Akashi Kaikyo Bridge Case Study: Towers, Cables and the 1995 Earthquake

The Akashi Kaikyo Bridge carries an expressway 3,911 m across the Akashi Strait, between Kobe on Honshu and Awaji Island in Japan. It was designed and built by the Honshu-Shikoku Bridge Authority and opened on 5 April 1998. Its 1,991 m centre span was the longest of any suspension bridge until 2022. This case study explains its towers, cables and sea foundations, and what the 1995 Kobe earthquake did to the bridge while it was half built.

Where to see the real drawings. HSBE's Akashi-Kaikyo Bridge page carries the official side view with span lengths. A 2009 paper by HSBE engineers Motoi Okuda, Susumu Fukunaga and K. Endo in Bridge Structures has the geology and earthquake figures. Our guide on how to do an architecture case study shows how to turn them into sheets.

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The brief and the client

The bridge is one link in the Kobe-Awaji-Naruto route, which joins Honshu to Shikoku by way of Awaji Island. HSBE's history records that Kobe's mayor, Chujiro Haraguchi, pressed for a site survey of an Akashi crossing in August 1953, and HSBA was set up in July 1970 (HSBE, History).

Client and designer were the same body. HSBA surveyed the strait and wrote its own design standards, because standards written for bridges of 200 m or less "became unreasonable" at this scale (HSBE, Survey design). Satoshi Kashima and Makoto Kitagawa described the design in Scientific American in December 1997 (TRID record of Kashima and Kitagawa, 1997).

Site and context: a strait of strong tides and busy shipping

HSBE gives the Akashi Strait as about 4 km wide and up to about 110 m deep; the tidal current at the foundation sites reaches about 4.5 m/s, and about 1,400 ships pass through each day (HSBE Bridge World, Akashi-Kaikyo Bridge). PBS's Building Big notes that the bridge was designed not to block that shipping (PBS, Akashi Kaikyo).

Okuda and colleagues write that surveys found faults under the strait, and the foundations were placed to avoid them. Granite lies more than 150 m down at the towers and Kobe anchorage, so those foundations rest on softer strata: weakly cemented sandstone and mudstone, or semi-consolidated gravel and sand (Okuda et al. 2009). HSBE adds that core samples showed the ground to be stronger than expected, allowing shallower bearing for the tower foundations (HSBE, Survey design).

Akashi Kaikyo Bridge design: what kind of bridge it is

HSBE describes the bridge as a "stiffened truss suspension bridge with three spans and two hinges" (HSBE, Akashi-Kaikyo Bridge). In plain terms:

• Suspension, three spans: two main cables hang over two towers and are anchored on each shore; the deck hangs from them in the side spans as well as the centre span.
• Two-hinged: each span of the stiffening truss is hinged at both ends, at the towers and anchorages, rather than running continuously over the towers. Okuda and colleagues describe tower links that suspend the truss at each tower, end links at the anchorages and wind shoes that restrain it sideways.
• Stiffening truss: a deep steel truss under the road gives the deck its bending stiffness. PBS notes that the open truss lets wind blow through the structure.

UT Austin says the 1,991 m centre span was 41 percent longer than the previous record (UT Austin, Satoshi Kashima). It held the record until the 1915 Çanakkale Bridge in Türkiye opened on 18 March 2022 with a 2,023 m main span (Popular Science, Sarah Wells, 27 March 2022).

Akashi Kaikyo Bridge dimensions: spans, supports and clearances

HSBE's side view gives spans of 960 m, 1,991 m and 960 m, a total of 3,911 m, and four supports numbered from the Kobe side: the 1A anchorage, the 2P and 3P towers in the strait, and the 4A anchorage on Awaji Island. The same drawing labels the tower foundations about 80 m (2P) and 78 m (3P) across.

HSBE gives the tower tops as about 300 m above the sea, the deck at mid-span about 97 m above it, and about 65 m of clearance for ships (HSBE Bridge World). PBS gives 928 ft (about 283 m) for each tower. HSBE measures from sea level; PBS does not say, so quote the source with the number.

HSBE also publishes the weights: the towers 46,200 t, the cables 57,700 t and the girder 89,300 t, a superstructure of 193,200 t in all, with each foundation designed for a vertical force of 120,000 t.

Akashi Kaikyo Bridge structure: towers, cables and the truss

The load path is that of any suspension bridge: deck and truss, hangers, main cables over saddles on the tower tops, towers, foundations, with the anchorages holding the cable ends. Scale is what changed the details.

The cables and their new steel

HSBE explains that wire of the conventional strength, 160 kgf/mm² (1,570 N/mm²), would have needed two cables of 1,000 mm diameter on each side. HSBE developed a wire of 180 kgf/mm² (1,760 N/mm²), and with it one cable of 1,100 mm diameter per side was enough (HSBE, Development of materials). Secondary sources often say "1,800 MPa"; 1,760 N/mm² is HSBE's figure.

