Q & A: How to determine the effective width in shear

Some time ago, I received a technical question on how to find the effective width in shear for a wide member subjected to a concentrated load.

Here’s the quick answer:

For flexural shear in wide members, an effective width needs to be determined. The effective slab width in shear is theoretically determined so that the reaction resulting from the total shear stress over the width of the support equals the reaction from the maximum shear stress over the effective width. For design purposes a method of horizontal load spreading method, depending on local practice, is chosen, resulting in the effective width b_eff at the support. In Dutch practice horizontal load spreading is assumed under a 45° angle from the centre of the load towards the support and in French practice from the far corners of the loading plate . Currently, the only code that prescribes an effective width for shear in wide members is the Model Code 2010 . The UK currently has no defined practice for defining the effective width in shear.

Based on the comparison between my experiments and these methods, I find the most consistent results using the French load spreading method, for loads that are close to the support.