Joist Models in Standard Structural Software - Microsoft · PDF fileJoist Models in Standard Structural Software September 24, 2015 Dave Samuelson, P.E. ... Quote from STAAD-Pro Technical

Joist Models in Standard Structural Software

September 24, 2015 Dave Samuelson, P.E. – Nucor New Product & Market Development

Joe Pote, P.E. – New Millennium Building Systems

Learning Objectives

•  What are the advantages and disadvantages to using classic tools to select conventional standard joists and Joist Girder designations?

•  What are a Virtual Joist and Virtual Joist Girder and how are they used? •  In what situation might it be advantageous for a Structural Engineer to

use the SJI Virtual Joist Table or Virtual Joist Girder Table? •  When a Virtual Joist or Virtual Joist Girder is used in the building design

model, how should it be specified on the contract structural drawings?

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Joist Models in Standard Structural Software Joists and Joist Girders in a RAM-Steel Rendering

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Learning Objectives


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Learning Objectives


•  What are a Virtual Joist and Virtual Joist Girder and how are they used?

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Learning Objectives



use the SJI Virtual Joist Table or Virtual Joist Girder Table?

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Learning Objectives





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Advantages and Disadvantages to using Classic Tools to select Standard Joists and Joist Girders

•  Classic Roof and Floor Framing Optimizers such as RAM-Steel or RISA-Floor

•  General Structural Analysis Software such as STAAD, RISA or STRUDL

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Classic Roof and Floor Framing Optimizers such as RAM-Steel or RISA-Floor

•  Excellent job of selecting optimum “Standard” joists (Pro)

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Standard Joists Selected based on Span and Loading

RAM-Steel Partial Framing Plan

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Classic Roof and Floor Framing Optimizers such as RAM-Steel or Risa-Floor

•  Excellent job of selecting optimum “Standard” joists (Pro) •  Cannot actually ‘select’ Joist Girders, as there are no ‘standard’ Joist

Girders to select from. Joist Girder Designation is specified based on loading and user-provided depth. (Con)

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Joist Girder Designations Assigned based on Loading and User-Provided Depth

RAM-Steel Partial Framing Plan without User-Provided Depth

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Classic Roof and Floor Framing Optimizers such as RAM-Steel



•  Joists and Joist Girders automatically appear on the Structural Drawings with correct designation needed by the Joist Manufacturer for quoting, designing and manufacturing. (Pro)

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Joist and Girder Designations displayed in Conventional Format

RAM-Steel Partial Framing Plan

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Joist and Girder Designations transferred to CAD in Conventional Format

AutoCAD Partial Framing Plan

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Classic Roof and Floor Framing Optimizers such as RAM-Steel



•  Joists and Joist Girders automatically appear on the Structural Drawings with correct designation needed by the Joist Manufacturer for quoting, designing and manufacturing. (Pro)

•  Joists can only be managed as simple-span infill joists supporting vertical gravity loads. ‘Standard’ joist designations and definition do not address negative moments, end moments, or axial loads. (Con)

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Advantages and Disadvantages to using Classic Tools to select Standard Joists and Joist Girders

•  Classic Roof and Floor Framing Optimizers such as RAM-Steel •  General Structural Analysis Software such as STAAD, RISA or STRUDL

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General Structural Analysis Software such as STAAD, RISA, or STRUDL

•  No Section Properties available for standard joists and girders. Therefore, the joists and girders cannot be included in the stiffness matrix model. (Con)

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Steel Joist and Joist Girder Stiffness are not included in the Structural Model

Quote from STAAD-Pro Technical Reference Manual

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General Structural Analysis Software such as STAAD, RISA, or STRUDL

•  No Section Properties available for standard joists and girders. Therefore, the joists and girders cannot be included in the stiffness matrix model. (Con)

•  Some general analysis software does include tools for selecting joists and treats the joist as a load distribution link…an infinitely rigid simply supported infill component between supporting members. (Pro)

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Joists Treated as Links with Simple Selection Tools

Screen Shot of STAAD-Pro Joist Database Table Tool

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Learning Objectives





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What are a Virtual Joist and Virtual Joist Girder?

