Experimental Study On Collapse Mechanism Of Multi-story RC Frame School Buildings

Multi-story reinforced concrete(RC) frame structures are widely used in schools,hospitals and other public buildings. A large amount of RC frames collapsed fragilely in the past several mega-earthquakes and left tremendous casualties. Earthquake investigations showed that the collapse ratio of RC frame structures is much higher than that of masonry structures at the same site.The fact tells us that our understanding on the collapse mechanism of RC frame structures is too limited. And there is a big difference between the reality and our expectation.Two typical RC frame structures in the epicenter of the Great Wenchuan Earthquake were chosen as the analytical prototype structures in this dissertation. A teaching building in Xuankou middle school representing the common teaching buildings collapsed during the earthquake, while a residence building in Beichuan Salt Bureau retrofitted by a few wing walls in the bottom story performed very well during the earthquake. Two shake table model tests were conducted to study the seismic performance of both structures, especially the collapse mechanism of the former and the dynamic response of the wing wall-frame structures. Major achievements of the dissertation are summarized as follows.1. The seismic damage characteristics of multi-story RC frames were summarized based on the seismic damage investigation of the past earthquakes. The construction and damage characteristics of two typical structures in the epicenter of the Great Wenchuan Earthquake were meticulously analyzed in detail.2. The seismic response and damage mode of a teaching building in Xuankou school were studied based on shake table test. The main reasons leading to the structural collapse were analyzed by the actual measured data on key points and the collapse process. Among which, the local half-height infilled walls is the key reason leading to structural collapse, which increased the stiffness and reduced the ductily.3. Pushover analysis was performed on a residence building in Beichuan Salt Bureau, which had an excellent seismic behavior during the catastrophic Wenchuan earthquake to study the influence of appropriate wing walls to the seismic performance and yielding mode of RC frames. The concept and anti-seismic mechanism of wing wall-frame structural system were theoretically studied.4. Shake table test of a 1:4 scale wing wall-frame model was conducted to verify the strengthening effect of this structural system. The dynamic characteristics, seismic responses and failure mechanism of the test model under a series of excitations with gradually increasing acceleration amplitudes were obtained. Further dynamic finiteelement analysis of the test model and the relevant numerical ordinary frame model were performed to study the difference of the seismic performance between these two structures. The above research proves that the wing wall-frame structure is a good solution to withstand earthquakes, and is simple, economical and practical for the large scale application.