Mechanical behavior of girders with corrugated webs: from quasi-static response to fatigue failure

Abstract

This thesis is devoted to study the mechanical behavior of girders with corrugated steelwebs, subjected to static loads as well as fatigue loads. The corrugated steel web is akind of bridge web element of high performance, low self-weight and aesthetic appearance. It has been used in a particular type of prefabricated composite box girderto increase the productivity of construction, in terms of speed and quality. However,previous research work could not provide sufficient knowledge of the mechanical behavior to promote the mass application. The reasons lie in the unique flange configuration and a poor collection of analyses performed on large-scale specimens whose web geometries and web inclined angles are consistent to those of actual bridges.Also, for a general corrugated steel web girder (CSWG), the phenomenon that its shear strength is dominated by the shear buckling of the webs has not been theoretically explained, and research work on the post-buckling shear behavior is in lack. This raises the interest of civil engineers to further study the responses and failure mechanisms of CSWGs under static and fatigue loads. In the present thesis, the topic is considered by structural experiments, numerical simulations and theoretical analyses.The main body of the thesis consists four parts. The first part emphasizes on flexural behavior of the particular type of composite box girder with corrugated steel webs. Afull-scale girder with the span of 32 m is tested, and then the girder is theoretically analyzed and compared to two hypothetical reference girders, gaining further insight into the flexural failure mechanism, the capacity and the contributions of various elements.The second part of the thesis refers to shear behavior of the particular type of composite box girder with corrugated steel webs. A large-scale I-girder specimen with inclined corrugated steel webs is tested under three-point loading, which is also simulated by nonlinear finite element analysis. The corrugated steel web is proved to be the main shear element, providing majority of the shear resistance and governing the shear strength. Stress states in the web until buckling and influence of the initial geometric imperfections on the development of shear buckling are also discussed.The third part extends the research to general CSWGs, dealing with stress states and shear failure mechanisms from the pre-buckling stage to the ultimate failure. Stress states in girders with corrugated steel webs under shear is theoretically analyzed by anapproach adopting the rotated field method, which is verified by experimental data and helps to explain the phenomenon that shear strength of a CSWG is determined by shearbuckling of the webs. Then, the post-buckling shear performance and the ultimate failure mechanisms of CSWGs are investigated by nonlinear finite element analyses.The last part discusses fatigue performance of the particular type of composite boxgirder with corrugated steel webs as fatigue damage is inevitable when structures are subjected to heavy traffic loads. A large-scale I-girder specimen with inclinedcorrugated webs is tested under four-point loading, given the scant fatigue test data forthis kind of girder and the inadequate validation of relevant fatigue detail category (FAT). The test results reveal the fatigue sensitive details, development of the critical cracks and the fatigue failure criterion. With further parametric numerical analysis,influence of corrugated web parameters on fatigue sensitive details and fatigue life isdetermined.The following conclusions are drawn from the research:1) For a general corrugated steel web girder: The assumption that the flanges provide almost all bending resistance is approved. The other assumption that the web bears all shear force is inconsistent with reality. It is possible to analyze stress states of a CSWG under shear by the approach adopting the rotated stress field method, following the stages of the prebucklingstage, the buckling stage and the post-buckling stage. Though the shear strength is dominated by shear buckling of the web, thegirder has a certain residual resistance after buckling. The ultimate failuremechanism is governed by the positions of the plastic hinges in the flanges,varying with its flange bending stiffness and web height/weight ratio. Corrugation geometric parameters of the web, especially the corrugationangle, θ, and the bending radius, R, affect the fatigue performance.2) For a particular composite box girder with corrugated steel webs: The flexural performance is mainly determined by the bottom flange. Though the capacities could meet the design requirements, the bottom flange should be further optimized in accordance with the contributions of various elements. The shear performance is closely related to the elastic--plastic interactiveshear buckling in the web and could meet the design requirements. The critical fatigue crack initiates at S-point (weld toe of the web-to-flangewelded detail) in the combined bending-shear region, and the fatigue failure criterion is defined as the critical crack reaches 1.6 times of the flange plate thickness in length or propagates through flange plate thickness. The fatigue sensitive detail (web-to-flange welded detail under four-point bending) can be defined as FAT 90 for the nominal stress approach, FAT 120 for the structural hot spot stress approach and FAT 225 for the effective notch stressapproach.The present thesis is beneficial to understand the mechanical behaviors of CSWGs,which helps to lay a solid foundation for the widely application of the particular type of composite box girder with corrugated steel webs.