JAPANESE CONCRETE BRIDGES. Alan Burden 1

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1 JAPANESE CONCRETE BRIDGES Alan Burden 1 INTRODUCTION Although less popular than steel, concrete is used extensively in Japanese bridge projects. The seismic loading condition has encouraged designers to keep bridge superstructures as light as possible, which has perhaps made concrete less popular than in non-seismic zones. Of the 80 major cable-stayed bridges constructed between 1960 and 1992 for example, about one third used concrete for the deck or pylons. For major arch bridges over the same period the proportion is closer to one quarter. This paper reviews some of the landmark Japanese bridges in concrete of the last 40 years. Some comparisons are drawn with practice in the UK. CABLE-STAYED BRIDGES Recent decades have witnessed a rapid global growth in the use of cable-stayed bridges for long spans. Japan has been one of the countries which has led this growth, producing more than one third of the world total since 1970 [1]. The quest for lightness in long-span structures has tended to encourage steel to be used more often than concrete, but where appropriate concrete is employed in both pylon and deck members. On the recent Iguchi Bridge for example with a steel main span of 490m, concrete was used for the back spans so that advantage could be taken of its weight as a balance to anchor the back-stays. and deck, although in the long Yobuko Bridge (Figure 1, 1988, 250m) the deck is kept completely free from the towers. Full fixity has been popular for bridges with single high towers where any temporary support from ground level during construction is uneconomic. Early deck structural systems using heavy beams along each edge have given way to the almost exclusive use of box sections. Concrete decks are erected exclusively by casting in situ. Use has not been made of the segmental precasting seen in other countries. Japan s first cable-stayed bridge, Katsuse Bridge in Kanagawa (1960, 128m) made passive use of concrete by re-using the concrete towers of the old suspension bridge and adding a steel suspended deck. It became the world s fifth modern cable-stayed bridge, and the first outside of the sphere of German technology. The use of concrete for pylons or towers alone is rather rare in Japan this is also true in the suspension bridge field where no towers have been built in concrete [2]. All-concrete bridges have tended to use either pinned or fully fixed connections between pylon Figure 1: Yobuko Bridge Outlines of the towers of Japanese concrete cable-stayed bridges are shown in Figure 2, approximately in chronological order. There has been a trend towards increased styling, and the strong diagonal lines found in traditional shrine architecture have sometimes appeared (Nichu 1 Principal, Structured Environment Limited, Tokyo; Professor, Kanto Gakuin University, Yokohama

2 and Shunda for example). The plastic qualities of concrete construction have allowed more experimentation in aesthetic treatment than similar examples in steel. The approach even in rural areas has tended towards the monumental, a different approach from say that in the UK where a common aim is for unobtrusiveness. Industrial designers have started to have an influence on bridge projects. The towers for Ashigara Bridge on the Tomei Expressway (Figure 3, 1991, 185m) were designed in collaboration with Sori Yanagi. His design for the surface treatment of the towers resulted in quite intricate surface form, incorporating many grooves and curved surfaces. Figure 3: Ashigara Bridge pier detail Figure 2: bridges Tower profiles of cable-stayed Another industrial designer group, M&M, advised on the form of the central concrete pier for Katsushika Harp Bridge (Figure 4, 1987, 220m), a bridge with a steel superstructure. This bridge has been highly acclaimed inside Japan.

3 urban fabric, and therefore made more use of decorative finishes. Similar arches were used in some other cities. The largest of the examples in this group is Bandai Bridge in Niigata (1929). There are six main spans of about 45m each. Outside of the urban areas, concrete was used for longer spans, but the structural systems remained unadventurous. The largest concrete arch of the period was Mannen Bridge (1940) over the Tama River near Tokyo, with a 76m span. Perhaps the most delightful bridges of the pre-war era though were smaller, low, deck-tied arches. An example in Nagano Prefecture is Himekawa Bridge (Figure 5, 1937). This form has similarities with some contemporaneous British bridges, notably Etive Bridge (1932) in the Scottish Highlands. Figure 4: Katsushika Harp Bridge pier detail ARCH BRIDGES The first concrete arches in Japan were constructed just after the start of the 20 th century. Engineer Tadahiko Hibi had traveled for study to Germany in On his return to Japan he produced a three-volume manual for reinforced concrete structures. This may have been the reason for the use of reinforcement in the form of steel frameworks rather than bars. This idea is attributed to the Austrian engineer Josef Melan, and the word meranzai has since been adopted to describe this method in Japanese. The system continues to be used in some sections of modern concrete bridges. Reinforced concrete arches proved particularly popular in the Osaka re-planning project of the 1920 s. Perhaps more than in Tokyo, design policies in Osaka gave more weight to the integration of new bridges into the surrounding Figure 5: Himekawa Bridge Figure 6: Hokawazu Bridge The adoption of more advanced concrete arch forms in Japan has been focused mainly on aspects of construction economy rather than physical form. Hokawazu Bridge (Figure 6, 1974,

