Structural Mechanics (Breadth)
Concepts
Statics and strength of materials: equilibrium, shear and moment diagrams, truss analysis by joints and sections, beam deflection, column buckling (Euler, slenderness), combined stresses, and load combinations. Construction candidates also need temporary structures: shoring, formwork, excavation bracing, and crane mats. Know ASCE 7 load combinations and the difference between ASD and LRFD.
Traps
Sign conventions; fixed-end versus simple-span moments (wL²/8 simple, wL²/12 fixed-end); point loads versus distributed loads; not converting units (kips, psi, feet, inches); treating a brace as a beam; ignoring second-order effects in slender columns. In LRFD, factored loads are compared to factored resistance; in ASD, service loads to allowable stress. Never mix the two.
Worked example
A simply supported beam spans 20 ft and carries a uniform load of 2 kip/ft including self-weight. Maximum moment = wL²/8 = 2(20²)/8 = 100 kip-ft. Maximum shear = wL/2 = 20 kips. Midspan deflection = 5wL⁴/(384EI) with consistent units. If the beam is not braced laterally, check lateral-torsional buckling, not just bending stress.
Rule of thumb
For a simply supported beam under uniform load, many design checks use L/360 for live-load deflection and L/240 for total load. For cantilevers, the moment is wL²/2 at the support and deflection is wL⁴/(8EI).