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MCEER/NCEER Bulletin Articles: Research

Report from the Hanshin-Awaji Earthquake: Overview of Performance of Highway Bridges

This article presents an overview of damage to highway bridges following the Hanshin-Awaji earthquake. Ian Buckle was a member of the U.S.-Japan Natural Resources (UJNR) reconnaissance team organized by the National Institute of Standards and Technology and partially supported by NCEER and the Federal Highway Administration. This team visited the Hanshin region from February 11-17. Dr. Buckle also visited the region from March 11-17 at the invitation of the Public Works Research Institute of the Ministry of Construction. Questions and comments should be directed to Dr. Buckle at (716) 645-3391. Two NCEER reconnaissance reports are currently being compiled and will be available later this year; one concerns the performance of lifelines and the other the performance of bridges.

Overview
The Hanshin region of Japan comprises parts of the Hyogo, Kyoto and Osaka Prefectures to the north and east of Osaka Bay. The population of 12.5 million people living and working in the region is served by a complex network of modern freeways and highways built in the last thirty years (since the early 1960's). These major transportation routes generally run parallel to the shoreline of Osaka Bay with major links to the east to Nara, to the northeast to Kyoto, and to the west to Himeji. As the mountains behind Kobe approach the Bay shoreline, the east-west routes are forced into a narrow corridor which is barely 3 km wide in some parts and which must be shared with three major rail lines. Soil conditions vary throughout the region but most of the highway structures are founded on sand-gravel terraces (alluvial deposits) which overlie gravel-sand- mud deposits at depths of less than 10 m. Liquefiable soils are present along the shoreline and in most ports and channels. As a consequence, piled foundations are used extensively and caisson foundations are common for those large bridges that are in port areas or cross shipping channels.

Responsibility for the design, construction and maintenance of these highway routes is divided between the Ministry of Construction and two Public Expressway Corporations. Highways under the jurisdiction of the Ministry of Construction are free for public use whereas those owned by an Expressway Corporation are toll roads and road user fees are collected. These latter Corporations are independent authorities but are nevertheless subject to government control and regulation.

The Ministry of Construction (MOC), through the Naniwa National Highway Work Office, has oversight for the National Highways (NH) in the region. These include Routes R-2 and R-43 which join Osaka with Kobe, as well as several other trunk roads such as Routes R-428 (Kobe to Chugoku Expressway), and R-171 (Nishinomiya to Kyoto and Route R-1). These arterial highways are generally surface routes but with some notable elevated sections. These include the Route 2 Hamate Bypass on the Kobe waterfront, the Port Island Connector and the 6.6 km-long, Airport Access Highway to the new Kansai International Airport in Osaka Bay.

One of the two Expressway Corporations noted above is the Japan Highway Public Corporation (JHPC) which is responsible for at least three major freeways (expressways) in the region. These are the Meishin Expressway (the first such expressway in Japan) and the Chugoku and Kinki Expressways. The Meishin runs in a northeasterly direction from Osaka Bay (at Nishinomiya) to Kyoto. Both the Chugoku and Kinki Expressways start from Suita City, just to the north of Osaka City, and run west and south respectively.

The second Expressway Corporation noted earlier, is the Hanshin Expressway Public Corporation (HEPC). It is one of the largest such Corporations in Japan and is, today, responsible for approximately 200 km of freeway-standard highway throughout the Hanshin region. Opened in 1964 with an initial length of 2.3 km in Osaka, it has grown in both size and capacity during the intervening 30 years. Almost a million vehicles per day used the system in 1994, with the highest traffic counts (131,500 per day) being recorded on the four lane, loop expressway in the center of Osaka City. For the fiscal year 1993, the average income from tolls was ¥340 million per day (approximately $3.4 million). More than 90% of the system is elevated, supported on about 8,500 spans. Of these, 83% are steel and 17% are concrete spans. Most substructures are single column concrete bents but single and multicolumn steel bents are also used to a significant degree.

The HEPC has an active maintenance program and currently spends about ¥30 billion per year (approximately $300 million) in this area. It also has an ongoing seismic retrofit program and has for many years used earthquake couplers to restrain the free ends of simply supported girders. The Corporation has recently begun to investigate the use of steel jackets for improving the performance of concrete columns and has installed some trial jackets on single column bents at the west end of Route 3.

Seismic design criteria for new structures meet or exceed those required by the Japan Road Association (Design Specifications, etc., 1990; Iwasaki et al., 1990). Furthermore, the HEPC has been proactive in the use of energy dissipators in bridges and, as early as 1981, completed the Yoshino-Tamagawa Viaduct on Route 3 in Osaka, using viscous shearing dampers. More recently, the HEPC has constructed two menshin (base isolated) bridges on Route 4 (the Wangan Route near the new Kansai Airport). These are the 4-span, Matsunohama bridge (1994) and the 6-span, Izumisano bridge (1994); both use lead-rubber (LRB) isolators. The Matsunohama bridge is instrumented for strong ground shaking with 9 accelerometers and a 23-channel data acquisition system.

