A continuous load path is essential to a building’s structural performance. Directing the diaphragm loads from roofs, floors and walls to the foundation in a prescribed continuous path is a widely accepted method to prevent shearwall overturning. The installation of continuous rod systems has grown in popularity with the increase in mid‑rise wood (3- to 6-story) construction. Specifying a Strong‑Rod Anchor Tiedown System (ATS) for shearwall overturning restraint from Simpson Strong‑Tie offers several advantages for specifiers and installers alike:
Beyond the tension and compression aspects of a continuous rod tiedown system, wood shrinkage must also be addressed. In these types of structures, shrinkage and settlement can cause a gap to develop between the steel nut and bearing plate on the wood sole or top plate (see photo below), as the shrinkage increases cumulatively up the building and is the greatest at the uppermost floor. This can cause the system not to perform as designed and can add to system deflection. As a result, take-up devices must be used with most wood structures greater than two stories tall as is noted in the 2018 IBC Section 2304.3.3 at each level to mitigate any gap creation and therefore ensure optimum system performance.
A traditional shearwall relies either on holdowns or straps attached to posts to transfer the net shearwall overturning forces to the foundation.
Lateral forces are transferred from the floor/roof to the boundary members (top plates) to the plywood sheathing. The following steps describe the traditional load path:
A continuous rod tiedown system utilizes a combination of threaded rods with bearing plates and take-up devices at each level to transfer the forces to the foundation. The following steps describe the continuous rod tiedown system load path: