = dfE

E

ysc

sc

+εε

= yf+000,87

000,87d. (UBC 1910.2.3, 1910.2.4)



The maximum allowed depth of the compression block is given by

amax = 0.75β1cb. (UBC 1910.2.7.1, 1910.3.3)

If a ≤ amax, the area of tensile steel reinforcement is given by

As =

−ϕ

2a

df

M

y

u .

This steel is to be placed at the bottom if Mu is positive, or at the top if Mu

is negative.

If a > amax, compression reinforcement is required (UBC 1910.3.3) and iscalculated as follows:

− The compressive force developed in concrete alone is given by

C = 0.85 'cf bamax, and (UBC 1910.2.7.1)

the moment resisted by concrete compression and tensile steel is

Muc = C

−

2maxa

d ϕ.

− Therefore the moment resisted by compression steel and tensile steel is

Mus = Mu - Muc.

− So the required compression steel is given by

'sA =

ϕ− )'(' ddf

M

s

us , where

'sf = 0.003Es

−

cdc '

. (UBC 1910.2.4)

− The required tensile steel for balancing the compression in concrete is


Design Beam Flexural Reinforcement Technical Note 11 - 5

As1 = ϕ

−

2maxa

df

M

y

uc , and

the tensile steel for balancing the compression in steel is given by

As2 = ϕ− )'( ddf

M

y

us .

− Therefore, the total tensile reinforcement, As = As1 + As2, and total com-

pression reinforcement is 'sA . As is to be placed at bottom and '

sA is to

be placed at top if Mu is positive, and vice versa if Mu is negative.

Design for T-BeamIn designing for a factored negative moment, Mu (i.e., designing top steel),the calculation of the steel area is exactly the same as above, i.e., no T-Beamdata is to be used. See Figure 2. If Mu > 0, the depth of the compressionblock is given by

a = d -fc

u

bf

Md

ϕ−

'2

85.0

2 .


amax = 0.75β1cb. (UBC 1910.2.7.1)

If a ≤ ds, the subsequent calculations for As are exactly the same as previouslydefined for the rectangular section design. However, in this case, the width ofthe compression flange is taken as the width of the beam for analysis. Com-pression reinforcement is required if a > amax.

If a > ds, calculation for As is performed in two parts. The first part is for bal-ancing the compressive force from the flange, Cf, and the second part is forbalancing the compressive force from the web, Cw, as shown in Figure 2. Cf isgiven by

Cf = 0.85 'cf (bf - bw) ds.


Tech

Fig

The

give

Agacarr

Thedep

nical Note 11 - 6 Design Beam Flexural Reinforcement

ure 2 Design of a T-Beam Section

refore, As1 = y

f

fC

and the portion of Mu that is resisted by the flange is

n by

Muf = Cf

−

2sd

d ϕ .

in, the value for ϕ is 0.90. Therefore, the balance of the moment, Mu to beied by the web is given by

Muw = Mu - Muf.

web is a rectangular section of dimensions bw and d, for which the designth of the compression block is recalculated as

a1 = d - wc

uw

bf

Md

ϕ−

'2

85.0

2.

If a1 ≤ amax, the area of tensile steel reinforcement is then given by



As2 =

−ϕ

21a

df

M

y

uw , and

As = As1 + As2.

This steel is to be placed at the bottom of the T-beam.

If a1 > amax, compression reinforcement is required (UBC 1910.3.3) and iscalculated as follows:

− The compressive force in web concrete alone is given by

C = 0.85 'cf bamax. (UBC 1910.2.7.1)

− Therefore the moment resisted by concrete web and tensile steel is

Muc = C

−

2maxa

d ϕ, and

the moment resisted by compression steel and tensile steel is

Mus = Muw - Muc.

− Therefore, the compression steel is computed as

'sA =

ϕ− )'(' ddf

M

s

us , where

'sf = 0.003Es

−

cdc '

. (UBC 1910.2.4)

− The tensile steel for balancing compression in web concrete is

As2 =

ϕ

−

2maxa

df

M

y

uc , and

the tensile steel for balancing compression in steel is



As3 = ( )ϕ− 'ddfM

y

us .

− The total tensile reinforcement, As = As1 + As2 + As3, and total compres-

sion reinforcement is 'sA . As is to be placed at bottom and '

sA is to be

placed at top.

Minimum Tensile ReinforcementThe minimum flexural tensile steel provided in a rectangular section in an Or-dinary moment resisting frame is given by the minimum of the two followinglimits:

As ≥ max

dbf

dbf

fw

yw

y

c 200 and

3 '

or (UBC 1910.5.1)

As ≥ 34

As(required) (UBC 1910.5.3)

Special Consideration for Seismic DesignFor Special moment resisting concrete frames (seismic design), the beam de-sign satisfies the following additional conditions (see also Table 1 for compre-hensive listing):

The minimum longitudinal reinforcement shall be provided at both the topand bottom. Any of the top and bottom reinforcement shall not be lessthan As(min) (UBC 1921.3.2.1).

As(min) ≥ max

dbf

dbf

fw

yw

y

c 200 and

3 '

or (UBC 1910.5.1, 1921.3.2.1)

As(min) ≥ 34

As(required). (UBC 1910.5.3, 1921.3.2.1)

The beam flexural steel is limited to a maximum given by

As ≤ 0.25 bwd. (UBC 1921.3.2.1)



Table 1 Design Criteria Table

Type ofCheck/Design

Ordinary MomentResisting Frames

(Seismic Zones 0&1)

Intermediate MomentResisting Frames(Seismic Zone 2)

Special MomentResisting Frames

(Seismic Zones 3 & 4)

ColumnCheck(interaction)

NLDa Combinations NLDa Combinations NLDa Combinations

ColumnDesign(interaction)

NLDa Combinations

1% < ρ < 8%NLDa Combinations1% < ρ < 8%

NLDa Combinationsα = 1.01% < ρ < 6%

ColumnShears NLDa Combinations

Modified NLDa Combinations(earthquake loads doubled)Column Capacityϕ = 1.0 and α = 1.0

NLDa Combinations andColumn shear capacityϕ = 1.0 and α = 1.25

BeamDesignFlexure

NLDa Combinations NLDa Combinations

NLDa Combinationsρ ≤ 0.025

ρ ≥ yy

c

ff

f 200,

3 '

≥ρ

Beam Min.MomentOverrideCheck

No Requirement

−+ ≥ uENDuEND MM31

{ }ENDuuuSPAN MMM −++ ≥ ,max51

{ }ENDuuuSPAN MMM −+− ≥ ,max51

−+ ≥ uENDuEND MM21


{ }ENDuuuSPAN MMM −−− ≥ ,max41

BeamDesignShear

NLDa Combinations

Modified NLDa Combinations(earthquake loads doubled)Beam Capacity Shear (Vp)with α = 1.0 and ϕ = 1.0plus VD+L

NLDa CombinationsBeam Capacity Shear (Vp)with α = 1.25 and ϕ = 1.0plus VD+L

Vc = 0

JointDesign No Requirement No Requirement Checked for shear

Beam/ColumnCapacityRatio

No Requirement No Requirement Reported in output file

NLDa = Number of specified loading


Technical Note 11 - 10 Design Beam Shear Reinforcement

At any end (support) of the beam, the beam positive moment capacity(i.e., associated with the bottom steel) would not be less than 1/2 of thebeam negative moment capacity (i.e., associated with the top steel) atthat end (UBC 1921.3.2.2).

Neither the negative moment capacity nor the positive moment capacityat any of the sections within the beam would be less than 1/4 of themaximum of positive or negative moment capacities of any of the beamend (support) stations (UBC 1921.3.2.2).

For Intermediate moment resisting concrete frames (i.e., seismic design), thebeam design would satisfy the following conditions:

At any support of the beam, the beam positive moment capacity wouldnot be less than 1/3 of the beam negative moment capacity at that end(UBC 1921.8.4.1).

Neither the negative moment capacity nor the positive moment capacityat any of the sections within the beam would be less than 1/5 of themaximum of positive or negative moment capacities of any of the beamend (support) stations (UBC 1921.8.4.1).

Design Beam Shear ReinforcementThe shear reinforcement is designed for each load combination at a user-defined number of stations along the beam span. The following steps are in-volved in designing the shear reinforcement for a particular beam for a par-ticular load combination at a particular station resulting from the beam majorshear:

Determine the factored shear force, Vu.

Determine the shear force, Vc, that can be resisted by the concrete.

Determine the reinforcement steel required to carry the balance.

For Special and Intermediate moment resisting frames (Ductile frames), theshear design of the beams is also based on the probable and nominal momentcapacities of the members, respectively, in addition to the factored load de-sign.


Design Beam Shear Reinforcement Technical Note 11 - 11


Determine Shear Force and Moment In the design of the beam shear reinforcement of an Ordinary moment

resisting concrete frame, the shear forces and moments for a particularload combination at a particular beam section are obtained by factoringthe associated shear forces and moments with the corresponding loadcombination factors.

In the design of Special moment resisting concrete frames (i.e.,seismic design), the shear capacity of the beam is also checked for thecapacity-shear associated with the probable moment capacities at theends and the factored gravity load. This check is performed in addition tothe design check required for Ordinary moment resisting frames. The ca-pacity-shear force, Vp, is calculated from the probable moment capacitiesof each end of the beam and the gravity shear forces. The procedure forcalculating the design shear force in a beam from probable moment ca-pacity is the same as that described for a column in section “Design Col-umn Shear Reinforcement” in Concrete Frame Design UBC97 TechnicalNote 10 Column Design. See also Table 1 for details.

The design shear force Vu is then given by (UBC 1921.3.4.1)

Vu = Vp + VD+L (UBC 1921.3.4.1)

where Vp is the capacity shear force obtained by applying the calculatedprobable ultimate moment capacities at the two ends of the beams actingin opposite directions. Therefore, Vp is the maximum of

1PV and 2PV ,

where

1PV = L

MM JI+− +

, and

2PV = L

MM JI−+ +

, where

−IM = Moment capacity at end I, with top steel in tension, using a

steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),



+JM = Moment capacity at end J, with bottom steel in tension, using a


+IM = Moment capacity at end I, with bottom steel in tension, using a


−JM = Moment capacity at end J, with top steel in tension, using a

steel yield stress value of αfy and no ϕ factors (ϕ = 1.0), and

L = Clear span of beam.

For Special moment resisting frames, α is taken as 1.25 (UBC 1921.0).VD+L is the contribution of shear force from the in-span distribution ofgravity loads.

