Study On Seismic Performance And Design Of Stepped Wall-frame Structures

Reinforced concrete (RC) frame takes a large proportion among all structuralsystems in China. It has become the preference selection for important publicmultistory buildings particularly in high seismic risk area. RC frames weretraditionally considered having good seismic performance. However, past seismicdisasters demonstrated that various damage modes were often obsorved in RC frames,such as the bottom story failure mode, which may lead to progressive collapse of upperstories once the first story collapsed. Even though the structure did not collapse duringthe earthquake, it would be very difficult to be repaired after the earthquake. Thisdissertation first discusses damage mechanism and failure development of the bottomstory yielding mode. Thus, a simple, economical and practical improvement method isproposed. The effect, seismic performance and design method of this proposed methodare systematically studied. Major achievements of the dissertation are as summarizedfollows.1. Based on the seismic damage characters of RC frames summarized from theexperience obtained from recent seismic disasters and theoretical analyses, a newstructural system named stepped wall-frame structure is proposed. Stepped wall systemaims at making the structure has uniformly distributed inter-story drift underearthquakes by adding RC walls with different widths by the height into a RC frame.The pushover analysis and incremental dynamic analysis proved the stepped wall canimprove the collapse resistance of RC frames in the terms of global loading resistance,lateral deformation, redundancy and rational yield mechanism.2. Shaking table test of a1:5scale ordinary RC frame model and a1:5scalestepped wall-frame model were conducted to study the seismic behavior of the newstructure system. The dynamic characteristics, seismic responses and failuremechanism of the two models under a series of excitations with gradually increasingacceleration amplitudes are presented in the dissertation. The test results demonstratethat the stepped wall-frame structure is an economical and practical solution toeffectively control the structural deformation and damage distribution, thussuppressing the bottom story failure mechanism.3. A RC frame model was tested to collapse in order to study when, how and whyRC frame structures collapse. A typical collapse process was represented by the testwith critical point, damage development and collapse mechanism well studied.4. A nonlinear design method based on the nonlinear static analysis was proposed, in which the target deformation requirement can be set artificially, thus fulfilles theidea of performance-based structural seismic design theory. At last, this method isapplied to an actual stepped wall-frame structure, and the seismic performance of thisstructure is analyzed.