Table 1: Location of Bridges with Major Damage

Route No./Expressway	Owner/Agency	No. of Bridges with Major Damage
2 (NH)	Ministry of Construction	3
3 (Hanshin)	Hanshin Expressway Public Corp.	11
5 (Hanshin)	Hanshin Expressway Public Corp.	4
43 (NH)	Ministry of Construction	1
171 (NH)	Ministry of Construction	2
Meishin	Japan Highway Public Corp.	4
Chugoku	Japan Highway Public Corp.	2
	TOTAL	27
Notes: (NH) = National Highway

Observed Damage
A large number of bridges were damaged in this earthquake and one estimate of the affected number is of the order of 60% of the total inventory. An exact number is difficult to count because of the use of long elevated sections that are tens of kilometers in length and the line where one bridge (or segment) ends and another begins is difficult to determine. Furthermore, several structures at the same interchange may be identified, in some damage reports, as one "bridge". A more precise measure of the extent of the damage is the number of collapsed and damaged spans but such information is not available at this time. Accepting these limitations, the number of highway "bridges" that sustained major damage (including collapsed spans) is on the order of 27. Many more suffered moderate-to-minor damage such as pounding, spalling of cover concrete and settlement of approach fills.

The 27 structures that were severely damaged by this earthquake are listed by route number in Table 1 and identified by name in Table 2.

Table 2: List of Highway Bridges with Major Damage

Highway (Route No.)	Bridge Name	Bridge Type
Hanshin (3)	Takashio District Overpass	Steel girders/concrete columns
	Futaba District Overpass	stell box girders/steel columns
	Tateishi District Overpass	steel box girders/steel columns
	Hirata-Fukae Overpass(1,2)	concrete girders/concrete columns
	Fukae District Overpass	steel box girders/concrete columns
	Mikage District Overpass	steel box girders/concrete columns
	Uozaki Ramps(1)	steel girders/concrete columns
	Kaigan-dori-Benten Overpass	concrete and steel girders/concrete columns
	Hyogo-Nagata District Overpass (1,3)	steel girders/steel and concrete columns
	Minatogawa Ramps (1)	steel girders/concrete columns
	Sanyo Rail Line Overpass (1)	steel box girders/concrete columns
Hanshin (5)	Nishinomiya-ko Bridge(1)	Nielsen-Lohse tied arch/steel columns
	Shukugawa Bridge(1)	steel box girders/concrete multicolumn bent
	Higashi-Kobe Bridge(1)	cable stayed deck/steel columns
	Rokko Island Bridge(1)	Lohse tied arch/steel columns
Meishin	Moribe Viaduct(1)	Concrete box girders/concrete pier walls
	Mukogawa Bridge(1)	steel girders/concrete columns
	Kawaraginishi Bridge(1)	concrete box girders/pin-ended concrete multi-column bent
	Nishinomiya Interchange
Chugoku	Takarazuka Viaduct(1)	Concrete box girder/concrete multi-column bent
	Toyonaka Overpass
National Highway (NH 2)	Hamate Bypass(1)	Steel box girders/steel columns
	Kobe-Port Island Ohashi(1)	steel box girders/concrete dual level 2-column bent
	Shioya Overpass
National Highway (NH 43)	Iwaya Overpass	Concrete girders/concrete columns
National Highway (NH 171)	Mondo Overpass Ikeda Overpass	Concrete girders/concrete columns
Notes: 1. Sites visited by UJNR Reconnaissance Team Feb. 11-17, 1995 2. Includes Higashi-Nada Viaduct 3. Includes Meiji District

It is seen in Table 1 that the HEPC suffered the largest loss, most probably because it has the largest inventory of elevated structures of any agency in the Hanshin region. One estimate for the direct cost of this damage is ¥500 billion (approximately $5 billion). Despite the ex-tent of this damage, Route 5 is expected to be reopened by Golden Week (the first week in May), except for access to Rokko Island. Route 3 will be open by the fall of 1995. Of the two routes, Route 3 is the oldest by about 30 years and this probably accounts for the higher dam-age rate compared to that on the newer Route 5.

Approximately 700 columns on Route 3 will be temporarily repaired and about 50 spans will be replaced before it is opened to traffic in the fall. Eventually, about 200 of these 700 columns will be replaced and the remainder will be strengthened to meet new seismic design criteria. By contrast, Route 5 did considerably better despite poorer soils and difficult foundation conditions. The most likely reason is the improvement in the seismic codes during the intervening 30 years and the fact that a major revision was completed to the design specification in 1990 (Design Specifications, etc., 1990; Iwasaki et al., 1990). This revision was in effect during the design of some, but not all, of the structures on this route.

