Designing A Tension Member
In order to design tension members, it is important to analyze how the member would fail under both yielding (excessive deformation) and fracture which considered the limit states. The limit state that produces the smallest design strength is considered the controlling limit state; which also prevent the steel structure from failure.
Using AISC (American Institute of Steel Construction), we could obtain the recommended load and resistance factor design approaches.
The ultimate load on a structure can be calculated from one of the following combination:
1.4 D
1.2 D + 1.6 L + 0.5 (Lr or S)
1.2 D + 1.6 (Lr or S) + (0.5 L or 0.8 W)
1.2 D + 1.6 W + 0.5 L + 0.5 (Lr or S)
0.9 D + 1.6 W
Where:
- D… is the dead load or the weight of the structure itself
- L… is the live load which vary for different structures
- S… is the snow load
- W… is the wind load
the central problem of designing a member is to find a cross section for which the required strength doesn't exceed the available strength:
Pu < ¢ Pn where Pu is the sum of the factored loads.
to prevent yielding
0.90 Fy Ag > Pu
to avoid fracture,
0.75 Fu Ae > Pu
therefore, to design a tension member, we have to consider the loads applied to this member, the design forces acting on this member (Mu, Pu, and Vu), and the point where this member would fail.
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