4 170m) is important in that a new cantilever technique was developed by the contractor, Sumitomo Corporation. Diagonal cabling was used between panel points to form a truss, which could be progressively extended from each bank (Figure 7). Although the method was used Figure 8: Usagawa Bridge Figure 7: Bridge Erection method for Hokawazu successfully, support of the tie-back cables during construction meant that heavy abutment spandrel walls were required, a feature which looks awkward in the completed bridge. Large flares were also given to the main rib springings to deal with lateral loads (again greatest during construction). Cantilever methods have been used on many large concrete arches since, and the large abutment spandrel walls are a common feature. The solid rib used on Usagawa Bridge (Figure 8, 1982, 204m), together with these thick end walls, make for a rather bulky impression overall. The main advance in terms of structural sophistication has been the adoption of the deck-stiffened form. Here the aim is to achieve material economy by relieving the arch rib of bending moments induced under asymmetric load.

5 Two important examples are Akatanigawa Rail Bridge (Figure 9, 1989, 126m), and Nakatanigawa Expressway Bridge (Figure 10, 1989, 100m). Both again have heavy abutment walls for ease of construction, but the thinness of the arch ribs brings a contrasting lightness to the structures overall. Figure 11: Kotsuru 1 Bridge Figure 9: Akatanigawa Bridge Figure 12: Higo Tunnel entrance Figure 10: Nakatanigawa Bridge On the same expressway, which became something of a showcase for new ideas in civil engineering aesthetics in the 1990 s, concrete has been used for sculptural effect in several other non-bridge locations. One prominent example is the entrance to Higo Tunnel, Figure 12. Smaller concrete arches have tried to exploit the sculptural possibilities of concrete with forms which make little attempt to express efficiency or lightness. Kotsuru 1 Bridge (Figure 11, 1989, 35m) on the Kyushu Expressway uses an arch rib which thickens at the crown and omits intermediate spandrel walls. The arch is thus used to carry a single concentrated load at mid-span, a structurally inefficient arrangement. The designers here have stated their desire to create a visually striking bridge within the remote valley setting [3]. GIRDER BRIDGES Concrete girder bridges have enjoyed increasing application to the extension of the expressway network. The need for lightness is a deterent, and the collapse of a large section of expressway

6 during the Kobe Earthquake of January 1995 provoked a nationwide programme of reinforcement work to concrete bridge piers. Figure 13: Hamana Bridge Generally on all-concrete projects the girder is made continuous with the piers. This allows cantilevered construction without bents, although this is always done by casting in-situ there has been no use of glued-segmental construction. One major example is the Hamana Bridge (Figure 13, 1976, 240m). A comparison of the profile of this bridge with the Orwell Bridge of similar scale in the UK is shown in Figure 14. Figure 14: Hamana and Orwell profiles Two further recent examples of expressway girders in concrete are shown in Figures 15, 16. Figure 15: Kyushu Expressway viaduct These are located on the Kyushu and Hokuriku expressways respectively. Both opened in the early 1990 s. The Hokuriku is in an exposed shoreline location, making durability an important design consideration.

7 appearance. Secondly, the width of the deck ribbon is reduced towards the center of each span. Figure 16: Hokuriku Expressway OTHER FORMS There is a reasonably strong tradition of experimentation and innovation in the Japanese bridge field. Two examples are introduced here. Iwahana Bridge (Figure 17, 1974, ) uses precast concrete elements to form a truss for the Shinkansen tracks near Hiroshima. This unusual choice of material for a truss was made with the aim of reducing maintenance and train noise. It has performed well, but economics seem to have precluded wider adoption of the technique on the rail network. Figure 17: Iwahana Bridge Soryu Bridge (Figure 18, 1984) in Kyushu is a stressed ribbon footbridge. Although stressed ribbons are now fairly common worldwide for footbridges, there are two noteworthy areas in this example. Firstly, the connection of the deck ribbon with the pier is handled well to give an integrated

8 Japanese suspension bridge design, Proceedings of the Institution of Civil Engineers, Part 1, 90, , London. 3. BURDEN, A.R., August 1993, Japanese arch bridge design, Proceedings of the Institution of Civil Engineers, Part 1, 99, , London. Figure 18: Soryu Bridge This adds aesthetic interest, decreases the monotony of the crossing for the user, and encourages pedestrians to gather over the pier rather than at midspan. SUMMARY Concrete has maintained a strong position in Japanese bridge construction over the last 40 years. It is employed in all forms and scale of bridge, including large cable-stayed and arch types. Superstructure weight has been a deterrent for use, and retrofitting of some bridges has been carried out following the Kobe Earthquake. Increasing care has been paid to the form and surface treatment of concrete elements to improve appearance. Designers from other fields have sometimes collaborated in these efforts. In comparison with European practice, there has been an approach to aesthetics which is less directed towards the classical engineering ideals of lightness and efficiency. REFERENCES 1. BURDEN, A.R., October 1991, Japanese cable-stayed bridge design, Proceedings of the Institution of Civil Engineers, Part 1, 90, , London. 2. BURDEN, A.R., February 1991, Modern