It's logical that seismically sound structures are environmentally superior. If a building remains standing and operable after an earthquake, it won't have to be demolished and rebuilt, which means that there's no construction waste.
As sustainability becomes increasingly important in all fields - especially in building design, construction, and operation - creative tactics can be implemented early in a project to save time and money, and to avoid unnecessary demolition and reconstruction following a major earthquake. There are three main points to consider with this topic: understanding/assessing building behavior, taking full advantage of existing structural elements, and utilizing recyclable construction material when required.
1. Evaluation and Action
The ultimate goal of any seismic design/renovation project is to give the building a seismic performance that stays within the building owner's budget while minimizing extraneous strengthening additions. The first step is to use a more advanced, nonlinear-analysis approach to evaluate building performance. Typically, a structural engineering firm will implement a linear-analysis approach - a process that can be very quick, but also overly conservative and unnecessarily expensive. The result: a drastic prescription that often includes razing the structure completely and reconstructing from the ground up. A cost-effective alternative, which produces far less construction waste, is to perform a detailed nonlinear analysis of the building using the properties of samples taken from the building vs. making judgments based solely on design plans, as is done in a linear-analysis approach. Advanced nonlinear-analysis procedures are more precise and, therefore, less conservative, and often result in reduced seismic strengthening scope.
By incorporating each structural element's expected strength and deformation capability into evaluation of the entire building for a specific target performance, full advantage can be taken of existing structural elements, weak locations can be pinpointed, and elements can be selectively replaced.
2. Cost-Effective Plans
On a recent seismic retrofit project in Portland, OR, after the initial building assessment, a structural engineering team discovered that the building had enough concrete shear walls, but that the floor slabs weren't able to deliver seismic forces to the exterior walls. Rather than erect new walls (which would include purchasing new raw materials, and several weeks of additional labor), the team extended the floor slabs to connect to the pre-existing exterior walls. This cost-cutting measure resulted in a fraction of the manhours and materials, but achieved the same level of seismic performance as four new walls.
3. Sustainable Structures
Another simple step to keep any project green is to use local, recycled construction material when appropriate. Recycled structural steel used on the Portland project comprised a majority of the building material used to extend the floor slabs.
Whether your projects are based in the healthcare, government, education, or high-tech industry, the most crucial step to integrating environmental sustainability with seismic retrofitting and structural design is education. Do research; ask your structural engineers about every decision and have them explain how particular measures will affect the longevity of a building, and then note the positive environmental impact that even simple choices can make.
Dr. Kent Yu is associate principal at San Francisco-based Degenkolb.
