Tension Member - Designing A Tension Member

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 (L_r or S)

1.2 D + 1.6 (L_r or S) + (0.5 L or 0.8 W)

1.2 D + 1.6 W + 0.5 L + 0.5 (L_r 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:

P_u < ¢ P_n where P_u is the sum of the factored loads.

to prevent yielding

0.90 F_y A_g > P_u

to avoid fracture,

0.75 F_u A_e > P_u

therefore, to design a tension member, we have to consider the loads applied to this member, the design forces acting on this member (M_u, P_u, and V_u), and the point where this member would fail.