Wind and Earthquake Loads
Wind
Wind pressure depends on basic wind speed, exposure category, height, and building geometry. The velocity pressure grows with height and exposure roughness. Internal pressure depends on enclosure classification (enclosed, partially enclosed, open). Traps include using the wrong exposure (B for suburban, C for open, D for water), forgetting internal pressure on roofs, and ignoring that uplift on roof overhangs is often the governing case.
Earthquake
Seismic base shear depends on seismic weight, spectral acceleration, response modification factor R, and the structure's period. Key concepts: seismic weight excludes live load except a fraction, R penalizes brittle systems, and the irregularity checks (plan and vertical) determine whether a simple equivalent lateral force method is allowed. Traps include confusing the redundancy factor, misapplying the overstrength factor, and forgetting that drift limits are serviceability checks separate from strength.
Worked rule of thumb
For an equivalent lateral force analysis, base shear V = Cs × W, where Cs is the seismic response coefficient. If W = 1,000 kip and Cs = 0.15, V = 150 kip. Distribute this over the height in proportion to wx hx^k, with k = 1 for short periods and k = 2 for long periods. Always verify the minimum base shear floor and the drift limit in the same run.