Experimental Research On The Transversal Mechanical Behavior Of Deck System In The New Type Of UHPC Box Girder Bridge

The new type of UHPC continuous box girder bridge in this paper is a new type of unidirectional prestressed structure which combines ultra high performance concrete with dense diaphragm.The new structure makes full use of the excellent mechanical properties of UHPC.Thus thinning of wall thickness of box girder.The weight of the superstructure can be reduced about 50%,The long term creep deformation is only 20% of the conventional beam.It is not only expected to solve the two major diseases of the traditional long span prestressed concrete beams,such as cracking and deflecting.At the same time it provides a competitive bridge type scheme to achieve 300 m to 400 m or even larger span.The mechanical characteristics of the deck system in the new type of UHPC box girder bridge are different from that of the traditional concrete box girder.In UHPC box girder bridge,the transverse diaphragm together with the box girder web plate support the bridge deck under wheel loading,The wheel load on bridge deck is transferred along vertical and horizontal direction.The force of the bridge deck system is very complicated.It is necessary to carry out the study of its local force performance.In view of this,this article mainly carries out the research work from the following aspects:(1)A trial design was conducted,basing on the cross embankment bridge of Shi-jiao side of Qing-xin bridge,in Guangdong Province.The design scheme of UHPC continuous box girder bridge was proposed.The overall calculation of the whole bridge showed that the mechanical performance of the trial design structural meets the requirements of the standard.Static and fatigue calculation of the bridge deck system in segmental model showed that the bottom of the upper plate of the diaphragm had the largest transverse stress.Whether the upper plate of the diaphragm can keep good condition while supporting to improve the force of the bridge deck worthy of attention.(2)The upper plate of the diaphragm scale model test and finite element numerical simulation were carried out to verify whether the anti crack performance and bearing capacity of the upper plate of the diaphragm can meet the engineering requirements At the same time toexplore the full-range mechanical characteristics of the upper plate of the diaphragm under the wheel load.The results showed that the anti cracking performance of diaphragm upper plate and the bearing capacity can both meet the engineering requirement.The whole process of its behavior is roughly divided into 3 stages:elastic stage,crack development stage and yield stage.The ultimate failure mode is bending damage.The reinforced bar at the bottom edge of the upper plate was broken when the test beam was damaged.(3)Basing on the Concrete Damaged Plasticity Model,the finite element analysis of experimental model using ABAQUS were carried out.After validating the reliability of the finite element model.The parametric analysis of the main characteristics affecting the anti cracking performance and bearing capacity of the upper plate was also carried out.The results showed that the finite element model was in good agreement with the test value.This showed that the material parameters of the UHPC and the reinforcing bar can be used to simulate the whole process.On this basis,the parameter analysis was carried out to explore the influence of the rebar diameter,the height of the upper plate and UHPC tensile strength on the flexible behavio of the test beam.The results showed that proper increase of reinforcement ratio can increase the stiffness after cracking and increase the ultimate bearing capacity.Increasing the height of upper plate can improve the bearing capacity and initial stiffness,and increase its ductility.Increasing the tensile strength of UHPC can result in elastic stiffness basically unchanged,and the post cracking stiffness and ultimate load-carrying capacity are improved.(4)Basing on the crack width formul of French standard,analyses of the crack resistance of the transverse mechanical behavior were conducted.The results showed that the French standard calculation results were close to the crack stress of the test beam.This showed the reliability of the French standard.Analysis of anti cracking performance parameters showed that increasing the reinforcement ratio generally can improve the cracking stress at the bottom edge of the upper plate.When the upper plate height of the test model increased from 24 cm to 36 cm,the change of cracking stress is not obvious.But the safety factor increased from 1.14 to 1.36.(5)According to the plane-section assumption,and the material nonlinearity of UHPC and steel bars was considered.A nonlinear analysis program for the full-range flexural of the test beam was developed.The results of numerical calculation were in good agreement with the experimental results.This showed the correctness of the strip method and the conjugate beam method used in the programming.