For Intermediate moment resisting frames, the shear capacity of thebeam is also checked for the capacity shear based on the nominal momentcapacities at the ends and the factored gravity loads, in addition to thecheck required for Ordinary moment resisting frames. The design shearforce in beams is taken to be the minimum of that based on the nominalmoment capacity and factored shear force. The procedure for calculatingnominal (ϕ = 1.0) moment capacity is the same as that for computing theprobable moment capacity for Special moment resisting frames, exceptthat α is taken equal to 1 rather than 1.25 (UBC 1921.0, 1921.8.3). Thefactored shear forces are based on the specified load factors, except theearthquake load factors are doubled (UBC 1921.8.3). The computation ofthe design shear force in a beam of an Intermediate moment resistingframe is also the same as that for columns, which is described in Con-crete Frame Design UBC97 Technical Note 10 Column Design. Also seeTable 1 for details.

Determine Concrete Shear CapacityThe allowable concrete shear capacity is given by

Vc = 2 'cf bwd. (UBC 1911.3.1.1)

For Special moment resisting frame concrete design, Vc is set to zero if boththe factored axial compressive force, including the earthquake effect Pu, is

less than 'cf Ag/20 and the shear force contribution from earthquake VE is



more than half of the total maximum shear force over the length of the mem-ber Vu (i.e., VE ≥ 0.5Vu) (UBC 1921.3.4.2).

Determine Required Shear ReinforcementGiven Vu and Vc, the required shear reinforcement in area/unit length is cal-culated as

Av = df

sVV

ys

cu )/( −ϕ. (UBC 1911.5.6.1, 1911.5.6.2)

The shear force resisted by steel is limited by

(Vu/ϕ - Vc) ≤ 8 'cf bd. (UBC 1911.5.6.8)

Otherwise, redimensioning of the concrete section is required. Here ϕ, thestrength reduction factor, is 0.85 for nonseismic design or for seismic designin Seismic Zones 0, 1, and 2 (UBC 1909.3.2.3) and is 0.60 for seismic designin Seismic Zones 3 and 4 (UBC 1909.3.4.1). The maximum of all the calcu-lated Av values, obtained from each load combination, is reported along withthe controlling shear force and associated load combination number.

The beam shear reinforcement requirements displayed by the program arebased purely on shear strength considerations. Any minimum stirrup require-ments to satisfy spacing and volumetric considerations must be investigatedindependently of the program by the user.




Technical Note 12Joint Design

This Technical Note explains how the program performs a rational analysis ofthe beam-column panel zone to determine the shear forces that are gener-ated in a joint. The program then checks this against design shear strength.

OverviewTo ensure that the beam-column joint of special moment resisting framespossesses adequate shear strength, the program performs a rational analysisof the beam-column panel zone to determine the shear forces that are gener-ated in the joint. The program then checks this against design shear strength.

Only joints having a column below the joint are designed. The mate-rial properties of the joint are assumed to be the same as those of thecolumn below the joint.

The joint analysis is completed in the major and the minor directions of thecolumn. The joint design procedure involves the following steps:

• Determine the panel zone design shear force,Vuh

• Determine the effective area of the joint

• Check panel zone shear stress

The algorithms associated with these three steps are described in detail in thefollowing three sections.

Determine the Panel Zone Shear ForceFigure 1 illustrates the free body stress condition of a typical beam-columnintersection for a column direction, major or minor.

Joint Design Concrete Frame Design UBC97

Technical N

Figure1

ote 12 - 2 Determine the Panel Zone Shear Force

Beam-Column Joint Analysis

Concrete Frame Design UBC97 Joint Design

Determine the Panel Zone Shear Force Technical Note 12 - 3

The force Vuh is the horizontal panel zone shear force that is to be calculated.

The forces that act on the joint are Pu, Vu, MuL and Mu

R. The forces Pu and Vu

are axial force and shear force, respectively, from the column framing into thetop of the joint. The moments Mu

L and MuR are obtained from the beams

framing into the joint. The program calculates the joint shear force Vuh by re-

solving the moments into C and T forces. Noting that TL = CL and TR = CR,

Vuh = TL + TR - Vu

The location of C or T forces is determined by the direction of the moment.The magnitude of C or T forces is conservatively determined using basic prin-ciples of ultimate strength theory, ignoring compression reinforcement as fol-lows. The program first calculates the maximum compression, Cmax, and themaximum moment, Mmax, that can be carried by the beam.

bdfC c'

max 85.0=

2maxmaxd

CM =

Then the program conservatively determines C and T forces as follows:

−−==

maxmax

)(11

M

MabsCTC

The program resolves the moments and the C and T forces from beams thatframe into the joint in a direction that is not parallel to the major or minordirections of the column along the direction that is being investigated, therebycontributing force components to the analysis. Also, the program calculatesthe C and T for the positive and negative moments, considering the fact thatthe concrete cover may be different for the direction of moment.

In the design of special moment resisting concrete frames, the evaluation ofthe design shear force is based on the moment capacities (with reinforcingsteel overstrength factor, α, and no ϕ factors) of the beams framing into thejoint (UBC 1921.5.1.1). The C and T forces are based on these moment ca-pacities. The program calculates the column shear force Vu from the beammoment capacities, as follows:


Technical N

H

MMV

Ru

Lu

u

+=

See Figure 2. It should be noted that the points of inflection shown on Figure2 are taken as midway between actual lateral support points for the columns.If there is no column at the top of the joint, the shear force from the top ofthe column is taken as zero.

Figure 2

ote 12 - 4 Determine the Panel Zone Shear Force

Column Shear Force Vu


Determine the Effective Area of Joint Technical Note 12 - 5

The effects of load reversals, as illustrated in Case 1 and Case 2 of Figure 1,are investigated and the design is based on the maximum of the joint shearsobtained from the two cases.

Determine the Effective Area of JointThe joint area that resists the shear forces is assumed always to be rectan-gular in plan view. The dimensions of the rectangle correspond to the majorand minor dimensions of the column below the joint, except if the beamframing into the joint is very narrow. The effective width of the joint area tobe used in the calculation is limited to the width of the beam plus the depth ofthe column. The area of the joint is assumed not to exceed the area of thecolumn below. The joint area for joint shear along the major and minor direc-tions is calculated separately (ACI R21.5.3).

It should be noted that if the beam frames into the joint eccentrically, theabove assumptions may be unconservative and the user should investigatethe acceptability of the particular joint.

Check Panel Zone Shear StressThe panel zone shear stress is evaluated by dividing the shear force Vu

h bythe effective area of the joint and comparing it with the following design shearstrengths (UBC 1921.5.3):

20ϕ cf ' for joints confined on all four sides

v = 15ϕcf ' for joints confined on three faces or on two

opposite faces{12ϕ cf ' for all other joints

where ϕ = 0.85 (by default). (UBC 1909.3.2.3,1909.3.4.1)

A beam that frames into a face of a column at the joint is considered in thisprogram to provide confinement to the joint if at least three-quarters of theface of the joint is covered by the framing member (UBC 1921.5.3.1).


Technical Note 12 - 6 Beam/Column Flexural Capacity Ratios

For light-weight aggregate concrete, the design shear strength of the joint isreduced in the program to at least three-quarters of that of the normal weight

concrete by replacing the 'cf with

'

, 4/3,'min ccfactorcs fff (UBC 1921.5.3.2)

For joint design, the program reports the joint shear, the joint shear stress,the allowable joint shear stress and a capacity ratio.

Beam/Column Flexural Capacity RatiosAt a particular joint for a particular column direction, major or minor, the pro-gram will calculate the ratio of the sum of the beam moment capacities to thesum of the column moment capacities. For Special Moment-Resisting Frames,the following UBC provision needs to be satisfied (UBC 1921.4.2.2).

∑Me ≥ 56

∑Mg (UBC 1921.4.2.2)

The capacities are calculated with no reinforcing overstrength factor, α, andincluding ϕ factors. The beam capacities are calculated for reversed situations(Cases 1 and 2) as illustrated in Figure 1 and the maximum summation ob-tained is used.


The column capacity summation includes the column above and the columnbelow the joint. For each load combination, the axial force, Pu, in each of thecolumns is calculated from the program analysis load combinations. For eachload combination, the moment capacity of each column under the influence ofthe corresponding axial load Pu is then determined separately for the majorand minor directions of the column, using the uniaxial column interaction dia-gram, see Figure 3. The moment capacities of the two columns are added togive the capacity summation for the corresponding load combination. Themaximum capacity summations obtained from all of the load combinations isused for the beam/column capacity ratio.


Beam/

The beam/column flexural capacity ratios are only reported for Special Mo-ment-Resisting Frames involving seismic design load combinations. If this ra-tio is greater than 5/6, a warning message is printed in the output file.

Figu

Column Flexural Capacity Ratios Technical Note 12 - 7

re 3 Moment Capacity Mu at a Given Axial Load Pu

Input Data Technical Note 13 - 1



Technical Note 13Input Data

This Technical Note describes the concrete frame design input data forUBC97. The input can be printed to a printer or to a text file when you clickthe File menu > Print Tables > Concrete Frame Design command. Aprintout of the input data provides the user with the opportunity to carefullyreview the parameters that have been input into the program and upon whichprogram design is based. Further information about using the Print DesignTables form is presented at the end of this Technical Note.

Input DataThe program provides the printout of the input data in a series of tables. Thecolumn headings for input data and a description of what is included in thecolumns of the tables are provided in Table 1 of this Technical Note.

Table 1 Concrete Frame Design Input DataCOLUMN HEADING DESCRIPTIONLoad Combination MultipliersCombo Design load combination. See Technical Note 8.

TypeLoad type: dead, live, superimposed dead, earthquake, wind,snow, reduced live load, other.

Case Name of load case.

Factor Load combination scale factor.

Code PreferencesPhi_bending Bending strength reduction factor.

Phi_tension Tensile strength reduction factor.

Phi_compression(Tied)

Compressive strength reduction factor for tied columns.

Phi_compression (Spi-ral)

Compressive strength reduction factor for reinforced columns.

Phi_shear Shear strength reduction factor.

Input Data Concrete Frame Design UBC97

Technical Note 13 - 2 Table 1 Concrete Frame Design Input Data

Table 1 Concrete Frame Design Input DataCOLUMN HEADING DESCRIPTIONMaterial Property DataMaterial Name Concrete, steel, other.

Material Type Isotropic or orthotropic.

Design Type

Modulus of Elasticity

Poisson's Ratio

Thermal Coeff Coefficient of thermal expansion.

Shear Modulus

Material Property Mass and WeightMaterial Name Concrete, steel, other.

Mass Per Unit Vol Used to calculate self-mass of structure.

Weight Per Unit Vol Used to calculate self-weight of structure.

Material Design Data for Concrete MaterialsMaterial Name Concrete, steel, other.

Lightweight Concrete

Concrete FC Concrete compressive strength.

Rebar FY Bending reinforcing steel yield strength.

Rebar FYS Shear reinforcing steel yield strength.

Lightwt Reduc Fact Shear strength reduction factor for light weight concrete; default= 1.0.

