STRENGTH RECOVERY OF STEEL BRIDGES WITH CORROSION NEAR BEARINGS

A lot of steel plate girder bridges were erected during the rapid growth in the 1960s in Japan. Currently, the condition of those aging bridges has become marked and a problem in society since over 50 years have passed. Particularly, the corrosion-induced deterioration and damage in railway steel plate girder bridges, which have an open deck, is becoming prominent. Despite that, the evaluations of residual strengths and the strengthening methods of corroded bridges are not always enough. Therefore, firstly, this paper shows analytical-based evaluation results that explain how the residual shear capacities of plate girders, having corrosion near bearings, depend on the condition of the corroded surface, such as a vertical stiffener or a web. The results show the fracture mode as buckling changes as well as the residual shear capacity, according to the degree and form of corrosion. Next, this study proposes a reliable reinforcement measure to recovery the shear capacity by applying said evaluation results and analytical models. Finally, the shear capacity could be improved tremendously by simple attachments as reinforced members.

Strengthening of Composite Castellated Beams Web with Corrugated Carbon Fiber Reinforced Polymer Struts

A total of seven simply supported composite specimens are tested under concentrated load at the mid-span of the beam to investigate the strength of specimens to resist the applied load if web buckling take place. A novel technique of using a corrugated CFRP struts to strengthen the web of the steel girder is presented in this study. This technique provides two layers of CFRP laminate which are from biaxial fabrics to provide a knitted material that can undergo the complex state of stress in the web. The studied specimens are divided into two groups in addition to the control specimen having the same length. There are three specimens in each group, these specimens have different castellation ratios of (33.3%, 43.3% and 54.3%), the first group is identical to the second one except that the second group was strengthened with the proposed CFRP corrugated struts while the first one kept unstrengthen as a reference. Composite beams have a vertical stiffener at the action area above the supports. The reference group showed decrease in deflection of (11.11, 20 and 26.67) % for (33.3, 43.3 and 54.3) castellation ratio while strengthened girders record (13.75, 6.11 and 13.93) % for the same opening depths, compared to the control specimen. In addition, CFRP struts decrease the web buckling from (1.6, 2.9 and 83.33) to (0.8, 0.4 and 0.3) mm for beams with castellation ratio of (33.3, 43.3 and 54.3) respectively.

Internal Force Transfer Mechanism and Bearing Capacity of Vertical Stiffener Joints in CFDST Structures

This paper firstly studied the internal force transfer mechanism of vertical stiffener joints in concrete-filled double steel tubular (CFDST) frame structures on the basis of finite element modeling (FEM). Analytical models of shear force and bending moment were established through the appropriate material constitutive equations and equilibrium theory. Then, the proposed models were used to predict and evaluate the shear and bending resistance of the vertical stiffener joint. Six joint specimens were tested to verify the rationality of the theoretical models, and the design suggestions for construction were subsequently discussed. The analysis indicated that the vertical stiffener together with the anchorage web played a dominated role in the internal force transfer mechanism. The computed bending resistance obtained by the tension model agreed well with the measured experimental data, and the shear resistance in the panel zone was sufficient to guarantee the ductile failure in the test. The vertical stiffener determined the plastic hinge so as to ensure the strong connection between the CFDST column and the steel beam. The ribbed anchorage web was an effective way of increasing the shear and bending resistance.

Shear Storage Capacity of Vertical Stiffener Joints between Concrete-Filled Double Steel Tubular Columns and Steel Beams

Based on the low cyclic loading test results of vertical stiffener joints between concrete-filled double steel tubular (CFDST) columns and steel beams, the shear transfer mechanism and shear resistance were analyzed in this paper. A conceptual model formulated was presented in terms of equilibrium and stress-strain relationships. The results calculated by the theoretical model and the available experimental data were compared, and then one new concept of shear storage coefficient was proposed for the determination of the shear storage capacity of the joint, which quantitatively explained the ductility failure progression of the joint specimens in the seismic performance test. It was concluded that the vertical stiffener joint had sufficient shear resistance, which met the seismic design principle of strong shear and weak bending. Results show that the ribbed joints have greater shear resistance than unribbed ones; lengthening the overhang of the vertical stiffener can both increase shear resistance and shear storage capacity of the joint; axial compression ratio can reduce the shear storage capacity. The paper also suggests that the joint design should ensure enough safety storage of shear resistance to improve the seismic performance.

EXPERIMENTAL STUDY ON H-SHAPED STEEL BEAM WITH CONTINUOUS BRACING SUBJECTED TO END MOMENT

As for H-shaped beams, concrete floor slab and purlins can be considered as bracing if they have enough stiffness and strength. There are many studies about bracing against lateral torsional buckling. However, the effect of lateral bracing cannot be properly considered in the practical design currently. The purpose of this study is to show the effect of the lateral bracing and vertical stiffener experimentally. The test on the lateral buckling of H-shaped steel beam with a steel plate which is a continuous bracing is carried out. Parameters are the position of bracing and presence or absence of vertical stiffener. The steel plate is welded on the compressive flange or the tensile flange. The vertical stiffener may be considered as the bracing for lateral buckling however the effects of them are not clear. The vertical stiffener is set at the position where the lateral deformation is assumed largest. The lateral buckling and local buckling occurs in the test specimens without bracing and with continuous bracing on the tensile flange. The maximum strength of the test specimen with a vertical stiffener is 5% smaller than that of the test specimen without a vertical stiffener. However, the strength degradation of the test specimen with a vertical stiffener is smaller and the load is 90 % more than the maximum load when the rotation angle is 0.07 rad.

FATIGUE BEHAVIOR AT THE UPPER END OF VERTICAL STIFFENERS CONNECTED WITH SWAY BRACINGS

Lots of fatigue crackings were reported at the upper end of vertical stiffeners connected to sway bracings in steel highway girder bridges. In this study, we investigate fatigue cracking behavior at the upper end of vertical stiffeners under RC slab, through fatigue tests using a large specimen with three main girders under alternative loading using two actuators. As a result, alternative loading can reproduce the alternative stress at the upper end of vertical stiffener in the middle girder when vehicles run on the driving lane and passing lane alternatively. Root cracks were initiated after 0.1 Mcycles loading and appeared on the bead surface when 0.6 Mcycles.