Experimental Study On The Shear Resistance Of HSC-UHPC Interfaces Cast In Different Times

Prefabricated buildings are widely used in actual projects because of their high construction efficiency,energy saving and environmental protection.Common prefabricated components in bridge engineering include: prefabricated hollow slabs,segmental prefabricated box girder and T-beams,etc.These prefabricated components are usually prefabricated from high-strength concrete(HSC),and they are connected as a whole by postcasting tape at the bridge site.The use of ultra-high performance concrete(UHPC)with super mechanical properties and durability as a post-cast belt material is an emerging method in engineering.At the same time,high-strength steel bars are being promoted and used because of their energy-saving advantages.Using such materials with good performance in weak structures can achieve both economical and efficient purposes.At present,related researches on the shear resistance of HSC-UHPC interface formed by this emerging method are relatively rare,and reports of interface configuration with high-strength steel bars(HTRB600)or setting of reserved grooves are even rarer.Whether UHPC and high-strength shear reinforcement can play the expected role in the interface shear resistance,and whether the current standard calculation formula can be used to evaluate the shear bearing capacity of the HSC-UHPC interface is a question worthy of study.In response to this,this article designed18 Z-shaped push-out specimens to study the effects of four variables: post-pouring concrete strength,interface treatment method,shear reinforcement strength and reinforcement ratio on the shear performance of the HSC-UHPC interface of successively pouring HSC-UHPC.According to the test results,the applicability of the current code clauses to the calculation of the interface shear capacity is evaluated.The shear force transfer mechanism of the interface is analyzed,and the calculation formula for the shear bearing capacity of the interface is proposed based on this.Specifically,the main conclusions obtained in this article are as follows:1.The use of UHPC in post-cast concrete has a significant influence on the shear resistance of the interface.Compared with the HSC-HSC(post-cast HSC compressive strength of 60MPa)interface,the shear resistance of the HSC-UHPC(post-cast UHPC compressive strength of 120MPa)interface increased by about37.24%.This increase in bearing capacity benefits from UHPC’s ability to effectively increase the cohesion of the interface.2.Both chiseling and reserved grooves on the interface can effectively increase the shear capacity of the HSC-UHPC interface.Chiseling increases the cohesive force of the interface by increasing the interface contact area,and the reserved groove can not only increase the interface contact area,but also generate a certain interface shear resistance by the groove teeth.The shear bearing capacity of the plain reserved groove interface is increased by 83% compared with the plain smooth interface,and the improvement rate of the former after reinforcement is as high as 127%.At the same time,compared with the chiseled and smooth interface,the failure of the reserved groove interface shows better ductility.3.When the yield strength of the interfacial shear reinforcement is increased from400 MPa to 600 MPa,the peak shear capacity and shear stiffness of the HSC-UHPC interface do not change significantly,but the residual bearing capacity after the interface peak will increase significantly.The reason for this phenomenon is that the high-strength shear steel bar does not yield at the peak bearing capacity.4.The configuration of steel bars can effectively increase the peak shear capacity and ductility of the interface,and with the increase of the reinforcement ratio,the increase rate of the peak bearing capacity and shear stiffness of the interface becomes smaller and smaller.This is because of the peak bearing capacity.Mainly from the contribution of concrete,the contribution of shear steel bars is not as large as expected.5.The shearing process of HSC-UHPC interface pouring successively includes five stages: elastic bearing stage,peak bearing stage,load release stage,residual bearing capacity stage and failure stage.Among them,the cracking load accounts for about60%-70% of the peak bearing capacity;the peak bearing capacity comes from the contribution of concrete(about 70% of the peak bearing capacity).6.The standards ACI,AASHTO,Eurocode 2 and JGJ are all too conservative in calculating the bearing capacity of the HSC-UHPC interface.The calculation accuracy of AASHTO,JGJ and Eurocode 2 is higher than that of ACI.The main reason is that AASHTO and JGJ consider the contribution of concrete to the bearing capacity more reasonably,but the calculation of Eurocode 2 and JGJ unreasonably overestimates the high strength.Shear resistance of steel bars.7.Based on the shear transfer mechanism of the HSC-UHPC interface of successive pouring,the proposed calculation formula for the interface shear capacity can better calculate the shear capacity of the test specimen.