Study On Mechanical Behavior And Calculation Method Of Steel-masonry Composite Underpinning Beam With Isolation Reinforcement In Existing Masonry Structures

When the masonry structure is reinforced by seismic isolation technology,the seismic isolation bearing is arranged under the underpinning beam.After the joist has reached strength,the seismic isolation bearing is installed and the wall under the underpinning beam is removed.As a new reinforcing member,the underpinning beam should be able to effectively transfer the upper structural load,but the force of the underpinning beam is more complicated.At present,the research on the load distribution and force analysis of the underpinning beam is still very rough,mostly based on engineering.Experiences are analyzed by reference to the force of the underpinning beam in the building translation technique.In fact,the underpinning reinforcement is supported by the underpinning beam at the isolation bearing,and the supporting form is different from the underpinning beam used for building translation.Secondly,if the underpinning beam adopts the steel-masonry composite beam,it can interact with th e upper wall.Work together,whether there is a wall beam effect,the current study is not clear.Therefore,this paper presents the structure,working mechanism,and construction process of the steel-masonry underpinning beam for seismic isolation of exis ting masonry structures.The finite element analysis is used to analyze the wall beam effect of the system.The internal force correction formula and calculation method of the system are given.The main research contents are as follows:(1)Aiming at the characteristics of isolation and reinforcement of existing masonry structures,a steel-masonry combination underpinning beam is proposed,and the construction method,working mechanism and construction technology of the beam are given.(2)In view of the characteristics of the steel-masonry composite underpinning beams used for the isolation and reinforcement of existing masonry structures,the influence of supporting conditions and the shape of the beam underpinnings was analyzed,and finite element analysis was used.The detailed finite element analysis of steel-masonry composite wall beams with no openings in the upper wall and openings in the upper wall is performed,and the stress distribution,failure modes,the stress state of the upper cross-section and internal forces of the joist are given.It shows that the wall beam effect of steel-masonry composite wall beams used in the isolation and reinforcement of masonry structures is different from that of general framed wall beams.(3)For steel-masonry composite wall beams with no openings in the upper wall,considering the ratio of the height ratio of the joist and the ratio of the upper wall to the upper one,the test components are designed using the orthogonal test design method.The finite element a nalysis is used to obtain the test components.The internal force of the joist is linearly returned and the internal force correction formula of the joist is linearly returned.The internal force calculation and design method of the steel-masonry composite underpinning beam for the isolation and reinforcement of the existing masonry structure without the upper wall are given.(4)For the steel-masonry composite wall beams with openings in the upper wall,the height ratio of the joist,the ratio of the upper wall to the upper wall,and the position of the opening of the wall are taken into account.Experimental components are designed using orthogonal test design methods,and finite element analysis is used to obtain The internal force of the joist in each tes t component is linearly returned to the internal force correction formula of the joist,and the internal force calculation and design of the steel-masonry composite underpinning beam for the isolation and reinforcement of the existing masonry structure wit h the opening of the upper wall are given.