High performance steel girders with tubular flanges.

摘要

High performance steels (HPS) are providing new opportunities to design cost-effective steel bridges that take advantage of the high strength, corrosion resistance, fracture toughness, and weldability of HPS. Under certain conditions, however, HPS bridge girder designs are controlled by design limits that are not influenced by steel strength and the use of HPS may be uneconomical. To overcome some of these design limits, I-shaped girders with tubular flanges have been proposed. This dissertation focuses on concrete-filled tubular flange girders (CFTFGs) in positive bending regions where the concrete-filled tube is the compression flange.; Design criteria for CFTFGs were proposed and an initial design study that shows the advantages of these girders compared to conventional I-girders was conducted. The CFTFGs were assumed to be either fully-composite with the deck or non-composite. The conventional I-girders were assumed to be fully-composite with the deck. The designs were minimum steel weight designs. The results from the initial design study indicate that composite CFTFGs are significantly lighter than composite conventional I-girders, even when a large diaphragm spacing is used.; Finite element (FE) models of CFTFGs were developed. Using these models, a parametric study was conducted to investigate the influence of girder geometry and material strength on the flexural strength. A single unbraced length was considered for the parametric study based on the assumption that at locations where girders are braced by diaphragms, the girders are perfectly braced laterally and torsionally. Design flexural strength formulas for construction and service conditions were developed based on the results of the parametric study.; A parametric study of FE models of CFTFGs braced torsionally without lateral bracing was conducted. The influence of initial geometric imperfections and torsional brace stiffness on the flexural strength of torsionally braced CFTFGs was investigated. Design flexural strength formulas for torsionally braced CFTFGs were developed based on the results of the parametric study.; An experimental study of non-composite CFTFGs, showing the advantages of CFTFGs and illustrating their ability to carry factored design loads under construction and service conditions, was conducted. The CFTFG test specimens supported loads exceeding their design loads, with limit states occurring as expected, and without unexpected vertical deflections or lateral displacements. Comparisons of experimental and FE analysis results indicate that the detailed behavior of CFTFGs can be accurately estimated using FE models.; The following conclusions were drawn. CFTFG bridges require less steel weight, and less fabrication and erection effort than conventional I-girder bridges. The proposed design flexural strength formulas considering torsional brace stiffness are recommended for the flexural strength of CFTFGs with torsional bracing provided by typical diaphragms. CFTFGs should be designed to have at least three evenly spaced intermediate transverse stiffeners to control cross-section distortion and thereby to maintain the lateral torsional buckling (LTB) strength. The structural behavior of CFTFGs, including the bending stiffness, neutral axis location, yield moment, and cross-section flexural capacity, can be estimated from cross-section analysis.