4 For the truss shown below calculate the maximum tension lo

4. For the truss shown below, calculate the maximum tension load. Use ASD method (loads provided are Pa) and select the smallest lightest W8 member (ASTM A992). Size for yielding only (ignore rupture check). (35 Points) 5k 10k 20k (TYP

Solution

Let us determine the support reactions

Support reaction at A can be determined using moment equilibrium about support I

R_A*32 = 5*24 + 10*20+ 20*16

R_A = 20 kips

R_I = 20+10+5-20=15 kips

The truss will having maximum bending moment under 20k load

Therefore members DE and EF will have highest tension in them

Let us determine force in member EF using method of section by considering a section cut through the truss depth between E and F

Moment about point N=0

Therefore,

20*20 - 5*12-10*8-20*4-F_FE*5=0

F_EF = 36 kips

From yielding point of view,the lightest W8 section that has ASD capacity greater than 36 kips is W8x10