Super long span cable-suspended bridges in Japan

Transcription

1 Super long span cable-suspended bridges in Japan Autor(en): Objekttyp: Ito, Manabu Article Zeitschrift: IABSE congress report = Rapport du congrès AIPC = IVBH Kongressbericht Band (Jahr): 15 (1996) PDF erstellt am: Persistenter Link: Nutzungsbedingungen Die ETH-Bibliothek ist Anbieterin der digitalisierten Zeitschriften. Sie besitzt keine Urheberrechte an den Inhalten der Zeitschriften. Die Rechte liegen in der Regel bei den Herausgebern. Die auf der Plattform e-periodica veröffentlichten Dokumente stehen für nicht-kommerzielle Zwecke in Lehre und Forschung sowie für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und den korrekten Herkunftsbezeichnungen weitergegeben werden. Das Veröffentlichen von Bildern in Print- und Online-Publikationen ist nur mit vorheriger Genehmigung der Rechteinhaber erlaubt. Die systematische Speicherung von Teilen des elektronischen Angebots auf anderen Servern bedarf ebenfalls des schriftlichen Einverständnisses der Rechteinhaber. Haftungsausschluss Alle Angaben erfolgen ohne Gewähr für Vollständigkeit oder Richtigkeit. Es wird keine Haftung übernommen für Schäden durch die Verwendung von Informationen aus diesem Online-Angebot oder durch das Fehlen von Informationen. Dies gilt auch für Inhalte Dritter, die über dieses Angebot zugänglich sind. Ein Dienst der ETH-Bibliothek ETH Zürich, Rämistrasse 101, 8092 Zürich, Schweiz,

2 1009 Super Long Span Cable-Suspended Bridges in Japan Manabu ITO M-It0 has been engaged Prof Emeritus in '«ching and research ~e t t c on bridges and structural The University of dynamics at the Tokyo University of Tokyo from Japan 1959 to 1991, and then at Saitama University until He has also been involved in many cablesuspended bridge projects, and is currently a Vice-President of IABSE. Summary The state-of-the-art of long span cable-suspended bridges in Japan is presented After describing some of their specific features, special mention is made ofthe Akashi-Kaikyo Bridge ofthe Suspension type and the Tatara Bridge ofthe cable-stayed type, both of which will respectively have the world's longest spans when completed in a few years. Finally several other projects of straits crossings under consideration, which contain further long span bridges, are referred to. 1. Introduction Japan consists of four major islands and many other small islands, whereas it has a fairly large population in the limited flat area. Never-the-less, any large bridge, the span of which exceeds 200m, had not been built before the middle of this Century. It might be due to such reasons that road networks were in poor condition; that rivers in this country did not require wide navigation Channel, and that the bull-headed military authorities did not like large bridge construction. The reconstruction of devastated facilities started after the Second World War, and with the development of vigorous socio-economic activities thereafter, the improvement of transportation networks has been promoted. Since 1960's many long span bridge projects to cross straits and river mouths in urban areas, or sometimes to connect areas of reclaimed land in coastal cities, have been undertaken. Above all, the Honshu-Shikoku linking project across the Seto Inland Sea at three different routes (cf. Fig 1) gave an impetus to the rapid progress of large bridge construction in Japan. When very long span is required, the lead is taken by cable-suspended bridges, namely Suspension or cable-stayed types It can be recognised from Fig 2 and Tables 1 and 2 that the Japanese bridges ofthe both types have made outstanding extension of span length in the past

3 i 1010 SUPER LONG SPAN CABLE-SUSPENDED BRIDGES IN JAPAN three decades. The effect of earthquake loading on Japanese bridges has led to the extensive use of steel as compared with other countries. In addition, a variety of steel materials are available at a reasonable price in this country Hokk Tsugaru St. Honshu Tokyo Bay Mouth Kyushu Sh Ho-vo St. Kitan St. /se Bay Mouth Figure 1 Strait Crossing projects in Japan 2000 i n OVERSEAS JAPAN > 500 OVERSEAS i i J I r I f r I- r «-JAPAN I J ee"jtk (a) Suspension (b) Cable-Slayed Fig 2 Record span lenglh of cable-suspended bridges in Ihe 20th Century

