Commercial Building Inspector B2Structural SystemsMedium
A structural engineer is designing a steel beam for a floor system in a commercial building. The beam is subjected to bending moments and shear forces. To ensure adequate shear strength, the engineer must consider the web of the beam. According to AISC 360, what is the primary limit state that governs the design of a steel beam web for shear?
- ABearing failure at support points.
- BOverall lateral-torsional buckling of the beam.
- CFlexural yielding of the flanges.
- DLocal buckling of the web.
Show answer & explanationAnswer & explanation
Correct answer: D. Local buckling of the web.
According to AISC 360, the primary limit state that governs the design of a steel beam web for shear is web yielding or web local buckling. For slender webs, local buckling (either shear buckling or flexural buckling of the web itself) can precede yielding and is a critical failure mode that must be prevented to ensure the beam's shear capacity. Flexural yielding of flanges and lateral-torsional buckling are limit states for bending, not primarily shear.
Why the other options are wrong
- A. Bearing failure at support points is a separate limit state related to concentrated loads, not the general shear strength of the web along the span.
- B. Overall lateral-torsional buckling is a limit state for bending, affecting the beam's flexural capacity, not its primary shear capacity.
- C. Flexural yielding of flanges is a limit state for bending moment, not shear strength of the web.
Steel Beam Web Shear Limit State
The primary failure mode that governs the design of a steel beam's web under shear forces, typically web yielding or web local buckling, as defined by AISC 360.
- Prevents premature failure under shear.
- Critical for slender webs.
- Considered in AISC 360 Chapter G.
Memory trick: Steel beam's web can buckle or yield under shear's stress.