The Index System And The Analysis Method For Seismic Appraisal Of Existing Multi-storey & High-rise Steel Frame Structures

With the rapid development of economy, the current seismic appraisal codes are behind the times. Especially for the existing steel structures, these codes have not contained any relational specifications to guide the inspection and seismic appraisal work. The thesis is concerned on the seismic appraisal of the existing multi-storey & high-rise steel frame structures. The corresponding index system and analysis methods are investigated and proposed.Based on the extensive survey of research references and reports, the current structure appraisal codes are summarized and compared from several aspects in this thesis, such as compiling backgrounds, reliability levels, inspection contents, appraisal grades and appraisal methods. Presently, the general appraisal codes and the seismic appraisal codes are both dropping behind design codes of the structures. These codes differ greatly from each other in compiling/revising backgrounds and theoretical bases. They show inconsistency with each other, and some contents even contradict with another one. To clear the confusion status of the current appraisal codes in China, several improvements are proposed as follows. A framework of appraisal codes should be established according to the system of structure design codes. The current appraisal codes should be revised compeletly. The performance based analysis method should be adopted to improve the two-level seismic appraisal method.The structural performance levels for seismic appraisal are researched. Corresponding to the seismic design codes and the characters of structure appraisal work, six performance levels are propoesd. Furthermore, these performance levels are classified into two groups: the elementary group and the general group. According to the perforcemence levels, a comprehensive seismic appraisal system is established. Several main factors affecting structure deformation are discussed. The storey drift limits are primarily brought forward for each structural performance level. The researches about the inelastic storey drift limits corresponding to the collapse prevetion for the multi-storey & high-rise steel frame structures are found few in China. The former values adopted in China design codes are from foreign codes. The background of current limit values, earthquake disaster statistics and the recent research references and reports are analyzed and compared. It is found that the current storey drift limit values for the collapse prevetion in China codes are unreasonable and need to be revised.The incremental dynamic analysis (IDA) method is adopted to investigate the inelastic limit states of the multi-storey & high-rise steel frame structures. The applied parameters for IM-DM (intensity measure of earthquake-damage measure of structure) are inveatigated thoroughly. The study reveals that the first mode spectral acceleration, S_a(T₁,5%), is an inadequate and incomplete IM parameter in generating IDA capacity curves. The corresponding improvement is conducted and the alternative IM parameter is proposed. Based on the study of the storey drift limits of multi-storey & high-rise steel frame structures, the results show that the use of seismic actions on the structure for IM reflects the structure capacity deterioration more directly. The IDA curves in V_bmax-θ_max format are adopted to express the change of storey drift. The storey drift limits corresponding to the collapse prevetion are researched using IDA curves in new format. Afterwards, a typical five-story a fifteen-story steel moment-frame buildings are analyzed using IDA in V_bmax-θ_max format. The IDA curve described in V_bmax-θ_max format is more direct and clear in seismic assessment. The characteristics of seismic capacity for different story structures are concluded. The suggestions of the inelastic storey drift limits for collapse prevetion are proposed.The performance based seismic appraisal methods are discussed. To satisfy the seismic performance for a structure, not only the common requirements in codes but also the personal needs presented by the owner should be considered during appraisal. Compared to other methods, the static pushover method is most practical to implement the performance based seismic appraisal analysis.An appraisal procedure for multi-storey & high-rise steel frame structures is proposed based on the traditional static pushover method. The method is improved in several aspects. The number of vibration modes considered in appraisal is limited through controlling the mass participation factor. This pushover method transforms the Multi-Degree-of-Freedom capacity curve to the Single-Degree-of-Freedom capacity curve based the equivalence between the work done in nonlinear static analyses for the MDOF system and the SDOF system. The energy-based pushover curve is proved to be more reasonable, especially for pushover analysis using higher mode loading pattern. The target displacement is determined using a numerical method without any iteration, which makes the method more practical for engineering. Finally, the performance evaluation of an eight-story steel moment-frame building under the moderate and strong earthquake is conducted using the above pushover method. The whole appraisal procedure is described in detail. The advantages of the proposed method are verified.