Experimental Study On Mechanical Behaviors Of Assembled Monolithic Concrete Shear Walls With Mortise-tenon Joints Under Different Shear Span Ratio

The structure of assembled monolithic concrete shear walls with mortise-tenon joints(hereinafter-“shear wall with mortise-tenon joints”)is a new type totally precast shear walls structure without protruding steel bars at the side,whose basic assembly unit is mortise-tenon slabs,which is a precast concrete wall slabs with transverse grooves and vertical square holes on the edge,the transverse grooves intersect the vertical square hole.In this paper,the shear span ratio is taken as a parameter to study and analyze the mechanical behaviors of the wall and the connection performance of the joint.The main conclusions:(1)Experimental study on mechanical behaviors of shear walls with mortise-tenon joints.One reinforced concrete shear wall with a shear span ratio of 1.5 and three shear walls with mortise-tenon joints with a shear span ratio of 1.0,1.5,2.0 were designed and fabricated,and the quasi-static tests under constant compression load were completed.The results show that the shear walls with mortise-tenon joints have good seismic performance,and the wall of shear span ratio of 1.5 bearing capacity and stiffness are slightly lower than reinforced concrete shear wall.Macroscopic vertical cracks are formed along with the convex roots and inside of the grooves of the mortise-tenon slabs,which can avoid brittle failure of the wall with low shear span ratio.The failure displacement angles of walls are all larger than 1/50,and the ductility coefficients are all greater than 5.0,indicating that they have good deformation ability.The mortise-tenon joints are reasonable with reliable connection and good integrity,the cracking displacement angle of the joints is greater than 1/500,under the peak load,the deformation of mortise-tenon joints is small,and the horizontal deformation and vertical deformation are only 1.0mm and 1.5mm,respectively.When the outermost longitudinal bars of the edge member yield,the strain distribution of the reinforcement at the bottom section still conforms to the plane section assumption,in peak load no longer conforms to the plane section assumption.The area of concrete collapse at the root of the wall is relatively small.When the shear span ratio increases,the bearing capacity of the wall decreases,the bearing stability and deformation capacity increase,and the stiffness degradation of the wall is slowed down.At the same time,the development of macroscopic vertical cracks can be delayed by increasing the shear span ratio,and the damage degree of the convex roots of mortise-tenon slabs can be reduced.The failure area of the shear wall with mortise-tenon joints is mainly distributed in the macroscopic vertical cracks area,which delays the concrete collapse at the root of the wall and effectively reduces the collapse area.The concrete shear wall still maintains good vertical bearing capacity when the displacement angle is greater than 1/35.(2)Numerical analysis of mechanical behaviors of shear wall with mortise-tenon joints.The numerical analysis model of shear wall with mortise-tenon joints was established by using the finite element software ABAQUS.The results show that the numerical model can well reflect the failure process and failure mode of shear wall with mortise-tenon joints,and is in good agreement with the test skeleton curve.The cohesive-friction hybrid model can be used to simulate the concrete bonding properties at mortise-tenon joints.The shear wall with mortise-tenon joints forms vertical cracks along with the transverse convex roots of the mortise-tenon joint,which obviously improves the deformation ability of the wall and prevents the brittle shear failure of the wall.The bearing capacity of shear wall can be improved by increasing the longitudinal reinforcement ratio of boundary element,and the increase is more obvious when the reinforcement ratio is low.When vertical square holes inside overlap with transverse grooves inside,if increasing the size of vertical square holes along the wall width,will increase the area of new and old concrete interface of the convex roots and grooves inside,which will accelerate the bearing capacity degradation rate.It is suggested to reduce the height of the grooves inside or reduce the size of vertical square holes along the wall thickness to reduce the area and improve the joints performance.(3)The design formula of shear bearing capacity of mortise-tenon joints is put forward.The shear capacity formula of vertical joints of shear wall with mortise-tenon joints is put forward,and the shear demand of mortise-tenon joints is discussed.The value of the Co-working coefficient of group convex of walls with different shear span ratios is proposed,for walls with a shear span ratio of less than or equal to 1.5,the recommended value of the existing large panel code can be adopted,for walls with a shear span ratio of more than 1.5,the recommended value should be lowered;for walls with a shear span ratio of 2.0,the recommended value is 0.4.The results show that the calculation results of the shear capacity formula with the Co-working coefficient of group convex can meet the shear demand well,and the proposed formula is reasonable.