Extensive advanced computer modeling demonstrated that using conventional braces to upgrade Watson Hall at Orange Coast College was more efficient and less costly than using more fashionable alternatives.

CALIFORNIA – Weidlinger Associates received an Excellence in Structural Engineering Merit Award from the Structural Engineers Association of Southern California for the seismic retrofit of Watson Hall at Orange Coast College in Costa Mesa. They shared the award with Roessler Design Group; Hill Partnership was the architectural consultant. (Subsequently, Weidlinger received an even more prestigious Structural Engineering Excellence Award from the statewide organization, the Structural Engineers Association of California.)

Watson Hall, a four-story reinforced-concrete building constructed in the mid-1960s, sat abandoned for several years because it could not provide the level of occupant life safety during large earthquakes required by the California Building Code. Having rejected a costly retrofit scheme, the school needed an alternative that could be built on an accelerated schedule and within budget. The much-needed building had many shortcomings. When it was built, for example, it wasn’t necessary to anchor the steel reinforcement in columns and beams to the core; and the soil conditions were poor.

The retrofit is notable for its extensive use of computer modeling and analysis to choose among the options of conventional braces, buckling-restrained braces, and viscous dampers. Several three-dimensional computer models of the building were developed to compare their efficiency in reducing displacement of structural elements during a major earthquake: To keep the comparison fair, Weidlinger created a novel genetic algorithm to optimize the damper design in terms of performance and cost. The analysis proved that, given the unique characteristics and configuration of the structure, the most cost-effective, constructible, aesthetic, and functional solution could be achieved with conventional braces.

In the final design, the braces were added to six bays in each major direction to reduce the structure’s drift, and foundations were strengthened to support the additional loads. The latest technology came into play with the choice of Fiber Reinforced Polymer (FRP) composites for strengthening the columns and increasing their deformation capacity. Analysis demonstrated that the structural elements satisfied life-safety criteria in 48 different structural failure or “pushover” scenarios. The architect’s preference for replacing the existing heavy masonry facade with a lighter glass and aluminum curtain wall system was helpful to the overall engineering plan, as it reduced seismic demand while transforming the building into a significant campus landmark.