For fully enclosed buildings GC pi 018 indicating that either positive or

# For fully enclosed buildings gc pi 018 indicating

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) = the internal pressure coefficient. For fully enclosed buildings (GC pi ) = 0.18, indicating that either positive or negative pressure can occur within the building. 20 The flat roof snow load (ASCE 7-10 S7.3): p f = 0.7C e C t I s p g where “flat” = roof slope 5 o C e = the exposure factor which depends on the terrain. C t = the thermal factor which refers to the average temperature within the building. I s = the snow importance factor p g = the ground snow load The minimum roof snow load for low-slope roofs: Where p g is 20 lb/ft 2 (0.96 kN/m 2 ) or less: p m = I s p g Where p g exceeds 20 lb/ft 2 (0.96 kN/m 2 ): p m = I s (20) Snow Loads 21 Structural Design Allowable-stress design (ASD) For ASD method, the elastic stress in the material must not exceed the allowable stress for each of various load combinations. ASD method include both the material and load uncertainties into a single factor of safety. Strength design or LRFD (Load and resistance factor design) Material uncertainty is separated from load uncertainty. For example, to account for the uncertainty of loads, this method uses load factors applied to the combinations of loads. 22 (ASCE 7-10 S2.3) 1. 1.4D 2. 1.2D + 1.6L + 0.5(L r or S or R) 3. 1.2D + 1.6(L r or S or R) + (L or 0.5W) 4. 1.2D + 1.0W + L + 0.5(L r or S or R) 5. 1.2D + 1.0E + L + 0.2S 6. 0.9D + 1.0W 7. 0.9D + 1.0E See exceptions in ASCE 7-10 S2.3.2 where D = dead loads; L = live loads L r = roof live loads; S = snow loads R = rain loads; W = wind loads E = earthquake loads Load Combinations for Strength Design 23 (ASCE 7-10 S2.4) 1. D 2. D + L 3. D + (L r or S or R) 4. D + 0.75L + 0.75 (L r or S or R) 5. D + (0.6W or 0.7E) 6. (a) D + 0.75L + 0.75(0.6W) + 0.75 (L r or S or R) (b) D + 0.75L + 0.75(0.7E) + 0.75 S 7. 0.6D + 0.6W 8. 0.6D + 0.7E See exceptions in ASCE 7-10 S2.4.1 Load Combinations for Allowable Stress Design 24 #### You've reached the end of your free preview.

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