Technical Note Structural Concrete Software System

E-Mail support@adaptsoft.com 1733 Woodside Road, Suite 220, Redwood City, California, 94061, USA, Tel: (650) 306-2400 Fax (650) 306 2401

TN230_PT_design_procedure_FP_12 053007

DESIGN STEPS USING ADAPT FLOOR-PRO1

Bijan O Aalami2 This Technical Note outlines the steps that you have to follow in designing a post-tensioned floor system, using the ADAPT- FLOOR Pro. FLOOR-Pro is a finite-element based program specifically developed and tailored for the design of post-tensioned floor systems. It is assumed that you are familiar with the basics of the program and, as a minimum, have gone through its tutorials and workshop examples. No attempt is made to provide extensive details of the steps listed. Where needed, you are advised to consult other literature by ADAPT. The proposed sequence of steps is summarized in the following flow chart. There are other alternatives to the proposed sequence. However, it is believed that the flow chart given reduces the likelihood of errors, and leads to early detection and correction of mistakes, if they occur. The numbers given in the circles indicate the availability of other literature from ADAPT that cover in greater detail the marked topic.

If you have an electronic file of the floor slab and also have some knowledge of AutoCad. o Create the layers in AutoCad that are going to be used by FLOOR-Pro3. o Create a “Framing Plan” referred to as “concrete outline.”4

Open FLOOR-Pro

Import and Calibrate the floor plan

Create and Validate the Structural Model

o If the dwg was preprocessed into proper layers either by you or a drafting technician in your office, open the layers of each of the structural components one after the other and transform them to structural components.

o If the dwg was not pre-processed, simplify and organize the imported information. You will create two groups of layers – one to generate the structural model and the other to help you generate the structural documents.

• Create layers for drafting the structural drawings (rebar and PT drawings)5. These layers will be used later to draft the concrete outline (framing plan).

• Create layers that you will be using to convert the drawing into structural model for analysis and design6

1 Copyright ADAPT Corporation 2006 2 Professor Emeritus, San Francisco State University 3 Refer to the Workshop manual, or the associated Technical Note on the creation of layers used in FLOOR-Pro 4 Contents of the “Framing Plan,” also referred to as “Concrete Outline.” See appendix of this Technical Note. 5 Refer to the workshop booklet for the procedure 6 Refer to the workshop booklet for the procedure

Technical Note

2

FLOW CHART OF DESIGN PROCEDURE IN BUILDER

Validate the modelunder selfweight

Enter loadsLoad combinations

Enter/editmaterial

Design_procedure_builder_10100306

Enter basereinforcement

Enter/import PT tendonsValidate the solution

Create design stripsCreate design sections

Design/code checkthe structure

Exit to generate structural documents

Rebar drawing

Examine thedesign

Is designacceptable

Generatestructural model

Prepare properlayers in AutoCad

Import dwgto Builder

Simplify/preprocessthe imported drawing

If you do not have adwg drawing of the floor

If you have a dwgdrawing of the floor

Do you have AutoCadExpertise?Yes No

Enter/editdesign criteria

PT drawingStructural calculation

report

Fabrication drawing(shop/installation drawing)

N

Modify structureor other parameters.

Try again

NoYes

1

2

53 4

1

Refer to notes and references1

Analyze structure

Technical Note

3

o Mesh the structural model o Obtain a solution for the selfweight of the floor system only o Validate the solution obtained by examining the deflected shape of the structure in 3D

viewer and evaluating the value of the maximum deflection reported o Make corrections to the model, until satisfied o Save data

View/Edit Material Properties7 o View/edit concrete material properties. Note the concrete weight specified for use in

selfweight calculation o View/edit steel material properties o View/edit Prestressing material properties o Save data

View/Edit Design Criteria o Select/verify the building code to be used o View/edit the items listed under “analysis and design options” o Select the type of reinforcement you prefer for punching shear design, stirrups or shear

studs o Select the size of reinforcement bars to be selected by the program for bending and one-

way shear o View each of the other tabs of the design criteria and edit the default values if necessary o Save data

Apply Loads

o If the load cases you plan to use are more than “dead”, “live”, “selfweight” and “prestressing” do the following8:

Go to “Load Case Library” and enter the label of the other load cases that you plan to use. Once the label is listed in the library, enables you to enter the associated loads.

o Enter the loads of each load case. Make sure that each load you enter is assigned to the correct load case listed in the load case library.

