Structural engineering models and applications
Analysis first
Structural questions usually reduce to statics, load combinations, and member behavior. Draw the free-body diagram, solve reactions, then construct shear and moment diagrams. For a simply supported beam with uniform load w over span L, maximum moment is wL²/8 at midspan and maximum shear is wL/2 at the supports. A frequent trap is using the wrong span, forgetting self-weight, or mixing service loads with factored loads.
Design codes and limits
Know the difference between ASD and LRFD. Load factors and combinations must be explicitly supplied or taken from the applicable current framework; serviceability and strength are separate checks. For steel, check yielding, rupture, buckling, and connection limit states. For reinforced concrete, verify tension-controlled behavior, minimum reinforcement, development length, and shear capacity. Column questions hinge on effective length K and slenderness; a pinned-pinned column has K = 1.0, fixed-free K = 2.0.
Worked example
A 20 ft simply supported beam carries w = 2.0 klf, including self-weight. Maximum moment = wL²/8 = 2.0(20²)/8 = 100 kip-ft. Maximum shear = wL/2 = 2.0(20)/2 = 20 kips. If a hypothetical exercise explicitly specifies the combination 1.2D + 1.6L and asks for factored moment and the 2.0 klf is all dead load, Mu = 1.2(100) = 120 kip-ft. The trap is applying both factors to a load that is entirely one type.
Detailing and load paths
Understand tributary area, one-way versus two-way action, diaphragm and collector behavior, and connection eccentricity. Wind and seismic questions often turn on load path continuity and whether a component is part of the lateral-force-resisting system. Check units: kip-ft versus kip-in.
Concrete, steel, masonry and dynamic response
Member strength and structural behavior are different levels of analysis. Reinforced concrete needs compatible strain assumptions, force equilibrium, material response and suitable reinforcement anchorage. Flexural resistance does not establish adequate shear, punching resistance, crack control or deflection. Material grades, partial factors and detailing rules belong to the specified current code and exposure conditions; no local minimum is supplied here.
For steel, distinguish local plate instability, overall member buckling and lateral-torsional buckling. Connection geometry can introduce eccentric forces or a net section weaker than the gross member. A weld or bolt count without the load path, geometry and applicable resistance model is insufficient. Masonry behavior depends on unit and mortar properties, slenderness, support and reinforcement where used. Timber adds direction-dependent behavior, connection effects and moisture-related changes.
In lateral systems, stiffness and strength distribution affect drift and force sharing. A diaphragm must transfer actions into collectors, frames or walls through actual connections. Ductile behavior is not equivalent to unlimited deformation or immunity from failure. Response spectra and an equivalent-static model describe assumptions about dynamic response and damping; they do not replace site-specific hazard and irregularity assessment. Test both the numerical calculation and whether the physical idealization represents the actual structural system.