D1.A.5.4 Design for Shear
The Design Shear Strength (LRFD), Qv×Vn , and the Allowable Shear Strength (ASD), Vn/Ωv , are calculated by the program, as per section G2 of the unified code specifications.
The Nominal Shear Strength, Vn , of un-stiffened or stiffened webs, is calculated taking care of limit states of shear yielding and shear buckling. The sections G4 to G7 of the code specifications are used to evaluate Nominal Shear Strength, Vn for different types of rolled sections.
Shear Capacity Along the Major Axis
For determining shear capacity, Vc in the major axis Clause G2, G3, G4 are followed based on the different shapes.
Shear Capacity Along the Weak Axis
The nominal shear strength, Vn, for each shear resisting element in doubly symmetric and singly symmetric shapes loaded in the weak axis (minor axis, or along the flanges) without torsion in is determined per AISC 360-16 G6 as follows:
|Vn = 0.6Fybf tfCv2||(G6-1)|
The use of the section dimensions bf& tf in the above equation will be based on the section profile type. The following table lists the value of the terms bf, tf , kv, Cv2 that are used in the calculation of shear capacities for various section profile shapes, when subject to shear along the z-axis of the section.
|Shape||Use of terms bftf in eqn G6-1||Dims used to calculate shear buckling coeff. Cv2 (Ref Cl G.2)||Ceoff kv used to calculate Cv2|
|Built Up Box||bf = 2.0 × (B – 2×wall thickness) & tf = flange thickness||h = (B – 2×wall thickness) & t = flange thickness||5.0|
|HSS Box||bf = 2.0 × Width between fillets & tf = wall thickness||h = Width between fillets & t = wall thickness||5.0|
|Rolled/ Channel||bf = 2.0 × Flange width & tf = flange thickness||h = Flange Width & t = Flange thickness||1.2|
|Rolled / Built Up I||bf = 2.0 × Flange width & tf = flange thickness||h = Flange Width & t = Flange thickness||1.2|
|I With Cover Plate(s):||Bf×tf = 2.0 × Flange width × flange thickness + width of top cover plate × thickness of top plate + width of bottom plate × thickness of bottom plate||h = Flange Width & t = Flange thickness for the base I shape & h = width of plate and t = thickness of plate||1.2|
|L- Section||bf = Length of leg along the X -axis & tf = thickness||h = Length of leg along the X -axis & t = thickness||1.2|
|T – Section||bf = Flange width & bf = flange thickness||h = Flange width (bf) & t = flange thickness (tf)||1.2|
|Solid bar / rod||Bf×tf = 0.5 × section area||1.0||-|
- For the shear in the weak axis, the value is determined using Bf and Tf alone. AZ cannot be used.
- The shear capacities of the base I section and the top and / or bottom cover plates are evaluated separately using the dims shown and a Kv = 1.2. These values are then added to get the final section shear strength.
- For solid rectangular bars and rods, half the total section area is assumed to resist the shear along the vertical axis and the other half to resist the shear along the horizontal axis. This could lead to conservative results in some cases.