•  Virtual Joists and Virtual Joist Girders are a set of pseudo section properties based on commonly available joist chord pairs.

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Excerpt from Virtual Joist Girder Table

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•  The major axis moment of inertia (IZ) is based directly on the pair of double angle joist chords and pre-adjusted for approximate deflection contribution from web strain. The Area is likewise based directly on the pair of double angle joist chords.

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Ax: Total Area of Top and Bottom Chords – Sum of top and

bottom chord areas D: Total VJG Depth Iz: VJG Strong-Axis Effective Moment of Inertia – Classically

calculated Moment of Inertia of the Chords divided by 1.15 to account for deflection effects from the joist web members.

Virtual Joist Girder Section Properties:

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Virtual Joist Section Properties, Iz

From SJI 43rd Edition Joist Catalog, Page 14:

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Virtual Joist Section Properties, Izz

From SJI Technical Digest 11, “Design of Lateral Load Resisting Frames using Steel Joists and Joist Girders”:

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•  All other section properties are equivalent wide-flange beam properties manipulated to encourage selection of the appropriate Virtual Joist and/or Virtual Joist Girder when checked against a Wide-Flange Beam selection routine.

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TD: Web Thickness – Total Depth/30; Ensures that the sec7on is

treated as "compact" when considering web shear. B: Flange Width – 2*Chord Angle Leg + 1" Chord Gap TB: Flange Thickness – (Chord angle thickness)/(chord angle leg) * B/2; This value results in the correct width/thickness ra7o when STAAD checks (B/2)/TB.

Sample VJ & VJG Section Properties:

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•  All other section properties are equivalent wide-flange beam properties manipulated to encourage selection of the appropriate Virtual Joist and/or Virtual Joist Girder when checked against a Wide-Flange Beam selection routine.

•  The Virtual Joist and Virtual Joist Girder tables provide approximate section properties suitable for use in a stiffness based structural analysis program. Testing at South Dakota School of Mine and Technology has verified that Virtual Joists and Virtual Joist Girders selected via STAAD and/or RAM using a broad range of loading scenarios result in section properties reasonably close to those in the final joist and Joist Girder designs.

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SDSM&T Comparison Study of VJ and VJG

K-Series Span/Load Test Matrix

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Moment of Inertia Variance –vs- Depth for Simply Supported K-Series Tests

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LH-Series Span/Load Test Matrix

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Moment of Inertia Variance –vs- Depth for Simply Supported LH-Series Tests

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Learning Objectives





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When might it be advantageous to use the SJI Virtual Joist Table or Virtual Joist Girder Table?

•  When sizing joists for special loads (anything other than full-length uniform design loads)

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Not all Design Loads are Uniformly Distributed

Sample Special Load Diagram from SJI COSP

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•  When sizing joists for special loads (anything other than full-length uniform design loads) –  A more accurate estimate of appropriate joist and/or Joist Girder

depth and weight can be found using the Virtual Joist and Virtual Joist Girder tables than by using equivalent uniform loads and standard joist load tables.

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•  When sizing joists for conditions with negative moments, such as cantilevered joists and/or joists with intermediate supports (multi-span conditions).

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Not all Joists are Simply Supported

Cantilevered Joist Diagram from SJI 43rd ed Catalog

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•  Anytime it is desirable to include the joists and/or Joist Girders directly in the structural model with appropriate approximate section properties.

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•  Anytime it is desirable to include the joists and/or Joist Girders directly in the structural model with appropriate approximate section properties. –  Particularly when joists and/or Joist Girders are used as part of a

lateral load resisting frame. The VJ and VJG tables allow easy selection of appropriate depths with appropriate approximate section properties for use in the structural model.

