On 12 May 2008, a magnitude 8.0 earthquake struck China, approximately 80 km west of Chengdu in the Sichuan (Wenchuan) province and 1550 km southwest of Beijing. The fatalities exceeded 70,000 and millions were injured or left homeless. Damage was estimated at over US $150 Billion. Thousands of unreinforced masonry and reinforced concrete buildings collapsed or sustained severe damage. Schools and hospitals were especially hit hard and many collapsed. Many factors contributed to the unprecedented level of devastation. For the collapsed buildings, the lack of ductility, the absence of a well-defined load path, and the building irregularity were primary contributors. Many used a hybrid structural system comprised of masonry columns, concrete beams, and hollow precast decks. This system was responsible for a disproportionate number of collapsed buildings. By comparison, non-ductile reinforced concrete framed buildings performed slightly better. Many of these buildings sustained significant damage, but did not collapse. For concrete framed buildings, the presence of masonry infills introduced additional failure modes. For many buildings, the infill walls were terminated at the first floor introducing weak story at the ground level. Captive column failure was also common resulting from attachment of partial height infill walls to concrete columns. The observed types of damage have previously been witnessed in many parts of the world in past earthquakes. Fortunately, robust, simply implemental, and cost-effective retrofit methodologies have been developed to alleviate such failures. Analytical tools, experimental data, and available knowledge provide the basis of the suggested retrofits with the objective of strengthening and adding ductility to the structure to protect vulnerable non-ductile components. Both conventional and innovative retrofits options are available. Many school and hospital buildings in Istanbul, Turkey also use the same type of construction and are hence vulnerable to collapse. To mitigate this, the government of Istanbul with under the auspices of the World Bank, has developed a program to retrofit thousands of such buildings. In this endeavor, local engineers, and international experts work together to identify suspect buildings (using available plans and site visits), assess the conditions, device a retrofit strategy, and inspect construction sites to ensure that the design, construction and quality control and assurance meet the current knowledge for adequate strengthening to ensure that the retrofitted buildings provide life safety. The authors were some of the first foreign structural engineers to reach the area and survey the damage. Their observations and recommendations for future mitigations are presented in this paper.
H.K. Miyamoto1, and A.S. Gilani, Miyamoto International, Inc.
Akira Wada, Tokyo Institute of Technology, Tokyo, Japan