Review/Edit Load Combinations

o Go to load combination dialog window. Depending on the building code you have selected, the program will display a number of load combinations.

Review/edit the load combinations displayed in the load combination dialog window for relevance and accuracy.

For each of the default load combinations and the ones you are going to add, make sure that the correct “Analysis/Design Option” is selected. In most cases you would select “No Code Check.” If not clear, click the “Help” button on the same dialog window to be guided in your selection.

It is not necessary, but is advisable to create a load case for prestressing only “PT” with no code check for evaluation of the post-tensioning you have entered.

7 If you also intend to use the structural model for export to PT, you need to enter the material properties for both Strip method (EFM) and the Finite Element Method (FEM) 8 Note that a “load case” is different from “load combination.” Using basic load cases, you can combine them in many different ways. The load cases are the basic constituents of the load combinations. The prestressing load case includes both “prestressing” and “hyperstatic” cases.

Technical Note

4

Likewise, if you have unusual load cases, make sure that for each of the load cases you define a load combination. The objective is to be able to view the results of the unusual load case on its own, in order to evaluate its validity.

Before closing the load combination by pressing “OK,” make sure that you have at least one instance each of the following required code checks: “Serviceability,” “Strength,” “Initial Condition,”

Enter/Edit Base Reinforcement Base reinforcement is the reinforcement you like to place in the structure, regardless of the outcome of the calculations. But, at the same time, you want presence of the reinforcement you have specified as base reinforcement to be fully accounted for in design. That is to say, you want the program to report only the reinforcement needed in excess of what you have specified. The base reinforcement generally consists of a bottom and or top mesh, pre-defined bars at the top of columns (number, size and length)9, and pre-defined longitudinal bars at the corners of beam cages.

o Enter mesh reinforcement, if any o Enter beam reinforcement (corner bars), if you require specific number and size o Enter single bars in size, length and number at locations of your choice. o Verify each of the reinforcement types on the computer screen o Save

Enter Post-Tensioning Tendons

o Enter the post-tensioning tendons for the entire structure.10 If not clear, use the “Guidelines for Tendon Layout.”11

o View the tendons in 3D viewer with a magnification factor of 6 or more for the Z-direction. Hide the walls and columns to obtain a good view of the slab and its interior. Make sure that the tendon profiles are acceptable. The most common modifications you need to do are:

Tendons in short spans should not have a full drape. This may result in excessive uplift.

In short cantilevers, tendons over the exterior support should be lowered, in order to avoid excessive uplift.

o Save

Analyze Structure o If, apart from post-tensioning, you have not applied a horizontal force to the structure,

simply click on “Analyze the Structure.” However, if you have applied a horizontal force to the structure click on the “Analysis Options” and disable the “Automatic Stabilization” of the program. Apply proper boundary conditions to keep the structure in position.12

o Save

9 In many instances, you may wish to place a given number of bars of pre-defined size and length over the support in a given direction. The program allows you to define these and will report whatever is needed in addition to your pre-defined bar layout. 10 Use “Guidelines for Tendon Layout” if you are not clear on the tendon layout. 11 A powerful alternative is to export the information to ADAPT-PT, determine the optimum post-tensioning and import the optimum values and layout back into FLOOR-Pro. Refer to FLOOR-Pro program manual for more information on this feature. 12 The automatic stabilization add adequate supports to what you have specified, in order to make sure that the structure is stable, without changing the outcome of load distribution of your project. But, if you disable the automatic stabilization, you must make sure that you specify adequate supports for the structure to resist the loads without moving.

Technical Note

5

View/Validate Analysis Results o Go to 3D viewer and view the deflected shape of the structure for the principal load

cases. These are “service”, “post-tensioning” and other load cases that you have defined. If the deflected shapes and their magnitudes appear acceptable, you may proceed to the design stage. Otherwise, adjust or correct the suspect data or parameters.

