Study On Failure Mode And Collapse Mechanism Of Masonry Structures Under Earthquakes

In recent years, a large number of masonry structures damage in many destructiveearthquakes occurred in China, which shows that the present seismic design theory andtechnology of masonry structure is still not perfect; How to improve the seismiccapacity of masonry structure and even anti-collapsing ability under strong earthquakesare still worth further research.Under earthquake the damage degree of masonry structure is directly related tothe seismic capacity of its load-bearing walls. The wall of masonry structure losingbearing capacity lead to collapsing or serious damage of the whole structurephenomena of earthquake damage, which shows that the different failure modes of thewalls reflect the essential difference of structure safety and seismic performances. Ifthe "like-couoling-beam" wall (e.g., spandrel wall) was firstly destroyed, the structurewill quickly get to nonlinear state, playing the seismic function of secondarycomponents and increasing the ductility of the whole structure can effectively avoidthe damage of load-bearing walls, protect the safety of structure as a whole, effectivelyreduce the collapse probabilities, which conforming to the design concept ofmulti-defence in our specification.In this paper, using the concept of "strong column and weak beam" of framestructure, the problem of whether the failure mode of masonry structure can becontroled through controling stiffness ratio between the spandrel wall and the wallbetween windows. Using this idea as a guide, two1:4reduced-scale models A and Bof masonry structure with different stiffness ratio were tested on shaking table.Dynamic characteristics and seismic reponse of the two models were compared andstudied, and focused on their the failure modes, at same time the collapse processes ofthe two models were analyzed.The finite element analysis model of the two test model were respectivelyestablished, using the software LS-DYNA. And the elastic-plastic time history analysison the two model were researched. comparative analysing the numerical simulationresults and the shaking table test results, proves the reasonability of the finite elementanalysis results and the experimental results, and that the shaking table test can moretruly reflects dynamic characteristics and seismic response of the actual structure underseismic action.Using LS-DYNA software, considering the contact and failure problems in the model, the computer simulation of two test model were carried on. Numericalsimulation and the collapsed process of the shaking table test model showed thatstiffness ratio between the spandrel wall and the wall between windows had obviousfunction on the yield mechanism of masonry structure. Collapse mode of masonrystructure can be controled by controling that stiffness ratio. In addition, the test andsimulation results also proved that the axial compression ratio is one of the key factorsof affecting the anti-collapsing ability of masonry structure, the collapse of structurealways starts from the larger axial compression side of the wall body; Reducing theaxial compression ratio can reduce the collapse probability of masonry structure, at thesame time increase the anti-collapsing ability of the structure.