A 1995 paper by Koji Kawaguchi, Susumu Fukunaga and colleagues records "prefabricated parallel wire strands": bundles of wire made in a factory and assembled into the cable on site (Kawaguchi et al., Doboku Gakkai Ronbunshu, 1995). HSBE says this suited strong winds and shortened erection; its projects also used a helicopter to carry the first pilot rope across busy waters (HSBE, Construction technology). Dry air is pumped into the cables to limit corrosion (HSBE Bridge World).

Towers and wind

The towers are steel. HSBE says wind tunnel tests led to vibration control devices for the towers and girders (HSBE, Construction technology). PBS states that each tower holds 20 tuned mass dampers; Okuda and colleagues mention oil dampers between girder and towers. HSBE gives design wind speeds of 60 m/s for the girder and 67 m/s for the towers, and says the bridge resists winds of 80 m/s, checked on whole-bridge models 40 m long. In the centre span, stay ropes tie the girder to the main cable (Okuda et al. 2009).

Akashi Kaikyo Bridge foundation: building in the strait

HSBE calls deep water and strong tides "the key" problem of its bridges. Its answer was the laying-down caisson method, with the seabed excavated by clamshell dredgers in the current (HSBE, Construction technology). A steel caisson set on the prepared bed then served as formwork for concrete placed under water in layers.

A 1991 paper by Satoshi Kashima, Takehisa Iho and Yoshitaka Nakagawa reports about 500,000 m³ of anti-washout underwater concrete for the two tower foundations, placed over a year in tidal currents of up to 8 knots and at depths of up to 60 m, with robots cleaning the bedrock surface and treating construction joints (ISARC 1991). HSBE gives the maximum current as about 4.5 m/s, about 9 knots, so the sources differ slightly. Scour protection came from hydraulic model tests, and for the anchorages HSBE developed workable concrete and low-heat cement to limit cracking (HSBE, Development of materials).

The Akashi Kaikyo Bridge and the 1995 earthquake

On 17 January 1995 a magnitude 7.2 earthquake struck beneath the Akashi Strait, very close to the bridge; Okuda and colleagues record that about 6,400 people lost their lives. The main cables had just been erected, and the stiffening truss had not yet been hung (Okuda et al. 2009).

Inspection found no serious structural damage, but all four foundations had moved with the crust, which the authors attribute to faults between the towers and between 3P and the Awaji anchorage. The centreline bent slightly; the span from 2P to 3P lengthened by 0.8 m and the span from 3P to 4A by 0.3 m. HSBE says the foundations moved with the ground without sliding.

The fix used the order of construction. Because the truss was still being fabricated, two panels at the centre of the span were each made 40 cm longer and one end panel at 4A 34 cm longer, so the truss fitted the new span lengths. The deformed bridge was then checked against the original design standards.

How much longer did it get? Okuda and colleagues give 0.8 m; a 2000 paper by Ninomiya, Fukunaga and Kashima says "about 80 cm" (TRID record); PBS says "an additional three feet", about 0.9 m; many popular sources round it to 1 m. The 1995 cable paper by Kawaguchi and colleagues gave the main span as 1,990 m; HSBE now gives 1,991 m.

Materials and construction process

The materials list is short: steel for the towers, truss and deck, high-strength wire for the cables and hangers, and concrete below. HSBE calls high tensile steel "indispensable" for reducing the weight of long-span bridges and developed weldable grades and fatigue-safe welding to suit. Construction ran from May 1988 to April 1998.

Light, climate and services

For a bridge this section is about weather and upkeep: wind, salt air and the tidal current. HSBE says the bridge is meant to stay in good condition for more than 200 years, and the dry-air system in the main cables is maintenance designed in from the start.

Reception: records, cost and later checks

UT Austin records that Satoshi Kashima received the Emperor's Trophy in 1998 for his contribution to the bridge. The wider programme's finances are also on record: HSBE's history notes that in May 2003 a special law passed HSBA's debt of 1.34 trillion yen to the national government, a figure for the whole authority, not this bridge alone.

The engineers have been open about the design's limits. Okuda and colleagues write that the original seismic design did not consider a large earthquake on a nearby inland fault, so HSBE studied the bridge, an emergency transport route, against site-specific earthquakes. Cables, hangers and girder stayed elastic; the tower bases and lower horizontal beam could locally buckle, judged repairable; but the expansion joints could fail and open gaps of about 2.3 m in the road. The paper said retrofit works were scheduled within a few years; we did not find a dated HSBE statement that they are complete.

What designers in India can take from it

These are our reading, not claims made by the bridge's engineers.

1. Map the ground before you place the structure. HSBA found the faults, kept the foundations clear of them and chose bearing strata from core samples. On Indian coastal and hill sites, a proper soil investigation before the column grid is fixed costs less than a redesign.
2. Keep the sequence able to absorb surprises. The truss panels could be lengthened because they had not yet been made. Fabricating some elements last, and leaving adjustable connections, gives room for site movement, survey errors or late changes.
3. Design maintenance in. Dry air in the cables, maintenance paths inside the truss and a 200-year target are design decisions. Near the sea, corrosion protection and inspection access belong in the first drawings; our guide to building near the sea in India covers the house-scale version.
4. Test the forces you cannot calculate with confidence. HSBA tested 40 m whole-bridge models in a large wind tunnel. Wind and daylight studies on physical or digital models are within a student's reach and make a strong thesis section; see our list of B.Arch thesis topics by typology for infrastructure ideas.

