Experimental And Theoretical Study On Shear Behavior Of Partially-encased Composite Open-web Beams

Under the background of vigorously advocating prefabricated buildings,partially-encased composite structures(PEC)have been ushering in development opportunities due to many advantages such as reliable performance,high construction efficiency,and can resolve excess capacity.However,they have not been widely applied due to high cost,low material utilization,and long production cycle.In order to make up for the above-mentioned shortcomings and better promote and apply PEC structures,this thesis innovatively proposes PEC open-web structures,determines the better structural form,and conducts experimental and theoretical studies on its shear performance.Therefore,in this thesis,two groups of 13 specimens were designed and fabricated with PEC open-web beams as the research object.Firstly,the structural research test was carried out on 5 open-web beams with different structures,and the better open-web structure forms were determined through comprehensive comparison,namely,rebar truss and π-type truss open-web structures.On this basis,the shear performance of eight open-web beam specimens was studied and tested with the variables of shear span ratio and web opening rate,and the changes of shear damage pattern,shear bearing capacity,deformation capacity and strain development of each specimen were analyzed.The shear bearing capacity calculation methods applicable to these two forms of open-web beams were determined.Meanwhile,the simulation verification and supplementary analysis were carried out with the help of finite element software ABAQUS.The main conclusions are as follows.(1)Compared with other open-web structures,rebar truss and π-type truss have higher bearing capacity,stronger deformation capacity,slower crack development and better comprehensive working performance.(2)The shear failure mode of PEC open-web beam is directly related to the shear span ratio,which can be divided into three categories:diagonal compression failure(λ=1),constrained shear compression failure(λ=2)and diagonal tensile bond failure(λ=3).The force-deformation process is characterized by three stages:elastic stage,elastic-plastic stage and bearing capacity decline stage.(3)With the increase of shear span ratio,the shear bearing capacity of each specimen decreases,the maximum decrease is 27.43%,the deformation capacity increases significantly,and the initial shear stiffness decreases.With the decrease of web opening rate,the shear bearing capacity increases,the maximum increase is 13.01%,the deformation capacity increases,and the stiffness degradation after elastic-plastic stage is relatively slow.In general,under the premise of controlling the same steel content,the influence of different open-web structural forms on shear bearing capacity and deformation performance is limited.(4)The strain distribution of main steel and concrete in mid-span section basically obeys the plane section assumption.With the increase of load,the strain of each part increases,and the connecting rod and X-shaped tie bar yield earlier than the web.(5)The calculation method based on superposition principle can better estimate the shear bearing capacity of PEC open-web beam.(6)The finite element simulation results are in good agreement with the experimental results,and on this basis,the influence of web thickness and concrete strength on the shear performance of PEC open-web beam is obtained,that is,with the increase of web thickness or concrete strength,the shear bearing capacity increases correspondingly,and the increase is about 4%and 2%.