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Frame Model with Joist Girders

24 @ 5'-0" = 120'-0"

23'-6"

FRAME MODEL @ GRID LINE B & E

P P P

WIN

D =

100

0 pl

f

1 2 3 4

5 6 7

WIN

D =

100

0 pl

fG3 G3G4P : DL = 2.4 kips LL = 4.0 kips TL = 6.4 kips WL = 7.0 kips

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Joist Girder End Moment Schedule

Mark

Target

Ix [in4]

Fixed-End Moments (Pos. is Counter-Clockwise) Couples between Top & Bottom Chord

Dead [ft-k] Live [ft-k] Wind [ft-k] Acting to Right

Wind [ft-k] Acting To Left

Left Ext’r Col.

Right Int’r Col.

Left Ext’r Col.

Right Int’r Col.

Left Ext’r Col.

Right Int’r Col.

Left Ext’r Col.

Right Int’r Col.

G1 931

G2 931 24.5 -24.5 38.2 -38.2 -204.9 -71.2 71.2 204.9

G3 1347 11.2 -51.5 17.8 -81.8 -55.5 -106.6 -5.8 396.0

G4 1521

G5 1521

G6 1236 44.0 -44.0 70.2 -70.2 -398.9 -153.3 153.3 398.9

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Learning Objectives





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How should a Virtual Joist or Virtual Joist Girder be Specified on the Structural Drawings?

•  It is important to specify all joists and Joist Girders using conventional SJI designation nomenclature.

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50’ Span 28” Joist Depth

ASD 28K7 Joist

185/100 Uniform Load (PLF)

Standard Joist Designation

ASD Allowable Strength Design

28 Joist Depth In Inches

K Joist

Series

7 Chord Size

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50’ Span 28” Joist Depth

ASD 28K Load/Load Joist

185/100 Uniform Load (PLF)

Load/Load Joist Designation


28 Joist Depth In Inches

K Joist

Series

185 Total Load Capacity

PLF

100 Live Load Capacity

PLF

ASD 28K 185/100 185 = Total safe uniformly distributed load carrying capacity in PLF of ASD K-Series Steel Joists 100 = Nominal LIVE loads per lineal foot of joist.

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Joist Girder Span (C.L. of Column to C.L. of Column)

44” Depth

Standard Joist Girder

Standard Joist Girder Designation


44G Depth of Girder in Inches

8N Number of

Joist Spaces

11.9K Load in Kips

at Each Panel Point

Joist Space 11.9K 11.9K 11.9K 11.9K 11.9K 11.9K 11.9K

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•  The VJ and/or VJG selections cannot be used as a substitute for the joist and Joist Girder designations. It may, at times, be helpful to include these as additional information. However, they do not provide the information needed by the joist manufacturer to design and manufacture the joists and joist girders required for the project.

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Virtual Joist Girder Designation

An Example from a set of Structural Drawings Standard Designation Above

VJG Designation Below

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•  For Joist Girders, specify the designation based on depth, number of joist spaces, and joist reaction. If the loading is unequal, unequally spaced, or includes special loads, use a load diagram and/or load schedule.

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Virtual Joist Girder

Mark

Designation

Panel Point Loads

Axial (Pos. causes Tens.) Split between Top & Bottom

Chord

Dead [kips]

Live [kips]

Total (D+L) [kips]

Wind [kips]

Dead [kips]

Live [kips]

Wind [kips]

G1 36G8N 1.2 2.0 3.2 ±3.5 ±5.88

G2 36G8N 1.2 2.0 3.2 ±3.5 1.04 1.63 ±2.84 G3 36G8N 2.4 4.0 6.4 ±7.0 0.48 0.76 ±9.39 G4 36G8N 2.4 4.0 6.4 ±7.0 1.71 2.72 ±4.85

G5 36G8N 2.4 4.0 6.4 ±7.0 ±11.75

G6 36G8N 2.4 4.0 6.4 ±7.0 1.87 2.99 ±5.23

Reporting Loads

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Mark

Target

Ix [in4]

Fixed-End Moments (Pos. is Counter-Clockwise) couples Between Top & Bottom Chord



Left Ext’r Col.

Right Int’r Col.

Left Ext’r Col.

Right Int’r Col.

Left Ext’r Col.

Right Int’r Col.

