For the general public, knowing that buildings are designed and built to modern building-code requirements provides some peace of mind with respect to how well those structures will withstand extreme loads such as earthquakes or windstorms. However, while modern structures do provide some degree of safety, it is not economically feasible to construct buildings that will resist extreme loads without sustaining damage. How much damage will actually be sustained depends on the quality of the design and the criteria that the building is designed to meet, and this realization has led to a recent paradigm shift in the field of structural engineering. It is often no longer sufficient to simply conform to minimum requirements prescribed by building codes. In performance-based design, owners and engineers work together to achieve the best possible balance between construction costs and ultimate performance.
Because the cost of the structural skeleton is usually a small part of the total cost of a new building—typically between 10% and 20%—owners can dramatically improve the structural performance of their building without a correspondingly dramatic price increase. For instance, the historical intent of building codes is to prevent collapse in a major seismic event; that is, significant (perhaps even irreparable) damage to a modern structure after a design-level earthquake is considered acceptable (and even expected!). With performance-based design, a high-tech manufacturer in Silicon Valley may decide that the cost of down time after an earthquake would be much higher than preventive hardening, and therefore might ask his engineer to design a facility that could be functional immediately afterward. While earthquake engineers have led the way, this design philosophy can also be applied to hurricanes, snow, and vibration-sensitive facilities.
Performance-based design requires the designer to go beyond code prescriptions and accurately predict how a structure will respond to its environment, often during extreme events. To make these predictions often requires sophisticated structural analysis using state-of-the-art computer software, and sometimes requires laboratory testing. Also, determining the damage mechanisms and their thresholds (“fragility curves”) can benefit greatly from failure investigation experience. Because of the complexities involved, it is desirable (and often required) that an independent peer reviewer check a performance-based design. Peer reviewers with experience investigating failures can bring valuable insight to the designer who wishes to avoid seeing those failures repeated.
For more than 40 years, Exponent has been investigating structural and equipment failures. Many of the failed structures were designed to conform to minimum requirements prescribed by building codes and standards, but did not ultimately meet the owner’s expectations. This experience has given us unique insight regarding the relationship between certain aspects of design quality and ultimate structural performance. In addition to this experience, Exponent routinely uses sophisticated computer analysis to predict the performance of complex structural systems under extreme conditions.
Our services include:
- Advanced structural analysis, including computer simulations incorporating geometric and material nonlinearities
- Peer review of building designs in areas of high seismic or hurricane hazard
- Peer review of special structures and equipment, such as equipment in nuclear facilities and automated storage systems