Designed and Built for Resilience – Drift-Ready Stair Systems

William Hallock
General Manager
CS Group Construction Specialties Company, Newark

There is an ever-increasing understanding that structures and communities need to become more resilient. Evacuation routes for buildings are a matter of life and death in earthquakes, but what if these paths become blocked? It is well understood that building codes have been written in an attempt to safeguard lives by limiting collapse risk but not necessarily to protect the structure from sustaining considerable damage in an event or ensuring safe egress for the inhabitants.

Safe egress of buildings is essential before, during, and after a disaster. Stairways, often the only choice for evacuation, are a key requirement for safe exit but based on several earthquake evaluations and testing reports, it is clear that stairs have significant vulnerabilities. Published test reports revealed that "safe egress from the building was compromised even when the associated drift demands were much lower than the design performance target of the building."

The ability of a building - and the stairs within it - to accommodate movement is a critical component of the building's overall resilience. In many cases, stair towers become unconsidered rigid braces in structures as they scissor back and forth from bottom to top. Engineered solutions for seismically resilient stairs that have been tested over several years may be the solution. Full-scale shake table testing of several different stair configurations has been conducted and shown to perform well. The presentation discusses the results from testing as well as the types of building movement that can be expected and the relevant design considerations and solutions that may be integrated to limit damage and provide safe egress and ingress after significant seismic events.