Concrete Column Property DataSection Label Label applied to section.

Mat Label Material label.

Column Depth

Column Width

Rebar Pattern Layout of main flexural reinforcing steel.

Concrete Cover Minimum clear concrete cover.

Bar Area Area of individual reinforcing bar to be used.

Concrete Frame Design UBC97 Input Data

Using the Print Design Tables Form Technical Note 13 - 3

Table 1 Concrete Frame Design Input DataCOLUMN HEADING DESCRIPTIONConcrete Column Design Element InformationStory ID Column assigned to story level at top of column.

Column Line Grid line.

Section ID Name of section assigned to column.

Framing Type Lateral or gravity.

RLLF Factor

L_Ratio Major Unbraced length about major axis.

L_Ratio Minor Unbraced length about minor axis.

K Major Effective length factor; default = 1.0.

K Minor Effective length factor; default = 1.0.

Concrete Beam Design Element InformationStory ID Story level at which beam occurs.

Bay ID Grid lines locating beam.

Section ID Section number assigned to beam.

Framing type Lateral or gravity.

RLLF Factor



Using the Print Design Tables FormTo print steel frame design input data directly to a printer, use the File menu> Print Tables > Concrete Frame Design command and click the checkbox on the Print Design Tables form. Click the OK button to send the print toyour printer. Click the Cancel button rather than the OK button to cancel theprint. Use the File menu > Print Setup command and the Setup>> buttonto change printers, if necessary.

To print steel frame design input data to a file, click the Print to File check boxon the Print Design Tables form. Click the Filename>> button to change the

Input Data Concrete Frame Design UBC97

Technical Note 13 - 4 Using the Print Design Tables Form

path or filename. Use the appropriate file extension for the desired format(e.g., .txt, .xls, .doc). Click the OK buttons on the Open File for Printing Ta-bles form and the Print Design Tables form to complete the request.

Note:


The Append check box allows you to add data to an existing file. The path andfilename of the current file is displayed in the box near the bottom of the PrintDesign Tables form. Data will be added to this file. Or use the Filename>>button to locate another file, and when the Open File for Printing Tables cau-tion box appears, click Yes to replace the existing file.

If you select a specific frame element(s) before using the File menu > PrintTables > Concrete Frame Design command, the Selection Only check boxwill be checked. The print will be for the selected beam(s) only.

Table 1 Concrete Column Design Output Technical Note 14 - 1



Technical Note 14Output Details

This Technical Note describes the concrete frame design output for UBC97that can be printed to a printer or to a text file. The design output is printedwhen you click the File menu > Print Tables > Concrete Frame Designcommand and select Output Summary of the Print Design Tables dialog box.Further information about using the Print Design Tables dialog box is pre-sented at the end of this Technical Note.

The program provides the output data in a series of tables. The columnheadings for output data and a description of what is included in the columnsof the tables are provided in Table 1 of this Technical Note.

Table 1 Concrete Column Design OutputCOLUMN HEADING DESCRIPTION

Biaxial P-M Interaction and Shear Design of Column-Type Elements

Story ID Column assigned to story level at top of column.

Column Line Grid lines.


Station ID

Required Reinforcing

Longitudinal Area of longitudinal reinforcing required.

Combo Load combination for which the reinforcing is designed.

Shear22 Shear reinforcing required.



Output Details Concrete Frame Design UBC97

Technical Note 14 - 2 Table 2 Concrete Column Joint Output



Table 2 Concrete Column Joint OutputCOLUMN HEADING DESCRIPTION

Beam to Column Capacity Ratios and Joint Shear Capacity Check

Story ID Story level at which joint occurs.


Section ID Assigned section name.

Beam-Column Capacity Ratios

Major Ratio of beam moment capacity to column capacity.

Combo Load combination upon which the ratio of beam moment ca-pacity to column capacity is based.

Minor Ratio of beam moment capacity to column capacity.



Major Ratio of factored load versus allowed capacity.

Combo Load combination upon which the ratio of factored load versusallowed capacity is based.

Minor Ratio of factored load versus allowed capacity.


Concrete Frame Design UBC97 Output Details


Using the Print Design Tables FormTo print concrete frame design input data directly to a printer, use the Filemenu > Print Tables > Concrete Frame Design command and click thecheck box on the Print Design Tables dialog box. Click the OK button to sendthe print to your printer. Click the Cancel button rather than the OK buttonto cancel the print. Use the File menu > Print Setup command and theSetup>> button to change printers, if necessary.

To print concrete frame design input data to a file, click the Print to File checkbox on the Print Design Tables dialog box. Click the Filename>> button tochange the path or filename. Use the appropriate file extension for the de-sired format (e.g., .txt, .xls, .doc). Click the OK buttons on the Open File forPrinting Tables dialog box and the Print Design Tables dialog box to completethe request.

Note:


The Append check box allows you to add data to an existing file. The path andfilename of the current file is displayed in the box near the bottom of the PrintDesign Tables dialog box. Data will be added to this file. Or use the File-name>> button to locate another file, and when the Open File for PrintingTables caution box appears, click Yes to replace the existing file.


Introduction to the ACI318-99 Series of Technical Notes Technical Note 15 - 1


CONCRETE FRAME DESIGN ACI-318-99

Technical Note 15General and Notation

Introduction to the ACI318-99 Series of Technical NotesThe ACI-318-99 Concrete Frame Design series of Technical Notes describes indetail the various aspects of the concrete design procedure that is used bythis program when the user selects the ACI-318-99 Design Code (ACI 1999).The various notations used in this series are listed herein.

The design is based on user-specified loading combinations. The programprovides a set of default load combinations that should satisfy requirementsfor the design of most building type structures. See Concrete Frame DesignACI-318-99 Technical Note 18 Design Load Combination for more information.

The program provides options to design or check Earthquake resistingframes; Ordinary, Earthquake resisting frames; Intermediate (moderateseismic risk areas), and Earthquake resisting frames; Special (high seismicrisk areas) moment resisting frames as required for seismic design provisions.The details of the design criteria used for the different framing systems aredescribed in Concrete Frame Design ACI-318-99 Technical Note 19 StrengthReduction Factors, Concrete Frame Design ACI-318-99 Technical Note 20 Col-umn Design, Concrete Frame Design ACI-318-99 Technical Note 21 Beam De-sign, and Concrete Frame Design ACI-318-99 Technical Note 22 Joint Design.

The program uses preferences and overwrites, which are described in Con-crete Frame Design ACI-318-99 Technical Note 16 Preferences and ConcreteFrame Design ACI-318-99 Technical Note 17 Overwrites. It also provides in-put and output data summaries, which are described in Concrete Frame De-sign ACI-318-99 Technical Note 23 Input Data and Concrete Frame DesignACI-318-99 Technical Note 24 Output Details.

English as well as SI and MKS metric units can be used for input. But the codeis based on Inch-Pound-Second units. For simplicity, all equations and de-scriptions presented in this chapter correspond to Inch-Pound-Second unitsunless otherwise noted.

General and Notation Concrete Frame Design ACI-318-99

Technical Note 15 - 2 Notation

NotationAcv Area of concrete used to determine shear stress, sq-in

Ag Gross area of concrete, sq-in

As Area of tension reinforcement, sq-in

'sA Area of compression reinforcement, sq-in

As(required) Area of steel required for tension reinforcement, sq-in

Ast Total area of column longitudinal reinforcement, sq-in

Av Area of shear reinforcement, sq-in

Cm Coefficient, dependent upon column curvature, used to calculatemoment magnification factor

Ec Modulus of elasticity of concrete, psi

Es Modulus of elasticity of reinforcement, assumed as 29,000,000psi (ACI 8.5.2)

Ig Moment of inertia of gross concrete section about centroidal axis,neglecting reinforcement, in4

Ise Moment of inertia of reinforcement about centroidal axis ofmember cross section, in4

L Clear unsupported length, in

M1 Smaller factored end moment in a column, lb-in

M2 Larger factored end moment in a column, lb-in

Mc Factored moment to be used in design, lb-in

Mns Nonsway component of factored end moment, lb-in

Ms Sway component of factored end moment, lb-in

Concrete Frame Design ACI-318-99 General and Notation

Notation Technical Note 15 - 3

Mu Factored moment at section, lb-in

Mux Factored moment at section about X-axis, lb-in

Muy Factored moment at section about Y-axis, lb-in

Pb Axial load capacity at balanced strain conditions, lb

Pc Critical buckling strength of column, lb

Pmax Maximum axial load strength allowed, lb

P0 Axial load capacity at zero eccentricity, lb

Pu Factored axial load at section, lb

Vc Shear resisted by concrete, lb

VE Shear force caused by earthquake loads, lb

VD+L Shear force from span loading, lb

Vu Factored shear force at a section, lb

Vp Shear force computed from probable moment capacity, lb

a Depth of compression block, in

ab Depth of compression block at balanced condition, in

b Width of member, in

bf Effective width of flange (T-Beam section), in

bw Width of web (T-Beam section), in

c Depth to neutral axis, in

cb Depth to neutral axis at balanced conditions, in

d Distance from compression face to tension reinforcement, in

d' Concrete cover to center of reinforcing, in

General and Notation Concrete Frame Design ACI-318-99

Technical Note 15 - 4 Notation

ds Thickness of slab (T-Beam section), in

'cf Specified compressive strength of concrete, psi

fy Specified yield strength of flexural reinforcement, psify ≤ 80,000 psi (ACI 9.4)

fys Specified yield strength of shear reinforcement, psi

h Dimension of column, in

k Effective length factor

r Radius of gyration of column section, in

α Reinforcing steel overstrength factor

β1 Absolute value of ratio of maximum factored axial dead load tomaximum factored axial total load

βd Absolute value of ratio or maximum factored axial dead load tomaximum factored axial total load

δs Moment magnification factor for sway moments

δns Moment magnification factor for nonsway moments

εc Strain in concrete

εs Strain in reinforcing steel

ϕ Strength reduction factor



CONCRETE FRAME DESIGN ACI318-99

Technical Note 16Preferences

This Technical Note describes the items in the Preferences form.

GeneralThe concrete frame design preferences in this program are basic assignmentsthat apply to all concrete frame elements. Use the Options menu > Prefer-ences > Concrete Frame Design command to access the Preferences formwhere you can view and revise the concrete frame design preferences.

Default values are provided for all concrete frame design preference items.Thus, it is not required that you specify or change any of the preferences. Youshould, however, at least review the default values for the preference itemsto make sure they are acceptable to you.

Using the Preferences FormTo view preferences, select the Options menu > Preferences > ConcreteFrame Design. The Preferences form will display. The preference optionsare displayed in a two-column spreadsheet. The left column of the spread-sheet displays the preference item name. The right column of the spreadsheetdisplays the preference item value.

