The Research For The Mechanical Characteristics And The Calculating Theory Of Three-truss Plate-truss Composite Bridges With Ballast Monolithic Deck Of High-speed Railways

Monolithic deck is one of the ideal structural types in long-span bridges of high-speed railways because of its big rigidity,good integrity, low noise,excellent dynamic behavior and so on.However,the mechanical behavior of bottom chord members(tied-girders)and deck system is complex in monolithic deck.Three-truss(arch)structure is a good choice for the four-line railway bridge.Deck load allocates among three trusses(arches)more complexly in three-truss(arch)bridges than in two-truss(arch)bridges.In this dissertation,the mechanical characteristics and the calculating theory of three-truss plate-truss composite bridges with ballast monolithic deck were studied on the background of Nanjing Dashengguan Yangtse River Bridge of Beijing-Shanghai high-speed railway which is under constructing.The main innovative achievements are as following:1.A method named transverse frame method for calculating the transverse allocation of deck load among three trusses(arches)was proposed.The influence factors,such as transverse bracing's stiffness, truss's stiffness and deck system's stiffness and so on,were studied. Based on energy principles,the formula of transverse allocation of deck load was deduced.And the reasonable stiffness of transverse bracing was advised.It is shown in the results that the value of the transverse allocation ratio among three trusses(arches)reaches 1:1:1 near the middle of the span where the load allocated to middle truss(arch)is a little more than edge truss(arch),and 1:3:1 near the support where the load allocated to middle truss(arch)is more than edge truss(arch)under the transverse uniformly distributed deck load when the stiffness of each truss(arch)is close.But the deck load near the support,most of which transfers to the support directly,impacts little on the deformation of the main truss(arch). The conclusion is proved by the results of model tests and 3D FEM.2.The problems,such as the bending effects of bottom chord member (tied-girder)in monolithic deck and the transferring force ratio of the transversal girder in the panel and the transversal girder in the joint and so on,were studied and the influence factors were discussed.The formula of the transferring force ratio was given.And the results calculated by the formula are in good agreement with the results of model tests and 3D FEM.3.Aiming at the Structural characteristics of ballast monolithic deck,a Space layered plate-girder element(LPGE for short),which includes multilayer plates,a longitudinal girder(rib)and a transverse girder(rib), was put forward and element rigidity matrix was deduced.The formulas of equivalent nodal force were given.The displacement field can be specified by an independent variation of the displacements and the angles. LPGE is a compatible element and takes shear deformation into account. With second development of ANSYS,LPGE was appended to ANSYS and the programme(LPGEP)was compiled.4.The truss model test and the arch model test had been completed and the FEM analyses were done.The conclusion is that the results of LPGEP agree with the results of Model test.Importantly,it's very convenient to set up FEM with LPGE which combines different materials Multilayer plates,a longitudinal girder(rib)and a transverse girder(rib)as a compatible element to make plate and plate,plate and girder(rib)deform compatibly at the junction between the surface.And the FEM has fewer freedoms and can reduce the computation time.5.LPGEP was applied to calculate Nanjing Dashengguan Yangtse River Bridge of Beijing-Shanghai high speed railway which is under building. And the mechanical characteristics and the calculating theory of three-truss plate-truss composite bridges with ballast monolithic deck were studied.Some valuable conclusions were obtained to provide a reference for designers.