Web stiffeners are nothing more than wood blocks. They're either made out of lumber, wood structural panels or APA Rated Rim Board. Their purpose is to reinforce the webs of I-joists at different locations. Web stiffeners are required in three different situations:
- If there is a chance the I-joist's webs might break through the flanges. This is caused by design reaction loads exceeding a specific level and can happen at any depth of the I-joist.
- If there's a chance the webs might buckle out of plane.
- If the sides of the hanger that supports the I-joist do not reach the top flange. Because of an unsupported top flange, the joist can twist the flange by deflecting laterally. In this case, web stiffeners offer support on a vertical axis.
The Difference Between Bearing Stiffeners and Load Stiffeners
There are two kinds of web stiffeners: bearing and load. Bearing stiffeners are placed at the reactions -- interior and exterior -- while load stiffeners are found between supports where the top flange of an I-joist must withstand significant point loads.
The two kinds of stiffeners can be differentiated by the placement of the gap between a top or bottom flange as well as the undersized stiffeners, and by the applied load.
Bearing stiffeners are required in cases when the hanger sides don't reach the top flange. In this case, the gap can be seen at the top.
- Load stiffeners are placed in areas where a concentrated load that's greater than 1500 lbf is applied between supports --to the top flange or between the support and the cantilever tip -- if a cantilever is used. This time, the gap can be seen at the bottom.