To change a preference item, left click the desired preference item in eitherthe left or right column of the spreadsheet. This activates a drop-down box orhighlights the current preference value. If the drop-down box appears, selecta new value. If the cell is highlighted, type in the desired value. The prefer-ence value will update accordingly. You cannot overwrite values in the drop-down boxes.

When you have finished making changes to the composite beam preferences,click the OK button to close the form. You must click the OK button for thechanges to be accepted by the program. If you click the Cancel button to exit

Preferences Concrete Frame Design ACI318-99

Technical Note 16 - 2 Preferences

the form, any changes made to the preferences are ignored and the form isclosed.

PreferencesFor purposes of explanation in this Technical Note, the preference items arepresented in Table. The column headings in the table are described as fol-lows:

Item: The name of the preference item as it appears in the cells at theleft side of the Preferences form.

Possible Values: The possible values that the associated preference itemcan have.

Default Value: The built-in default value that the program assumes forthe associated preference item.

Description: A description of the associated preference item.


ItemPossibleValues


Design Code Any code inthe program

ACI 318-99 Design code used for design ofconcrete frame elements.

Phi BendingTension

>0 0.9 Unitless strength reduction factor perACI 9.3.

Phi Compres-sion Tied


Phi Compres-sion Spiral


Phi Shear >0 0.85 Unitless strength reduction factor perACI 9.3.

Number Inter-action Curves

≥4.0 24 Number of equally spaced interactioncurves used to create a full 360-degreeinteraction surface (this item should bea multiple of four). We recommend thatyou use 24 for this item.

Concrete Frame Design ACI318-99 Preferences

Preferences Technical Note 16 - 3


ItemPossibleValues


Number Inter-action Points

Any odd value

≥4.0

11 Number of points used for defining asingle curve in a concrete frameinteraction surface (this item should beodd).

Time HistoryDesign

Envelopes orStep-by-Step

Envelopes Toggle for design load combinationsthat include a time history designed forthe envelope of the time history, ordesigned step-by-step for the entiretime history. If a single design loadcombination has more than one timehistory case in it, that design loadcombination is designed for theenvelopes of the time histories,regardless of what is specified here.




Technical Note 17Overwrites

GeneralThe concrete frame design overwrites are basic assignments that apply onlyto those elements to which they are assigned. This Technical Note describesconcrete frame design overwrites for ACI318-99. To access the overwrites,select an element and click the Design menu > Concrete Frame Design >View/Revise Overwrites command.

Default values are provided for all overwrite items. Thus, you do not need tospecify or change any of the overwrites. However, at least review the defaultvalues for the overwrite items to make sure they are acceptable. Whenchanges are made to overwrite items, the program applies the changes onlyto the elements to which they are specifically assigned; that is, to the ele-ments that are selected when the overwrites are changed.

OverwritesFor explanation purposes in this Technical Note, the overwrites are presentedin Table 1. The column headings in the table are described as follows.

Item: The name of the overwrite item as it appears in the program. Tosave space in the formes, these names are generally short.

Possible Values: The possible values that the associated overwrite itemcan have.

Default Value: The default value that the program assumes for the asso-ciated overwrite item.

Description: A description of the associated overwrite item.

An explanation of how to change an overwrite is provided at the end of thisTechnical Note.

Overwrites Concrete Frame Design ACI318-99



ItemPossibleValues


ElementSection

ElementType

Sway Special,Sway Interme-

diate,Sway

OrdinaryNonSway

Sway Special Frame type per moment frame defini-tion given in ACI 21.1.

Live LoadReduction

Factor

>0

≤1.0

1. Used to reduce the live load contribu-tion to the factored loading.

HorizontalEarthquake

Factor

>0

≤1.0

1


(Major)

>0

≤1.0

1.0


(Minor)

>0

≤1.0

1.0


(K Major)

>0

≤1.0

1 See ACI 10.12, 10.13 and FigureR10.12.1.


(K Minor)

>0

≤1.0

1 See ACI 10.12, 10.13 and FigureR10.12.1.

MomentCoefficient(Cm Major)

>0

≤1.0

1 Factor relating actual moment diagramto an equivalent uniform moment dia-gram. See ACI 10.12.3.

MomentCoefficient(Cm Minor)

>0

≤1.0

1 Factor relating actual moment diagramto an equivalent uniform moment dia-gram. See ACI 10.12.3.


(Dns Major)

>0

≤1.0

1 See ACI 10.12.

Concrete Frame Design ACI318-99 Overwrites



ItemPossibleValues



(Dns Minor)

1 See ACI 10.13.

Sway MomentFactor

(Ds Major)

1 See ACI 10.13.

Sway MomentFactor

(Ds Minor)

1 See ACI 10.13.

Making Changes in the Overwrites FormTo access the concrete frame overwrites, select an element and click the De-sign menu > Concrete Frame Design > View/Revise Overwrites com-mand.

The overwrites are displayed in the form with a column of check boxes and atwo-column spreadsheet. The left column of the spreadsheet contains thename of the overwrite item. The right column of the spreadsheet contains theoverwrites values.

Initially, the check boxes in the Concrete Frame Design Overwrites form areall unchecked and all of the cells in the spreadsheet have a gray backgroundto indicate that they are inactive and the items in the cells cannot bechanged. The names of the overwrite items are displayed in the first columnof the spreadsheet. The values of the overwrite items are visible in the secondcolumn of the spreadsheet if only one element was selected before the over-writes form was accessed. If multiple elements were selected, no values showfor the overwrite items in the second column of the spreadsheet.

After selecting one or multiple elements, check the box to the left of an over-write item to change it. Then left click in either column of the spreadsheet toactivate a drop-down box or highlight the contents in the cell in the right col-umn of the spreadsheet. If the drop-down box appears, select a value from

Overwrites Concrete Frame Design ACI318-99


the box. If the cell contents is highlighted, type in the desired value. Theoverwrite will reflect the change. You cannot change the values of the drop-down boxes.

When changes to the overwrites have been completed, click the OK button toclose the form. The program then changes all of the overwrite items whoseassociated check boxes are checked for the selected members. You must clickthe OK button for the changes to be accepted by the program. If you click theCancel button to exit the form, any changes made to the overwrites are ig-nored and the form is closed.

Resetting Concrete Frame Overwrites to Default ValuesUse the Design menu > Concrete Frame Design > Reset All Overwritescommand to reset all of the steel frame overwrites. All current design resultswill be deleted when this command is executed.

Important note about resetting overwrites: The program defaults for theoverwrite items are built into the program. The concrete frame overwrite val-ues that were in a .edb file that you used to initialize your model may be dif-ferent from the built-in program default values. When you reset overwrites,the program resets the overwrite values to its built-in values, not to the val-ues that were in the .edb file used to initialize the model.

Design Load Combinations Technical Note 18 - 1



Technical Note 18Design Load Combinations

The design load combinations are the various combinations of the prescribedload cases for which the structure needs to be checked. For the ACI 318-99code, if a structure is subjected to dead load (DL) and live load (LL) only, thestress check may need only one load combination, namely 1.4 DL + 1.7 LL(ACI 9.2.1). However, in addition to the dead and live loads, if the structure issubjected to wind (WL) and earthquake (EL) loads and considering that windand earthquake forces are reversible, the following load combinations shouldbe considered (ACI 9.2).

1.4 DL1.4 DL + 1.7 LL (ACI 9.2.1)

0.9 DL ± 1.3 WL0.75 (1.4 DL + 1.7 LL ± 1.7 WL) (ACI 9.2.2)

0.9 DL ± 1.3 * 1.1 EL0.75 (1.4 DL + 1.7 LL ± 1.7 * 1.1 EL) (ACI 9.2.3)

These are also the default design load combinations in the program wheneverthe ACI 318-99 code is used. The user is warned that the above load combi-nations involving seismic loads consider service-level seismic forces. Differentload factors may apply with strength-level seismic forces (ACI R9.2.3).

Live load reduction factors can be applied to the member forces of the liveload condition on an element-by-element basis to reduce the contribution ofthe live load to the factored loading. See Concrete Frame Design ACI 318-99Technical Note 17 Overwrites for more information.

Strength Reduction Factors Technical Note 19 - 1



Technical Note 19Strength Reduction Factors

The strength reduction factors, ϕ, are applied on the nominal strength to ob-tain the design strength provided by a member. The ϕ factors for flexure, ax-ial force, shear, and torsion are as follows:

ϕ = 0.90 for flexure (ACI 9.3.2.1)

ϕ = 0.90 for axial tension (ACI 9.3.2.2)

ϕ = 0.90 for axial tension and flexure (ACI 9.3.2.2)

ϕ = 0.75 for axial compression, and axial compressionand flexure (spirally reinforced column) (ACI 9.3.2.2)

ϕ = 0.70 for axial compression, and axial compressionand flexure (tied column) (ACI 9.3.2.2)

ϕ = 0.85 for shear and torsion (ACI 9.3.2.3)




Technical Note 20Column Design

This Technical Note describes how the program checks column capacity or de-signs reinforced concrete columns when the ACI-318-99 code is selected.

OverviewThe program can be used to check column capacity or to design columns. Ifyou define the geometry of the reinforcing bar configuration of each concretecolumn section, the program will check the column capacity. Alternatively, theprogram can calculate the amount of reinforcing required to design the col-umn. The design procedure for the reinforced concrete columns of the struc-ture involves the following steps:

Generate axial force/biaxial moment interaction surfaces for all of the dif-ferent concrete section types of the model. A typical biaxial interactionsurface is shown in Figure 1. When the steel is undefined, the programgenerates the interaction surfaces for the range of allowable reinforce-ment 1 to 8 percent for Ordinary and Intermediate moment resistingframes (ACI 10.9.1) and 1 to 6 percent for Special moment resistingframes (ACI 21.4.3.1).

Calculate the capacity ratio or the required reinforcing area for the fac-tored axial force and biaxial (or uniaxial) bending moments obtained fromeach loading combination at each station of the column. The target capac-ity ratio is taken as one when calculating the required reinforcing area.


The following four sections describe in detail the algorithms associated withthis process.

Column Design Concrete Frame Design ACI-318-99

Technical Note 20 -

Figure 1 A Ty

GenerationThe column caof discrete pofailure surfacemulation allowinteraction dia

The coordinatestrain in three

2 Generation of Biaxial Interaction Surfaces

pical Column Interaction Surface

of Biaxial Interaction Surfacespacity interaction volume is numerically described by a seriesints that are generated on the three-dimensional interaction. In addition to axial compression and biaxial bending, the for-s for axial tension and biaxial bending considerations. A typicalgram is shown in Figure 1.

s of these points are determined by rotating a plane of linear dimensions on the section of the column. See Figure 2. The

Concrete Frame Design ACI-318-99 Column Design

Generation of Biaxial Interaction Surfaces Technical Note 20 - 3

linear strain diagram limits the maximum concrete strain, εc, at the extremityof the section, to 0.003 (ACI 10.2.3).

