Rocking Spine for Enhanced Seismic Performance of Reinforced Concrete Frames with Infills

摘要

A rocking spine system is introduced as an alternative to more conventional approaches to improve the seismic collapse safety of concrete frames with masonry infills. Although infill frames are not formally recognized in ASCE 7 or other current U.S. building codes for new buildings, infills are present in many existing buildings, and infill frames are still a prevalent type of new construction that is permitted in many parts of the world. The proposed technique uses structural spines, constructed using either strong infill panels or concrete walls, to resist earthquake effects through controlled rocking action. The primary sources of overturning resistance are gravity loads on the spine and the restraint provided by beams and infill panels in framing bays adjacent to the spine. Equations are developed to describe the rocking response of the spine, relating the rigid-body kinematics to the internal deformations, forces and limit states in beams, columns, and infill panels. The main aspects of the design method are presented, including guidelines for assessing and allocating the required overturning strength and for sizing and detailing key structural components to avoid undesirable failure mechanisms. The seismic design approach is illustrated for a six-story infill frame building, and nonlinear static and dynamic analyses are performed to evaluate its response. The analyses confirm the reliability of the simplified design procedures and demonstrate that the rocking spine system is effective in meeting drift limits in ASCE 7 and the collapse safety criteria of the FEMA P695 guidelines.