Study On Seismic Performance And Earthquake Damage Mechanism Control Of Mansonry School Buildings

Considerable brick masonry school buildings suffered severe damage or even totally collapsed due to the formation of weak pier story mechanism during the Wenchun Earthquake. The seismic behavior and anti-collapse performance of masonry school buildings has become a major concern for researchers. Masonry school buildings that characterized by large bay, few walls and high percentage of openings in longitudinal walls are vulnerable to earthquake action. However, no special provisions are provided in the current seismic design code for earthquake collapse prevention design of masonry schoolhouses during a seismic event. A number of recommendations have been proposed based on earthquake damage investigation and analysis. Less attention has been paid on seismic performance of masonry school buildings, structural control of strong pier-weak spandrel damage mechanism and seismic behavior of wall piers and transverse walls within masonry structures. Quasi-static tests on reduced-scale sub-structure model of brick masonry school buildings were carried out in order to study the seismic performance and earthquake damage mechanism control of large bay masonry structures. The major contents and conclusions are summarized as follows:1) The structural characteristics and typical earthquake damage of masonry school buildings are summarized. The two types of earthquake damage mechanism of masonry structures, strong pier-weak spandrel and strong spandrel-weak pier, are analyzed. The reason of typical earthquake damage are studied and some recommendations on seismic design of brick masonry school buildings are presented.2) Five reduced-scale masonry wall specimens were subjected to in-plane quasi-static reversed cyclic lateral loads to study the seismic performance of piers between window and door openings and the influences. The results indicate that the specimen designed in accordance with current code provisions just exhibits good seismic behavior. Increasing the cross section size of structural column can ensure better seismic performance. The failure modes, ductility and energy dissipation capacity of specimen are significantly improved. However, to some extent, increasing the reinforcement ratio of structural column can decrease the ductility and energy dissipation capability. Therefore, increasing the section size of structural column properly and controlling the reinforcement ratio reasonably is of crucial important in seismic design of masonry school buildings.3) Quasi-static tests on five transverse wall specimens are conducted to study the failure modes and seismic performance of transverse walls. The results indicate that the arrangement of structural measures in transverse wall specimens has a significant effect on the seismic performance of transverse wall specimens. The specimen designed in accordance with the current code for seismic design generally exhibits good seismic behavior while ensuring that there is no slip between the wall and the base. The presence of additional structural column or additional structural column and ring beam in composite wall specimens does not improve the seismic performance significantly. However, the specimen with additional structural column and ring beam exhibits better integrity even under ultimate deformation conditions.4) A half-scale two-story sub-structure brick masonry house model was subjected to in-plane reversed cyclic lateral displacements at roof level in order to investigate the earthquake damage mechanism and seismic performance of masonry school buildings with pilastered piers. The reinforcement ratio of pilaster is1.67%. Failure characteristics, seismic performance of the model, as well as failure modes of piers between window and door openings and the failure mechanism of longitudinal walls are studyed. The results indicate that damage of the model mainly concentrates in piers, because increasing reinforcement ratio of pilaster to some extent can decrease the deformation compatibility between pilaster and masonry. A soft story mechanism occurs with piers fail in shear failure and spandrels slightly damaged. And the longitudinal walls exhibit strong spandrel-weak pier failure mechanism. Some piers are severely damaged or even collapsed and a collapse mechanism forms, resulting in the poor ductility and energy dissipation capacityof model.5) Quasi-static tests on two half-scale two-story sub-structure house models were carried out. The reinforcement ratio of structural column within wall piers is0.77%. The failure characteristics, load bearing capacity, deformability, ductility and energy dissipation capacity of two models, as well as failure modes of piers and failure mechanism of longitudinal walls and the control condition were investigated. The results indicate that a weak pier story mechanism occurs in ordinary masonry model with the piers fail in shear failure. And the longitudinal walls exhibit strong spandrel-weak pier failure mechanism, resulting in the collapse failure mode of model. However, partially reinforced piers with anchored reinforcements are characterized by flexural failure with horizontal cracking in the mortar bed joints. Spandrels are severely damaged due to the formation of global failure mechanism. Strong pier-weak spandrel failure mechanism is guaranteed with uniform drift distribution. The level of damage, global ductility and energy dissipation capacity of masonry structure are significantly improved. It is necessary to ensure that the moment bearing capacity of piers is higher than that of spandrels to the development of strong pier-weak spandrel mechanism.6) A strengthening method aimed at enhancing the seismic performance and ensuring the strong pier-weak spandrel failure mechanism of longitudinal walls is present in order to improve the anti-collapse capacity of existing brick masonry school buildings. The wall piers are partially strengthened with steel mesh mortar splint. Quasi-static test on a reduced scale sub-structure brick masonry model is carried out. The failure characteristics and seismic performances of test model, as well as failure modes of piers and failure mechanism of longitudinal walls are investigated. The results indicate that the model exhibits global failure mechanism, and the partially strengthened piers are characterized by flexural failure. The analysis indicates that the proposed seismic retrofitting method can improve the global failure modes and seismic performance significantly due to the formation of strong pier-weak spandrel failure mechanism. Therefore, the desired ductility failure mechanism can be developed.