4 M. ITO 1011 On the other hand, quite high design wind speeds are required for Japanese bridges because of frequent attack of strong typhoons. The state-of-the-art of Japanese cable-suspended bridges in general is reviewed in the papers by A. R. Bürden [1,2] and the author ofthe present article [3,4], name max. span (m) year remarks Kanmon truss-stiffened In-no-shima truss-stiffened Ohnaruto truss-stiffened, designed for highway+railway Ohshima twin-trapezoidal box girder Shimotsui continuous double-deck truss, road & rail North Bisan continuous double-deck truss, road & rail South Bisan continuous double-deck truss, road & rail Tokyo Port double-deck truss Hakucho 720 * streamlined box girder, snowy district Kurushima I 600 * Kurushima II 1020 * box section, three 3-span bridges linked Kurushima III 1030 * with two shared anchorages E\kashi 1991 * truss-stiffened Table 1 Major Suspension bridges in Japan (as of 1995), note: * under construction name max. span (m) year remarks Yamato River trapezoidal box girder, very skew Meikoh-West hexagonal box with fairing truss-stiffened Katsushika S-shape curved, box girder with fairing Katsushika twin box, R/C tower, snowy district Iwakuro Is double deck truss (highway & railway), Hitsuishi Is standing in line Yokohama Bay doubledeck truss with shallow box upperchord Tempozan flat hexagonal box with Splitter plate East Kobe double deck truss Ikuchi twin hexagonal box, P/C girder in side spans Tsurumi streamlined box girder Meikoh-Central 590 $ trapezoidal box girder Meikoh-East 410 $ trapezoidal box Tatara 890 * streamlined box girder, P/C girder in sidespans Table 2 Major cable-stayed steel bridges in Japan (as of 1995), note: * under construction

5 1012 SUPER LONG SPAN CABLE-SUSPENDED BRIDGES IN JAPAN 2. Specific Features In Design And Construction 2.1 Design and Construction Process Very long span bridges in Japan are usually built by the public corporations invested by the central and local governments, and put to use as toll bridges after completion. The organisations which commission the project control its design work and have a leading role in the main decision process, although Consulting firms undertake the substantial work. The authority has expertise in-house to evaluate design and supervise construction as well. Another feature in the design and construction process for large projects in Japan is the use of committees comprising academics and experienced engineers, though the members of private enterprises are rarely included there. They discuss particular issues on the project and give advices upon consultation ofthe owner. There are sometimes more than one committees in parallel, such as technical and aesthetic. So far big projects have been not tendered on a competitive design-and-built basis in Japan, and several Joint ventures are formed for the construction stages of substructures and superstructures, respectively. 2.2 Effects of Environmental Actions Earthquakes and strong winds are frequently the dominant actions in designing long span bridges. Generally speaking, earthquakes govern the proportioning of substructures and towers, while wind affects the design of superstructures. Dynamic analysis is now the routine procedure in designing flexible structures [5]. A feature worthy of special mention on long span Japanese cable-stayed bridges is the use of elastic constraint in the longitudinal direction by connecting the girder and the tower, the piers or the abutment with steel bars, layered plate Springs, shear-type rubber shoes, or links, in order to control seismic forces applied to the substructures and optimise the sectional forces due to not only seismic but also temperature effects [6]. Design wind speeds for the Japanese cable-suspended bridges are quite high (between about 50 to 75 m/s at deck level), and the critical wind speed for aerodynamic instability predicted from wind tunnel model tests is required to be above 2 times these design wind 1 speeds. Accordingly, many ofthe long span bridges are provided with means suppressing wind-induced vibrations [7]. The first choiee is to select an aerodynamically stable cross section and, if necessary, fairings, flaps or other aerodynamic appendages are attached. With the growth of scale of structures these days, the use of various damping devices on towers, girders and stay cäbles has also increased. 2.3 Cäbles Parallel wire cäbles consisted of galvanised steel wires of about 5 mm in diameter have been exclusively used on long span Suspension bridges in Japan. The type of cable formation used on them has been mostly the prefabricated parallel wire Strand (PPWS) method even on the

