多々羅大橋は中央支間890mで計画されており、これまでの約2倍の規模の斜張橋となるため、支間の増大に伴う構造特性の把握は重要な問題となった。そこで、多々羅大橋の支間890mが従来の斜張橋に比べてどのような位置づけにあるかを探るため、中央支間を500m、890m、1400m、2000mと変化したときの概略設計を行いその構造特性(作用応力、座屈特性、振動特性等)について解析を行った。本文は、この概略設計の解析結果を紹介するものである。

The Tatara Bridge will have a center span of 890m, which almost doubles the record of center span length of conventional cable-stayed bridges. This required a precise study on structural characteristics associated with elongation of the center span .To seek a viewpoint from which the center span of 890m of Tatara Bridge should be examined, the study included a series of comparative designs that clarified differences in structural characteristics (induced stresses, buckling properties, vibration characteristics, etc.) inhered to respective center span of 500m, 890m, 1400m, and 2000m. This paper introduces results and findings of this analytical study.

舞子トンネルの周辺は市街化された地域であり、施工にあたっては、周辺住宅環境への影響をできる限り少なくする必要がある。

そこで、トンネル掘削土の運搬用車両が市街地内を走行することを避けるため本坑着手に先立ち、掘削土搬出用の導坑を硬質花崗岩区間で施工している。

掘削には、従来の発破工法による施工が困難なため、TBM(Tunnel Boring Machineを採用している。

大きな障害も無く工事期内に完了することができたTBM掘削工事の施工実績を報告する。

Work execution of the Maiko Tunnel should be done with the least influence on the surrounding environment of highly - populated area.

To avoid trespassing of work vehicles into this residential area, a pilot tunnel was first bored to convey excavated rocks and soils over the section composed of hard granite.

Excavation was carried out by the tunnel Boring Machine (TBM) instead of the blasting method that might cause adverse effects on social environment.

This report outlines the work procedure of excavation by TBM for the Maiko Tunnel, which was finished in time, without any trouble.

吊橋のケーブルバンドは、ハンガーロープからの荷重をケーブルに伝達させるという重要な役割を担っており、バンドに所要のすべり安全率を確保するようにバンドボルトの軸力を管理する必要がある。瀬戸大橋の吊橋(下津井瀬戸大橋、南北備讃瀬戸大橋)では、平成元年から3年にかけて供用後始めてボルトの再締付を行った。

バンドボルトの軸力測定実績を整理するとともに、全バンドのボルト軸力及びすべり安全率を把握する方法として統計的推定法を提案した。また、超音波によるボルト軸力計測法の適用を検討し、来島大橋等の新規橋梁に有効であることを示した。

The cable clamp (band) plays an important role in carrying the load from the suspender rope to the main cable of suspension bridge; the bolt tension to fasten the cable clamps should be induced under control so that required friction force could be obtained between both surfaces of clamp and cable. Re-tightening of the cable clamp bolts for the suspension bridges in the Seto Ohashi (Shimotsui-seto, Minami and Kita Bisan-seto bridges) were carried out during 1989 - 1991 for the first time since its opening to the traffic.

This paper proposes a statistical estimation procedure for both to process selectively measured data on the cable clamp bolt tensions and to estimate, from such selected data, tensions of the rest bolts and safety factors for the friction force in the entire bolts. The paper also examines the ultrasonic measurement system for the bolt tension, and shows the system can effectively be applied to the quality control in construction for newly-erected bridges, such as the Kurushima Bridge.

長大斜張橋である多々羅大橋の耐荷力について、弾塑性有限変位解析を行った結果、塔近傍で桁が座屈して終局状態に至る結果を得た。これは、既存の斜張橋の終局状態が塔の座屈によるものと異なったモードであり、長大化したことによる変化と考えられる。問題は、ケーブルと塔により多点で弾性固定した桁の終局状態が解析により十分精度良く評価できるか否かであった。解析による耐荷力評価は単純な構造についてのみ妥当性が確認されている。そこで、多々羅大橋全橋模型を用いた耐荷力試験を実施した結果、耐荷力、終局状態とも解析と良い整合が得られ、多々羅大橋の構造系の耐荷力評価に数値解析を用いる妥当性が確認された。

Results from a elasto-plastic deformation analysis on the Tatara Bridge, the unprecedented long-span cable-stayed bridge, predicted the bridge would terminate itself with the buckling of the girder at a section near the tower. This forecast differed from the conventional understanding that the cable-stayed bridge would normally have its limit state with the buckling of the tower shaft; this difference seemed to be caused by the elongation of the center span.

