3.6 Shear capacity

Introduction to shear capacity

The fifth limit state for beams is Shear Capacity. The shear capacity of a beam is the maximum amount of shear thebeam can withstand before failure. Usually the shear capacity is the controlling limit state on short spans withlarge loads.

Equations for shear capacity

The shear strength relationship is:

• $V_u$ = maximum shear based on the controlling combination of factored loads
• ${\phi }_v=0.9$ = resistance factor for shear
• $V_n$ = nominal shear strength

The design shear strength then can be found depending, first, on whether or not the web is stiffened. If the webof a singly or doubly symmetric beam is unstiffened and $\frac{h}{t_w}\le 260$ , then Chapter F2 in the Specification Section of the Manual (page 16.1-35) can be used to define $V_n$ , otherwise, Appendix F2 in the Manual (page 16.1-102) can be used.

As long as the shear strength, $V_u$ , of a beam satisfies the maximum shear strength, ${\phi }_v{V}_n$ , value, shear is not a limiting factor of the beam design. If the shear strength, does exceed the maximum allowableshear, a different load or a different cross-section must be chosen.