| Balanced cantilever erection method,construction fast,precast segmental concrete curing conditions guaranteed,small disturbance to the environment,the advantages of strong adaptability,is one of the important construction methods of longspan PC girder Bridges.However,the mechanical performance and durability of the joints between the precast girders are unsecured,which is the weak part of the bridge structure,and also limits the further application of the conventional balanced cantilever erection in the long-span PC girder bridge.Ultra-high performance concrete(UHPC)is considered to be a suitable material for field-cast joint due to its excellent properties and high bond strength with normal strength concrete(NSC),but the performance of common UHPC develops slowly in the early stage and shrinks greatly under natural curing,so it may not meet the requirements of balanced cantilever erection method which have requirements for construction speed.Using high early strength characteristics of high early strength ultra-high performance concrete(HESUHPC),the field-cast HESUHPC wet joint can not only solve the problems of low bond strength and insufficient durability of the joint in balanced cantilever erection method,but also ensure the speed of construction.This study investigates developments of materials properties of HESUHPC and HESUHPC-NSC interface shear and tensile performance with HESUHPC’s age under summer,autumn and winter three kinds of natural curing conditions by means of a large number of material properties tests,double-side direct shear tests and axial tensile tests.At the same time,using finite element analysis software establish two finite element models of bridges by cantilever erection method and cantilever cast-in-place method,which are used to explore the potential advantages of long-span PC grider bridges constructed by cantilever erection method.The main conclusions are as follows:(1)The material properties of HESUHPC developed dramatically in the early stage(1～3 days)and were greatly affected by curing conditions.At 3 day age,HESUHPC obtained more than 87.7%,71.9% and 64.4% of the material properties under three natural curing conditions of summer autumn and winter,respectively.(2)The shear and tensile performance of HESUHPC-NSC interface is excellent,the interface of most specimens was not damaged,which showed that a layer of NSC debonded near the interface or the shear/tensile failure of concrete;the bond strength of most specimens was greater than that of NSC-NSC control group.Only under extremely unfavorable conditions(winter and early age),the interface appears pure interface failure and the bond strength is lower than the NSC-NSC control group.(3)The shear and tensile strength of the HESUHPC-NSC interface increases with age,and develops rapidly in the early stage,but it is obviously affected by the curing conditions.At the age of 3 days,most of the bonding strength of the interface has been obtained under the three curing conditions in summer,autumn and winter,the shear strength was 95.4%,77.4% and 70.4%,respectively,and the tensile strength was83.9%,75.3% and 65.0%,respectively.(4)The shear and tensile bond strength of the HESUHPC-NSC interface decreases with the decrease of the curing temperature,and the smaller the age,the greater the impact.At the age of 1 day,the interface shear strength of the specimens cured in autumn and winter is 69.8% and 17.7% of the specimens cured in summer,and the tensile strength is 67.8% and 10.6%,respectively.However,the shear and tensile strength of the interface under the three curing conditions of summer,autumn and winter is slightly different at the age of 28 days.(5)Compared with cantilever cast-in-place method,the mechanical properties and durability of long-span PC girder Bridges constructed by cantilever erection method are better in operation stage.The downdeflection of the main span and prestress losses caused by shrinkage and creep are reduced and the reserve of compressive stress of the cross section is increased. |
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