Tilt-up buildings are popular because they’re relatively economical to construct and require minimal maintenance. However, because of their design, they’re extremely vulnerable to earthquakes. While newer tilt-up structures were built under more stringent building codes, tilt-ups constructed prior to the late 1990s are primary candidates for seismic retrofitting.
Tilt-up buildings are popular in commercial and industrial uses, so they’re likely often occupied with workers or machinery and business inventory. Damage or collapse during an earthquake could be costly in both human and material terms, which is why there are multiple benefits to retrofitting an aging tilt-up building. These benefits include:
Tilt-ups, which get their name from their construction method, consist of concrete walls cast on a slab before being pulled – or tilted – into place. The roof is then lifted and set into place, tying the structure together.
Tilt-up buildings grew in popularity in California following World War II. But the 1971 San Fernando earthquake revealed shortcomings of tilt-up construction in relation to earthquakes. In many cases, the connection between the roof and walls was simply inadequate to provide proper support at the top of the walls. Thus, the heavy concrete walls separated from the roof, leading to partial or total collapse.
Despite updated building codes following the San Fernando quake, the Northridge earthquake in 1994 again illustrated deficiencies with tilt-up construction, as some 400 tilt-up structures sustained significant damage. According to Structure magazine, any tilt-up building erected prior to the Northridge quake represents a moderately low to high chance of partial collapse during a moderate earthquake.
The primary concern with tilt-up structures related to seismic movement is often a deficiency in the roof-to-wall anchorage systems, such as poorly constructed, flexible or eccentric anchors. But other factors that can create seismic deficiencies include:
The good news is that retrofitting a tilt-up structure is typically a relatively easy and inexpensive process. A full-service tilt-up building retrofit may commonly include: