The main girders in a steel I girder bridge are connected with the slab, sway bracings and cross frames behaving together as a system. These members do not behave independently but behave as a structural system and have high redundancy. In this study, the effect of corrosion damage on load carrying capacity was evaluated using an FEM model of the bridge system assuming one or a few girders are corroded. As a result, the effect of load carrying capacity to the different corrosion damage were clarified quantitatively and an evaluation index for the load carrying capacity has been found.
Fatigue cracks are initiated due to stress concentration and tensile residual stress existing at crack initiation point, and reducing these factors leads to enhanced fatigue strength of the welded joints. The induction heating (IH) is effective to introduce compressive residual stress for welded joints, but there are some problems toward the practical use in fabrication plants or repairing sites of steel bridges. In this study, a newly developed IH application with better workability was applied to the out-of-plane welded joints specimen, and fatigue tests and FE analyses on the specimen were conducted to investigate the improving effect related with the heating conditions and the residual stresses. The results showed that the fatigue strength of the specimen was improved by 2 grades due to the change in the residual stresses.
Effective bridge management can be achieved by grasping salt damage locally and taking a maintenance strategy according to the corrosive environment classification of the area. The purpose of this study is to understand the corrosive environment by region, and to clarify the corrosion rate by region by exposure tests using monitoring steel plates. Then, by regression analysis of the corrosion and their causes, we clarify the tendency of the corrosive environment and the amount of adhering salt, and propose a method for estimating the corrosive environment based on the river distance.
The authors proposed a joint in which vertical double-rib plates are welded on the side of the steel pipe pile and the reinforcing bars connected with their edges. This method had increased the bending moment resistance of the pile head joints with less reinforcing bars. The purpose of this study is to present the calculation formula of the bending moment resistance-rotation angle relationship of the pile head joints. The bending moment resistance of the pile head joints is assumed to be through the summation of resistance of a circular reinforced concrete column with effective diameter and the bearing resistance of the embedded pile head.
Corrosion protection of steel structures is a key for a long-term use of them and blast cleaning is generally used as surface preparation in recoating a deteriorated paint coating of steel bridges. However, when the blast cleaning is not available due to environmental limitations and any other reason, alternative surface preparation and corrosion protection technique are to be adopted. Then, focused on in this study is a new corrosion protection technique using thermal Al-Mg alloy sprayed coating by using grinding treatment together with high permeable sealing agent, not by the blast cleaning. Durability of the technique is verified through adhesion test and accelerated corrosion test up to 1,200 cycles.
This paper focuses on the residual performance of high-strength bolt friction joints, a typical joining method for steel bridges. In this study, the residual axial forces of high-strength hexagonal bolt friction joints were evaluated using steel roadway plate girder bridges that had been removed after more than 30 years of service. As a result of the investigation, it was confirmed that the residual axial forces were sufficiently higher than the design values in all except in a few cases, and that the joints of steel roadway bridges that had been in service for 30 years had sufficient residual axial forces. Additionally, it was confirmed that the residual axial force of box girder tended to be lower than that of plate girder bridges.
For investigating riveting methods by using high-frequency induction heating (IH), a series of experiment was conducted. In the proposed methods, rivets were heated by IH before or after inserting into holes in steel plates. The temperature required for riveting could be achieved by the proposed methods. However, the temperatures were relatively low when the rivets were heated after inserting into holes in steel plates. Therefore, phase transformation and work hardening did not proceed sufficiently in these heating methods. Although the shear strengths of rivets heated by these methods were lower by 20 % than that of conventional coke heating method, the shear capacity based on yield stress was satisfied.
Fatigue damage cases in steel I-girder highway bridges have been reported mostly at main girders-cross member connection. These fatigue cracks are known as displacement-induced fatigue, and there are many uncertainties in crack propagations. In order to take appropriate action to damaged bridges, it is important to evaluate the cause and the occurrence tendency of the fatigue cracks efficiently. In this paper, for the purpose of identifying fatigue-damaged bridges with high priority for countermeasures, the relationship between the crack conditions and the structural/in-service conditions in existing bridges were investigated on the basis of periodic bridge inspection data.
Non-structural elements such as folded roof plates are usually set up on the upper flange of main beams. Previous study shown that non-structural elements have bracing effect to lateral buckling of H-shaped beams as continuous braces. In the FEM analysis, folded roof plates are replaced with lateral and rotational springs in the FEM model that are fixed on the upper flanges of the H-shaped beams. However, in real case the joint between H-shaped beams and folded roof plates are using tight frames and bolts. When the torsional moment of H-shaped beam by lateral buckling occurs, the joint parts and the bolt holes will be broken easily so that the rotational bracing stiffness cannot be exerted. In this study, torsion experiments with different kinds of joints are used to find out the rotational bracing stiffness and the deformation mechanism of folded roof plates to be used as continuous braces.
In this study, fatigue crack growth was retarded by injecting corrosion accelerator, Nitric acid (HNO3), into the crack to induce corrosion. The presence of the corrosion products is expected to reduce the crack opening width and act as a wedge to control the crack closure. Fatigue tests were carried out on the compact tension (CT) specimens. The test revealed that the corrosion process due to HNO3 injection ends after 24 hours. Then, the reduction in crack opening displacement range can be observed. Retardation in the crack growth was observed regardless of the load range and the effective stress intensity factor range (ΔKeff) at injection. Meanwhile, the retardation level tends to be affected by the ΔKeff and crack length at injection.