The Seismic Behavior And Fragility Of Masonry Infills In Reinforced Concrete Frame Structures

To reasonably evaluate the seismic performance and seismic loss of buildings infilled with masonry walls,it is necessary to correctly grasp the in-plane and out-ofplane mechanical behavior of masonry infill walls and their seismic damage characteristics,and to establish probabilistic fragility models of masonry infill walls for seismic loss assessment.The objectives of this study are the mechanical behavior and seismic fragility of masonry infill walls,which are most-commonly used in RC structures in China.The main work of this study is summarized as follows.1.Nine full-scale masonry-infilled RC frame specimens were subjected to quasistatic loading to study the mechanical behavior of the infill walls of either clay bricks or hollow concrete blocks and those with plastic-steel framed doors and windows.The results indicate that the maximum crack width of the masonry infill walls was approximately linearly related to the inter-story drift ratio,regardless of the masonry type.When other parameters were the same,clay brick infill walls had a better ductility and energy dissipation capacity and higher strength than hollow block infill walls.2.A quasi-static test database of masonry infill walls was established.It was used to evaluate the accuracy of the existing equations for estimating the stiffness and strength of masonry infill walls.The results show that the equation based on a flexible-shear model gives acceptable estimates for the initial stiffness,that the equation in ASCE 5,which is based on a diagonal strut model,gives the best estimates for the secant stiffness at the peak strength,and that the equation based on the failure modes of diagonal crushing is shown to yield the best estimates for the peak strength.3.Seismic fragility functions of masonry infill walls were derived based on the descriptive visible damage of the specimens in the aforementioned test database.The influence of the definition of damage states(DS),type of masonry and existance of plaster finish on the fragility functions was investigated.The results show that the DS definition based on descriptive damage lacks of objectivity,while the DS definition based on loaddisplacement skeleton curves lead to exccesive dispersion.Therefore,the DS definition based on measured maximum crack width is recommended for fragility analysis of mansonry infills.When this definition was adopted,neither the masonry type nor the finish plaster have an significant influence on the fragility functions.4.The mechanism for the lateral resistance of plastic-steel framed windows embedded in masonry infills was experimentally examined.The lateral strength contribution of the plastic-steel frame of the window was 25% to 36% of the lateral strength of the surrounding RC frame in the present test.DS states were defined for the embedded doors and windows according to their functional loss,based on which the fragility functions of plastic-steel framed doors and windows were established.The results show that there is a greater than 50% probability for sliding windows and sidehung doors not to be able to open when the structure remains essentially elastic.In addition,the glass panel is unlikely to break and fall under in-plane action.5.A series of in-plane-out-of-pline(IP-OOP)coupled loading tests on seven fullscale masonry infill walls were conducted to study the effect of the prior in-plane damage on the out-of-plane behaviour of masonry infills.An empirical equation for the OOP strength reduction was established as a function of the prior in-plane drift ratio and the slenderness of the wall panel.A numerical example of the seismic loss assessment for masonry infill walls demonstrated a substantial underestimation of the seismic loss related to masonry wall damage if the IP-OOP interaction was neglected.