ASCE 7 Section 2.3 specifies load combinations for ultimate strength design (USD) and allowable stress design (ASD). LRFD (Load and Resistance Factor Design) uses factored loads and factored resistances. Ultimate strength design combines loads with factors: 1.2D + 1.6L + 0.5S (or H) represents the worst-case combination of dead load, live load, and snow or other load. Seismic design uses: 1.2D + 1.0E + 0.5L where E is the seismic load. Wind design uses: 1.2D + 1.6W where W is wind load. The load combination producing the maximum stress or deflection governs the design. Many load combinations are evaluated to determine the critical case.