The formulation is based consistently upon the general principles of ultimatestrength design (ACI 10.3), and allows for any doubly symmetric rectangular,square, or circular column section.

The stress in the steel is given by the product of the steel strain and the steelmodulus of elasticity, εsEs, and is limited to the yield stress of the steel, fy(ACI 10.2.4). The area associated with each reinforcing bar is assumed to beplaced at the actual location of the center of the bar and the algorithm doesnot assume any further simplifications with respect to distributing the area ofsteel over the cross section of the column, such as an equivalent steel tube orcylinder. See Figure 3.

The concrete compression stress block is assumed to be rectangular, with a

stress value of 0.85 'cf (ACI 10.2.7.1). See Figure 3. The interaction algorithm

provides correction to account for the concrete area that is displaced by thereinforcement in the compression zone.

The effects of the strength reduction factor, ϕ, are included in the generationof the interaction surfaces. The maximum compressive axial load is limited toϕPn(max), where

ϕPn(max) = 0.85ϕ[0.85 'cf (Ag-Ast)+fyAst] spiral column, (ACI 10.3.5.1)

ϕPn(max) = 0.80ϕ[0.85 'cf (Ag-Ast)+fyAst] tied column, (ACI 10.3.5.2)

ϕ = 0.70 for tied columns, and (ACI 9.3.2.2)

ϕ = 0.75 for spirally reinforced columns. (ACI 9.3.2.2)

The value of ϕ used in the interaction diagram varies from ϕ(compression) toϕ(flexure) based on the axial load. For low values of axial load, ϕ is increasedlinearly from ϕ(compression) to ϕ(flexure) as the ϕPn decreases from the

smaller of ϕPb or 0.1 'cf Ag to zero, where ϕPb is the axial force at the balanced

condition. The ϕ factor used in calculating ϕPn and ϕPb is the ϕ(compression).In cases involving axial tension, ϕ is always ϕ(flexure), which is 0.9 by default(ACI 9.3.2.2).


Technical Note 20 - 4 Generation of Biaxial Interaction Surfaces

Figure 2 Idealized Strain Distribution for Generation of Interaction Source


Ca

F

CTpcap

Tid

Tth

lculate Column Capacity Ratio Technical Note 20 - 5

igure 3 Idealization of Stress and Strain Distribution in a Column Section

alculate Column Capacity Ratiohe column capacity ratio is calculated for each load combination at each out-ut station of each column. The following steps are involved in calculating thepacity ratio of a particular column for a particular load combination at a

articular location:

Determine the factored moments and forces from the analysis load casesand the specified load combination factors to give Pu, Mux, and Muy.

Determine the moment magnification factors for the column moments.

Apply the moment magnification factors to the factored moments. Deter-mine whether the point, defined by the resulting axial load and biaxialmoment set, lies within the interaction volume.

he factored moments and corresponding magnification factors depend on theentification of the individual column as either “sway” or “non-sway.”

he following three sections describe in detail the algorithms associated withis process.


Technical Note 20 - 6 Calculate Column Capacity Ratio

Determine Factored Moments and ForcesThe factored loads for a particular load combination are obtained by applyingthe corresponding load factors to all the load cases, giving Pu, Mux, and Muy.The factored moments are further increased for non-sway columns, if re-quired, to obtain minimum eccentricities of (0.6+0.03h) inches, where h isthe dimension of the column in the corresponding direction (ACI 10.12.3.2).

Determine Moment Magnification FactorsThe moment magnification factors are calculated separately for sway (overallstability effect), δs and for non-sway (individual column stability effect), δns.Also, the moment magnification factors in the major and minor directions arein general different (ACI 10.0, R10.13).

The moment obtained from analysis is separated into two components: thesway (Ms) and the non-sway (Mns) components. The non-sway components,which are identified by “ns” subscripts, are predominantly caused by gravityload. The sway components are identified by the “s” subscripts. The swaymoments are predominantly caused by lateral loads, and are related to thecause of side sway.

For individual columns or column-members in a floor, the magnified momentsabout two axes at any station of a column can be obtained as

M = Mns + δsMs. (ACI 10.13.3)

The factor δs is the moment magnification factor for moments causing sidesway. The moment magnification factors for sway moments, δs, is taken as 1because the component moments Ms and Mns are obtained from a “second or-der elastic (P-delta) analysis” (ACI R10.10, 10.10.1, R10.13, 10.13.4.1).

The program assumes that it performs a P-delta analysis and, therefore, mo-ment magnification factor δs for moments causing side-sway is taken as unity(ACI 10.10.2). For the P-delta analysis, the load should correspond to a loadcombination of 1.4 dead load + 1.7 live load (ACI 10.13.6). See also Whiteand Hajjar (1991). The user should use reduction factors for the moment ofinertias in the program as specified in ACI 10.11. The moment of inertia re-duction for sustained lateral load involves a factor βd (ACI 10.11). This βd forsway frame in second-order analysis is different from the one that is definedlater for non-sway moment magnification (ACI 10.0, R10.12.3, R10.13.4.1).The default moment of inertia factor in this program is 1.



The computed moments are further amplified for individual column stabilityeffect (ACI 10.12.3, 10.13.5) by the nonsway moment magnification factor,δns, as follows:

Mc = δnsM, where (ACI 10.12.3)

Mc is the factored moment to be used in design.

The non-sway moment magnification factor, δns, associated with the major orminor direction of the column is given by (ACI 10.12.3)

δns =

c

u

m

PP

C

75.01 −

≤ 1.0, where (ACI 10.12.3)

Cm = 0.6 +0.4b

a

MM

≥ 0.4, (ACI 10.12.3.1)

Ma and Mb are the moments at the ends of the column, and Mb isnumerically larger than Ma. Ma / Mb is positive for single curvaturebending and negative for double curvature bending. The above ex-pression of Cm is valid if there is no transverse load applied betweenthe supports. If transverse load is present on the span, or the lengthis overwritten, Cm=1. The user can overwrite Cm on an element-by-element basis.

Pc = 2

2

)( ukl

EIπ, where (ACI 10.12.3)

k is conservatively taken as 1; however, the program allows theuser to override this value (ACI 10.12.1).

lu is the unsupported length of the column for the direction ofbending considered. The two unsupported lengths are l22 and l33,corresponding to instability in the minor and major directions ofthe element, respectively. See Figure 4. These are the lengths


Technical No

Figure 4

The magone. Theor equal

te 20 - 8 Calculate Column Capacity Ratio

Axes of Bending and Unsupported Length

between the support points of the element in the correspondingdirections.

EI is associated with a particular column direction:

EI = d

gc IE

β+1

4.0 , where (ACI 10.12.3)

maximum factored axial sustained (dead) loadβd = maximum factored axial total load(ACI 10.0,R10.12.3)

nification factor, δns, must be a positive number and greater thanrefore, Pu must be less than 0.75Pc. If Pu is found to be greater thanto 0.75Pc, a failure condition is declared.



The above calculations are performed for major and minor directions sepa-rately. That means that δs, δns, Cm, k, lu, EI, and Pc assume different values formajor and minor directions of bending.

If the program assumptions are not satisfactory for a particular member, theuser can explicitly specify values of δs and δns.

Determine Capacity RatioAs a measure of the stress condition of the column, a capacity ratio is calcu-lated. The capacity ratio is basically a factor that gives an indication of thestress condition of the column with respect to the capacity of the column.

Before entering the interaction diagram to check the column capacity, themoment magnification factors are applied to the factored loads to obtain Pu,Mux, and Muy. The point (Pu, Mux, Muy) is then placed in the interaction spaceshown as point L in Figure 5. If the point lies within the interaction volume,the column capacity is adequate; however, if the point lies outside the inter-action volume, the column is overstressed.

This capacity ratio is achieved by plotting the point L and determining the lo-cation of point C. The point C is defined as the point where the line OL (if ex-tended outwards) will intersect the failure surface. This point is determined bythree-dimensional linear interpolation between the points that define the fail-

ure surface. See Figure 5. The capacity ratio, CR, is given by the ratio OCOL

.

If OL = OC (or CR=1), the point lies on the interaction surface and thecolumn is stressed to capacity.

If OL < OC (or CR<1), the point lies within the interaction volume and thecolumn capacity is adequate.

If OL > OC (or CR>1), the point lies outside the interaction volume andthe column is overstressed.

The maximum of all the values of CR calculated from each load combination isreported for each check station of the column along with the controlling Pu,Mux, and Muy set and associated load combination number.


Tech

Figu

ReIf thmenthe

DeTheandsignbina

nical Note 20 - 10 Required Reinforcing Area

re 5 Geometric Representation of Column Capacity Ratio

quired Reinforcing Areae reinforcing area is not defined, the program computes the reinforce-t that will give a column capacity ratio of one, calculated as described inprevious section entitled "Calculate Column Capacity Ratio."

sign Column Shear Reinforcement shear reinforcement is designed for each load combination in the major minor directions of the column. The following steps are involved in de-ing the shear reinforcing for a particular column for a particular load com-tion resulting from shear forces in a particular direction:



Determine the factored forces acting on the section, Pu and Vu. Note thatPu is needed for the calculation of Vc.

Determine the shear force, Vc, that can be resisted by concrete alone.

Calculate the reinforcement steel required to carry the balance.

For Special and Intermediate moment resisting frames (Ductile frames), theshear design of the columns is also based on the Probable moment and nomi-nal moment capacities of the members, respectively, in addition to the fac-tored moments. Effects of the axial forces on the column moment capacitiesare included in the formulation.


Determine Section Forces In the design of the column shear reinforcement of an Ordinary moment

resisting concrete frame, the forces for a particular load combination,namely, the column axial force, Pu, and the column shear force, Vu, in aparticular direction are obtained by factoring the program analysis loadcases with the corresponding load combination factors.

In the shear design of Special moment resisting frames (i.e., seismicdesign), the column is checked for capacity shear in addition to the re-quirement for the Ordinary moment resisting frames. The capacity shearforce in a column, Vp, in a particular direction is calculated from the prob-able moment capacities of the column associated with the factored axialforce acting on the column.

For each load combination, the factored axial load, Pu, is calculated. Then,

the positive and negative moment capacities, +uM and −

uM , of the column

in a particular direction under the influence of the axial force Pu is calcu-lated using the uniaxial interaction diagram in the corresponding direction.The design shear force, Vu, is then given by (ACI 21.4.5.1)

Vu = Vp + VD+L (ACI 21.4.5.1)

where, Vp is the capacity shear force obtained by applying the calculatedprobable ultimate moment capacities at the two ends of the column acting



in two opposite directions. Therefore, Vp is the maximum of 1PV and

2PV ,

where

1PV =L

MM JI+− +

, and

2PV =L

MM JI−+ +

, where

−+II MM , , = Positive and negative moment capacities at end I of the

column using a steel yield stress value of αfy and no ϕfactors (ϕ = 1.0),

−+JJ MM , , = Positive and negative moment capacities at end J of the

column using a steel yield stress value of αfy and no ϕfactors (ϕ = 1.0), and

L = Clear span of column.

