Summary on Investigation to Buildings Damaged by 1999 Kocaeli Earthquake in Turkey

1999年8月17日、トルコ共和国西部のコジャエリ県ギョルジュク付近を震源とする大地震が発生し、イズミット市などトルコ西部地域に甚大な被害をもたらした。筆者は日本建築学会調査団の一員として主に建物被害調査に従事した。トルコでは中・低層の鉄筋コンクリート造集合住宅が多く、耐震壁のほとんどない柱・梁骨組構造が主である。柱のみで・水平力に抵抗することになるが、柱断面が小さいために保有耐力が極めて小さかった。壁として用いられる中空レンガは地震力にはほとんど抵抗せずに脆性的に破壊した。また、主筋として用いられる丸鋼の定着詳細などが不適切であった。これらが層崩壊を含む激しい被害の生じた原因と考えられる。ギョルジュク市では2300棟余の建物の被害状況を調査した結果、完全に崩壊した建物の割合(全壊率)は13.2%であった。震源の東にあるアターパザル市街の建物被害はコジャエリ県についで多く、地盤の液状化による建物の転倒が多く観察された。建設途中で大破した6階建て鉄筋コンクリート集合住宅を詳細に調査したところ、1階柱の柱頭・柱脚の曲げ破壊が多数生じていた。また1階および2階の梁の曲げひびわれやせん断ひびわれも目立った。略算によるベース・シア係数は0.25であり、日本における純フレーム建物の80%程度と小さかった。A big earthquake with the Magnitude of7.4 whose epicenter was located on the vicinity of Golcuk City occurred on August 17,1999, in the west part of the Republic of Turkey. The earthquake caused severe damage to buildings and many casualties. The author engaged in the damage investigation to buildings as the one of the members of the Architectural Institute of Japan Reconnaissance Team. There are many low-or middle-rise apartment houses made of reinforced concrete (R/C) in Turkey. These buildings resist the earthquake horizontal load by only the columns since the buildings consist of the open frames without shear walls. The horizontal load carrying capacity in the buildings was very poor because of the small cross sectional area of columns. The hollow bricks used as the curtain-walls could not resist the earthquake attacks and failed brittlely. The anchorage details of plain steel bars arranged as the longitudinal reinforcement was inappropriate in many buildings. It is supposed that these factors caused the story collapse of buildings. The damage investigation to whole buildings in the specified areas in Golcuk was carried out. The ratio of the number of entirely collapsed buildings to the investigated buildings of approximately 2300 was 13.2 percent. Many buildings suffered from severe damage by the earthquake in Adapazari (Sakarya) similarly with Kocaeli Prefecture. Several buildings inclined such as the rigid body due to the liquefaction of the soil. The six story reinforced concrete apartment house under the construction was researched in details since the drawings for the structural design was obtained accidentally. Many columns in the first story failed by the flexural compression of the concrete at the top and bottom ends. The cracks along columns and beams were remarkable. The base shear coefficient was 0.25 approximately by the quick computation. This is 0.8 times that of frame buildings designed generally in Japan