Tension Members Notes

Last reviewed 16 Sept 2026 · 5 min read

Tension members

A tension member carries axial pull: ties of roof trusses, bottom chords of bridge trusses, hangers, bracing members, cables and suspension rods. Because tension straightens a member, buckling is not a concern; the strength depends on the area, connection and material.

Common sections: flats and plates, round bars and rods, single and double angles (on one or both sides of a gusset), channels, tees, built-up sections, wire ropes.

Design strength (IS 800:2007)

The design tensile strength $T_{d}$ is the least of:

Formula1. Yielding of the gross section

T_{d g} = \frac{A _{g} f _{y}}{γ _{m 0}}, γ_{m 0} = 1.10

Excessive elongation of the whole member makes it unserviceable.

Formula2. Rupture of the critical net section

Plates: $T_{d n} = \frac{0.9 A _{n} f _{u}}{γ _{m 1}}$ , $γ_{m 1} = 1.25$

Threaded rods: $T_{d n} = \frac{0.9 A _{n} f _{u}}{γ _{m 1}}$ with $A_{n}$ = net root area at the threads.

Single angle connected through one leg (accounts for shear lag — the outstanding leg is not fully effective near the connection):

T_{d n} = \frac{0.9 A _{n c} f _{u}}{γ _{m 1}} + \frac{β A _{o} f _{y}}{γ _{m 0}}

$A_{n c}$ = net area of the connected leg; $A_{o}$ = gross area of the outstanding leg; $β = 1.4 - 0.076 (\frac{w}{t}) (\frac{f _{y}}{f _{u}}) (\frac{b _{s}}{L _{c}})$ , with $0.7 \leq β \leq \frac{0.9 f _{u} γ _{m 0}}{f _{y} γ _{m 1}}$ .

Simplified (preliminary) form: $T_{d n} = \frac{α A _{n} f _{u}}{γ _{m 1}}$ , with $α$ = 0.6 for one or two bolts, 0.7 for three bolts, 0.8 for four or more bolts in the end connection or equivalent welded length.

Formula3. Block shear

A block of the connected plate tears out: shear along the line of bolts and tension across the end. The block shear strength is the smaller of

T_{d b 1} = \frac{A _{v g} f _{y}}{3 γ _{m 0}} + \frac{0.9 A _{t n} f _{u}}{γ _{m 1}}

T_{d b 2} = \frac{0.9 A _{v n} f _{u}}{3 γ _{m 1}} + \frac{A _{t g} f _{y}}{γ _{m 0}}

$A_{v g}$ , $A_{v n}$ = gross and net areas in shear along the bolt line; $A_{t g}$ , $A_{t n}$ = gross and net areas in tension perpendicular to the load.

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Tension Members

Tension members

Design strength (IS 800:2007)

This chapter is in the syllabus of

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