Visiting the Akashi Kaikyo Bridge

• Maiko Marine Promenade: a walkway built into the bridge on the Kobe side, about 47 m above the sea and about 317 m long, opened on 5 April 1998. The park lists hours of 9:00 a.m. to 6:00 p.m. (longer in peak holidays) and an adult fee of 250 yen on weekdays and 300 yen at weekends and on holidays (Hyogo Prefectural Maiko Park).
• Bridge Exhibition Center: a museum of the bridge's technology at Maiko, open 9:15 to 17:00 and closed on Mondays, according to its site (Bridge Exhibition Center).
• Bridge World tower-top tour: HSBE's guided tour walks the maintenance path and goes up to a tower top about 300 m above the sea, led by people who worked on its construction. It runs on set days from April to November 2026 and in March 2027, takes 2 hours 50 minutes and must be booked (HSBE, Overview of the Tour).
• Walking or cycling across: HSBE's page on paths for bicycles and pedestrians lists only the Nishi-Seto Expressway (Shimanami Kaido) bridges, not the Akashi-Kaikyo Bridge (HSBE, bicycle and pedestrian path).

FAQ

When was the Akashi Kaikyo Bridge built?

The ground-breaking ceremony was on 26 April 1986, construction on site began on 1 May 1988, and the bridge opened to traffic on 5 April 1998.

Who designed the Akashi Kaikyo Bridge?

The Honshu-Shikoku Bridge Authority, the government corporation that built and ran the Honshu-Shikoku bridges, now Honshu-Shikoku Bridge Expressway Company Limited. UT Austin names Satoshi Kashima as its lead designer and engineer. It is an engineering work; no architect is credited in the sources we read.

How long is the Akashi Kaikyo Bridge?

3,911 m in total, about 3.9 km, with a 1,991 m centre span between the towers and two side spans of 960 m each.

How much did the 1995 earthquake lengthen the bridge?

HSBE's engineers give 0.8 m for the centre span and 0.3 m for the Awaji side span. Other sources say about 80 cm, three feet or one metre.

What materials is the Akashi Kaikyo Bridge made of?

Steel towers, a steel stiffening truss and deck, main cables of high-strength steel wire rated at 1,760 N/mm², and concrete foundations and anchorages, including about 500,000 m³ of underwater concrete in the two tower foundations.

Planning a project that needs an engineer's eye from day one? Find an architect on MOA.

Sources

• Honshu-Shikoku Bridge Expressway (HSBE): Akashi-Kaikyo Bridge, with the official side view (accessed 4 Nov 2026)
• HSBE Bridge World: Akashi-Kaikyo Bridge, facts, weights, wind and earthquake (accessed 4 Nov 2026)
• HSBE: Development of materials (accessed 4 Nov 2026)
• HSBE: Construction technology (accessed 4 Nov 2026)
• HSBE: Survey design (accessed 4 Nov 2026)
• HSBE: History (accessed 4 Nov 2026)
• HSBE: Bridge World, Overview of the Tour (accessed 4 Nov 2026)
• HSBE: Motorcycle (125cc or less), bicycle and pedestrian path (accessed 4 Nov 2026)
• Okuda, M., Fukunaga, S. and Endo, K.: Seismic design and seismic performance retrofit study for the Akashi Kaikyo Bridge, Bridge Structures 5 (2009), pp. 109 to 118 (accessed 4 Nov 2026)
• TRID: Ninomiya, Fukunaga and Kashima, Verification of earthquake resistance of Akashi-Kaikyo Bridge, REAAA conference, 2000 (accessed 4 Nov 2026)
• TRID: Kashima and Kitagawa, The longest suspension bridge, Scientific American 277(6), December 1997, pp. 88 to 92 (accessed 4 Nov 2026)
• J-STAGE: Kawaguchi et al., Quality control of factory fabricated products for the Akashi Kaikyo Bridge cable work, 1995 (accessed 4 Nov 2026)
• IAARC: Kashima, Iho and Nakagawa, Automation and robotics of underwater concreting in huge scale steel caisson, 8th ISARC, 1991 (accessed 4 Nov 2026)
• PBS, Building Big: Akashi Kaikyo (accessed 4 Nov 2026)
• University of Texas at Austin, Department of Civil, Architectural and Environmental Engineering: Satoshi Kashima (accessed 4 Nov 2026)
• Popular Science, Sarah Wells: At 15,118 feet across, this new suspension bridge is the longest in the world, 27 March 2022 (accessed 4 Nov 2026)
• Hyogo Prefectural Maiko Park: Maiko Marine Promenade (accessed 4 Nov 2026)
• Bridge Exhibition Center: Hashi no Kagakukan (accessed 4 Nov 2026)
• Wikimedia Commons: Copyright rules by territory: Japan (freedom of panorama) (accessed 4 Nov 2026)