Composite Beam Secondary Member (LRFD & ASD) Verification Example
Description
This verification example represents the analysis and design of a composite steel beam (secondary member) utilizing Tekla Structural Designer (TSD). This example is based on Design Example I.1 of the Companion to the AISC Steel Construction Manual Volume 1: Design Examples Version 15.1 (Pages I-4 through I-14). Comparisons and contrasts are tabularized and discussed regarding the results from TSD and the AISC Design Example. The TSD model used in this example is also provided via the link below.
Problem statement
Select an appropriate ASTM A992 W-shaped beam and determine the required number of ¾” ⌀ steel headed stud anchors. The beam will not be shored during construction.
References
International Building Code (IBC) 2018
AISC Steel Construction Manual 15th ed.
Companion to the AISC Steel Construction Manual Volume 1: Design Examples Version 15.1
ANSI/AISC 360-16: Specification for Structural Steel Buildings
ACI 318-14: Building Code Requirements for Structural Concrete and Commentary
Tekla Structural Designer models
The comparisons given below were made using ASD and LRFD example models (dated 22.11.2024) which were created in Tekla Structural Designer 2024 Service Pack 2. A zip file containing the example models can be downloaded from this page.
Note that the downloaded models can only be opened in the same, or a later version of the application.
Example information
4-½” normal weight concrete on 3” x 18 ga. (Vulcraft 3VLI-36) composite deck (total slab thickness = 7-½”)
γconcrete = 145 lb/ft3
f’c = 4 ksi
ASTM A992
Fy = 50 ksi
Fu = 65 ksi
¾” ⌀ Steel stud anchors
Fu = 65 ksi
Stud height = 3” + 1-½” = 4-½” (AISC Section I3.2c)
Short-term to long-term concrete elastic modulus = 3:1 (assumed)
Figure 1: Composite beam floor
layout with secondary member analyzed in TSD
| Applied Loads | ||
|---|---|---|
| Pre-Composite (Construction Stage) | ||
|
Dead Load |
75 lb/ft2 | Composite slab and deck |
| 5 lb/ft | Self-weight of steel members. Automatic self-weight of steel determined by TSD was not used, and a self-weight load case of 5 lb/ft2 was used instead. | |
| Construction Live Load | 25 lb/ft2 | Light duty (ASCE 37-14 Table 4-4) |
| Post-Composite | ||
| Dead | 10 lb/ft2 | Miscellaneous (HVAC, ceiling, floor covering, sprinklers, etc.) |
| Live | 100 lb/ft2 | Assembly occupancy (non-reducible). Live load is assumed to be 100% long-term as no information is provided in the Design Example. This value is found in the Load Case section for Live Load in TSD |
| Serviceability Criteria | ||
|---|---|---|
| Pre-Composite (Construction Stage) | ||
| Concrete (wet) + Self-weight | < L/360 or 1” | AISC Design Guide 3 Ch. 5 recommendations |
| Post-Composite | ||
| Dead+Live | < L/240 | IBC 2018 Table 1604.3 |
| Live | < L/360 | IBC 2018 Table 1604.3 |
| 50% Live | < 1” | AISC Design Guide 3 Ch. 5 recommendations |
| Comparison of Results between Tekla Structural Designer and AISC Example I.1 (LRFD) | |||
|---|---|---|---|
| Component | TSD Result | AISC Example I.1 | % Difference a |
| Pre-Composite (Construction Stage) | |||
| Flexural Demand (Mu) | 344 k-ft | 344 k-ft | 0.0% |
| Flexural Capacity (φMn) | 413 k-ft | 413 kip-ft b | 0.0% |