Probability of this prediction depended on how accurate the numerical analysis could estimate a limit state of the girder of cable-stayed bridge that had numerous elastic supports by the cables and the Towers. Suitability of the numerical analysis for loading capacity had been confirmed only for simple structures. A full model loading test was thus carried out for the Tatara Bridge.

Results of this model test well agreed with the numerical solution for both the loading capacity and the limit state, and thereby clarified fitness of the numerical analysis to evaluation of the loading capacity on the structure of Tatara Bridge.

生口橋は、中央径間490mの斜張橋で、我国で初めて中央径間が鋼桁、側径間がPC桁という複合主桁構造を採用している。本報は本橋において大型起振機を用いて行った振動実験について報告するものである。実験は、固有振動数や構造減衰等の把握と斜張橋に特有の現象であるケーブルの動的連成効果について知見を得ることを主目的に行った。実験の結果、固有振動数、振動モードの計測値はよく一致し、対数減衰率は、本四耐風設計基準に定める値(箱桁0.02)と同程度あるいはそれ以上であった。一方、ケーブルの連成振動は、桁とケーブル単体の固有振動数が近接したときに生じ、ケーブルの減衰率が桁単独の減衰率を上回る場合、減衰率付加効果のあることが確認された。

The Ikuchi Bridge, which is a cable-stayed bridge having a center span of 490m, adopted a composite girder system, composed of steel for the center span and prestressed concrete for both side spans, for the first time in Japan. This paper outlines the vibration test carried out on the real Ikuchi Bridge, using a large oscillatory machine.

The test was conducted to obtain knowledge on a resonance effect expected to be observed in the dynamic response of the cables in cable-stayed system, as well as to grasp vibration characteristics of the structure such as natural frequency and structural decrement, etc.

As a result, natural frequencies and modes of vibration of the structure measured were well agreed with those calculated by numerical analysis. Obtained values of logarithmic decrement were as equal as or greater than the values specified in the Wind-Proof Design Standard of HSBA (0.02 for box girder).

多島海に建設される3連吊橋である来島大橋補剛桁の耐風性を検討するにあたって、各種の風洞試験及び解析を行った。主な検討結果は次の通りである。①来島大橋の地形模型風洞試験を行い、来島大橋に作用する風のスパン方向風速、傾斜角や乱れ強さ等の特性が明らかとなった。②完成時に対する、偏平六角断面の耐風性を調査するためにバネ支持試験を行い、基本断面を選定した。また、桁高・フェアリング形状・検査車レール・管理路ネット構造の影響についても検討した。③偏平六角形断面に替わる断面として中央に閉口部を設けた二箱桁断面の耐風性を検討し、良好な断面が得られた。④三分力を考慮したガスト応答解析を行った結果、偏平六角形断面のガストファクターとして約2.0が得られた。⑤桁架設時の耐風性について3次元弾性模型による風洞試験を行い、架設段階毎のフラッター特性が明らかとなった。

Aerodynamic performance for the Kurusima Bridge, three suspension bridges in alignment, was studied through wind tunnel tests and analyses. The center span lengths of three bridges are 600m, 1,020m, and 1,030m respectively. Wind characteristics at the bridge site were investigated by wind tunnel test using a terrain model, and the result was compared with field observation data. Major results obtained through this study are:

① Wind tunnel test using a terrain model proved to be useful for estimating wind characteristics. Wind properties such as wind profile, distribution of mean wind velocity, inclination angle, and turbulence intensity were obtained at tower height and spanwise.

②Wind stability at completion stage was studied by section models. Flat-hexagonal sections of the girder which satisfy required wind stability were obtained. In the wind tunnel tests, girder depth.shape of fairing, rail for inspection vehicle, and net fence for pedestrian-bike ways also were, studied.

③Wind stability for a 2-box section with center air-gap was also investigated.

④Gust response due to three components of aerostatic forces was analyzed for the flat-hexagonal section and the 2-box section with center air-gap. Obtained gust factor was for the former section approximately 2.0.

⑤Wind stability during erection stage was studied by a three-dimensional elastic model.