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a) BD, slack, AB=AD=0, BC=-L, AC=5L/4, CD=-3L/4 b) BD, slack, AB=AD=BC=0, CD=-3L

ID: 1849525 • Letter: A

Question

a) BD, slack, AB=AD=0, BC=-L, AC=5L/4, CD=-3L/4 b) BD, slack, AB=AD=BC=0, CD=-3L/4, AC=5L/4

The rectangular frame is composed of four perimeter two-force members and two cables AC and BD which are incapable of supporting compression. Determine the forces in all members due to the load L in position (a) and then in position (b).

Explanation / Answer

a) Only compressive fore if possible exists in BD, but it incapable of compressive force ==> BD is slak also AD = 0 AB exters only horizontal force ==> AB = 0 (as no horizontal force at B) For Vertical equlibrium BC = -L (compressive) Consider point C Vertical Force by BC = Vertical component of AC ==> L = 4/5 * AC ==> AC = 5L/4 Horizontal force at C ==> Force by DC = Horizontal component of AC ==> DC = -3L/4 (compressive) b) Similarly, here also BD is slak also AD = 0 AB exters only horizontal force ==> AB = 0 (as no horizontal force at B) For Vertical equlibrium BC = 0 Consider point C Vertical Force by BC + Vertical component of AC = L , but BC = 0 ==> L = 4/5 * AC ==> AC = 5L/4 Horizontal force at C ==> Force by DC = Horizontal component of AC ==> DC = -3L/4 (compressive)