| Shear Demand (Vu) | 30.6 kips | 30.6 kips | 0.0% |
| Shear Capacity (φVn) | 237 kips | 237 kips | 0.0% |
| Dead Load Deflection w/ camberc | 2.614” - 2” (camber) = 0.614” | 2.59” - 2” (camber) = 0.59” | 4.0% (less than 1/32”) |
| Post-Composite | |||
| Total number of shear studs | 46 studs d | 46 studs | |
| Flexural Demand (Mu) | 678 k-ft | 678 kip-ft | 0.0% |
| Flexural Capacity (φMn) | 773 kip-ft | 769 kip-ft | 0.5% |
| Compression Block Depth (a) | 0.959” | 0.946” e | 1.4% |
| Steel Anchor Shear Capacity (∑Qn) | 391 kips | 390 kips | 0.3% |
| % Composite Action | 53.2% | 53.1% | 0.2% |
| Shear Demand (Vu) | 60.3 kips | 60.3 kips | 0.0% |
| Shear Capacity (φVn) | 237 kips | 237 kips | 0.0% |
| Total Deflection | 1.90” = L/284 < L/240 | N/A | N/A |
| Live Load Deflection (based on full design live load) | 1.26” = L/429 < L/360 | 1.26” = L/429 < L/360 | 0.0% |
| Live Load Deflection (based on 50% design live load) | 0.63” < 1” | 0.63” < 1” | 0.0% |
| Comparison of Results between Tekla Structural Designer and AISC Example I.1 (ASD) | |||
|---|---|---|---|
| Component | TSD Result | AISC Example I.1 | % Difference a |
| Pre-Composite (Construction Stage) | |||
| Flexural Demand (Ma) | 266 k-ft | 266 kip-ft | 0.0% |
| Flexural Capacity (Mn/Ω) | 274 k-ft | 274 kip-ft b | 0.0% |
| Shear Demand (Va) | 23.6 kips | 23.6 kips | 0.0% |
| Shear Capacity (Vn/Ω) | 158 kips | 158 kips b | 0.0% |
| Dead Load Deflection w/ camberc | 2.614” - 2” (camber) = 0.614” | 2.59” - 2” (camber) = 0.59” | 4.0% (less than 1/32”) |
| Post-Composite | |||
| Total number of shear studs | 46 studsd | 46 studs | |
| Flexural Demand (Ma) | 481 k-ft | 481 kip-ft | 0.0% |
| Flexural Capacity (M/Ω) | 514 kip-ft | 512 kip-ft | 0.4% |
| Compression Block Depth (a) | 0.959” | 0.946” e | 1.4% |
| Steel Anchor Shear Capacity (∑Qn) | 391 kips | 390 kips | 0.30% |
| % Composite Action | 53.2% | 53.1% | 0.2% |
| Shear Demand (Va) | 42.8 kips | 42.8 kips | 0.0% |
| Shear Capacity (Vn/Ω) | 158 kips | 158 kips | 0.06% |
| Total Deflection | 1.90” = L/284 < L/240 | N/A | |
| Live Load Deflection (based on full design live load) | 1.26” = L/429 < L/360 | 1.26” = L/429 < L/360 | 0.0% |
| Live Load Deflection (based on 50% design live load) | 0.63” < 1” | 0.63” < 1” | 0.0% |
Comparison Notes
a - The manufacturer’s data of 75 lb/ft2 uses an approximation of the deck weight (2.5 lb/ft2). TSD uses exact weight based on deck properties (i.e. 3” x 18 ga deck has a weight of 2.8 lb/ft2). The weight of the deck in TSD was changed to 2.5 lb/ft2 to align with the AISC Design Example.
b - AISC Table 3-2
c - Camber is based off of 80% self-weight and pre-composite dead load with a minimum ¾” camber and a maximum 2” camber.
d - Tekla Structural Designer autodesigns a more economical solution with 45 required studs, however to align with the AISC Design Example, 46 studs were used.
e - The compression block depth in the AISC Design Example is determined from the required horizontal shear (386 kips) instead of the provided shear strength of 46 anchors (390 kips).
Conclusion
Upon reviewing the results above, it is evident that the solutions for composite beam analysis and design determined by Tekla Structural Designer match the AISC Design Example I.1 (apart from minor differences due to rounding and precision).