Efficient prestressed concrete-steel composite girder for medium-span bridges.

摘要

In this dissertation, a new Prestressed Concrete-Steel Composite (PCSC) girder system is introduced. The PCSC girder is composed of a lightweight W-shape steel section with shear studs on its top and bottom flanges to achieve composite action with the pretensioned concrete bottom flange and the cast-in-place concrete deck. The PCSC girder is lightweight, economical, durable and easy to fabricate. To prove its feasibility and potential, this study is to investigate design and fabrication issues associated with the PCSC girder. A service design procedure is proposed using Age-adjusted Elasticity Modulus Method (AEMM) to evaluate the time-dependent stresses and strains in the PCSC girder due to creep and shrinkage effects of concrete and relaxation of strands. The strength design method, as a rational approach replacing the current working stress method, is proposed for the design of PCSC girders at prestress release, to assist engineers to accomplish economic design and production of PCSC girders. Finite Element Analysis (FEA) of PCSC girders at prestress release is performed to understand stress distributions and the transfer of the prestressing force from the strands to the composite section and investigate the influence of stud distribution on the stresses in the concrete bottom flange. A PCSC girder specimen was successfully fabricated and instrumented in the structural lab following the proposed fabrication procedure. Design using AEMM and FEA were validated against the strain profiles at different sections, concrete surface strains and camber at mid-span. Flexural and shear tests were conducted to evaluate the flexural and shear capacities of the fabricated specimen. The crack moment, ultimate moment and ultimate shear obtained in tests satisfy the demand of bridge girders and well predicted using design calculations.