1. Design of Tension Members To avoid yielding: A g  P u / 0.9 F y To avoid fracture: A e  P u / 0.75 F u Or : A n  P u / 0.75 F u U where P u is the sum of the factored loads.

2. Design of Tension Members If the axial load in a slender tension member is removed and small transverse loads are applied, undesirable vibrations or deflections may occur. Thus AISC recommends: r  L/300 ( not for cables or rods) where r is the minimum radius of gyration of the cross section and L is the length of the member.

3. Threaded Rods and Cables When slenderness is not a consideration, circular rods and cables are often used (hangers, suspended bridges). Rods are solid and cables are made from individual strands wound together. Threading the end of a rod reduces the cross sectional area ( upset end prevents such reduction, but is expensive).

5. Threaded Rods and Cables  t P n = 0.75 (0.75 A b F u ) A b = nominal (unthreaded) area It is common to use a min diameter of 5/8 in. for rods.

6. Threaded Rods and Cables A strand consists of individual wires wound helically around a centrl core. A wire rope is made of several strands laid helically around a core.

7. Tension Members in Roof Truss Trusses are used where the cost and weight of a beam could be prohibitive (long spans). A truss may be thought of as a deep beam with much of the web removed. Tension members in roof trusses include some truss members and sag rods.

8. Sag Rods Sag rods are used to provide lateral support for the purlins (to prevent sag in direction parallel to a sloping roof due to vertical applied loads). They are designed to support the component of roof loads parallel to the roof.

11. Sag Rods Each segment between purlins is assumed to support everything below it; thus the top rod is designed for the load on the roof area tributary to the rod, from the heel of the truss to the peak.

13. Sag Rods The tie rod between ridge purlins must resist the load from all of the sag rods on either side.