The Failure Mechanism And Seismic Evaluation Of Long-span Canti Lever Truss Structure Under Earthquakes

The long-span cantilever truss structure can have simple shapes and diverse forms of structures. It is economically efficient and behaves excellently as an engineering structure. However, although it is widely used in constructions, its responses to severe earthquakes and corresponding failure mechanisms are not thoroughly understood. The research in this thesis is carried out in such a background that related researches in this field are rare and further studies are needed to provide references for application in high-risk areas, making a systematic analysis of the failure mechanisms of cantilever truss structure subject.Firstly, analysis of the free vibrantion characteristics of cantilever truss structure is made. The modes of vibration are studied by means of massive parameter analysis of three specific cantilever truss structures with spans of 20m, 30m and 40m respectively. The changes of the characteristic vibrant frequency of the structure with variations of parameters including ratio of section stress, roof mass, span-depth and span are observed and discussed.Secondly, the the failure mechanisms of cantilever truss structure subjected to severe earthquakes are studied. A cantilever truss structure with typical example is analyzed, and its responses to severe earthquakes are concluded at several aspects including the deformation of the whole structure, the different yielded element ratio and so on, leading to the conclusion that the structure collapsed in a dynamic strength failure mode. Furthermore, the influences of geometric and loading parameter variations on reaction behaviors are analyzed and summarized on the basis of analysis results obtained from a mass of specific structures, with the damage cumulation and the initial geometric imperfections taken as the variable loading and geometry parameters respectively.Lastly, an evaluation of the seismic behavior of the cantilever truss structure is made. As an introduction, the evaluation method Incremental Dynamic Analysis (IDA) is explained in details. The theorems and execution procedure of IDA are explicitly described, especially the essentials on the determination of relating parameters. Then the IDA method is implemented into the evaluation of the seismic behavior of the cantilever truss structure, producing a probability based assessment of the reliability of cantilever truss structures subjected to possible earthquakes in the future.