I\'m trying to find the lightest W shape to carry 1.compressive load 195k and 2.
ID: 1713676 • Letter: I
Question
I'm trying to find the lightest W shape to carry 1.compressive load 195k and 2. tension load 182kips on figure shown?
To make things more simple just answer these two questions:
if 1. tension member Pu=182 kips What is (KL)x (strong axis) and (KL)y (weak axis)? (the effective lengths)
if 2. compression member Pu=195 kip What is (KL)x (strong axis) and (KL)y (weak axis)?
Given: A572 grade 50, symmetric, connections of truss elements are pinned, beam-column should be considered as part of no sway frame, beam-column support to the foundation is fixed support.
Explanation / Answer
1. When a member is subjected to tensile load, there will not be any buckling. The member is selected based on yielding of gross area of section, fracture of net section and blcok shear. The member thus selected should however be checked for slenderness ratio, (KyLy/ry), which should not be greater than 300 (limit for tension members). For W sections, ry will always be lesser than rx and hence only (KyLy/ry) need to be checked.
Since the member is pin-connected, Ky = 1.0 and Ly= 10 ft. Thus, ry for the member should be such that
ry > 1.0x (10 ft x 12) in /300 =0.4
2. For compression members, there will be buckling. SInce the truss members are pin-connected, Kx = Ky =1.0. Therefore, KxLx = Ky Ly = 10 ft. Since ry is always lesser than rx for W sections, (KyLy/ry) will decide the buckling strength.
For a beam-column compression member, since the bottom end is fixed and top end is pinned, Kx = Ky = 0.8