Create Design Strips in X-direction

o Use the support line wizard to create support lines along one of the principal axes of the structure. If the supports do not line up, the support line will not be straight. This should not be a concern, since the program can automatically adjust the direction of the calculated reinforcement to that of your choice independent from the orientation of associated support lines.

o Create “Design Strips” for the support lines created above. Use the FEM option for design strip creation.

o Use the color rendering of the design strips to make sure that the strips created cover the entire floor area. Each part of the floor area must have been assigned to a design strip.

o Correct the errors if any. o If based on your judgment, the geometry of the strips created by the program is

not a good arrangement, use splitters to modify the program’s choice. o Re-create the design strips, until the selection is acceptable to you. o Save

Create Design Strips in Y-direction

o Follow the above procedure to create design strips orthogonal to the first direction. Select the X and Y strips to be as close to orthogonal condition as practical.

o Save

Create Design Sections o Click on the “Create Design Sections Automatically” to generate design sections

for each of the design strips. o Activate the “Display Design Sections” tool from the “Support Line Results/Scale

Toolbar” to view the design sections generated for each of the two orthogonal directions. Verify the following:

If the number of sections for any given span is not adequate, select the associated support line and increase the number of design sections.13

There should be a design section at each face of a support (wall, column, beam)

There should be a design section at the face of each drop cap/panel. Make sure that for each direction the design sections adequately cover the

entire surface of the floor. o Save

Design the Design Sections

13 The default of the program is 12 sections in each span. This can be modified by opening the property box of a support line and changing the default value.

Technical Note

6

o Activate the code check of the structure and the calculation of the necessary reinforcement by selecting “Design the Design Sections.”

o The program reports the design sections that do not meet the minimum requirements of the code in broken magenta lines. Otherwise, the design sections will be shown in green. Green display of a design section means that the code requirements for that section are met.

View Details of the Design Outcome and Make Adjustments if Necessary

o To accept the design, select several of the critical design strips one after the other, and view the outcome of the design by displaying the following:

Reinforcement reported for each code check and the envelope of reinforcement

The layout of reinforcement (selection of bar size, and length) Computed stresses and their comparison with the allowable values

o View the stress details of each of the design strips that have failed the code check. Based on the location of the design section, use your judgment to determine which of the entry values have to be adjusted. In most cases, the amount and profile of post-tensioning is the choice. Make the necessary modification and repeat the analysis/design.

Perform Punching Shear Check14

o Select the “Punching Shear Check” tool to perform code check for punching shear.

o View the values of the punching shear reported by the program on the screen. If necessary and permissible, the program reports the necessary reinforcement. The program also reports, if a section does not pass Code.

o Save data

CONCLUSION OF DESIGN Once you reach this stage, your design is completed. The steps to follow are to prepare the structural documents. These are:

Generation of rebar drawings Generation of post-tensioning drawings Generation of shop drawings Generation of the package of structural calculations

The procedure for the generation of the each of the above is detailed in a different document.

14 Punching shear check can also be performed after the completion of the “analysis” and prior to the “design.” However, the advantage of performing punching shear check after the “design” option is that at each location the program uses the actual value of precompression. In the former option, the program uses the minimum value of the code (125 psi), assuming that an acceptable design must meet this value.

Technical Note

7

APPENDIX This Appendix explains in greater details some of the terms used in the Technical Note FRAMING PLAN Framing Plan is a drawing that is part of the structural documents and defines the outline of the concrete floor system with all the details necessary for its forming and finish. It provides a complete definition of the geometry of the concrete forming the floor system. In contains the following information:

• Full definition of concrete geometry o Concrete outline o Openings o Steps above and below slab o Drop caps/panels o Slab bands o Beams o Slab thickness and beam dimensions o Concrete strength o Proposed construction joints o Proposed closure (pour) strips

• Supports

o Location of all wall supports15 o Location of all column supports16 o Type of connection of slab to supports (extent and type of releases)

15 Walls identification and dimensions are shown on other drawings 16 Column identification and dimensions are shown on other drawings