The design of wall anchorage in tilt-up walls has been influenced most by past failures during seismic events.  While many failures were the result of cross-grain bending in wood roof designs, many problems were found also in steel structures, where the steel lacked the necessary ductility and overstrength required during an earthquake.  How do ACI and ASCE 7 address the design of wall anchorage to ensure these past failures are not repeated?

In the July 2019 SE University session, John Lawson, PE, SE, from Cal Poly – San Luis Obispo, presented Engineering Tilt-Up: Design Provisions Born from Past Experience. John reviewed how past failures have influenced current design practices and explained the implementation of current slender wall provisions and how to classify wall elements.  He also covered wall anchorage forces and how they get transferred into the diaphragm and potential issues with both steel and wood deck roofs. 

John noted during the session that even in regions where wind typically governs the building design, seismic can still govern in the case of the wall anchorage design force.  After noting past failures at the wall anchorage, the design force has been increased to maximum expected forces to ensure the connection can withstand the required ductility and strength required during an earthquake. Since the wall anchorage force is 3-4 times the ground acceleration, this design force can often exceed the design wind force, even though wind may control the design of the tilt-up wall panel.

John explained the process to determine the required design force for wall anchorage.  Watch the following 4 minute video to hear John walk through the wall anchorage design equation, including some valuable tips for this design process.