For Special moment resisting frames α is taken as 1.25 (ACI 10.0,R21.4.5.1). VD+L is the contribution of shear force from the in-span distri-bution of gravity loads. For most of the columns, it is zero.

For Intermediate moment resisting frames, the shear capacity of thecolumn is also checked for the capacity shear based on the nominal mo-ment capacities at the ends and the factored gravity loads, in addition tothe check required for Ordinary moment resisting frames. The designshear force is taken to be the minimum of that based on the nominal (ϕ =1.0) moment capacity and modified factored shear force. The procedurefor calculating nominal moment capacity is the same as that for comput-ing the probable moment capacity for special moment resisting frames,except that α is taken equal to 1 rather than 1.25 (ACI 21.10.3.a,R21.10). The modified factored shear forces are based on the specifiedload factors, except the earthquake load factors are doubled (ACI21.10.3.b).

Determine Concrete Shear CapacityGiven the design force set Pu and Vu, the shear force carried by the concrete,Vc, is calculated as follows:



If the column is subjected to axial compression, i.e., Pu is positive,

Vc = 2

+

g

uc A

Pf

000,21' Acv, where (ACI 11.3.1.2)

'cf ≤ 100 psi, and (ACI 11.1.2)

Vc ≤ 3.5 'cf

+

g

u

AP

5001 Acv. (ACI 11.3.2.2)

The term Pu / Ag must have psi units. Acv is the effective shear area, whichis shown shaded in Figure 6. For circular columns, Acv is taken to be equalto the gross area of the section (ACI 11.3.3, R11.3.3).

If the column is subjected to axial tension, Pu is negative

Vc = 2 'cf

+

g

u

AP

5001 Acv ≥ 0 (ACI 11.3.2.3)

For Special moment resisting concrete frame design, Vc is set to zeroif the factored axial compressive force, Pu, including the earthquake effect,

is small (Pu < 'cf Ag / 20) and if the shear force contribution from earth-

quake, VE, is more than half of the total factored maximum shear forceover the length of the member Vu (VE ≥ 0.5Vu) (ACI 21.4.5.2).

Determine Required Shear ReinforcementGiven Vu and Vc, the required shear reinforcement in the form of stirrups orties within a spacing, s, is given for rectangular and circular columns by

Av = df

sVV

ys

cu )/( −ϕ, for rectangular columns and (ACI 11.5.6.1, 11.5.6.2)

Av = )8.0()/(

DfsVV

ys

cu −ϕ, for circular columns. (ACI 11.5.6.3, 11.3.3)

Vu is limited by the following relationship.

(Vu / ϕ-Vc) ≤ 8 'cf Acv (ACI 11.5.6.9)


Technical Note 20 - 14

Figure 6 Shear Stress

Otherwise, redimensiostrength reduction factculated Av values obtamajor and minor direcforce and associated lo

The column shear reinbased purely on shearments to satisfy spacinric considerations mustuser.

Design Column Shear Reinforcement

Area, Acv

ning of the concrete section is required. Here ϕ, theor, is 0.85 (ACI 9.3.2.3). The maximum of all the cal-ined from each load combination are reported for thetions of the column, along with the controlling shearad combination label.

forcement requirements reported by the program are strength consideration. Any minimum stirrup require-g considerations or transverse reinforcement volumet- be investigated independently of the program by the


Reference Technical Note 20 - 15

ReferenceWhite, D.W. and J.F. Hajjar. 1991. Application of Second-Order Elastic Analy-

sis in LRFD: Research to Practice. Engineering Journal. American In-stitute of Steel Construction, Inc. Vol. 28. No. 4.




Technical Note 21Beam Design

This Technical Note describes how this program completes beam design whenthe ACI 318-99 code is selected. The program calculates and reports the re-quired areas of steel for flexure and shear based on the beam moments,shears, load combination factors and other criteria described herein.

OverviewIn the design of concrete beams, the program calculates and reports the re-quired areas of steel for flexure and shear based on the beam moments,shears, load combination factors, and other criteria described below. The re-inforcement requirements are calculated at a user-defined number ofcheck/design stations along the beam span.

All beams are designed for major direction flexure and shear only.Effects resulting from any axial forces, minor direction bending, andtorsion that may exist in the beams must be investigated independ-ently by the user.

The beam design procedure involves the following steps:

Design beam flexural reinforcement

Design beam shear reinforcement

Design Beam Flexural ReinforcementThe beam top and bottom flexural steel is designed at check/design stationsalong the beam span. The following steps are involved in designing the flex-ural reinforcement for the major moment for a particular beam for a particu-lar section:

Determine the maximum factored moments

Determine the reinforcing steel

Beam Design Concrete Frame Design ACI-318-99


Determine Factored MomentsIn the design of flexural reinforcement of Special, Intermediate, or Ordinarymoment resisting concrete frame beams, the factored moments for each loadcombination at a particular beam section are obtained by factoring the corre-sponding moments for different load cases with the corresponding load fac-tors.

The beam section is then designed for the maximum positive +uM and maxi-

mum negative −uM factored moments obtained from all of the load combina-

tions.

Negative beam moments produce top steel. In such cases, the beam is al-ways designed as a rectangular section. Positive beam moments producebottom steel. In such cases, the beam may be designed as a Rectangular- ora T-beam.

Determine Required Flexural ReinforcementIn the flexural reinforcement design process, the program calculates both thetension and compression reinforcement. Compression reinforcement is addedwhen the applied design moment exceeds the maximum moment capacity ofa singly reinforced section. The user has the option of avoiding the compres-sion reinforcement by increasing the effective depth, the width, or the gradeof concrete.

The design procedure is based on the simplified rectangular stress block asshown in Figure 1 (ACI 10.2). It is assumed that the compression carried byconcrete is less than 0.75 times that which can be carried at the balancedcondition (ACI 10.3.3). When the applied moment exceeds the moment ca-pacity at this designed balanced condition, the area of compression rein-forcement is calculated assuming that the additional moment will be carriedby compression and additional tension reinforcement.

The design procedure used by this program for both rectangular and flangedsections (L- and T-beams) is summarized below. It is assumed that the de-

sign ultimate axial force does not exceed 0.1 'cf Ag (ACI 10.3.3); hence, all the

beams are designed for major direction flexure and shear only.

Concrete Frame Design ACI-318-99 Beam Design


Figure 1 Design of Rectangular Beam Section

Design for Rectangular BeamIn designing for a factored negative or positive moment, Mu (i.e., designingtop or bottom steel), the depth of the compression block is given by a (seeFigure 1), where,

a = d - bf

Md

c

u

ϕ−

12

85.0

2, (ACI 10.2.7.1)

where, the value of ϕ is 0.90 (ACI 9.3.2.1) in the above and the followingequations. Also β1 and cb are calculated as follows:

β1 = 0.85-0.05

−000,1

000,4'cf , 0.65 ≤ β1 ≤ 0.85, (ACI 10.2.7.3)

cb = dfE

E

ysc

sc

+εε

= yf+000,87

000,87d. (ACI 10.2.3, 10.2.4)




amax = 0.75β1cb. (ACI 10.2.7.1, 10.3.3)

If a ≤ amax, the area of tensile steel reinforcement is then given by

As =

−ϕ

2a

df

M

y

u .

This steel is to be placed at the bottom if Mu is positive, or at the top if Mu

is negative.

If a > amax, compression reinforcement is required (ACI 10.3.3) and is cal-culated as follows:

− The compressive force developed in concrete alone is given by

C = 0.85 'cf bamax, and (ACI 10.2.7.1)

the moment resisted by concrete compression and tensile steel is

Muc = C

−

2maxa

d ϕ.

− Therefore the moment resisted by compression steel and tensile steelis

Mus = Mu - Muc.

− So the required compression steel is given by

'sA =

ϕ− )'(' ddf

M

s

us , where

'sf = 0.003Es

−

cdc '

. (ACI 10.2.4)

− The required tensile steel for balancing the compression in concrete is



As1 =

ϕ

−

2maxa

df

M

y

uc , and

the tensile steel for balancing the compression in steel is given by

As2 = ϕ− )'( ddf

M

y

us .

− Therefore, the total tensile reinforcement, As = As1 + As2, and total

compression reinforcement is 'sA . As is to be placed at bottom and '

sA

is to be placed at top if Mu is positive, and vice versa if Mu is negative.

Design for T-BeamIn designing for a factored negative moment, Mu (i.e., designing top steel),the calculation of the steel area is exactly the same as above, i.e., no T-Beamdata is to be used. See Figure 2. If Mu > 0, the depth of the compressionblock is given by

a = d - fc

u

bf

Md

ϕ−

'2

85.0

2.

The maximum allowed depth of compression block is given by

amax = 0.75β1cb. (ACI 10.2.7.1, 10.3.3)

• If a ≤ ds, the subsequent calculations for As are exactly the same as previ-ously defined for the rectangular section design. However, in this case thewidth of the compression flange is taken as the width of the beam foranalysis. Compression reinforcement is required if a > amax.

• If a > ds, calculation for As is performed in two parts. The first part is forbalancing the compressive force from the flange, Cf, and the second partis for balancing the compressive force from the web, Cw, as shown in Fig-ure 2. Cf is given by

Cf = 0.85 'cf (bf - bw)ds.

Beam esign Concrete Frame Design ACI-318-99

Techn

Figu

T

g

At

Ts

D

ical Note 21 - 6 Design Beam Flexural Reinforcement

re 2 Design of a T-Beam Section

herefore, As1 = y

f

fC

and the portion of Mu that is resisted by the flange is

iven by

Muf = Cf

−

2sd

d ϕ.

gain, the value for ϕ is ϕ(flexure), which is 0.90 by default. Therefore,he balance of the moment, Mu to be carried by the web is given by

Muw = Mu - Muf.

he web is a rectangular section of dimensions bw and d, for which the de-ign depth of the compression block is recalculated as

a1 = d - w

ic

uw

bf

Md

ϕ−

85.0

22 .

If a1 ≤ amax, the area of tensile steel reinforcement is then given by

As2 =

−ϕ21a

df

M

y

uw , and



As = As1 + As2.

This steel is to be placed at the bottom of the T-beam.

