In my last post I talked about our two universal test machines (UTM) and noted that machines like these, especially the smaller bench top units, are somewhat common in testing labs. Here I want to describe a custom piece of equipment in our product testing lab that we fondly refer to as “The Racker.” Unlike the benchtop UTM I described previously, this type of test equipment is not very common in labs, especially not one with the size and capacity of ours.
While its name might conjure up images of a middle ages torture machine or a modern-day MMA move, our Racker is actually used to understand the shear wall performance of building assemblies. Homes and buildings have assemblies, typically walls, designed to resist shear (or racking) forces. When the wind blows on the side of the house, much like the Big Bad Wolf, it wants to huff and puff and blow the house down like a house of cards. The shear wall assemblies, which are perpendicular to the wall the wind is impinging on, resist this force and keep the house upright.
The typical shear wall in residential construction is a 2x4 wood-framed wall with OSB or plywood sheathing attached. The performance of this type of construction depends in part on the number, type, and spacing of the nails holding the assembly together. The more nails and closer spacing, the more shear strength the wall generally has. But shear performance can also be achieved or enhanced by a number of other approaches including let-in-diagonal bracing, hold down brackets, strapping, advanced sheathing materials, special fasteners, and various combinations of these.
The required shear strength of the wall depends on a number of factors including the size and type of the building, size and type of openings in the wall, as well as geographic location of the building. Location dictates special requirements such as added strength to weather high wind (e.g., hurricane) or seismic conditions. While the codes have some prescriptive approaches to meeting the shear resisting (or lateral bracing) requirements, as new materials, products, and concepts are developed, actual physical testing of these assemblies is needed.
Home Innovation’s shear wall test apparatus was custom-speced and built by our staff, and can test wall systems up to 20 feet long and 9 feet tall. Our system can do the standard ASTM E72 shear wall test as well as the ASTM E2126 cyclic protocol for developing seismic design parameters. With the capability of applying 60,000 pounds of force, there are not many residential wall constructions that we cannot push to failure, which is important in order to understand the outer limits of a system's performance capabilities.
And our equipment can also be used for other non-wall shear testing. We've previously conducted research in this apparatus studying the shear performance of anchor bolts.
Do you have a wall system that needs to be put to the test? Or a component that is used in wall systems that you want to push to its limits? Contact me to discuss your shear wall and other building product or system testing needs.***