Seismic Protective Systems

Feasibility Studies and Preliminary Design

For projects with enhanced seismic performance goals, structural design often must consider custom solutions that adapt to the particular function and geometry of the facility. Achieving this enhanced level of performance requires the control of both deformations and accelerations within the structure, as these demand parameters both contribute to the level of damage expected in structural systems, non-structural components, and contents. Very few conventional structural systems allow the engineer to simultaneously reduce both deformations and accelerations, creating a dilemma whereby mitigation of one type of damage may increase the vulnerability to another. Advanced seismic protective systems such as base isolation, passive and semi-active damping devices, re-centering walls and frames, and other emerging technologies help avoid this dilemma, improving the damage-resistance and post-earthquake functionality predictably and reliably. The design approach requires a deep understanding of the mechanics of these protective systems and the practical experience to implement them in an appropriate and cost-effective way. Exponent staff has extensive expertise in both of these areas, and can assist clients in developing designs for new facilities or rehabilitation strategies for existing ones. Our experience encompasses the commercial, industrial, nuclear, and healthcare domains, and enables us to work successfully with the regulatory bodies and peer reviews specific to each.

Detailed Analysis of Structures

Once the decision has been made to implement seismic protective systems for a project, there is a great deal of analysis that must be conducted, including detailed nonlinear dynamic finite element analysis. This type of analysis, often required by the building code, requires the development of suites of ground motion records for a site and assembly of a three-dimensional nonlinear model that captures the strength and stiffness of the structural system and the oftentimes complex behavior of the seismic protective devices. Exponent staff has extensive expertise in the selection and scaling of ground motion records, development of nonlinear finite element models that advanced seismic protective devices, and efficient post-processing of results for use in design and detailing. In addition, we can assist with probabilistic risk assessments of structures equipped with these devices to better assess their benefits relative to conventional designs.

Testing of Devices

The application of innovative structural systems nearly always features a testing component. These tests, generally required by building codes, are meant to assess the safety, reliability, and functionality of the device under the range of force and deformation demands to which it will likely be subjected given design and beyond-design basis earthquake shaking. Exponent can provide guidance and assistance in developing a code-compliant and technically-informative testing program for characterization and performance evaluation of prototype and production devices. A properly-devised testing program ensures that the key design parameters are investigated in a thorough and cost-effective manner, and that installed devices meet the performance requirements outlined in the project specifications.

Peer Review

Structural design incorporating advanced methods and systems is often subject to expert per review. In fact, for design of structures incorporating seismic isolation bearings or energy dissipation devices, a peer review is generally mandated by ASCE 7 (for new structures) and ASCE 41 (for existing structures.) This review encompasses seismic hazard and ground motion selection, structural analysis, design and detailing, drawing production, and prototype and production testing. Exponent engineers have substantial experience on both sides of the peer review process, having addressed comments and questions from expert peer review panels as well as having served on such panels for major projects.