3. Observed Damage in Railway Viaducts

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1 Structural Damage of Tohoku Shinkansen Viaducts by the Off the Pacific Tohoku Earthquake First Report on March 16, 2011 Dr. Yoshikazu Takahashi, Associate Professor Disaster Prevention Research Institute, Kyoto University (Translated by S. Otani, University of Tokyo) 1. Overview The author investigated the structural damage of the Tohoku Shinkansen viaducts from Kitakami station to Inohana No. 5 Viaducts on March 15; this portion of viaducts was severely damaged by the 2003 South Sanriku Earthquake. 2. Design of Viaducts The Shinkansen railway viaduct was constructed in 1977 and 1978 in accordance with Shinkansen Network Structural Design Standards (specifically for the Tohoku, Joetsu and Narita Lines) and Structural Design Standards for Reinforced Concrete Structures, Unreinforced Concrete Structures and Prestressed Concrete Structures, Compared to the present standards, the level of design earthquake force, the verification procedure of earthquake resistance (static seismic coefficient method used) and the required amount of lateral reinforcement are different. The Tohoku Shinkansen line was severely damaged by the 2003 South Sanriku Earthquake. Ministry of Infrastructure, Land and Transport (MLIT) ordered JR companies to study the retrofit methods of existing railway viaducts. Out of 51,000 columns of the Tohoku Shinkansen Line between Tokyo and Hachinohe, 12,500 columns were found necessary for strengthening work; the retrofit work for shear failure type columns was completed by Finally, JR-East completed the strengthening of 31,100 railway viaduct columns and 2,880 piers by April The second stage retrofit program for flexural failure type RC columns was announced to start for additional 6,700 railway viaducts from 2009 fiscal year using 5 year period. 3. Observed Damage in Railway Viaducts 3.1 Waga No. 1 Viaducts (447 km from Tokyo, 309 m long) Rigid frame viaducts with mid-height beams (Photo 1). Columns above the mid-height beams were strengthened by steel plates. No damage was observed.

2 Photo 1: Waga No. 1 Viaducts 3.2 Okajima No. 3 Viaducts (452 km from Tokyo, 279 m long) Single story rigid frame viaducts. No retrofit work was carried out, but no damage was observed in the structure. Elevated electricity poles were tilted toward the rail (Photo 2). Separation was observed at the base of piers and surrounding soil (Photo 3), which possibly indicates the vibration in the direction perpendicular to the direction of the viaduct. Photo 2: Tilting of electricity poles Photo 3: Gaps at the base of a pier and soil 3.3 Torigui No. 5 Viaducts (453 km from Tokyo, 489 m long) (Photo 4) Near the top of Pier R9 (end pier toward Tokyo), shear cracks were observed normal to the direction of the viaduct (Photo 5). Corner concrete of an RC simple girder fell, indicating the deformation in the direction normal to the viaduct. Some piers show separation at the base and soil; and also boil out sands due to liquefaction was observed (Photo 6).

3 Photo 4: Torigui No. 5 Viaducts Photo 5: Shear cracks normal to the viaduct Photo 6: Trace of boil sands at pier base 3.4 Nakasone No. 1 Viaducts (456 km from Tokyo, 103 m long) In two successive viaducts, serious damage was observed near the top of piers; near and further ends of the viaducts, concrete was separated along the placing joint; core concrete was also broken, and the column lost capability to support the weight of the structure. Intermediate columns between the ends also developed shear cracks; inclined cracks were observed in the direction normal and parallel to the viaduct, these cracks may be associated with torsion. In columns at the end of a viaduct, cracks were observed along the cover concrete from the base to the top. Repair work was started even three days after the earthquake; soil was removed to the top of the foundation girder, but no damage was observed in the foundation.

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5 Photo 7: Damage in Nakasone No. 1 Viaducts Some viaducts suffered serious shear failure at the upper part of piers near the ends of each viaduct; in one viaduct near Tokyo end, and in another viaduct further end. These shear cracks were observed in the viaduct direction. Photo 8: Shear failure observed at the top of columns in Nakasone No. 1 Viaducts 3.5 Ohki No. 1 Viaducts (456 km from Tokyo, 717 m long) Single story rigid frame viaducts. Retrofit work by steel plate jacketing was completed; no damage was observed. Further end columns were not strengthened, but damage was not observed by external

6 observation at a distance Photo 9: Ohki No. 1 Viaducts 3.6 Inohana No. 5 Viaducts (469 km from Tokyo, 301 m long) R15-1. This viaduct was severely damage by the 2003 South Sanriku Earthquake with spalling of concrete at the end columns and shear cracking in the intermediate columns without concrete spalling. In the repair work, cracks were injected with plastic resin and spalled cover concrete was replaced, followed by strengthening with steel plate jacketing. In some severely damaged columns, aramid fiber sheet was used for strengthening. Separation at the base of piers and surrounding ground was observed in the direction normal to the viaduct, but no structural damage was found. The effective strengthening work was noted. The water level is relative high in this area, and corrosion of strengthening steel plates is observed due to high humidity.

7 Photo 10: Inohana No. 5 Viaducts