Study On Out-of-plane Mechanical Performance Of Damped Infill Wall

In recent years, the earthquake damage shows that the collapse of the infill masonry wall of the infill wall is a prominent phenomenon,which causes harm to the safety of people and property. Damping infill wall (DIW) is a new type of damping wall with self-owned intellectual property rights,which possesses excellent damping performance in the in-plane direction and fundamentally solve the common problems of infill masonry wall. However,due to the unique construction of DIW, which is quite different from infill masonry wall,analysis on the mechanical performance of DIW is not able to simply copy the existing research results. In this paper, finite element method (FEM) and theoretical method are both used to study the mechanical and deformation characteristics of main components of DIW,the mechanical performance,classification of working process and mechanism and types of deformation of DIW frame, effect of design parameters on the out-of-plane (OOP) mechanism performance of DIW, as well as the simplified mechanics model of DIW, etc. The main work and conclusions are as follows:(1) Infill masonry wall FEM model and DIW FEM model are designed based on infill masonry wall frame and DIW frame specimens in the previous experiment. OOP monotonic static load is applied to analyze the response of the main components of infill masonry wall and DIW. The deformation mode,bearing capacity,stiffness characteristics is studied. The OOP working process is summed up and the working mechanism of DIW is revealed. The results shows that, 1) the out-of-plane (OOP) deformation of DIW mainly focus on the middle two damping layers and its OOP deformation pattern is trilinear curve which is different from CIW. The OOP working mechanism of DIW can be concluded that, DIW resist OOP loading by arching mechanism in the vertical direction and collaborative bending mechanism of masonry unit and tie bars. 2) Reinforced concrete (RC) frame is as the boundary constraints of masonry units. RC frame is as the boundary constraints of masonry units, and the top beam is under bending, shear and torsion state resulted from the push effect brought by OOP deformation of masonry units. The plastic degree of beam-column joints are higher than other parts, but RC frame as a whole is under intact and slight damaged indicators. 3) Tie bars enhance the interaction between masonry units and RC frame, and improve the OOP stability and safety reserve of DIW. 4) The OOP bearing capacity and OOP stiffness is decreased significantly as the result of the sliding between RC beams and the adjacent masonry units. 5)It is the key to ensure the OOP performance by strengthening the interaction between top,bottom masonry and its adjacent RC beam.(2) 20 FEM models are designed for different constraint of contact interface between masonry units and reinforcement frame. Influences on OOP mechanism performance of DIW are analyzed, which are brought by the shear strength of damping layers and elastic module of filler in flexible connection between masonry and RC column. The better deformation mode and working mechanism of DIW is clear. The result shows that, 1) OOP working mechanism of DIW in the horizontal or vertical direction is only affected by the constrained strength of masonry-frame contact interface in the same direction. Four types of working mechanism are classified according to the forming of arching mechanism in vertical and horizontal direction.2) OOP deformation mode of DIW in the horizontal or vertical direction is only affected by the degree of slip between masonry units and beam constrained by masonry units-beam contact interface. Three types of deformation mode are classified according to the degree of contact and separate phenomenon as well as the amount of slip between masonry units as well as masonry units and beam. 3) Compared with increasing the elastic module of filler in flexible connection between masonry units and column, it is more effectively to increase OOP bearing capacity and OOP stiffness by increasing the shear strength of damping layer.It is advised to use motar of which is greater 1.2MPa as damping layer. 4) The working mechanism manifests as the combined of horizontal and vertical arching mechanism as well as masonry units-tie bars OOP mechanism in the vertical direction, and arching mechanism in the horizontal direction, which is able to resist 9 degree rare earthquake. It is expected to control the slip between masonry units and beam and use filler whose elastic module is more than 1.5MPa in the flexible connection between masonry units and column.(3) 4 control groups including a total of 20 FEM models are designed based on optimal OOP deformation pattern and working mechanism. The OOP response of main components of DIW and the influence rule of OOP mechanical performance of DIW is analyzed under different masonry strength, slenderness ratio, tie bars strength and axial compression ratio of column. The results show that, 1) with the increasement of masonry strength, the plastic degree of masonry is reduced, the OOP bearing capacity and OOP stiffness is increased,which enable to control the OOP deformation of DIW, the descent rate of OOP load after the peak load is reduced and the ability of maintaining the capacity in the large displacement. 2)With the increasement of slenderness ratio, the masonry units of DIW become more slender and the plastic degree of masonry is reduced. Additionally,the bearing capacity and stiffness is decreased, which is against the stability and safety of DIW. It is advice that the depth of masonry is larger than 120mm. 3) The tie bars connecting masonry units and column is one of most important parts of OOP working mechanism. Also, tie bars with larger strength enable to decrease the descent rate of OOP load after peak load, improve the ability to maintain the bearing capacity and increase the safety reserve. It is advice that the ultimate strength of tie bars is larger than 335MPa and the diameter is larger than 8mm. 4) With the increasement of axial compression ratio of column, there is no obvious change in the OOP bearing capacity,stiffness and deformation. However, the OOP bearing capacity of DIW is increased because of the constraints applied by axial compression. Meantime, the mechanism characteristic of frame is changed and the plastic degree of bottom column-beam joint is reduced.(4) Based on the finite simulation results, OOP working mechanism of DIW is revealed,and simplified mechanics model for this wall is established and validated. The results show that, 1) under the uniform load, it is conservative and saft to take vertical arching mechanism into consideration only, which ignores the horizontal arching mechanism and tie bars. 2) The OOP load patterns and various design parameters show no effect on the OOP working mechanism under the combined of horizontal and vertical arching mechanism as well as masonry units-tie bars OOP mechanism. 3) Simplified mechanics model of DIW is with explicit physics meaning,which reflects the macro OOP mechanical properties,achieves satisfactory simulation results.