Seismic Retrofitting of Residential Frame with Outrigger Rocking Wall

Abstract

Existing frame structures are known to exhibit shear-type deformation attributed to the flexural behavior of components such as columns and beams. To improve their strength and stiffness, this paper intends to utilize the axial capacity of columns to contribute to the overall flexural resistance and proposes a novel outrigger rocking wall (ORW) system for the seismic retrofitting of frame structures. First, the free-vibration characteristics of the ORW are analytically investigated to elucidate its fundamental dynamic properties. Subsequently, a distributed-parameter model of the ORW–frame system is developed, and closed-form expressions for the displacement, rotation, wall bending moment, and wall shear force responses are comprehensively discussed and evaluated under an inverted triangular load distribution. The influence of outrigger elevation on structural behavior is examined, and the results indicate that the optimal outrigger location lies within 0.3–0.4 times the total structural height. Moreover, a simplified seismic design methodology of the ORW–frame system is developed by combining pushover analysis with the capacity spectrum method. Finally, an eight-story frame structure example is adopted as a reference to examine the seismic performance of the ORW–frame system and the proposed design procedure. Numerical results demonstrate that the proposed ORW system significantly enhances the stiffness, strength, and ductility of the frame, effectively prevents weak-story failure, similar to pin-supported wall systems, and further reduces the maximum interstory drift of pin-supported wall systems by approximately 30% and 40% under design-basis and maximum-considered earthquakes, respectively, indicating reduced seismic damage.