Masatsugu Nagai

Steel bridges: new steels and innovative erection methods

High performance steels for bridges can possess any of the following properties that have been improved relative to conventional steels: high strength with low yield-to-tensile strength ratio, high fracture toughness, longer fatigue life, high corrosion resistance, better weldability, easy fabrication and high Youngs modulus. The materials need to be economically competitive with other construction materials. Some of the recently developed steels used in bridges in Japan are: • new steel with constant material strength up to 100 mm plate thickness, • low yield steel with excellent ductility, • longitudinally profiled plate, • surface-treatment weathering steel, • reduced preheat-type high strength steel, and • titanium-clad steel plates. The second part of this article reviews current innovative erection methods for long-span cable-supported bridges. Emphasized in the erection methods are topics related to pilot rope erection with helicopter, lifting method in busy sea lanes with complex tidal currents, and catwalks without storm cable system. The review focuses mainly on developments in Japan. Finally, in conclusion, the review identifies future research needs.

Repairing Method for the Steel Members by CFRP Strand Sheets

The steel structure is corroded by various mechanisms, and thus its performance decreases. As a repairing method of the corroded steel member, a method in which carbon fiber sheets is bonded to the steel member with glue has been studied. In recent years, as more efficient repairing method using FRP materials, the strand sheet method which has high mass per unit area has been developed. The purpose of this study is to propose the repairing method for corroded steel member by using the strand sheets. In order to confirm a reinforcing effect, the tensile and flexural tests using steel plates and girders reinforced with strand sheets were performed. Test results showed effectiveness of strand sheets for the reinforcement of the steel members.

Design and Construction of a Cable-Trussed Girder Bridge

Takehana No. 3 Bridge is a cable-trussed girder bridge constructed on a highway route in Shikoku Island, Japan. This is the first application of a cable-trussed girder bridge to a highway bridge in Japan. The cable-trussed bridge (or reversed cable-stayed girder bridge) consists of relatively slender steel plate I-girders, a spatial frame-type post arranged beneath the girders at the middle of the span, and external cables anchored at the ends of the girders. The structural details, static and dynamic characteristics, and design and construction of the bridge are presented. In addition, the efficiency of this type of bridge is emphasized.

Proposal of Repair for Corroded Steel Members by Carbon Fiber Sheets

The authors propose the repair method for corroded steel members by carbon fiber sheets and its effectiveness is presented using at site measurement data. Based on our theoretical and experimental researches, the design and construction method are given. Working procedures or order of execution at the site is also explained. Finally, using at site measurement data of strain in steel members in a truss bridge in use, the effectiveness of our proposed repair method using carbon fiber sheets is emphasized.

Performance Evaluation of Hinges in Cantilever Steel Truss Bridges by Temperature Induced Strain

In this study, short-term monitoring using more than a hundred sensors was carried out for an existing long-span bridge, which has been administrated by a local government, with the aim of evaluating its present performance toward planning future maintenance strategy. The bridge studied is a cantilever (Gerber) steel through truss bridges that was completed and opened to the traffic in 1937. Consequently, the performance of Gerber hinges were evaluated, then information for prior repair was obtained.

Application of Structural Health Monitoring System for Long-span Cantilever Steel Truss Bridges

In this study, on-site loading test and short-term monitoring using more than a hundred sensors were carried out for an existing long-span bridge, which has been administrated by a local government, with the aim of evaluating its present performance toward planning future maintenance strategy. The bridge studied is a cantilever (Gerber) steel through truss bridges that was completed and opened to the traffic in 1937. As a result, the performance of Gerber hinges were evaluated, then information for prior repair was obtained. doi: 10.12783/SHM2015/34

Structural Health Monitoring of Existing Bridges by Vibration Measurement

This paper describes some studies relating to structural health monitoring techniques based on vibration measurement using laser Doppler vibrometer (LDV) and MEMS based sensor. 1) Compact and portable LDV measurement system was developed and applied to tensile force measurement of cables in a cable-stayed bridge. 2) The system combining LDV with Total Station was developed for the purpose of automated remote measurement for whole large bridge. 3) A new wireless LAN accelerometer based on MEMS technology was evaluated and applied to field measurement of bridges.

Effect of inelastic behavior of cables on ultimate behavior and strength of a 600-m steel cable-stayed bridge

Publisher Summary This chapter describes the effect of inelastic behavior of cables on ultimate behavior and strength of steel cable-stayed bridges based on elastoplastic finite-displacement analysis. Since the main girder is subjected to large compressive force, the plastic elongation of cables leads immediately to the buckling of the girder or collapse of the bridge. The load parameter at ultimate state of the bridge is estimated from a simple calculation. It is a ratio of the proof stress of the cable to maximum working stress in the cable. Because of calculation, it clears the effect of the safety factor or cable size on the ultimate behavior and strength and proposes a simple formula for estimating the load parameter at ultimate state.

ULTIMATE BEHAVIOR, STRENGTH AND STABILITY DESIGN OF GIRDERS IN CABLE-STAYED BRIDGES

本研究では, スパン600mの斜張橋を対象に, 弾塑性有限変位解析を用い, 桁高, 材質, 塔位置のケーブル吊間隔, 中央径間と側径間のスパン比が終局挙動や強度に与える影響を明らかにするとともに, 安定照査を不要とできる最小桁高選定に関する設計資料を提供している. 検討結果から, スパン600m程度までのマルチケーブルタイプ斜張橋であれば, 材質に関係なく桁高として2m以上を選べば全体の座屈安定性に関する照査は不要とできる可能性を示す.

EFFECT OF INELASTIC BEHAVIOR OF CABLES ON ULTIMATE BEHAVIOR AND STRENGTH OF CABLE-STAYED BRIDGES AND THE POSSIBILITY OF REDUCTION OF THE SAFETY FACTOR

本文ではケーブルの非弾性挙動を考慮した弾塑性有限変位解析を用い, ケーブルの安全率の設定が斜張橋の終局挙動, 強度に与える影響を明らかにする. 斜張僑では, 桁に大きな圧縮軸力が生じていることから, ケーフウレの塑性伸びにより終局状態となる. そのため, 終局強度はケーブルの塑性化または桁の降伏が生じるいずれか小さい方の荷重倍率で支配される. また, 面内耐力の観点からは, ケーブルの降伏点に対する安全率として現行の2.0から1.7へ低減できる可能性を示す.