Collapse Mechanism And Seismic Retrofitting Design Of Multi-story Masonry Structure With First Weak Story

China is an earthquake prone country, and suffered from the most severeearthquake disasters. Building collapse is the most important reason for life losses.Field investigation on Wenchuan earthquake indicated that multi-story masonrystructure with first soft story (MSMSFSS), RC frame structure and multi-storymasonry structure are the primary structure styles in towns which have sustainedserious damage. The collapsing ratio of MSMSFSS is about85%in the meizoseismalareas of Wenchuan earthquake. It is necessary to analyze the collapse mechanism andpropose the anti-seismic design methods and the retrofitting design methods for theexisting buildings.Compare and analyze the structural configuration difference between therole-model buildings and common buildings in this dissertation. Analyze the collapsemechanism and propose the anti-seismic design methods and the retrofitting designmethods for the existing buildings by theoretical analysis, shaking table test andpseudo-static test. The main conclusions are as follows:(1)The field investigation showed construction features and collapse modeobjectively. The longitudinal wall in the first story of MSMSFSS is the anti-seismicweak link, and most of the object structures collapsed in longitudinal direction.(2)The seismic force is based on principle of stiffness distribution, and stiffness isdiscrepancy obviously among longitudinal walls in the first floor of typical MSMSFSSbuildings. Model shaking table test illustrated that three longitudinal walls did notfailed simultaneously. The internal longitudinal wall which had the maximum stiffnessfailed first and lost carrying capacity. Meanwhile, the seismic and gravity loads weretransferred to the two relatively weak longitudinal walls. The carrying capacity of thetwo walls is obviously insufficient and building collapse is hard to avoid.(3)Lateral stiffness of longitudinal walls was obtained by typical wallspseudo-static test. The test results verified the rationality of the inference that threelongitudinal walls did not failed simultaneously.(4)Basing on former studies, more ideal calculation formula for calculating thelateral stiffness of walls with openings is proposed. The lateral stiffness calculationformula provides the theoretical foundation for analyzing the collapse mechanism andproposing the anti-seismic design methods and the retrofitting design methods for theexisting buildings. (5)According to the ‘balanced stiffness and increased ductility’ principle, theconstruction method of retrofitting method for the existing buildings was proposed inthis dissertation.