'Yield Link' Connection Providing Ductility and Hysteretic Energy Dissipation with Easily Replaceable Elements to Reduce Earthquake Damage and Recovery Time

摘要

Seismic retrofitting of "soft, weak, or open front" (SWOF) buildings presents tactical challenges for engineers. Utilities and other obstructions often make moment-resisting frames difficult to install. The most viable retrofit component is often a cantilevered column with appropriate new foundation. The author has designed conventional cantilevered columns for about thirty SWOF retrofits. The SEAOC Blue Book suggests strategies that rationalize designing cantilevered columns using the R factor for the overall building. Plywood shear walls are typically used as the lateral force resisting system in SWOF buildings. Using the R factor for plywood shear walls instead of R for cantilevered column systems reduces seismic design forces, thus reducing construction costs. However, building officials may not accept the Blue Book rationale; furthermore, designers may wish to increase the ductility of cantilevered columns. This paper describes a patent-pending lateral force resisting assembly made using standard HSS and rolled steel shapes, with yield links cut from steel bar or plate stock. All components bolt together, further reducing costs by eliminating welding and related special inspection fees. After an earthquake the components can be disassembled relatively easily to replace damaged yield links. Preliminary testing indicates the method has very high ductility. Following modified CUREE test protocol, preliminary test specimens consistently withstood ten or more load cycles at "scaled" story drift of 3% (the limit of the testing apparatus). Engineers can design the yield links to accommodate loading demands from typical wood-framed SWOF buildings using a single bracing assembly at the weak wall. Since the anticipated use of this method is in combination with plywood shear walls, analysis and testing focuses on meeting the ductility, overstrength, and deflection characteristics to comply with ASTM and NEHRP requirements for plywood shear walls and pre-fabricated shear-wall components. This would justify using R for plywood shear walls when designing cantilevered columns with yield links connecting them to the structure above.