Structural Engineering
Structural Engineering tests load combinations, structural analysis, reinforced-concrete and steel member design, connections, serviceability, and seismic detailing. The exam expects you to select the governing strength combination, compute demand, and compare it with a factored resistance using the correct resistance factor.
Load and resistance framework
ASCE 7 strength combinations include 1.2D + 1.6L for gravity-controlled design, with wind and seismic combinations governing in other cases. ACI 318 uses φMn ≥ Mu for flexure and φVn ≥ Vu for shear. Steel design uses LRFD with factored loads and nominal strengths. Serviceability checks use service loads and compare deflection or vibration to limits.
Worked example
A simply supported beam spans 20 ft and carries a dead load of 1.0 klf, including its own weight, and a live load of 1.5 klf. The governing gravity combination is wu = 1.2(1.0) + 1.6(1.5) = 3.6 klf. Maximum moment is Mu = wuL²/8 = 3.6(20²)/8 = 180 kip-ft. If the section's φMn is 200 kip-ft, flexure is satisfactory. If the analyst omits self-weight from the dead load, the demand is underestimated and the check is unconservative.
Detailing and connections
Reinforcement must satisfy development length, anchorage, and spacing limits. Shear design requires stirrups where Vu exceeds φVc. Steel connections must be checked for block shear, bolt bearing, and weld capacity. Seismic detailing requires ductile behavior through confinement and capacity-designed connections.
Traps
Do not confuse service and factored loads. Keep kip-ft and kip-in consistent when using moment equations with d in inches. Verify whether a given dead load already includes self-weight. Flexure uses φ = 0.90 for tension-controlled concrete sections; shear uses φ = 0.75. Do not assume a section is tension-controlled without checking strain.
Key points
- Use 1.2D + 1.6L for the basic gravity strength combination.
- Compare factored demand with factored resistance.
- Include member self-weight in dead load unless it is already stated.
- Check shear and deflection, not only flexure.
- Confirm tension-controlled behavior before using φ = 0.90.