Shun-ichi Nakamura

New technologies of steel/concrete composite bridges

Abstract Steel plates have high tensile strength but are relatively vulnerable against buckling caused by compressive forces. However, when steel plates are combined with concrete, the resistance against buckling increases and heavy stiffeners are not necessary, which makes steel bridges economical and competitive against concrete bridges. New structural forms of steel/concrete composite bridges have been actively sought and developed in Japan and several actual bridge projects have been presented in this paper. New ideas for the future steel/concrete composite bridges utilizing concrete filled steel girders are also introduced and proved to be feasible and economical by analyses, experiments and trial designs.

Experimental Study on Fatigue Strength of Corroded Bridge Wires

AbstractFatigue tests were conducted for corroded galvanized steel wires on three corrosion levels, showing that fatigue strength of corroded wires lowers as corrosion progresses. Corrosion pits were measured on the corroded specimens, showing severer corrosion produced deeper pits in more condensed areas. Fatigue tests were then conducted for wire specimens with artificial pits whose sizes were decided by the measured corrosion pit data. Three different pit shapes were assumed: round, triangle, and triangle with a notch. The wire specimens with round pits did not break until 1 million cycles in the stress range of 400 MPa. The fatigue strength of wires with the triangular pit was lower than that with a round shape. Triangular pit specimens broke at fewer cycles for shorter pit length. The fatigue strength of wires with a notched triangle further decreased, and critical cycles did not depend on pit length. As the S-N relation of the wire specimens with triangular pits and notched triangular pits has a sim...

Bending and shear strengths of partially encased composite I-girders

Abstract This paper has proposed the use of partially encased composite I-girders as bridge girders. Reinforcing bars were welded to the upper and lower flanges and concrete was poured into the area surrounded by the flanges and web. Bending and shear tests were performed, showing that the bending strength of the partially encased girder model is 2.08 times higher and the shear strength is 2.98 times higher than the conventional steel I-girder model. In the model where the reinforcing bars were not welded to the flanges, the bending strength slightly decreases but it is still 1.75 times higher than the steel I-girder model. When the buckled steel I-girder model is encased with concrete, its bending strength is greatly improved and rose to 1.89 times of that of the non-buckled steel I-girder model. Analytical methods were proposed to calculate the bending and shear strength of the encased composite girders and are validated by the experimental data.

CORROSION MECHANISM AND PROTECTION METHODS FOR SUSPENSION BRIDGE CABLES

The main cables of several Japanese suspension bridges were found to be corroded. To determine the corrosion mechanism, the environments inside the cables were investigated, and corrosion simulation tests of galvanised wires were carried out. These studies showed that the corrosion environment depends on the position within the cable, with the side parts being most susceptible to corrosion. A new anti-corrosion system was developed using S-shaped wrapping wires and improved pastes to overcome this problem. Cables protected by this system were compared in long-term exposure tests with cables protected by conventional systems, and showed improved anti-corrosion performance. Another new method, namely to pass dry air through the cables, is proposed. Preliminary tests showed this system to be promising in terms of improving the anti-corrosion properties of the cables.

NEW STRUCTURAL FORMS FOR STEEL/CONCRETE COMPOSITE BRIDGES

A design strategy aimed at making steel bridges more economical is proposed, which combines steel with concrete and avoids welding during fabrication. Concrete-filled steel girders have high strength and ductility and would provide a rational and economical solution for bridges. Steel mill products or cold-forming work during the fabrication process can substantially reduce the amount of welding and should be used more for the main girders. Five composite bridges have been developed using steel pipes or cold-formed steel girders. The structural behaviour and strength of these bridges have been studied, and their forms have been used in designs of target projects. These studies show that the construction of these composite bridges is feasible and economical.

MECHANICAL PROPERTIES AND REMAINING STRENGTH OF CORRODED BRIDGE WIRES

Corroded galvanized steel wires at different corrosion levels were produced, and their mechanical properties and remaining strength were investigated. It was found that the actual tensile strength of corroded wires does not decrease, whereas the elongation, torsional and fatigue strength decrease sharply. The amount of hydrogen absorbed in the corroded wires was measured, showing that it did not reach the level to cause hydrogen embrittlement. The surface of corroded wires is uneven and this s urface roughness seems to decrease ductility of corroded wires. Broken wires cut from an old suspension bridge were also investigated. The fracture surface is similar to that caused by corrosion fatigue rather than by hydrogen embrittlement. It is estimated that the wires were fractured by the mixed effects of corrosion, cyclic stresses, high residual stresses, hydrogen and fretting.