6 M. ITO 1013 Akashi-Kaikyo Bridge, the cable length of which exceeds 4 km. A recent exception was the Shimotsui-Seto Bridge (main span of 920m) where the air spinning method was used because ofthe limitation of space at the north anchorage. As shown in Fig.3, the tensile strength ofthe steel wires used in Suspension bridge cäbles has not changed drastically in the past seven decades, but high-strength steel wire with the tensile strength of 1,800 MPa was developed by adding appropriate amount of Silicon to use on the main cäbles ofthe Akashi-Kaikyo Bridge. Its motivation will be discussed in the next chapter. The most prevailing stay cäbles in long span cable-stayed bridges in Japan are the so-called non-grout-type Strand in which each wire is bundled with a lay angle of not more than 4 degrees to enable the reeling ofthe Strand and ensure the mechanical properties of parallel wire Strand. The Polyethylene sheath is completely shop-fabricated by a directly extruded jacket after corrosion protection measures are taken. The coloured surface for aesthetic requirement and the notched or dimpled surface for aerodynamic stability are now available on the Polyethylene covering. 2.4 Bridge Decks Truss girder has been employed on double-deck bridges in Japan, in both Suspension and cablestayed bridges. Mhough the stiffening truss was also adopted for the Mashi-Kaikyo Suspension bridge, which is a single-deck road bridge, as mentioned later, the use of shallow box-section is now prevailing on the girder of Japanese cable-suspended bridges. The type of steel girders in these cases has been based on generally similar concepts: single or twin boxes with orthotropic decks forming trapezoidal or hexagonal cross sections mainly for aerodynamic reasons. Even if a truss girder is used, aerodynamic appendages have been attached on some bridges. 2.5 Towers Combination of steel girder and concrete towers has been seen in Japan for only a few cablestayed bridges with a main span of less than 250m. What follows is, therefore, all concerned with steel towers. Suspension bridge towers are usually classified into X-braced type and rigid frame type In Japanese bridges where earthquake and wind effects are large, the former has been conventional for long span. Although the latter has been increasingly adopted from the aesthetic preference, it is not yet used on the Suspension bridge larger than 1,030m span the other hand, towers of cable-stayed bridges have more varied forms. In case that span length is very large, however, A-shaped or inverse Y-shaped types are usually selected for the reasons of structural stability and higher torsional rigidity ofthe whole system. Since the towers of cable-suspended bridges are noticeable, their visual design is highly put stress. Sometimes industrial designers and architects are involved in it For example, the use of curved elements appears to be a developing trend in Japanese designs. The position of bracing or horizontal strut and the proportion of constituting elements are the primary objects of visual On

7 1014 SUPER LONG SPAN CABLE-SUSPENDED BRIDGES IN JAPAN design. The general softening of form is also apparent in the design of gravity cable anchorages. There has been increasing use of strongly textured surfaces on their massive body Akashi 160 bü M Manhattan G.Washinqtön Kanmon New Port Seto xs W)140 wllliamsburg oo Brooklyn Fig 3 Tensile Slrength of steel wire for Suspension bridge cable Year 2.6 Large Block Erection When steel bridge is built at the sites where an area of open and deep water is available, large block erection by floating cranes is very frequently used in Japan. The advantages ofthe method are shortening of construction period, reduction of labour at the site, better and easier control of erection, increasing safety by reducing work at high positions. However, the restrictions may be associated with compromises with navigational traffic and fisheries, and caused by erection scheme and rapid water flow. Cost saving may not always attained because of additional facilities and temporary or local reinforcement ofthe structure during erection. The number of large floating cranes with lifting capacities of 3,000 tonf or more is now six in Japan, and the biggest has a maximum lifting capacity of 4,100 tonf. The maximum erection weight of one structural block ever experienced is 7,300 tonf. In this case, three floating cranes were used together.

8 M. ITO World's Longest Cable-Suspended Bridges 3.1 The Akashi-Kaikyo Bridge The Akashi-Kaikyo Bridge, which will cross the Akashi Straits with a shore to shore distance of about 4 km, is part ofthe Honshu-Shikoku Bridge project that includes ten Suspension and five cable-stayed bridges. It is a three span Suspension bridge as seen in Fig 4. Carrying six lanes of highway traffic. the bridge is scheduled to be completed in 1998 after a ten-year construction period. Despite its world's longest span of 1,990m, the foundations ofthe tower piers reach as deep as 70m below sea surface under the severe marine conditions ofa sea depth of 40m and a maximum tidal current speed of 4.5m/s. The foundations are placed on the granite bedrock and were constructed by the laying-down caisson method which used steel cylindrical caisson with double walls. Kobe 960 3, Awaji Island 3J_l-4-^ A 2P 3P 4A 36.5 (a) General View ZS 2 5 Road Level : Main Tower Fig 4 The Akashi Kaikyo Bridge Stiffening Girder (b) Main Tower and Stiffening Girder At the 1995 Hyogoken-Nanbu Earthquake which devastated Kobe and its vicinity, the construction stage of this bridge was during the squeezing of main cäbles after finishing cable erection. Although the epicentre was nearly under the bridge site, no damage was found on the

