Assessing Seismic Collapse Capacity Of Reinforced Concrete Frames Based On Redundancy Theory

In this thesis, overview of the research on seismic collapse of building structures is present. Based on the theory of redundancy, the seismic collapse capacity of reinforced concrete frames subjected to strong earthquakes is studied. Major achievements of this dissertation are as follows:1. The concept of redundancy is introduced, the design method of redundancy in several American seismic codes is available, and the state of research on redundancy is present. According to the capacity-spectrum method based on equivalent linearization, a new index called redundancy demand ratio is proposed. An example is provided to make sure that the proposed index can quantitatively evaluate the redundancy of a structure and effectively determine the importance of some components of the structure.2. The performance of five reinforced concrete frames is evaluated; the results show that their seismic collapse capacity can be quantitated by the redundancy demand ratio which can reflect the strength and deformation of the whole structures. Also, it is quantitatively determined that the collapse-resistant capacity of three RC frames whose measure grades are separately taken as grade1st,2nd and3rd by IDA analysis. By contrast with the increase of the intensity of design ground motion, the enhancement of the measure grade of structure is a more effective way to prevent seismic collapse for RC frame structures subjected to the large earthquake beyond fortification intensity. Furthermore, the pertinences between collapse margin ratio, redundancy demand ratio and design spectral acceleration at the first-mode period of vibration of the structures are studied.3. Factors affecting seismic base shear and the minimum requirements of seismic base shear for modal response spectrum analysis in several foreign seismic codes are present. Comparing with considering factors in seismic shear factor between the Chinese seismic code (GB50011-2010) and American seismic code (ASCE7-10) and discussion about influence of higher-mode response on seismic base shear of long-period structure are performed and two necessary conditions of seismic shear factor are summed up. Subsequently, it is provided that proposed seismic shear factor calculation formulae for remedying the shortcomings of the original one in Chinese Code for Seismic Design of Buildings (GB50011-2010).4. By taking partial teaching building of a middle school in Wenchuan earthquake as prototype, shake table tests are designed to observe the process of the ground motion damage and dynamic response for the two models with different redundancy. Furthermore, elastoplastic analysis is performed to determine redundancy demand ratio of the two models and find out plastic hinges of the structural components.