The importance of design for seismic performance of non-structural elements
Life safety and property loss prevention are just two key reasons behind the importance of seismic restraint.
We were recently given a wider view of the field of seismic performance of non-structural elements, in a course my colleague, Max Waters, and I attended. The course was hosted by the University of Canterbury and presented by André Filiatrault, Professor at the State University of New York at Buffalo, and an internationally recognised authority on seismic performance of non-structural elements. Professor Filiatrault is the president of the International Association for the Seismic Performance of Non-Structural Elements (SPONSE). It goes without saying that there were some very good takeaway points from the course, some technical and some not so technical, but the biggest one we wanted to share, is the importance of seismic restraint of non-structural elements and all the reasons for it.
Modern buildings are all designed to withstand a certain level of seismic action. The methods for analysing the seismic response of structures are well developed when compared to the methods for analysing the non-structural elements attached to the structure, including HVAC systems, suspended ceilings, partition walls, and ornamental facades and parapets. The first and foremost reason for restraining non-structural elements is life safety. As we learn more about how non-structural elements respond to seismic actions through research and experimentation, it remains an important task to do our best to make sure these elements don’t pose significant risk to life during and after an earthquake.
The second reason for ensuring all components within and on the outside of buildings are effectively restrained is property loss, or cost/time to repair. Research out of the USA shows that non-structural elements typically account for more than 50% of the capital investment of a new building, with the rest made up of the structure and building contents. This means that even if the structure of a building survives a moderate seismic event without significant damage, if the non-structural elements weren’t designed for seismic performance, it could be economically feasible to write the building off due to the cost associated with replacing the non-structural elements only.
Another aspect of the economic considerations is the lost revenue due to buildings rendered inoperable for extended periods for repairs to non-structural elements. A prime example of this is extensive water damage caused by automatic fire sprinkler systems when damaged during a seismic event. Building contents stored in large volumes such as on pallet racking have also been shown to cause large economic losses due to the structural inadequacy of the racking itself.
Overall, there are many good reasons for putting just as much emphasis on the seismic performance of non-structural elements as we typically put on the seismic performance of structures. However, the industry has lagged behind structural engineering because traditionally, structural engineers haven’t been interested in the light stuff, and not a lot of importance was placed on the seismic performance of these elements. Until now that is. We at BVT are committed to driving knowledge of seismic performance of non-structural elements forward both with installers and building owners, and with manufacturers of non-structural elements.