If a1 > amax, compression reinforcement is required (ACI 10.3.3) and iscalculated as follows:

− The compressive force in web concrete alone is given by

C = 0.85 'cf bamax. (ACI 10.2.7.1)

− Therefore, the moment resisted by concrete web and tensile steelis

Muc = C ϕ

−

2maxa

d , and

the moment resisted by compression steel and tensile steel is

Mus = Muw - Muc.

− Therefore, the compression steel is computed as

'sA =

ϕ− )'(' ddf

M

s

us , where

'sf = 0.003Es

−

cdc '

. (ACI 10.2.4)

− The tensile steel for balancing compression in web concrete is

As2 = ϕ− )

2( maxadf

M

y

uc , and

the tensile steel for balancing compression in steel is

As3 = ϕ− )'( ddf

M

y

us .



− The total tensile reinforcement, As = As1 + As2 + As3, and total

compression reinforcement is 'sA . As is to be placed at bottom and

'sA is to be placed at top.

Minimum Tensile ReinforcementThe minimum flexural tensile steel provided in a rectangular section in an Or-dinary moment resisting frame is given by the minimum of the two followinglimits:

As ≥ max

dbf

dbf

fw

yw

y

c 200 and

3 '

or (ACI 10.5.1)

As ≥ (4/3)As(required). (ACI 10.5.3)

Special Consideration for Seismic DesignFor Special moment resisting concrete frames (seismic design), the beam de-sign satisfies the following additional conditions (see also Table 1):

The minimum longitudinal reinforcement shall be provided at both the topand bottom. Any of the top and bottom reinforcement shall not be lessthan As(min) (ACI 21.3.2.1).

As(min) ≥ max

dbf

dbf

fw

yw

y

c 200 and

3 '

or (ACI 10.5.1)

As(min) ≥ 34

As(required). (ACI 10.5.3)

The beam flexural steel is limited to a maximum given by

As ≤ 0.025 bwd. (ACI 21.3.2.1)

At any end (support) of the beam, the beam positive moment capacity(i.e., associated with the bottom steel) would not be less than 1/2 of thebeam negative moment capacity (i.e., associated with the top steel) atthat end (ACI 21.3.2.2).

Neither the negative moment capacity nor the positive moment capacityat any of the sections within the beam would be less than 1/4 of the



maximum of positive or negative moment capacities of any of the beamend (support) stations (ACI 21.3.2.2).

For Intermediate moment resisting concrete frames (i.e., seismic design), thebeam design would satisfy the following conditions:

At any support of the beam, the beam positive moment capacity wouldnot be less than 1/3 of the beam negative moment capacity at that end(ACI 21.10.4.1).

Neither the negative moment capacity nor the positive moment capacityat any of the sections within the beam would be less than 1/5 of themaximum of positive or negative moment capacities of any of the beamend (support) stations (ACI 21.10.4.1).

Design Beam Shear ReinforcementThe shear reinforcement is designed for each load combination at a user de-fined number of stations along the beam span. The following steps are in-volved in designing the shear reinforcement for a particular beam for a par-ticular load combination at a particular station due to the beam major shear:

• Determine the factored shear force, Vu.

• Determine the shear force, Vc, that can be resisted by the concrete.

• Determine the reinforcement steel required to carry the balance.

For Special and Intermediate moment resisting frames (ductile frames), theshear design of the beams is also based upon the probable and nominal mo-ment capacities of the members, respectively, in addition to the factored loaddesign.




Table 1 Design Criteria Table

Type ofCheck/Design

Ordinary MomentResisting Frames

(non-Seismic)

Intermediate MomentResisting Frames

(Seismic)

Special MomentResisting Frames

(Seismic)

ColumnCheck(interaction)

NLDa Combinations NLDa Combinations NLDa Combinations

ColumnDesign(interaction)

NLDa Combinations1% < ρ < 8%

NLDa Combinations1% < ρ < 8%

NLDa Combinationsα = 1.01% < ρ < 6%

ColumnShears NLDa Combinations

Modified NLDa Combinations(earthquake loads doubled)Column capacityϕ = 1.0 and α = 1.0

NLDa CombinationsColumn shear capacityϕ = 1.0 and α = 1.25

BeamDesignFlexure

NLDa Combinations NLDa Combinations

NLDa Combinationsρ ≤ 0.025

ρ ≥ y

c

f

f '3 , ρ ≥ yf

200

Beam Min.MomentOverrideCheck

No Requirement

ENDuuEND MM −+ ≥31


{ }ENDuuuSPAN MMM −+− ≥ ,max51

ENDuuEND MM −+ ≥21


{ }ENDuuuSPAN MMM −−− ≥ ,max41

BeamDesignShear

NLDa Combinations

Modified NLDa Combinations(earthquake loads doubled)Beam Capacity Shear (Vp)with α = 1.0 and ϕ = 1.0plus VD+L

NLDa CombinationsBeam Capacity Shear (Vp)with α = 1.25 and ϕ = 1.0plus VD+L

Vc = 0

Joint Design No Requirement No Requirement Checked for shear

Beam/ColumnCapacityRatio

No Requirement No Requirement Reported in output file

NLDa = Number of specified loading



Determine Shear Force and Moment• In the design of the beam shear reinforcement of an Ordinary moment

resisting concrete frame, the shear forces and moments for a particularload combination at a particular beam section are obtained by factoringthe associated shear forces and moments with the corresponding loadcombination factors.

• In the design of Special moment resisting concrete frames (i.e.,seismic design), the shear capacity of the beam is also checked for thecapacity shear resulting from the probable moment capacities at the endsand the factored gravity load. This check is performed in addition to thedesign check required for Ordinary moment resisting frames. The capacityshear force, Vp, is calculated from the probable moment capacities of eachend of the beam and the gravity shear forces. The procedure for calculat-ing the design shear force in a beam from probable moment capacity isthe same as that described for a column in section “Design Column ShearReinforcement” of Concrete Frame Design ACI318-99 Technical Note 20Column Design. See also Table 1 for details.

The design shear force Vu is then given by (ACI 21.3.4.1)

Vu = Vp + VD+L (ACI 21.3.4.1)

where Vp is the capacity shear force obtained by applying the calculatedprobable ultimate moment capacities at the two ends of the beams actingin two opposite directions. Therefore, Vp is the maximum of

1PV and 2PV ,

where

1PV = L

MM JI+− +

, and

2PV =L

MM JI−+ +

, where

−IM = Moment capacity at end I, with top steel in tension, using a


+JM = Moment capacity at end J, with bottom steel in tension, using

a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),



+IM = Moment capacity at end I, with bottom steel in tension, using

a steel yield stress value of αfy and no ϕ factors (ϕ = 1.0),

−JM = Moment capacity at end J, with top steel in tension, using a

steel yield stress value of αfy and no ϕ factors (ϕ = 1.0), and

L = Clear span of beam.

For Special moment resisting frames α is taken as 1.25 (ACI 21.0,R21.3.4.1). VD+L is the contribution of shear force from the in-span distri-bution of gravity loads.

• For Intermediate moment resisting frames, the shear capacity of thebeam is also checked for the capacity shear based on the nominal momentcapacities at the ends and the factored gravity loads, in addition to thecheck required for Ordinary moment resisting frames. The design shearforce in beams is taken to be the minimum of that based on the nominalmoment capacity and modified factored shear force. The procedure forcalculating nominal (ϕ = 1.0) moment capacity is the same as that forcomputing the probable moment capacity for Special moment resistingframes, except that α is taken equal to 1 rather than 1.25 (ACI 21.10.3.a,R21.10). The modified factored shear forces are based on the specifiedload factors, except the earthquake load factors are doubled (ACI21.10.3.b). The computation of the design shear force in a beam of anIntermediate moment resisting frame is the same as described for col-umns in section “Determine Section Forces” of Concrete Frame DesignACI318-99 Technical Note 20 Column Design. See also Table 1 for details.

Determine Concrete Shear CapacityThe allowable concrete shear capacity is given by

Vc = 2 'cf bwd. (ACI 11.3.1.1)

For Special moment resisting frame concrete design, Vc is set to zero if boththe factored axial compressive force, including the earthquake effect Pu, is

less than 'cf Ag/20 and the shear force contribution from earthquake VE is

more than half of the total maximum shear force over the length of the mem-ber Vu (i.e., VE ≥ 0.5Vu) (ACI 21.3.4.2).



Determine Required Shear ReinforcementGiven Vu and Vc, the required shear reinforcement in area/unit length is cal-culated as

Av = df

sVV

ys

cu )/( −ϕ. (ACI 11.5.6.1, 11.5.6.2)

The shear force resisted by steel is limited by

(Vu / ϕ - Vc) ≤ 8 'cf bd. (ACI 11.5.6.9)

Otherwise, redimensioning of the concrete section is required. Here, ϕ, thestrength reduction factor for shear, is 0.85 by default (ACI 9.3.2.3). Themaximum of all the calculated Av values, obtained from each load combina-tion, is reported along with the controlling shear force and associated loadcombination number.

The beam shear reinforcement requirements displayed by the program arebased purely on shear strength considerations. Any minimum stirrup require-ments to satisfy spacing and volumetric considerations must be investigatedindependently of the program by the user.




Technical Note 22Joint Design

This Technical Note explains how the program performs a rational analysis ofthe beam-column panel zone to determine the shear forces that are gener-ated in a joint. The program then checks this against design shear strength.

OverviewTo ensure that the beam-column joint of special moment resisting framespossesses adequate shear strength, the program performs a rational analysisof the beam-column panel zone to determine the shear forces that are gener-ated in the joint. The program then checks this against design shear strength.

Only joints having a column below the joint are designed. The material prop-erties of the joint are assumed to be the same as those of the column belowthe joint.

The joint analysis is completed in the major and the minor directions of thecolumn. The joint design procedure involves the following steps:

Determine the panel zone design shear force, Vuh

Determine the effective area of the joint

Check panel zone shear stress

The algorithms associated with these three steps are described in detail in thefollowing three sections.

Determine the Panel Zone Shear ForceFigure 1 illustrates the free body stress condition of a typical beam-columnintersection for a column direction, major or minor.

Joint Design Concrete Frame Design ACI318-99

Tech

Fig

nical Note 22 - 2 Determine the Panel Zone Shear Force

ure 1 Beam-Column Joint Analysis

Concrete Frame Design ACI318-99 Joint Design

Determine the Panel Zone Shear Force Technical Note 22 - 3

The force Vuh is the horizontal panel zone shear force that is to be calculated.

