Analysis On Seismic Performance Of Masonry Structure With Bottom-Frame And Influence Of Story Stiffness Ratio

Shear-wall and bottom-frame masonry structure satisfies the requirement of large space at the bottom, and the cost is lower comparatively, this style of buildings is prevalent in small and middle cities. However, character of"upper's stiffness is stronger than bottom, and upper's weight is heavier than bottom"is one of characters of shear-wall and bottom-frame masonry structure, and when the bottom is damaged, progressive collapse maybe happen in the upper. During Wenchuan Earthquake, the bottom (shear-wall and bottom-frame) is severely damaged, even progressive collapse, and some of them are damaged lightly. Damaged location is also different, and is divided into two categories, such as upper structure and bottom structure. Therefore, as a whole, to understand the seismic performance of shear-wall and bottom-frame masonry structure, to analyze the main influential elements of seismic performance, to find the weak part of structure, to provide the fortification measures are significantly necessary, and the designer of shear-wall and bottom-framed masonry structure can infer from this paper.Characteristic of seismic disaster for shear-wall and bottom-frame masonry structure is fully analyzed in this paper, based on the real damaged buildings. Using space structure elastic model, plane structure elastic and elastic-plastic model, and the real structure in Wenchuan, the contrasts between shear-wall and bottom-frame masonry structure and masonry structure are analyzed. Control index of stiffness ratio between the upper (masonry structure) and shear-wall and bottom-frame is called story stiffness ratio, the influencing extent of story stiffness ratio is systematically analyzed, by establishing space structure elastic model, plane structure elastic and elastic-plastic model.The main conclusions of this paper are as follows:â‘ Seismic performance of the shear-wall and bottom-frame masonry structure after reasonable design is almost the same as that of masonry structure, and damage pattern of shear-wall and bottom-frame masonry structure (earthquake action of upper structure reduced by bottom dissipation) has a great controllability, therefore it's significantly necessary to be strict with seismic design of shear-wall and bottom-frame masonry structure, especially in definition of stiffness ratio between bottom story and transition story, integration design of upper wall. â‘¡It's the key point to guarantee the seismic performance of bottom-frame masonry structure, by controlling the stiffness ratio between different story and carrying out the thought of multiple seismic-proof. The present regulations about the stiffness ratio between different story can make the seismic performance of shear-wall and bottom-frame masonry structure safe, however, crack prevention is lack; therefore, the lower limit of stiffness ratio should be modified form 1.0 to 1.5, in order to fully play the dissipation of shear-wall and bottom-frame, and to decrease the seismic effect of masonry structure on the shear-wall and bottom-frame.â‘¢Transition story of shear-wall and bottom-frame masonry structure may be easily damaged during earthquake, because of inconsistent deformation between bottom-frame and transition story. The more stiffness ratio of the shear-wall and bottom-frame masonry structure, the worse transition story is damaged. Therefore, adopting the reinforced masonry, adding tie-column or increasing the strength of material and so on, are advised, in order to improve the ductility and shear strength of transition story, to prevent walls of transition story damaged caused by the inconsistent deformation, requirement on transition story of masonry structure is added to new code (a draft for discussing).â‘£Mechanical behavior of shear-wall and bottom-frame masonry structure is complex. Mechanical behavior of shear-wall and bottom-frame will be changed, after transition story damaged during great earthquake. The pattern of"strong column and weak beam"is difficultly accomplished. The reasonable damage pattern of shear-wall and bottom-frame masonry structure should be adopted during seismic design.