Mal-function and damages of expansion joints not only affects the smooth traveling of vehicles on the bridge, but are also sources of inconvenient noises and vibrations. In addition, impact due to live loads may cause damages to the girder end structures, being worsened in case a smooth transition between adjacent girders is not assured. The present study performed a series of field and loading tests to investigate the accoustic and vibrational structural effects of vehicles traveling on the surface of steel finger expansion joints. Effects of vertical misalignment between the plates of the joint fingers were investigated and a diagnosis method based on acoustic evaluation is also proposed.
It is well known that fatigue strength and fatigue crack propagation rates of welded joints do not depend on the static strength of steel. FCA (Fatigue Crack Arresting) steel has been newly developed as steel with high resistance against fatigue crack propagation. Its high fatigue resistance has already been confirmed by fatigue crack propagation tests on the steel plates and fatigue tests on structural models simulating ship's shell structures. In this study, fatigue crack propagation rates and fatigue strength of FCA steel are examined using steel plate with TIG-dressing which induces tensile residual stresses and those results are compared with ones of conventional steel.
This paper presents effects of parameters, which are the input earthquake direction, hysteresis characteristics of steel members, actual strength of steel material, the composite action of floor slab, and the additional axial force of columns, on plastic deformation of steel members. Seismic responses of steel structures against bi-directional earthquake are obtained by using the proposed plane-frame analytical model. As a result, the following conclusions are reached; (1) strength of columns are larger than that of beams and panel in order to contain damage of the columns, (2) damage of the steel members with the actual strength decreases from the nominal strength, and (3) effects of the composite action of floor slab and the additional axial force on damage of steel members are quite little for object frames.
The purpose of this research is to examine fatigue strength of under-matched welded joints applied to load-carrying cruciform fillet welded joints made of high strength steel. First, in order to grasp influences of the magnitude of stress concentration on differences between fatigue strength of under-matched welded joints and over-matched welded joints, fatigue tests under axial loading and bending were carried out. Next, fatigue test data obtained this research were compared with results reported in previous research. Based on the comparisons, fatigue strength of under-matched welded joints is similar to that of over-matched welded joints not depending on the magnitude of stress concentration.
This study examined the effects of corroding process under loading on the ultimate strength of the plate girder. In order to simulate the behavior of the corroded girder under loading, a series of the elastic-plastic large deformation analyses was carried out by using the FEM program, which had developed based on the shell element, with considering the stress redistribution due to loss of thickness. As results, the effects of corroding process under bending and shearing on the ultimate strength and the deformation of the plate girder were small. Therefore, it was concluded that the ultimate strength and the deformation could be predicted without monitoring the change of thickness in the corroding process.
Vertical stiffeners are connected to deck plates to prevent out-plane-buckling of webs in steel girder bridges with steel plate decks. When wheel loads are located close to stiffeners, high stress concentration is prone to occur at the edge of the stiffener because the stiffener restricts deformation of the deck plate. In recent years, many cracks have been observed there. Therefore, a method for reinforcing and/or repairing the connection between the deck plate and the stiffener is essential. In this paper, the method is proposed to reinforce the connection with L-shaped steel plates which are pushed up to the deck plate by a small hydraulic jack. An effect of the method has been confirmed through fatigue tests.
Laser peening is an innovative surface enhancement technology to introduce a compressive residual stress on metallic materials. In this paper, residual stress, Vickers hardness and surface profile of four grades of structural steel were examined to clarify the applicability of laser peening. The results obtained are summarized as follows. 1) Laser peening conditions, which can generate large and deep compressive residual stress, were established for 400 to 780MPa grade steels. 2) Compressive residual stress becomes deeper with the increase of material strength, whereas the hardened layer becomes shallower in the same laser peening conditions. 3) The surface got dented by 10 to 30μm from the initial surface and the surface roughness (Ra) became 3.5 to 13μm after laser peening.
The JSSC Fatigue Design Recommendations specify fatigue design curves on the basis of a lot of fatigue test data for various types of welded joints. These data were obtained earlier than 20 years ago. In the last 20 years, common welding method has been changed from shielded metal arc welding to gas metal arc welding. The difference may mean that the existing fatigue strength categories cannot be applicable to present welded joints. A new fatigue test database was constructed including data after the last issue. Through the database, we have clarified influences of steel grade, welding materials, plate thickness and post weld treatment on the fatigue strength. Based on these results, the JSSC Recommendations have been revised.