This paper deals with influence of slenderness ratio about a buckling restrained brace (BRB) experimentally and shows a design method of BRB of large slenderness ratio based on the test results. It is found that a residual deformation accumulate by repetition loading in a BRB of large slenderness ratio. As a result, we suggest the equation to estimate the residual deformation and show that the proposed design method should avoid global buckling.
Fatigue cracks were observed recently in lighting poles or overhead sign structures installed on elevated highway bridges. The fatigue cracks normally occurred at weld toes of ribs, which stiffen joints between base plate and tubular section. The fatigue cracks that occurred in actual structures were once repaired by two methods. One was to glue carbon fiber reinforced polymer (CFRP) sheets on and the other was to weld additional ribs for reinforcement. The structures were removed after two years, and the fatigue cracks were inspected to evaluate the effectiveness of the two retrofit measures. Then, static and fatigue tests were carried out on these structures to observe fatigue crack propagation life and to compare those without retrofit measure. Reduction of stress due to the retrofit measures was further confirmed by FEM stress analysis.
The effect of transverse in- plane compressive stress on the buckling strength of wide steel decks in bridges has to be considered in their design as the width of the steel deck becomes larger. Moreover, not only biaxial in-plane stresses but also wheel live loading should be considered in their design against the buckling strength of wide steel decks. However, there are no specifications for their design. This paper deals with the ultimate strength and its interaction curves of stiffened plates subjected to the biaxial in-plane compressive stresses and wheel loading for the purpose of providing reference data for developing an appropriate design method against the buckling of these wide steel decks.
An analytical method is proposed to find structural shape and initial stress of tension structures. Nodal coordinates and cable tensions are sequentially modified from the initial ones by operation of constraint conditions with respect to stress so that the tensions in the whole structure can remain within the specified range. In order to examine validity of the solution and difficulty of construction, a structural model obtained from the present method was actually built and loading test was carried out.
Fatigue tests and stress analyses have been performed on specimens modeling web-gusset welded joints, which are as-welded and finished with burr-grinders or disc-grinders. Based on the above experimental and analytical results, fatigue strength category is proposed as to types of grinder and finishing method applied. Furthermore influences of weld toe radius, fillet radius, depth of ground area and plate thickness on stress concentration are made clear through three dimensional finite element stress analyses.
This paper showed the fatigue strength of base metal and butt welded joint of SUS304A austenitic stainless steel, especially fatigue strength of corroded welded joint by salty environment. The main results of fatigue tests of base metals and butt welded joints using SUS304A austenitic stainless steel were as follows; (1) m-values which were the exponent of slope of S-N curve of base metal were 5∼15. This values were higher than JSSC standard-value m=3, so that JSSC standards estimated danger-side for fatigue strength under 1×106 stress cycles. (2) The 2×106 fatigue strength of no-corroded butt welded specimens fell to about 70% fatigue strength of base metal's ones. (3) The 2×106 fatigue strength of corroded butt welded specimens fell to about 80% fatigue strength of no-corroded butt welded ones, and fell to about 55% of base metal's ones. And the 2×106 fatigue strength of corroded and acted bending-moment specimens fell to about 70% of corroded butt welded ones, about 55% of no-corroded butt welded ones, and about 50% of base metal's ones.
Design engineer must be attentive to structural landscape on the repair work of bridge. The purpose of this study is proposal for the new method of structural landscape design on the repair work of bridge. This method was made use of the change order of fractal dimension, that we calculated at fractal dimension on before and after the repair work of bridge. Generally reported, the fractal dimension was calculated by the software of image processor. However, we used only digital image and spreadsheet software. This paper was reported about that we applied in this method on existing highway bridge. We reported about influence on structure landscape of repair work on exsiting highway bridge.
This paper describes a fabrication and construction of extremely long buckling-restrained braces (BRBs) which have been developed for seismic retrofit of a steel bridge. In order to both improve constructional process and reduce deformation by its own weight, it is devised to lighten the BRB. And the parallel structural system of BRBs is applied for the purpose of safety under construction. The structural details are determined based on the knowledge obtained by tests and analysis. Furthermore, waterproofing for rust prevention, monitoring conditions inside of the BRB, and recording deformation of the BRB under large earthquake are proposed and applied to the system.
Many kinds of weathering steel were widely used in steel bridges. This report summarized the welding procedure tests using the weathering steel which we carried out in 2006-2007. In these welding tests, four kinds of weathering steel were employed to fabricate welded joint specimens, which were SMA570WQ, SMA570W-TMC and SMA570W-MODIFY(1%&3% Ni-advanced steel). In this report, the results of tensile strength and charpy absorbed energy were shown. Tensile strength exceeded 600N/mm2 in all tensile coupon specimens. Charpy absorbed energy of HAZ(heat affect zone) also exceeded 180J on an average in each type of steel. However, there were a few specimens beyond 100J in charpy absorbed energy of Depo(weld metal), regardless of welding wire and welding method. It was shown that the performance of welding materials did not reach the performance of steel.