The forces that act on the joint are Pu, Vu, MuL and Mu

R. The forces Pu and Vu

are axial force and shear force, respectively, from the column framing into thetop of the joint. The moments Mu

L and MuR are obtained from the beams

framing into the joint. The program calculates the joint shear force Vuh by re-

solving the moments into C and T forces. Noting that TL = CL and TR = CR,

Vuh = TL + TR - Vu

The location of C or T forces is determined by the direction of the moment.The magnitude of C or T forces is conservatively determined using basic prin-ciples of ultimate strength theory, ignoring compression reinforcement as fol-lows. The program first calculates the maximum compression, Cmax, and themaximum moment, Mmax, that can be carried by the beam.

bdfC c'

max 85.0=

2maxmaxd

CM =

Then the program conservatively determines C and T forces as follows:

−−==

maxmax

)(11

M

MabsCTC

The program resolves the moments and the C and T forces from beams thatframe into the joint in a direction that is not parallel to the major or minordirections of the column along the direction that is being investigated, therebycontributing force components to the analysis. Also, the program calculatesthe C and T for the positive and negative moments, considering the fact thatthe concrete cover may be different for the direction of moment.

In the design of special moment resisting concrete frames, the evaluation ofthe design shear force is based on the moment capacities (with reinforcingsteel overstrength factor, α, and no ϕ factors) of the beams framing into thejoint (ACI 21.5.1.1, UBC 1921.5.1.1). The C and T force are based on thesemoment capacities. The program calculates the column shear force Vu fromthe beam moment capacities, as follows:


Technical Note 22 - 4 Determine the Effective Area of Joint

H

MMV

Ru

Lu

u

+=

See Figure 2. It should be noted that the points of inflection shown on Figure2 are taken as midway between actual lateral support points for the columns.If there is no column at the top of the joint, the shear force from the top ofthe column is taken as zero.

The effects of load reversals, as illustrated in Case 1 and Case 2 of Figure 1,are investigated and the design is based on the maximum of the joint shearsobtained from the two cases.

Determine the Effective Area of JointThe joint area that resists the shear forces is assumed always to be rectan-gular in plan view. The dimensions of the rectangle correspond to the majorand minor dimensions of the column below the joint, except if the beamframing into the joint is very narrow. The effective width of the joint area tobe used in the calculation is limited to the width of the beam plus the depth ofthe column. The area of the joint is assumed not to exceed the area of thecolumn below. The joint area for joint shear along the major and minor direc-tions is calculated separately (ACI R21.5.3).

It should be noted that if the beam frames into the joint eccentrically, theabove assumptions may be unconservative and the user should investigatethe acceptability of the particular joint.

Check Panel Zone Shear StressThe panel zone shear stress is evaluated by dividing the shear force Vu

h bythe effective area of the joint and comparing it with the following design shearstrengths (ACI 21.5.3, UBC 1921.5.3):

20ϕ cf ' for joints confirmed on all four sides

v = 15ϕcf ' for joints confirmed on three faces or on two

opposite faces{12ϕ cf ' for all other joints


Determi

where

A beaprogrface 1921.

Figur

ne the Effective Area of Joint Technical Note 22 - 5

ϕ = 0.85 (by default). (ACI 9.3.2.3, UBC 1909.3.2.3,1909.3.4.1)

m that frames into a face of a column at the joint is considered in thisam to provide confinement to the joint if at least three-quarters of theof the joint is covered by the framing member (ACI 21.5.3.1, UBC5.3.1).

e 2 Column Shear Force Vu


Technical Note 22 - 6 Beam/Column Flexural Capacity Ratios

For light-weight aggregate concrete, the design shear strength of the joint isreduced in the program to at least three-quarters of that of the normal weight

concrete by replacing the 'cf with

''

, 4/3,min ccfactorcs fff (ACI 21.5.3.2, UBC 1921.5.3.2)

For joint design, the program reports the joint shear, the joint shear stress,the allowable joint shear stress and a capacity ratio.

Beam/Column Flexural Capacity RatiosAt a particular joint for a particular column direction, major or minor, the pro-gram will calculate the ratio of the sum of the beam moment capacities to thesum of the column moment capacities (ACI 21.4.2.2).

∑Me ≥ 56 ∑Mg (ACI 21.4.2.2)

The capacities are calculated with no reinforcing overstrength factor, α , andincluding ϕ factors. The beam capacities are calculated for reversed situations(Cases 1 and 2) as illustrated in Figure 1 and the maximum summation ob-tained is used.


The column capacity summation includes the column above and the columnbelow the joint. For each load combination, the axial force, Pu, in each of thecolumns is calculated from the program analysis load combinations. For eachload combination, the moment capacity of each column under the influence ofthe corresponding axial load Pu is then determined separately for the majorand minor directions of the column, using the uniaxial column interaction dia-gram; see Figure 3. The moment capacities of the two columns are added togive the capacity summation for the corresponding load combination. Themaximum capacity summations obtained from all of the load combinations isused for the beam/column capacity ratio.


Be

The beam/column flexural capacity ratios are only reported for Special Mo-ment-Resisting Frames involving seismic design load combinations. If this ra-tio is greater than 5/6, a warning message is printed in the output file.

Fi

am/Column Flexural Capacity Ratios Technical Note 22 - 7

gure 3 Moment Capacity Mu at a Given Axial Load Pu

Input Data Technical Note 23 - 1



Technical Note 23Input Data

This Technical Note describes the concrete frame design input data forACI318-99. The input can be printed to a printer or to a text file when youclick the File menu > Print Tables > Concrete Frame Design command. Aprintout of the input data provides the user with the opportunity to carefullyreview the parameters that have been input into the program and upon whichprogram design is based. Further information about using the Print DesignTables form is presented at the end of this Technical Note.

Input DataThe program provides the printout of the input data in a series of tables. Thecolumn headings for input data and a description of what is included in thecolumns of the tables are provided in Table 1 of this Technical Note.

Table 1 Concrete Frame Design Input DataCOLUMN HEADING DESCRIPTIONLoad Combination MultipliersCombo Design load combination. See Technical Note 8.

TypeLoad type: dead, live, superimposed dead, earthquake, wind,snow, reduced live load, other.

Case Name of load case.

Factor Load combination scale factor.

Code PreferencesPhi_bending Bending strength reduction factor.

Phi_tension Tensile strength reduction factor.

Phi_compression(Tied)

Compressive strength reduction factor for tied columns.

Phi_compression (Spi-ral)

Compressive strength reduction factor for reinforced columns.

Phi_shear Shear strength reduction factor.

Input Data Concrete Frame Design ACI318-99

Technical Note 23 - 2 Table 1 Concrete Frame Design Input Data

Table 1 Concrete Frame Design Input DataCOLUMN HEADING DESCRIPTIONMaterial Property DataMaterial Name Concrete, steel, other.

Material Type Isotropic or orthotropic.

Design Type

Modulus of Elasticity

Poisson's Ratio

Thermal Coeff Coefficient of thermal expansion.

Shear Modulus

Material Property Mass and WeightMaterial Name Concrete, steel, other.

Mass Per Unit Vol Used to calculate self-mass of structure.

Weight Per Unit Vol Used to calculate self-weight of structure.

Material Design Data for Concrete MaterialsMaterial Name Concrete, steel, other.

Lightweight Concrete

Concrete FC Concrete compressive strength.

Rebar FY Bending reinforcing steel yield strength.

Rebar FYS Shear reinforcing steel yield strength.

Lightwt Reduc Fact Shear strength reduction factor for light weight concrete; default= 1.0.

Concrete Column Property DataSection Label Label applied to section.

Mat Label Material label.

Column Depth

Column Width

Rebar Pattern Layout of main flexural reinforcing steel.

Concrete Cover Minimum clear concrete cover.

Bar Area Area of individual reinforcing bar to be used.

Concrete Frame Design ACI318-99 Input Data


Table 1 Concrete Frame Design Input DataCOLUMN HEADING DESCRIPTIONConcrete Column Design Element InformationStory ID Column assigned to story level at top of column.



Framing Type Lateral or gravity.

RLLF Factor



K Major Effective length factor; default = 1.0.

K Minor Effective length factor; default = 1.0.

Concrete Beam Design Element InformationStory ID Story level at which beam occurs.

Bay ID Grid lines locating beam.

Section ID Section number assigned to beam.

Framing type Lateral or gravity.

RLLF Factor



Using the Print Design Tables FormTo print concrete frame design input data directly to a printer, use the Filemenu > Print Tables > Concrete Frame Design command and click thecheck box on the Print Design Tables form. Click the OK button to send theprint to your printer. Click the Cancel button rather than the OK button tocancel the print. Use the File menu > Print Setup command and theSetup>> button to change printers, if necessary.

To print concrete frame design input data to a file, click the Print to File checkbox on the Print Design Tables form. Click the Filename>> button to change

Input Data Concrete Frame Design ACI318-99

Technical Note 23 - 4 Using the Print Design Tables Form

the path or filename. Use the appropriate file extension for the desired format(e.g., .txt, .xls, .doc). Click the OK buttons on the Open File for Printing Ta-bles form and the Print Design Tables form to complete the request.

Note:




Table 1 Concrete Column Design Output Technical Note 24 - 1



Technical Note 24Output Details

This Technical Note describes the concrete frame design output for ACI318-99that can be printed to a printer or to a text file. The design output is printedwhen you click the File menu > Print Tables > Concrete Frame Designcommand and select Output Summary on the Print Design Tables form. Fur-ther information about using the Print Design Tables form is presented at theend of this Technical Note.

The program provides the output data in a series of tables. The columnheadings for output data and a description of what is included in the columnsof the tables are provided in Table 1 of this Technical Note.


Biaxial P-M Interaction and Shear Design of Column-Type Elements

Story ID Column assigned to story level at top of column.

Column Line Grid lines.


Station ID

Required Reinforcing

Longitudinal Area of longitudinal reinforcing required.





Output Details Concrete Frame Design ACI318-99

Technical Note 24 - 2 Table 2 Concrete Column Joint Output



Table 2 Concrete Column Joint OutputCOLUMN HEADING DESCRIPTION

Beam to Column Capacity Ratios and Joint Shear Capacity Check

Story ID Story level at which joint occurs.


Section ID Assigned section name.

Beam-Column Capacity Ratios

Major Ratio of beam moment capacity to column capacity.


Minor Ratio of beam moment capacity to column capacity.



Major Ratio of factored load versus allowed capacity.


Minor Ratio of factored load versus allowed capacity.


Concrete Frame Design ACI318-99 Output Details


Using the Print Design Tables FormTo print concrete frame design input data directly to a printer, use the Filemenu > Print Tables > Concrete Frame Design command and click thecheck box on the Print Design Tables form. Click the OK button to send theprint to your printer. Click the Cancel button rather than the OK button tocancel the print. Use the File menu > Print Setup command and theSetup>> button to change printers, if necessary.

To print concrete frame design input data to a file, click the Print to File checkbox on the Print Design Tables form. Click the Filename>> button to changethe path or filename. Use the appropriate file extension for the desired format(e.g., .txt, .xls, .doc). Click the OK buttons on the Open File for Printing Ta-bles form and the Print Design Tables form to complete the request.

Note:




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Etabs Concrete Frame Design