| Due to self-weight of concrete slab,long-term effect of timber and concrete and low tensile strength of concrete,traditional timber-concrete composite beams have problems such as self-weight,large long-term deformation and insufficient durability.In order to solve the above technical problems fundamentally,UHPC(Ultra-High Performance Concrete)material with high strength and performance is introduced into timber-concrete composite beams in this paper,and a new type of glulam-UHPC composite beam structure composed of glulam beams and UHPC plates is proposed in order to reduce the dead weight,reduce long-term deformation,improve durability and improve its span ability of the composite beams.Reliable connection of the joint surface of the new composite beam is the necessary condition to ensure the structural feasibility.The glulam-UHPC joint surface mainly bears the repeated shear action caused by the whole force and local load,and is also affected by many factors,such as UHPC creep,glulam creep,ambient temperature and humidity.The shear and failure mechanism is complex.It is very important to study its mechanical behavior,connection mechanism and failure mode.In this paper,the horizontal steel plate+studs(HSP+studs)with higher stiffness and better bearing capacity are selected as the shear connectors of the new composite girder.The experimental research,numerical simulation and theoretical analysis are used to carry out the research,in order to explore the mechanical performance of HSP+studs connectors in Glulam-UHPC composite girder.The main tasks are as follows:(1)Five groups of 15 specimens were designed and tested.The effects of main design parameters on failure modes,load-slip characteristics and shear behavior of connections were studied.The test results show that the typical failure modes are studs shear failure and glulam shear failure,both of which are ductile failure.The load-slip curves of five groups of push-out members are basically the same,which can be divided into:Ⅰ.elastic stage,Ⅱ.plastic stage,Ⅲ.failure stage and Ⅳ.screw bearing stage(only glulam shear failure specimens exist at this stage);The height of studs has little influence on the shear bearing capacity of the connections.The thickness of steel plate is positively correlated with the shear capacity of the joint.The increase of concrete strength can effectively improve the shear rigidity of the joint.When the peak load is reached,the joint shows good peak-back ductility behavior.(2)Based on ANSYS finite element software and considering material nonlinearity only,a non-linear finite element model of composite structure of glulam-UHPC HSP+studs is established,and the test process is simulated numerically.The finite element analysis results are in good agreement with the test results.The obtained plate thickness,The influence laws of the height of bolts and the strength grade of concrete on the mechanical properties of the joint are in accordance with the actual test conclusions.(3)Based on the mechanical mechanism of HSP+students connector and the typical failure mode of push out test,the applicability of the current calculation theory to the calculation of shear bearing capacity of HSP+students connector is verified.The results show that when the glulam shear failure occurs at the joint surface,the NZS 3603 formula has good guiding significance to predict the shear bearing capacity;When the stud shear failure occurs,the accuracy of the existing calculation formula and the test results is not good.Due to the small number of stud shear failure specimens,a large number of push out tests are needed to put forward the shear bearing capacity calculation formula with good applicability. |
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