Out-of-Plane Wall Anchorage Design

While the Simpson Strong-Tie Tye Gilb R&D lab in Stockton is a large testing facility, the world’s largest R&D lab is Mother Nature herself. Natural disasters such as earthquakes or storms put our engineering designs to the test. In this week’s blog post, I’ll be turning attention to wall anchorage for out-of-plane forces and the lessons we have learned from Mother Nature so far.

The 1979 building code incorporated many of the lessons learned from the 1971 San Fernando earthquake. In 1994, Mother Nature put the 1979 building code to the test with the January 17 Northridge earthquake. The Northridge earthquake showed that some of the increased design and detailing requirements in the 1979 building code worked well to improve performance over what was observed in 1971. However, it also revealed to researchers that acceleration at the roof level of single story warehouse buildings were three to four times the ground acceleration. The combination of higher than expected acceleration and excessive deformation of the wall anchorage assembly caused many wall anchorage failures.

Figure 1 Out-of-Plane Wall Anchorage Assembly

Several changes in the design forces used for wall anchorage and additional detailing requirements were incorporated in the 1997 Uniform Building Code. The requirements have been refined with each new building code, but overall the requirements and design forces have remained about the same under the current International Building Code. Wall anchorage design is governed by ASCE 7-05 and ASCE 7-10 Section 12.11. These provisions aim to mitigate the brittle wall anchorage failures observed in past earthquakes by increasing the design force and in Seismic Design Categories C through F, requiring:Continue Reading