Kocaeli (Izmit), Turkey Mw 7.4 Earthquake

On August 17, 1999, at 3:02 a.m. local time, an Mw 7.4 earthquake occurred along the North Anatolian fault in northwestern Turkey.

Fig. 1. Fault rupture on the North Anatolian fault (inset map). Numbers without circles or parentheses show horizontal offset (m); numbers in parentheses, vertical offset (m). Circled numbers show recorded peak ground accelerations (percentage of g). (Map, and fault displacement data compiled, by F. Swan of GEOMATRIX.)

The epicenter was near Izmit, the capital of Kocaeli province, 90 km east of Istanbul. As of September 29, 1999, the Prime Minister's Crisis Management Center (PMCMC) reported 15,802 people dead; 43,872 injured; and thousands homeless. The majority of deaths and injuries were in the provinces of Kocaeli, Sakarya, and Yalova (fig. 1). According to a survey by the PMCMC, more than 66,441 houses have been destroyed, 67,242 are moderately damaged, and 80,160 are lightly damaged.

The PEER Center sent to the epicentral region a structural engineering reconnaissance team consisting of Kenneth Elwood, Khalid Mosalam, Halil Sezen, and Andrew Whittaker of UC Berkeley, John Stanton of the University of Washington, John Wallace of UCLA, and Atila Zekioglu of Ove Arup and Partners, Los Angeles. The team was joined by Jay Love and Chris Smith of Degenkolb Engineers, and Nesrin Basoz of K2 Technologies. This team was complemented by a geotechnical engineering team supported by PEER and others.

Geological and Geotechnical Aspects

The 900-km-long North Anatolian fault, which has many characteristics similar to the San Andreas fault in California, is one of most extensively studied right-lateral strike-slip faults in the world. During the August 17 earthquake, the North Anatolian fault ruptured for approximately 110 km, with a maximum horizontal offset of 4.1 m measured east of Sapanca Lake and a maximum vertical offset of more than 2.3 m observed in the region east of Gölcük (figs. 1 and 2).

Fig. 2. Vertical settlement with no damage to nearby building

The distribution of recorded peak ground acceleration in the region affected by the earthquake is also shown in fig. 1. Liquefaction and settlement caused much of the damage in the epicentral region. Subsidence of a large area around Gölcük and Degirmendere, caused flooding and extensive damage to buildings close to the shoreline.

Building Codes and Construction Practice

The first seismic code in Turkey was developed following the 1939 M 7.9 Erzincan earthquake. The code was revised several times in the 1940s, and in 1953, 1961, 1968, 1975, and 1997. In each period, the design philosophies and requirements were as modern as other seismic codes. Reduction factors for system ductility were indirectly introduced in the 1975 code. The 1997 code is similar to the 1994 Uniform Building Code; for ductile reinforced concrete moment frame buildings, the response reduction factor is 8.

Reinforced concrete moment-resisting frames are the most common lateral-force-resisting system in Turkey. Shear walls are not commonly used. Concrete components are generally cast in place with site batching common for residential construction. Precast concrete is used only for beams, columns, and walls in industrial buildings. Steel moment-resisting frames and braced frames are used for industrial construction but almost never for residential construction.

Damage to Residential Construction

During the Kocaeli earthquake, thousands of four- to seven-story reinforced concrete frame buildings fully or partially collapsed, and a number of buildings overturned. Damage was localized in the larger cities with the greatest concentrations of collapsed buildings located at sites where the foundation materials failed due to liquefaction. Only a few residential structures were constructed using reinforced concrete shear walls, and these buildings performed well.

Most of the structural failures in the reinforced concrete frame buildings observed by the reconnaissance team could be traced to a lack of transverse reinforcement in columns and beam-column joints, to inadequately anchored longitudinal reinforcement, to poorly located lap splices of longitudinal reinforcement, and to plan and vertical irregularities. Poor quality concrete was observed in a number of the failed buildings. Insufficient transverse reinforcement resulted in column shear failures such as that shown in figure 3.

Fig. 3. Shear failure in lightly reinforced concrete column

Several buildings experienced multiple column shear failures without collapse. One building (fig. 4) lost a second-story corner column due to collapse of the neighboring building but did not collapse.

Fig. 4. Column lost due to collapse of adjacent building

These examples of severe component failures that did not result in system failures raise important questions regarding the relation between component performance and system performance and the often-used design assumption that system failure (or exceedance of a limit state) is directly related to the failure of individual components. (Such relations are currently being studied at the PEER Center.)

Damage to Industrial Facilities

The earthquake struck the industrial heartland of Turkey. The most significant damage to an industrial facility observed by the reconnaissance team was at the Tüpras refinery in Körfez, located approximately 20 km from the epicenter. Eight tanks containing naphtha fuel burned following the earthquake (fig. 5).

Fig. 5. Fire damage to naphtha tanks at Tüpras refinery.

Oil was spilled into the Sea of Marmara. Other damage at the refinery, which was designed and constructed in the 1960s, included the failure of floating roofs in crude oil tanks; failure and fire in a cooling tower; collapse of the upper 80 m of a 115-m-tall smokestack onto a processing unit and piping system; and fractured piles beneath a jetty that supported fuel-oil piping that served oil tankers.

Structural damage was observed at a number of industrial facilities including the failure of components of precast concrete warehouses, collapse of concrete column supports for tanks of liquid oxygen, and significant translation and rotation of above-ground tanks containing propane and other flammable gases.

The reconnaissance team visited two power generation/transmission stations. At the 380-kV substation in Adapazari, older porcelain disconnect switches and aluminum castings were damaged in the switching yard, and large transformers moved up to one meter on their rails. At the Enerjisa power generation facility, an 80-ton boiler dislodged from its pedestal foundation; transformers moved upwards of one meter; one transformer rolled off its pedestal foundation and overturned; the foundation of a heat exchanger was badly damaged; and porcelain switches failed.

Conclusions

The M 7.4 Kocaeli earthquake resulted in great human and economic loss. Failures of older residential construction were widespread and severe, especially in zones that liquefied. Fault rupture, liquefaction, subsidence, and strong ground shaking caused such failures. Reinforced concrete moment-resisting frames were the most common lateral-force-resisting system and such construction routinely employed details similar to those used in the United States prior to the 1970s. Shear wall buildings performed well with no observed failures.

Industrial facilities suffered significant damage but complete structural failures were few in number. Fire following the earthquake caused severe damage to the Tüpras refinery. Other observed structural failures in the refinery were to a 115-m-tall smokestack, floating roofs in crude oil tanks, and piles supporting a jetty. Substations and one power generation facility suffered damage ranging from overturned transformers to fractured porcelain switches.

Acknowledgments

The PEER reconnaissance team received advice and support from many institutions and individuals. The faculty of the Department of Civil Engineering at Bogaziçi University and Professor Mete Sozen of Purdue University are due special thanks for assisting the PEER reconnaissance team and for providing insight into design and construction practice in Turkey.

Halil Sezen and Kenneth J. Elwood
Graduate Student Researchers
UC Berkeley