| In traditional analysis and design of steel structure, beam-column joints is recognized as the ideal articulated connections or rigid connections. Such idealized assumptions can simplify the analysis and design of steel frame, but in many cases such idealized assumptions can’t reflect the practical work of beam-column joints of structures. Semi-rigid nodes can not only transfer shear but also can pass some moment. They have good ductility and energy dissipation capacity, and have got more and more attention, especially the study of its seismic performance. The current research on seismic performance of semi-rigid connections is essentially deterministic analysis. It rarely gets the adoption of large enough sample space to fully consider the earthquake effect as well as the randomness of the structure itself. The results are not able to fully determine the seismic performance of the structure. Seismic fragility analysis is one of the main content of the earthquake disaster risk analysis. It provides a new way to evaluate the seismic performance of structure, and can consider all kinds of uncertainties. It researches all kinds of damage state probability of structure under the action of different intensity earthquake from the aspect of probability. Up to now, for the semi-rigid structure as the research object of seismic fragility analysis were rare. Design specification only wants us to consider the influence of semi-rigid nodes, but gives no specific design methods. So the seismic fragility analysis of semi-rigid structure is not only helpful to study the seismic performance of the structure, but also can help designers grasp the characteristics of the structure and thus for the correct structure design.This paper studies the characteristics of the semi-rigid nodes, and using finite element software SAP2000 to numerical simulation was carried out. Contrasting the results of numerical simulation and experimental data shows the method is feasible. Then, this paper designs the 6-layer semi-rigid,6-layer rigid,9-layer semi-rigid,9-layer rigid steel frame as the research object. Use Latin hypercube sampling technique to generate 100 samples respectively for probabilistic seismic demand analysis, considering randomness of the earthquake action and the related parameters of the structure itself. Establish the seismic demand model, and select the appropriate intensity of ground motion parameters and structure parameters. Then, according to the field characteristics and seismic grouping information,100 suitable seismic waves were selected as the ground motion input. Respectively for each sample, use finite element software SAP2000 to conduct the dynamic elastic-plastic time history analysis. According to the chosen earthquake demand parameters, conduct the logarithm linear regression analysis respectively to get function relation between the demand parameters and seismic intensity parameters. And then conduct the probabilistic seismic capacity analysis through conducting the static elastic-plastic analysis of each sample to get their random resistance curve. Base on the different performance levels of structures defined by the specification, use the resistance curve to study the failure process of structure, and determine the boundary value of different limit state of the corresponding performance index.Finally, conduct the probabilistic seismic fragility analysis basing on the probabilistic seismic demand analysis and the probabilistic seismic capacity analysis of the 6-layer semi-rigid,6-layer rigid,9-layer semi-rigid,9-layer rigid steel frame. Theory based on traditional reliability analysis method is used to study the failure probability of the seismic demand beyond the seismic capacity. Use the vertex maximum displacement angle (RDA), the maximum interlayer displacement angle(ISDA), the displacement ductility ratio(μ d) and stiffness damage index (SDI) as the performance index to draw their seismic fragility curves. Compare the semi-rigid steel frame with the rigid steel frame to research the difference of failure probability under the effect of different seismic intensity, to reflect the influence of semi-rigid nodes on seismic performance of structures. At the same time, study the differences of fragility curve by using different performance indicators. Analyse if it is reasonable by using the interlayer displacement angle value given by Specification. And give some recommendations on seismic fragility analysis. |
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