Typical damage sustained by these structures includes shear and flexural failures in nonductile concrete columns, flexural and buckling failures in steel columns, steel bearing failures under lateral load, and foundation failures due to liquefaction (see figures 1, 3 and 4). In addition, there was pounding between spans, failure of several earthquake couplers, and settlement of many approach fills. Not so typical was the failure of a skewed bridge on pin-ended columns and the fracture of a set of holding down bolts in a wind shoe of a cable-stayed bridge which then led to the failure of the seismic energy dissipators and other hardware at this location.

Lessons for the United States
To bridge engineers and owners in the central and eastern United States, this particular earthquake is perhaps of greater significance than recent earthquakes in California (e.g., Loma Prieta, 1989 and Northridge, 1994). One reason for this opinion is that the predominant type of bridge in Japan is the steel girder superstructure (simple and/or continuous spans) supported by bearings on concrete columns and foundations. This class of bridge is also found throughout the central and eastern U.S., whereas bridges in California tend to be concrete box girders with monolithic bents and abutments, especially in shorter bridges.

A second reason is that an earthquake of this size was considered to be a rare event for this part of Japan. Although bridges in this region are designed for seismic loads, the design coefficients are considerably lower than those recorded during this earthquake. The possibility of an earthquake larger than the design earthquake was considered to be so unlikely that only nominal attention had been given to the problem and then only for structures designed since 1990. This difference between the maximum credible earthquake and the design earthquake is clearly very large for this region of Japan - a situation that is also considered to exist in the U.S., but to a greater degree in the eastern and central states than in the west.

It follows that the eastern and central U.S. may have more to learn from Japan than from California. Some of these lessons are as follows:

• Large earthquakes can be very destructive.
• Large damaging earthquakes can occur in areas that are considered to have, on average, only a moderate exposure to seismic hazards.
• Capacity design procedures, ductile details and generous seat widths are necessary to prevent catastrophic collapse during large earthquakes.
• Minimum connection forces need to be enforced for all seismic zones unless such connections can be shown to be fully protected by acceptable yielding of the substructures. Redundancy in connection detailing is particularly important for essential structures. Alternative load paths are necessary if the primary load path fails due to unforeseen circumstances.
• Critically important structures must be designed to a higher level of performance than that provided by current specifications, if full service is to be maintained after a large earthquake. Dual-level performance criteria and corresponding design strategies are necessary for important bridges.
• Retrofit measures reduce damage but inappropriate use and/or installation can defeat their purpose and perhaps even trigger collapse. This observation is made with particular reference to couplers (restrainers).
• Lateral spreading due to liquefaction can lead to span collapse even in modern structures with massive foundations (caissons) and well-engineered fills.
• Premature failure of some bearings appear to have reduced the seismic loads in their supporting substructures by uncoupling the superstructure from its supports. This fuse-like action may have saved a number of spans from collapse and columns from shear and flexural failure.
• Accelerations in isolated superstructures are less than in conventional structures.
• Skewed bridges are susceptible to in-plane rotation leading to displacements at supports that are larger than anticipated and subsequent collapse.

Conclusion
Damage to highway bridges was both widespread and catastrophic. Most of this distress was confined to older structures built more than 30 years ago and before the introduction of modern seismic codes. The poor performance of these older bridges and elevated expressways confirms previous lessons learned in California and elsewhere about the pressing need to retrofit the existing inventory of deficient bridges.

However, some new bridges also suffered serious damage which suggests a need to re-evaluate the design loads and procedures for these structures. There is strong evidence to indicate that the peak ground accelerations were considerably higher than the seismic coefficients used for bridge design in the region. The occurrence of this damaging but "rare" earthquake raises doubt, once again, about the correct level of the design load and reinforces the need for dual-level performance criteria. These criteria should clearly state the expected performance under both large and small, rare and frequent, earthquakes and identify design strategies and procedures that will satisfy these criteria.

Both of these observations are also applicable to the United States and in particular to those States where moderate-to-large earthquakes are considered to be possible, but rare, events.

The closure of three major expressways in the Hanshin region has had a major societal and economic impact on the region. It is expected that the indirect costs due to loss of use will exceed the direct costs of repair and replacement by the time these routes are reopened for traffic. The simultaneous closure of other transportation routes in the region, principally the rail lines, further aggravated the situation and paralyzed the region as emergency access and relief teams were forced to use surface streets. The interdependency of these lifelines, especially when collocated in narrow corridors, deserves further study.

References

"Design Specifications of Road Bridges; Part V: Seismic Design," (1990), Japan Road Association.

Iwasaki,T., Kawashima, K. and Hasegawa, K., (1990), "New Seismic Design Specifications of Highway Bridges in Japan," Proc. 22nd Joint Meeting US-Japan Panel on Wind and Seismic Effects, UJNR, Gaithersburg, MD.

 

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NCEER Bulletin, April 1995, Vol. 9, No. 2