Experimental Research On Shear Performance Of UHPC-NC Steel Plate Connector With Opening

Ultra-High-Performance Concrete(UHPC)is a high-performance structural material with ultra-high strength and ultra-high durability.It is a reasonable material choice for improving bridge performance.The full UHPC bridge has excellent structural performance,but its economic efficiency is poor,and the high cost restricts the promotion of UHPC.Therefore,the effective combination of UHPC and Normal Concrete(NC)can reduce cost and improve performance.The UHPC-NC combined structure makes reasonable use of the tensile performance of UHPC and the compression performance and cost advantages of NC.The effective transmission of the shear force at the interface between the two determines the overall performance of the structure.In order to effectively connect the UHPC-NC interface,the interface generally adopts methods such as chipping and grooving at the interface.Such methods will cause initial micro-cracks in the UHPC and cannot guarantee that the UHPC-NC interface has sufficient bonding strength.For this reason,our research group has innovatively proposed UHPC-NC open-hole steel plate connectors,aiming to improve the sliding stiffness,shear strength and fatigue resistance of the UHPC-NC interface.This study designed and implemented 10 sets of 20 UHPC-NC combinations and interface push-out specimens for the perforated steel plate connectors,and studied the shear resistance,sliding stiffness and shear failure mechanism of the interface.The work and conclusions are as follows:(1)The research parameters include the hole diameter of the steel plate with holes(45mm,60mm),whether the steel plate has holes,the type of concrete(UHPC and NC),the wettability of the concrete interface and the NC strength grade(C30/C40/C50).The load-slip curve is obtained through the test results,and the distribution law of the peak slip of the specimen is analyzed.The results show that: Compared with the NC strength C30,the peak slip of the C40 and C50 push-out specimens increased by 17.6% and 22.7%,respectively.Compared with the NC-NC40601 group push-out specimens,the UHPC-NC40601 group push-out specimens peak slip increased by 166.6 %;UHPC-NC interface or NC-NC interface non-porous steel plate composite test piece is about twice as small as the peak slip corresponding to the open-hole steel plate composite test piece.Compared with the composite test piece with the aperture of 45 mm,the aperture of 60 mm The peak slip of the UHPC-NC interface composite specimen is increased by 38.1%;compared with the interface dry composite specimen,the peak slip corresponding to the interface wet composite specimen is increased by about 2.5 times,and the UHPC-NC composite specimen is higher than the NC-The peak slip of the NC composite specimen is 2 to3 times smaller;the shear strength of the UHPC-NC composite specimen is 2 to 3 times greater than that of the NC-NC composite specimen,indicating that UHPC and NC have better bonding strength.(2)The ultimate bearing capacity,initial shear stiffness,load-slip curve of the DIC method and displacement meter method and the height slip distribution law along the interface of the specimen are analyzed for the ultimate bearing capacity,initial shear stiffness,DIC method and displacement meter method of UHPC-NC perforated steel plate connectors.The results show that:Compared with C30,the contribution of C40 and C50 concrete tenon to the ultimate shear capacity of UHPC-NC interface specimens increased by 16.8% and 20.9%,respectively.Compared with NC-NC interface specimens,UHPC-NC interface specimens.The ultimate shear capacity is increased by 104.5%;with the increase of the steel plate diameter,the ultimate bearing capacity of the UHPC-NC composite specimen is increased.The composite specimen with a diameter of 45 mm and a diameter of 60 mm is higher than that of the non-porous steel plate composite specimen.The ultimate bearing capacity is increased by 39.1% and 51.7%,respectively;the ultimate bearing capacity of the wet interface composite specimen is 44.8%lower than that of the dry interface composite specimen;the peak slip measured by the displacement meter and the DIC method is almost the same,the DIC method The measured slip stiffness is generally greater than the result measured by the displacement meter method,but the law of peak slip and slip stiffness obtained by the DIC method is completely consistent with the law measured by the displacement meter method;the same specimen is in The slip at different heights under all levels of load is basically the same,but due to the eccentricity of the specimen,the difference in slip between the left and right sides of the specimen is obvious.(3)Based on the experimental data,the calculation formulas for the shear bearing capacity of the concrete tenon and the UHPC-NC interface bonding force in the hole of the steel plate in this article are respectively calculated,and the calculation formulas for the shear bearing capacity of the specimens in this article are further obtained.The proposed new formula is verified,and the results showed that the formula for shear resistance of UHPC-NC perforated steel plate connectors has a clear physical meaning,which is very consistent with the measured data of the specimens in this article,it can provide a reference for the calculation of theoretical value of a new combination structure similar to this article.