It’s difficult to talk about connectors without talking about fasteners. Simpson Strong-Tie developed the Strong-Drive® SDS Heavy-Duty Connector screw as a high-capacity alternative to nails or bolts, and the first connector using them was the PHD Predeflected Holdown. We released in both the PHD and the SDS screw in 1997.
Our R&D Engineers do a lot of testing. In the course of breaking many, many holdowns, we noticed that at failure, the flat seat of the holdown rounded as the steel yielded. Knowing that the holdown seat rounded under load, we asked, “What if we made the seat round?” It took a lot of collaboration between engineering and manufacturing to develop the final PHD shape that met our performance requirements and could be produced efficiently. The HDU holdown was an improvement on the PHD design that we introduced in 2006. We discontinued the original PHD in 2009.
Another product released in 1997 that used SDS screws was the UFP10 universal foundation plate. I will discuss that in a separate post.
The PHD holdown and SDS screws were extremely popular with contractors. High-capacity screws meant you could reduce the number for each connection, and the SDS did not require predrilling, so installed costs were lower. Over the next several years, we expanded the number of SDS screw sizes and incorporated their use into many other connector designs.
We had CB column bases that used bolts, so we created the CBSQ, which used SDS screws and incorporated a 1″ standoff in the base. Bolted CC column caps were complemented with SDS-screwed CCQ column caps. The “Q” stands for quick.
The SDS screw was a revolutionary innovation that gave us a great platform to create many new connectors in subsequent years: THGQ truss girder hangers, EGQ high-capacity top-flange hanger, MPBZ moment post base, LGU MGU HGU HHGU girder hangers, LGT light girder tiedowns, and many, many others.