| The collapse of civil engineering structures in earthquakes will cause tremendous casualties and economic losses. The accurate assessment of structural collapse resistant capacity is a key step in the Performance-Based Earthquake Engineering(PBEE). In order to estimate the casualties and economic losses, the structural collapse resistant capacity should be accurately predicted firstly. The accurate assessment of structural collapse resistant capacit y has significant meaning to guarantee the structural security and mitigate disaster in earthquakes. In this paper, a three-story reinforced concrete(RC) frame structure was studied on the following topics: the complete collapse shaking table test and simulation, the assessment method of collapse resistant capacity and the influence of ground motion directivity on collapse resistant capacity. The main contents are as the following:(1) The prototype three-story RC frame structure was designed according to the current Chinese building codes. The model specimen was contrasted as 1/5-scale of the corresponding prototype structure. It was tested on shaking table to simulate the seismic load. The model specimen transformed from an elastic state to a highly nonlinear state, then experienced dynamic instability, and finally collapsed to the ground. The binocular stereo vision technique was firstly utilized to record the displacements of the structure during the whole process of collapse, which provided experimental basis for collapse mechanism reaearch and a new method for the large displacement measurement when the structures are in collapse state.(2) The finite element model is modeled based on the Open Sees software, which was used to simulate the structural responses, collapse mode and the variation of dynamic properties under different intensities of seismic load. The correctness of modeling approach and accuracy are validated by comparion between the simulation results and the shaking table test results. The structural period will be elongated due to the decrease of strength and stiffness in earthquake. The influence of structural period elongation on the intensity index of ground motion is analyzed. Then, a new intensity index Sa(Teq) which is based on spectra acceleration of equivalent period is proposed. Compared with the traditional intensity index which is based on spectra acceleration of elastic period Sa(T1), Sa(Teq) can indicate the influence of structural period elongation and effectively reduce the dispersion of results in collapse vulnerability analysis.(3) Based on the dynamic time history analysis validated by the shaking table test results, the accuracy and effectiveness of Pushover analysis is discussed. T he Pushover analysis and dynamic history analysis are compared from an elastic state to a highly nonlinear state and finally d ynamic instability. The discrepancies and causes are analyzed on the target displacement, inter-story shear force, inter-story drift ratio and curvature.(4) Considering the angle between ground motion record and fault, the 28 sets of near-field ground motions and 22 sets of far-field ground motions recommended in FEMA P695 are used to generate ground motion records of different direction compared with the fault direction. For both near-field and far-field ground motions, the influence different of direction angle of ground motions on structural collapse resistant capacity is studied. The discrepancies of collapse resistant capacity between near-field and far-field are compared. The goal of rapid assessment of structural collapse resistant capacity under ground motions of different direction is preliminary achieved. A new idea for the selection of ground motion records for structural seismic design(collapse-resistant checking under rare earthquake) is proposed. |
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