Structural Analysis
Structural Analysis
(OP)
Please help me understand how the author came up with the formula for his analysis. He made it very simple and i don't know how he solved this. I tried to check one of the forces in O2 and O1 and they are correct. Thanks!






RE: Structural Analysis
DaveAtkins
RE: Structural Analysis
Mike McCann, PE, SE (WA)
RE: Structural Analysis
In the case of O1, consider a vertical section cut through the top chord between F1 and F2. The moment about A is 2(Av-F1). The slope is tan-1(2.42/6) = 21.97o. The normal distance d=2sinθ = 0.748 which the author rounded to 0.75. The force O1 is M/d = 2(Av-F1)/0.75 as he shows.
In the case of O2, consider a vertical section through point A cutting the top chord. The moment about A is the bracketed expression. The normal distance is unchanged, leading to the expression shown by the author.
BA
RE: Structural Analysis
for me -D1*cos(17.5) = F2*cos(22) ? D1 = -F2*0.97 close to -1.5/1.54*F2 ?
another day in paradise, or is paradise one day closer ?
RE: Structural Analysis
Your answers are the same as his. You are using the method of joints whereas the author is using the method of sections.
BA
RE: Structural Analysis
another day in paradise, or is paradise one day closer ?
RE: Structural Analysis
you're right, he's using method of sections.
however, i find i hard to solve O3, D3, D4, D5 & D6 using method of sections. I used method of joints for these members.
can you also explain how he gOt D6 = D7 - D5 ?
Thanks!
RE: Structural Analysis
I could not find a calculation of O3 by the author, but he appears to be using the method of joints for D5 and D6. The stress diagram for the joint between D6 and D7 is shown on the second page, explaining why D6 = D7 - D5. It is a graphical representation of the method of joints.
For D3, he is using the method of sections but has to include the effect of D4 in his calculation. By inspection, D3 and D6 should be numerically equal but of opposite sign; the author found D3 = -7.3kN and D6 = 7.25kN.
BA
RE: Structural Analysis
another day in paradise, or is paradise one day closer ?
RE: Structural Analysis
another day in paradise, or is paradise one day closer ?