R502.7

Section R502.7 is titled 'Lateral restraint at supports' and covers the requirements for the prevention of wood joist twisting at the bearing or cantilevered ends. The methods to prevent twisting at joist ends is established. The purpose of this section is to prevent structural failure. This section has 2 exceptions. The 1st defers to manufacturer's recommendations for end support for specific types of premanufactured or engineered products. The 2nd requires lateral support at mid-span joist supports, in addition to the end support, where installed in seismic design category D locations. The purpose of the 1st exception is to allow for methods which are compatible with specially designed products. The purpose of the 2nd exception is to require additional support, where buildings are subject to high levels of ground shaking, so as to prevent structural failure.

The model shows a lumber joist which has not been supported on one end which is twisting. (The time for this twisting to occur has been sped up for demonstration, but could still happen fairly quick with rapid changes in air moisture content.)