2023 IMTC Display - Buckling Restraining Brace

Wood is, yet again, involved in an innovative product that University of Utah is designing and researching: the first Timber Buckling Restrained Brace (TBRB). These reduce bending, or restrain buckling as the name implies, but why?

Earthquake loads shake a building in all directions, predominantly laterally, or side-to-side. Builders aim to resist these lateral forces by means of shear walls, moment frames, diagonally braced frames, and more.

Buckling Restrained Braces (BRB) are one of the best new design elements for seismic design. Why are they so effective? They dissipate energy through the yielding of steel. BRBs look like a typical diagonally-braced steel frame; however, the diagonal section is where they differ.

With a conventional diagonally-braced frame, the diagonal piece is typically slender and used in tension. When the building sways one way, it puts this piece in tension. But when it sways the other way, the diagonal piece goes into compression and will buckle at a much lower load. Once it buckles it is not able to resist any more load.

With BRB, the compression phase resists the buckling and forces the steel to yield. Yielding is where the steel molecules dislocate and cause permanent deformation. This yielding is dissipating energy and is the key to a good design for seismic forces. It’s easy to make a strong and rigid system, but this causes high forces for all the other elements of the building and leads to substantial damage. We want to dampen the forces like a shock in a car and yielding is how this is accomplished.