Loads applied to a TJI® joist must transfer through the bottom of the joist into the support structure-typically by means of a wood plate or joist hanger. Adding web stiffeners at the bearing location will increase the reaction capacity of the joist if the design is limited by flange splitting, rout bearing strength or web crushing. Because web stiffeners transfer vertical load from the web to the bearing interface between the flange and the web stiffener, the web stiffener must be square and flush at this interface in order to work properly. Web stiffeners may also be required to help resist web buckling forces or to resist rotation when a joist hanger does not support the joist top flange.
Here are some common applications of web stiffeners:
- Continuous span joist may require web stiffeners to help increase the internal load capacity of the joist at the intermediate bearing.
- When joist hangers are used and the top flange is not lateral supported, the joist can rotate and will require web stiffeners.
- When TJIs are used as roof joist, a web stiffener is always required if the low end is birdsmouth cut at the top plate.