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2014 TCA Convention

A More Rational Approach to the Seismic Design of Tilt-Up Concrete Buildings

John Lawson, PE, SE, Assistant Professor at Cal Poly, San Luis Obispo

 

The seismic behavior of low-rise tilt-up concrete buildings supported by flexible wood or steel deck roof diaphragms is significantly different than the underlying assumptions embedded in the equivalent lateral force (ELF) method engineers commonly use.

When subject to earthquake forces single story buildings comprised of heavy rigid walls couple with flexible diaphragms have actual seismic responses that are dominated more by the diaphragms instead of the walls. Additionally, diaphragm ductility and overstrength capacity is unique to its own construction, and yet current design practices employed by engineers derive diaphragm shears and diaphragm strength inappropriately from the characteristics of the tilt-up wall elements.

This disconnect between the building code’s design process and the actual behavior and performance has led to a past of “trial and error” wall anchorage provisions and illogical diaphragm design forces.

Lawson is part of an ongoing FEMA funded study using a special numerical computer model to predict tilt-up building performance and recommend a new code-based design methodology. This presentation will provide a glimpse into what may become the future of seismic design for this class of building.

 

About the TCA

Founded in 1986, the Tilt-Up Concrete Association (TCA) strives to improve the quality and acceptance of site-cast Tilt-Up construction, a method in which concrete wall panels are cast on-site and tilted into place. Tilt-Up construction is one of the fastest growing industries in the United States, combining the advantages of reasonable cost with low maintenance, durability, speed of construction and minimal capital investment. At least 10,000 buildings, enclosing more than 650 million square feet, are constructed each year using this construction method.

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