Given the ‘braced frame’ below that may be subjected to the stated load cases, d
ID: 1713060 • Letter: G
Question
Given the ‘braced frame’ below that may be subjected to the stated load cases, determine the following: (assume LRFD Load combinations are to be used)
1.) Which load combination will control for designing the “anchorage” of Joint A to the foundation, to resist uplift forces? (Give the equation only, no numbers)
2.) Will the “brace” be in Tension, Compression, or Bending due to the Wind load only?
3.) Find the maximum design ‘Tension force’ in the anchors to the foundation at Joint A, using the controlling LRFD load combination. Why does the combination given in #1 ‘control’ in this specific situation?
4.) Find the maximum ‘Compressive force’ in the Column reaction to the foundation at Joint B, using the controlling (worst case) LRFD load combination.
wind (Io Kip) Joint A Joint BExplanation / Answer
1) The load combination that will give give maximum uplift force at joint A will be 0.9DL+1.0WL
2)Due to wind load only, the brace will be in tension
3)Force at A due to dead load = 200*20/2=2000lb=2 kips(compressive)
Force at A due to wind load = 10*15/20=7.5 kips(tension)
Per load combination of 0.9DL+WL,net tension at A=(0.9*-2)+(7.5)= 5.7 kips
The reason load combination 0.9DL+WL governs is because only in this combination,towal gravity load is least and effect of wind is maximum .Therefore, tension at Joint A will be maximum in this load combination.
4) Let us consider 2 load combinations out of which 1 will govern the maximum compression at B:
Compression at B due to dead load = 200*20/2=2 kips (compression)
Compression at B due to live load = 500*20/2=5 kips(compression)
Compression at B due to wind load = 10*15/20=7.5 kips(compression)
Total compression at B due to 1.2DL+1.6LL = (1.2*2)+(1.6*5)=10.4 kips
Total compression at B due to 1.2DL+W+LL = (1.2*2)+(7.5)+(5)=14.9 kips
Therefore, maximum compression at B = 14.9 kips
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