Study On The Mechanical Performance Of Segmentally Assembled Unreinforced Prestressed UHPC Beams

Ultra High Performance Concrete is a new type of cement-based material with the advantages of high strength,high toughness and excellent durability,which has a broad application prospect in bridge engineering.Prefabricated assembled unreinforced prestressed UHPC girders utilize the shear capacity of steel fibers in UHPC without the configuration of ordinary steel reinforcement,and are a new type of bridge structure that relies solely on prestressing tendons for tensile strength and splicing.It reduces the amount of ordinary reinforcement and tying work,making construction easy and fast,which has become a hot spot for assembled bridge construction in recent years.However,there is a lack of research on segmental assembled unreinforced prestressed UHPC beams,and the force performance of prefabricated assembled unreinforced prestressed UHPC beams needs to be urgently investigated.In this paper,a combination of experimental research and finite element method is used to study the precast and assembled unreinforced prestressed UHPC beams.The work done in this paper is as follows:(1)Considering four influencing factors,namely the number of different joint tooth keys,prestressing magnitude,prestressing type and joint type,preliminary numerical simulations of the mechanical performance of segmental assembled unreinforced prestressed UHPC beams were carried out using ABAQUS finite element software and compared with the whole cast model beams without joints.The results show that the joint is the weak position of the UHPC segmental beam,and the final damage locations are all near the joint;the bearing capacity of the segmental beam is lower than that of the whole cast beam,and the degree of reduction matches the discount factor of the segmental precast spliced beam proposed by the American AASHTO code.(2)Experimental study of the segmental assembled unreinforced prestressed UHPC beams.A four-point bending test study of six groups of 12 specimens was carried out considering the factors influenced by joint type,prestressing degree,number of tooth keys,and prestressing type.The results showed that all segmental beams were damaged at the joint location,and the final damage mode was that the prestressing tendons in the span reached yielding and the concrete in the compressed area at the top of the joint crushed.The number of tooth bonds has no significant effect on cracking load and ultimate load;the larger the prestress,the smaller the cracking load,but the prestress tension size has little effect on the ultimate load;the bonded prestress type has higher stress bearing capacity than the unbonded one;the glued joint increases the bond force at the interface of the joint,delays the opening at the bottom of the joint,and increases the ultimate bearing capacity.(3)ABAQUS software was used to analyse the mechanical performance parameters of segmental assembled unreinforced prestressed UHPC beams,taking into account the concrete strength,strand reinforcement rate,the location of the splice and the splice construction factors.The results show that: the area of the strand in the tensile zone is the most important factor influencing the ultimate load carrying capacity;when dividing the sections,the joints should be located at the position with less bending moment,which is conducive to improving the load carrying capacity of the section beams;the form of double-tooth bonded joints with epoxy glue is more conducive to the overall force of the UHPC section beams.(4)Parametric analysis of unreinforced prestressed UHPC spliced beams was carried out by using ABAQUS software,considering concrete strength,strand reinforcement rate,location of joints,and joint construction factors.The results show that: the area of the strand in the tensile zone is the most important influencing factor of the ultimate load capacity;when the sections are divided,the joints should be located in the position with less bending moment,which is conducive to improving the load capacity of the section beams;the epoxy adhesive double-tooth key joint form is more conducive to the overall force of the UHPC section beams.