9 1016 SUPER LONG SPAN CABLE-SUSPENDED BRIDGES IN JAPAN 4 structures. It was observed, however, that the foundations showed permanent displacements, and in its consequence, the main span and one side span expanded 0.8m and 0.3m, respectively The resultant verticality ofthe main towers remained within the allowance of construction, though the maximum velocity response ofthe tower top exceeded 100 Kines. Therefore, the erection ofthe bridge could be continued by slight modification of some truss members before fabrication, and the bridge will be completed nearly on schedule. imter the wind tunnel tests with various alternative section models including streamlined boxes with opening, a truss girder with high torsional stiffness was selected This decision was made also from the erection constraints at the site High-strength tempered steel of 780 MPa class of the reduced preheated type is used for highly stressed members in the regions where bending moments are large. As mentioned previously the newly developed high-strength steel wires were used on the Mashi-Kaikyo Bridge The primary motivation was to reduce the dead weight because more than 90 percent ofthe cross section ofthe main cäbles is used to carry the bridge's own weight. Secondary advantages of its use were to simplify the structural details by using two main cäbles instead of four in the original design and to reduce the height of main towers by decreasing the sag to span ratio ofthe main cäbles. As a consequence, each main cable with a diameter of 1.1 m consists of approximately 37 thousand parallel wires of 5.2 mm in diameter. The two towers supporting the main cäbles have height of about 300m above water level. The steel tower shafts have a constant width of 6.6m in the tower plane and a varying width of 14.8m to 10 0m in the direction of bridge axis. High-strength, quenched and tempered steel was mainly used on the 40 to 48 mm thick plates composing the tower shafts. On these tall slender towers, tuned-mass dampers are installed in addition to the corner eut as one ofthe aerodynamic means. 3.2 The Tatara Bridge The Tatara Bridge is also one ofthe Honshu-Shikoku linking bridges on the most western route ofthe Island Sea. The original scheme was naturally a Suspension bridge for such long span as nearly 900m. However, the execution for a massive anchorage on the Ikuchijima side would have forced serious change to the ground configuration and the road alignment on the same side has a sharp curve near the end ofthe bridge. As a result, the alternative cable-stayed bridge design was adopted. The main span length ofthe bridge was decided to be 890m, which will be the world's longest in cable-stayed bridges, because ofthe topographical features and geological conditions at the site and for navigational requirement. Since the both side spans are relatively short and have different lengths as shown in Fig. 5, intermediate piers are provided in the side spans and the continuous girder consists ofa steel box portion throughout most ofthe girder length and prestressed concrete portions on certain length of both girder ends in order to avoid the uplift at the end supports and to improve the behaviour ofthe bridge. In addition, the shear-type aibber shoes with the spring constant of 3.9 MN/m per bridge are going to be used considering the distribution of seismic force, the effect of temperature change, the longitudinal displacement ofthe girder, and the elasto-plastic stability ofthe whole structural system [8]. The bridge is now under construction, and will be completed in 1999.

10 M. ITO Ikuchi Island Omishima Island l ower Girder Cross Section ,2.5, ^ TZIilZ"^^ (unit Im) Fig. 5 The Tatara Bridge 4. Future Projects It is important to hand down the developed technology to successors. Nowadays printed documents and Computer disc records can be left to give the necessary information But some parts ofthe essential techniques or know-how may be kept in the engineers who have been engaged themselves in the actual project. New straits crossing projects after the completion ofthe Honshu-Shikoku Bridge project are fortunately contemplated in Japan. Although the realisation will be in the next Century, the committees concerned are now discussing the schemes of these projects. Referring to Fig l, the projects under investigation are listed in Table 3. Super long Suspension bridges having centre span of more than 2,000m will be needed to realise these projects Marine conditions to build substructures and design requirements for strong wind and earthquakes will be more severe as compared with the Honshu-Shikoku bridges. Cost saving is also required from the viewpoint of financial feasibility.

11 SUPER LONG SPAN CABLE-SUSPENDED BRIDGES IN JAPAN location shore to shore distance (km) max water depth (m) expected water depth at pier (m) Tsugaru St 270 east west Tokyo Bay Ise Bay Kitan St Ho-yo St Table 3 Future slraits crossing projects in Japan Therefore, further innovations in design and construction of these projects shall be pursued Concerted studies are underway that are aimed at imparting higher reliability to higher strength steel wire with the ultimate goal of realising such super long Suspension bridges as abovementioned In order to clear up the aerodynamic issues, the use of auxiliary cable System, a variety of damper Systems, open grating floor and so forth are also now investigated 5. References 1 Bürden, A R Modern Japanese Suspension bridge design, Proc ICE, Part 1, Vol 90, Feb Bürden, A R Japanese cable-stayed bridge design, Proc ICE, Part 1, Vol 90, Oct Ito, M Cable-stayed bridges in Japan, "Cable-Stayed Bndges-Recent Developments and their Future". M Ito et al (ed Elsevier, Ito, M Long span steel bridges in Japan, Rep IABSE Symposium, Leningrad, Ito, M Design practices of Japanese cable-stayed bridges against wind and earthquake effects, Proc Intl Conf Cable-Stayed Bridges, AIT, November Ito, M, Supporting devices of long span cabie-stayed bridge girder, Innovative Large Span 7 Structures, Vol l, Canadian Soc Civil Engr, Ito, M Measures against wind-induced vibrations of bridges, Proc Structures Congress '87, ASCE, August Ito, M and Endo, T The Tatara Bridge-World's longest cable-stayed span, Proc Structures Congress'94 Vol 1 ASCE 1994