Question

All given loads are service loads. A column in a building is subjected to the following load effects: 9 kips compression from dead load 5 kips compression from roof live load 6 kips compression from snow 7 kips compression from 3 inches of rain accumulated on the roof 8 kips compression from wind a. If load and resistance factor design is used, determine the factored load Note 2-1 (required strength) to be used in the design of the column. Which AISC load combination controls? b. What is the required design strength of the column? c. What is the required nominal strength of the column for a resistance factor φ of 0.90? d. If allowable strength design is used, determine the required load capac ity (required strength) to be used in the design of the column. Which AISC load combination controls? e. What is the required nominal strength of the column for a safety factor Ω of 1.67?

Answer 1

Solution: For the combination of design load and design resistance factor: As per code ASCE-2010 Combination: 1 1.4(Dead load) 1.4(9kips) 12.6kips Combination: 2 1.2(Dead load)+1.6(live load)+0.5(rain accumulated on roof) -1.2(9kips)+1.600)+0.5(7kips) 14.3kips Combination: 3 1.2(Dead load)+1.6(rain accumulated on roof)+0.8W -1.2(9kips)+1.6(7)+0.8(8) 28.4kips Combination: 4 1.2(Dead load)+1.6(W)+0.5(rain load) -1.2(9kips)+1.6(8)+0.5(7) 27.lkips Therefore, the combination-3 gets more compression compared to other combinations

b) Calculate of column: The required factored load in design of column is 28.4kips. strength of the design(pR)sR,(strength required) the factored load in design

c) Required design strength of the column: Using LRFD equation 20 28.4 n0.9 R, s 31.56kips Therefore, the required design strength is 31.56kips.

d) Calculate Controlload combination: Combination: 1 Dead load-9kips Combination: 2 Dead load+live load-9+0-9kips Combination: 3 Dead load+roof load-9+7 16kips Combination: 4 Dead load+0.75(live load)+0.75(R.L)-9+0.75 8)+0.75(7) 20.25kips Therefore, the AISC combination 4 controls, (load combination) are 20.25kips

E) Calculate nominal strength 20 P (P2) P (20.25x1.67) P,-33.8 Ikips Therefore, the strength of column is 33.81kips