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Long slender elastic structures, such as railroad tracks, pipelines, and pavements, may experience buckling owing to axial compressive forces developed in them as a result of thermal or other effects, and in many cases these structures can be simplified as a beam on an elastic foundation. This paper presents an investigation of the critical buckling and postbuckling of such an elastic structure on a nonlinear foundation that has softening and restabilizing effects. The method of minimization of the total potential energy of the beam-foundation system is invoked to develop a differential equation of equilibrium and a differential equation of critical buckling (or bifurcation) of the beam. The analysis shows that critical buckling may be in a symmetric or in an antisymmetric mode, depending on the length of the beam, and when the length is extremely large, the two buckling modes are indistinguishable. The equations of the postbuckling equilibrium of the beam are highly nonlinear. To elucidate the response of the beam, a multiple-scale perturbation technique as used in modal analysis and a numerical solution based on a shooting technique are developed. It is shown that the postbuckling equilibrium of the beam has two stages after its critical buckling: a postbuckling localization stage that is unstable, and a subsequent postbuckling snaking stage characterized by a zigzag of the equilibrium configuration, and this snaking stage is dependent on the relative effects of the softening and restabilizing parameters. Comparisons of the perturbation solutions with the results of the numerical formulation show that the former semianalytical technique is accurate in the initial stages of postbuckling during which localization develops, but not in the subsequent snaking stage. The effect of the foundation parameters is also investigated in the paper. [ABSTRACT FROM AUTHOR]

A reliable and robust shear connection is required in the cast in situ portion of a segmental composite bridge girder to carry the shear force between the steel and concrete.When the shear connectors are arranged with close spacing in order to satisfy design requirements, group effects will have a significant influence on the structural behavior of the shear connection. This paper presents an investigation of the static behavior of group-arranged stud-bolt hybrid shear connection in long-span segmental bridges, with the bolt shear connectors as the threaded outstands of the high-strength bolts used in the splice connections needed in segmental construction. Seven specimens with different arrangements of the studs and high-strength bolts were fabricated and tested. The failure modes, load-slip relationships, and shear strength were obtained and discussed. The results showed that the bolts could increase the shear strength of the connection and that the embedded length of the bolts had a marked effect on the structural response when the bolt diameter was large. In deference to stud connectors, the failure modes of the specimens with bolts were characterized by crushing the concrete at the ultimate-strength limit state. [ABSTRACT FROM AUTHOR]

Perfobond rib shear connectors are used widely in bridge engineering, and expressions for their shear capacity can be found in various codes and standards. Empirical expressions available for the strength of perfobond rib shear connectors have been obtained mostly by the numerical regression analysis of push-out test results. Because of discrepancies in both specimen dimensions and the test procedures, the various test results do not agree with each other, and the empirical strength predictions so derived are quite different. To resolve this discrepancy, the authors investigated the modes of failure of perfobond shear connections using a novel push-out test procedure. The mechanisms for the resistance to load of perfobond rib shear connectors were analyzed, and the effects of the concrete and transverse reinforcement on the shear resistance were investigated. An empirical expression for the shear strength of perfobond rib shear connectors with transverse reinforcement is proposed here. The calculated results agree well with test results reported elsewhere, which indicates that the new empirical expression has adequate accuracy and can be used in engineering design. [ABSTRACT FROM AUTHOR]

The application of prestress is a very effective way to prevent the cracking of the concrete slab in the negative-moment region of continuous composite girders, and using a prefabricated prestressed-concrete slab in this region is an easier option than posttensioning. To elucidate the structural response of a continuous composite box girder with a prefabricated prestressed-concrete slab, two large, 18-m-long specimens were fabricated and tested under short-term loading, and the results are reported in this paper. One, a control specimen, was a conventional composite girder with its concrete slab cast in situ, whereas the other was a composite box girder with a prefabricated prestressed-concrete slab in the negative-moment region. The relative slip between the steel girder and the concrete slab; the load-deflection response; the distribution of strain in the steel girder, reinforcement, and concrete slab; as well as the crack widths in the concrete slab were measured during the tests. The paper shows that, although the ultimate strengths of the two specimens are almost the same, the initial cracking load and serviceability limit state load of the specimen with a prefabricated prestressed-concrete slab are 3.16 and 2.61 times, respectively, those of the specimen with a conventional concrete slab. It is also shown that simple linear-elastic analysis leads to a close prediction of the load for initial cracking. By comparison, a continuous composite bridge beam with a prefabricated prestressed slab over its internal support is stiffer and less likely to experience the ingress of corrosive materials than one with a conventional RC slab is. [ABSTRACT FROM AUTHOR]