Left Ext’r Col.

Right Int’r Col.

G1 931

G2 931 24.5 -24.5 38.2 -38.2 -204.9 -71.2 71.2 204.9

G3 1347 11.2 -51.5 17.8 -81.8 -55.5 -106.6 -5.8 396.0

G4 1521

G5 1521

G6 1236 44.0 -44.0 70.2 -70.2 -398.9 -153.3 153.3 398.9

Reporting Loads

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•  For joists, specify the designation using either a standard joist designation or a load/load joist designation. For special loading conditions, show all loads on the framing plan, in load diagrams and/or a load schedule.

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•  For joists, specify the designation using either a standard joist designation or a load/load joist designation. For special loading conditions, show all loads on the framing plan, in load diagrams and/or a load schedule.

•  For joists and/or Joist Girders used as part of a lateral load resisting frame, provide the Joist Moment of Inertia used in the structural model (from the VJ and/or VJG tables) as a target value for the Joist Manufacturer. It is recommended to specify that the Joist Manufacturer is to contact the Structural Engineer of Record regarding moments of inertia that deviate from the target values by more than 10%.

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Reporting Loads

Mark

Target

Effective Ix

[in4]

Fixed-End Moments (Pos. is Counter-Clockwise) couples Between Top & Bottom Chord



Left Ext’r Col.

Right Int’r Col.

Left Ext’r Col.

Right Int’r Col.

Left Ext’r Col.

Right Int’r Col.

Left Ext’r Col.

Right Int’r Col.

G1 931

G2 931 24.5 -24.5 38.2 -38.2 -204.9 -71.2 71.2 204.9

G3 1347 11.2 -51.5 17.8 -81.8 -55.5 -106.6 -5.8 396.0

G4 1521

G5 1521

G6 1236 44.0 -44.0 70.2 -70.2 -398.9 -153.3 153.3 398.9

Note: Please contact the Project Structural Engineer of Record if the final effective Joist Girder Moment of Inertia (Ix) varies from the tabulated target value by more than 10%

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Current Access to VJ and VJG in Structural Software

•  STAAD / STAAD-Pro –  VJG Table available as a built-in –  VJ Table available as a User Defined Table which can be

downloaded from the SJI website •  RAM / RAM-Structural

–  VJG Table available as a built-in •  RISA and RISA-Floor

–  VJG Table available as a built-in •  Scia Engineer (scheduled for October release)

–  VJG Table available as built-in •  Uses VJG Depth for Conventional Girder Designation

–  VJ Table available as built in •  Uses VJ Depth for Load/Load Joist Designation

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RAM-Steel Screen Shot with VJG Designations

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RISA-Floor Screen Shot with VJG Designations

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RISA-3D Screen Shot with VJG Designations

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Virtual Joist and Virtual Joist Girder Scia uses VJ & VJG Designations for Stiffness Modeling

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Virtual Joist and Virtual Joist Girder Scia overlays the VJ/VJG Designations with Conventional Designations

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Virtual Joist and Virtual Joist Girder Scia uses the VJ/VJG Depths in Defining Special Joist and Joist Girder

Designations

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Learning Objectives





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Conclusions

•  The classic tools, though limited, provide a very effective means of selecting standard joists with appropriate designations.

•  Popular structural design packages are beginning to incorporate Virtual Joists and Virtual Joist Girders, thereby allowing more modeling flexibility.

•  For simple-span uniformly loaded conditions, the classic tools are simple, accurate and easy to use.

•  For complex loading and/or complex support conditions, the VJ and VJG tables provide a good tool for incorporation in the structural model.

•  Current use of VJ and VJG requires the user to manually follow up with their own standard format designation for use on Structural Framing Plan.

•  Some structural software packages are now working toward incorporating VJ and VJG in such a way as to automate the accompanying standard format designation.

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Documents

Joist Models in Standard Structural Software - Microsoft · PDF fileJoist Models in Standard Structural Software September 24, 2015 Dave Samuelson, P.E. ... Quote from STAAD-Pro Technical