Verification Example - Composite Steel Beam Design Secondary Member (LRFD & ASD)

Tekla Tedds
Modificado: 4 Jul 2024
2024
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Verification Example - Composite Steel Beam Design Secondary Member (LRFD & ASD)

Description

This verification example represents the analysis and design of a composite steel beam (secondary member) utilizing Tedds. 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 Tedds and the AISC Design Example.

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.

Tedds calculation

Composite beam design (AISC360) - Compared using version 1.0.16

Running the example in Tedds

The Tedds verification examples referenced in this document can be run in Tekla Tedds from the Engineering library index, in the Verification Examples\Composite beam design (AISC360) folder.

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

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)


Figure 1: Composite beam floor layout with the secondary member to be analyzed

 
Applied Loads
Pre-Composite (Construction Stage)

Dead Load

75 lb/ft2 Composite slab (72-½ lb/ft2 (slab) and 2-½ lb/ft2 (deck))
50 lb/ft Self-weight of steel beam
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)
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
Comparison of Results between Tedds and AISC Example I.1 (LRFD)
Component Tedds Result AISC Example I.1 % Difference
Pre-Composite (Construction Stage)
Beam Size W21x50 W21x50 -
Flexural Demand (Mu) 344.25 k-ft 344 kip-ft 0.1%
Flexural Capacity (φMn) 412.50 k-ft 413 kip-fta 0.1%
Shear Demand (Vu) 30.6 kips 30.6 kips 0.0%
Shear Capacity (φVn) 237.1 kips 237 kips 0.0%
Dead Load Deflection w/ camberb 2.59” - 2” (camber) = 0.59” 2.59” - 2” (camber) = 0.59” 0.0%
Post-Composite
Total number of shear studs 46 studsc 46 studs
Flexural Demand (Mu) 678.37 k-ft 678 kip-ft 0.0%
Flexural Capacity (φMn) 769.71 kip-ft 769 kip-ft 0.0%
Compression Block Depth (a) 0.946” 0.946”c 0.0%
Steel Anchor Shear Capacity (∑Qn) 385.94 kips 390 kips 1.0%d
% Composite Action 52.5% 53.1% 1.1%d
Shear Demand (Vu) 60.3 kips 60.3 kips 0.0%
Shear Capacity (φVn) 237.1 kips 237 kips 0.0%
Total Deflectione 2.05” = L/263 < L/240 N/A
Live Load Deflection (based on full design live load)e 1.329” = L/406 < L/360 1.26” = L/429 < L/360 5.5%
Final Beam Design W21x50 (46) c=2” W21x50 (46) c=2” -
Comparison of Results between Tedds and AISC Example I.1 (ASD)
Component Tedds Result AISC Example I.1 % Difference
Pre-Composite (Construction Stage)
Beam Size W21x50 W21x50 -
Flexural Demand (Ma) 265.78 k-ft 266 kip-ft 0.1%
Flexural Capacity (Mn/Ω) 274.45 k-ft 274 kip-fta 0.2%
Shear Demand (Va) 23.6 kips 23.6 kips 0.0%
Shear Capacity (Vn/Ω) 158.1 kips 158 kipsa 0.1%
Dead Load Deflection w/ camberb 2.59” - 2” (camber) = 0.59” 2.59” - 2” (camber) = 0.59” 0.0%
Post-Composite
Total number of shear studs 46 studsc 46 studs
Flexural Demand (Ma) 480.94 k-ft 481 kip-ft 0.0%
Flexural Capacity (M/Ω) 512.11 kip-ft 512 kip-ft 0.0%
Compression Block Depth (a) 0.946” 0.946”c 0.0%
Steel Anchor Shear Capacity (∑Qn) 385.65 kips 390 kips 1.0%d
% Composite Action 52.5% 53.1% 1.1%d
Shear Demand (Va) 42.8 kips 42.8 kips 0.0%
Shear Capacity (Vn/Ω) 158.1 kips 158 kips 0.1%
Total Deflectione 2.05” = L/263 < L/240 N/A
Live Load Deflection (based on full design live load)e 1.329” = L/406 < L/360 1.26” = L/429 < L/360 5.5%
Final Beam Design W21x50 (46) c=2” W21x50 (46) c=2” -

Comparison Notes

aAISC Table 3-2

bTedds calculates the total construction stage deflection which includes all preconstruction dead loads and construction live loads. The value shown is with the construction live load removed.

cThe 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).

dIn Tedds, the maximum number of available ribs to midspan of the beam is (21), so (19) ribs has (1) stud and (2) ribs have (2) studs, which leads to slightly different values of total strength of provided steel anchors and percent of composite action.

eIn Tedds, the effective moment of inertial for the partially composite beam is calculated using a reduction factor of 0.75, consistent with AISC 360-10. It is understood that the commentary in AISC 360-16 states that this factor could not be substantiated, and to use the lower-bound approach. Tedds is currently implementing this alternate design approach to calculate deflection for composite members.

Conclusion

Upon reviewing the results above, it is evident that the solutions determined by Tedds match the AISC Design Example I.1 (apart from minor differences due to rounding and precision).

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