Steel tension members to IS 800: yielding, rupture and block shear

Tension members appear as truss ties, bracing and hangers. IS 800:2007 takes the design strength as the least of three checks.

1. Yielding of the gross section

The whole member stretches too much once the gross area yields:

T_dg = A_g f_yγ_m0 γ_m0 = 1.10

2. Rupture of the net section

At a bolt line, holes reduce the area, and the member can tear there:

T_dn = 0.9 A_n f_uγ_m1 γ_m1 = 1.25

For an angle connected through one leg, IS 800 uses:

T_dn = 0.9 A_nc f_uγ_m1 + β A_go f_yγ_m0

with A_nc the net area of the connected leg, A_go the gross area of the outstanding leg, and β a shear lag factor (between 0.7 and 1.44) that depends on the leg width, thickness and connection length.

3. Block shear

A block of steel tears out around the bolt group: shear along one plane and tension across another. IS 800 gives T_db as the smaller of:

A_vg f_y√3 γ_m0 + 0.9 A_tn f_uγ_m1 and 0.9 A_vn f_u√3 γ_m1 + A_tg f_yγ_m0

Worked example: plate

A 150 × 10 mm flat, E250 steel (f_y = 250, f_u = 410 N/mm²), with one row of 18 mm holes across the width.

T_dg = 150 × 10 × 2501.10 = 341 kN

T_dn = 0.9 × (150 − 18) × 10 × 4101.25 = 390 kN

Yielding governs here (block shear depends on the bolt layout and is checked separately), so T_d = 341 kN.

Slenderness

IS 800 also limits the slenderness ratio of tension members so they don't vibrate or sag: 400 for ordinary tension members, 350 where stress can reverse because of wind or earthquake, and 180 where it can reverse because of other loads.