Static and Aero-Dynamic Studies on Cable-Stayed Bridges using Steel Pipe-Girders

Two types of new cable-supported bridges using steel pipe-girders and steel orthotropic decks have been proposed in this paper: the two-pipe-girder bridge with two cable planes and the three-pipe-girder bridge with one cable plane. The cable-stayed bridges with a main span of 500 m were designed for these new bridge systems and validated to be feasible by static analyses. Wind tunnel tests were conducted in order to investigate the aerodynamic behaviour of these bridges. For the two-pipe-girder bridge models torsional flutter occurred at a wind speed – over 75,0 m/s for the attack angle of 0o and +3o. In the three-pipe-girder bridge models torsional flutter occurred at a wind speed of over 115 m/s and the three-pipe-girder bridges showed superb aero-dynamic stability. Aesthetics of these new bridges were also studied by computer graphics and wood models, which showed that the new bridges are not only structurally rational but also – attractive, impressive and in harmony with the surrounding environments.

Anti-corrosion performance of bridge strands consisting of steel wires galvanised with zinc–aluminium alloy

Strands consisting of 19 parallel steel wires galvanised with zinc (Zn, 90%) and aluminium (Al, 10%) alloy were produced and accelerated corrosion tests were conducted, and the anti-corrosion performance was compared with the conventional strands galvanised with Zn. The strands were placed at a relative humidity (RH) of 60%, RH of 100% and the wet condition in the thermo-hygrostat at 40°C for 150 days. The mass loss due to corrosion of the strands galvanised with Zn–Al at an RH of 60% and 100% was small, and the strands had good corrosion resistance. The corroded mass of the strands at the wet condition was 15 times larger than that at RH of 100%. The strands galvanised with Zn–Al had lesser corrosion than those galvanised with Zn under the three environmental conditions. Corroded mass was larger in the surface wire, the inside wire and the centre wire in this order. The cross-sections of corroded strands were investigated by using a microscope and an electron probe micro-analyser showing that the corrosion product of Zn was porous and coarse. By contrast, the corrosion product of Zn–Al alloy was dense and hard to exfoliate from the steel layer. This difference made Zn–Al galvanised wire strands superior to Zn galvanised wire strands.

DURABILITY OF TITANIUM-CLAD STEEL PLATES USED AS AN ANTI-CORROSION SYSTEM

A new anti-corrosion system that uses titanium-clad steel plates has been developed and applied to the splash and tidal zones of the steel piers on the Trans-Tokyo Bay Bridge. The 4-mm-thick steel plates, clad with 1-mm-thick titanium, are welded to the steel piers. To investigate the durability of this method, steel pipes 60 cm in diameter were protected by this method, exposed to a marine environment, and monitored for five years. No corrosion of the titanium-clad steel plate was observed after five years, showing that the method has sufficient long-term durability.

Steel Concrete Composite Structures : Part II: Introduction

This paper deals with prefabricated composite bridges with full-depth precast decks. For steel–concrete composite bridges, a new shear connection and its design provisions were suggested by extensive experiments and finite element (FE) analyses. The shear connection for precast decks was investigated to consider the effects of bedding layer, filling material in shear pockets and group arrangement. For the integrity of the precast decks, longitudinal prestressing was introduced and design guidelines for the magnitude of prestress were proposed. It is necessary to keep the joints compressive during the service life of the bridge to prevent cracking and leakage at the joints. Bonding strength was neglected in the design. In order to take full advantage of precast slabs, the concept of incremental prestressing was adopted for continuous prestressed concrete (PSC) girders. Based on the experimental research on joints and connections, several model tests were performed to verify the suggested design guidelines. There are several applications using precast decks not only for steel bridges and but also for concrete ones. Among them, design characteristics and enhanced details for construction were introduced for two bridges.