In April 2009, a moment magnitude Mw=6.3 earthquake struck the central region of Italy near the city of L’Aquila. While the earthquake was tragic — 305 people killed, 1500 injured, and thousands of buildings destroyed — its aftermath provides lessons for earthquake professionals. Within 10 km of the epicenter, the recorded horizontal peak ground acceleration exceeded 0.35g and the ground shaking had high-frequency content with relatively short duration. The damage indicated strong effects of site conditions, where heavy damage occurred to structures founded on young sediments. Old unreinforced masonry buildings made of mortar and multi-wythe rubble-stone or clay bricks were significantly damaged. These buildings were typically two or three stories tall and the damage ranged from wall cracking to severe damage and collapse. Some buildings with retrofitted cross-ties to reduce out-of-plane wall deformation performed reasonably well with limited cracking and no out-of-plane collapses. Reinforced concrete (RC) buildings ranged from two to eight stories tall. The majority of modern RC buildings were designed for horizontal acceleration of about 0.25g. In the epicentral region, little attention was paid to ductility requirements (e.g., smooth reinforcing bars, short lap splices, and insufficient column ties and transverse reinforcement in the beam-column joints were used). The designs appear to have ignored the effect of infill walls and some construction material was of poor quality. Although these deficiencies are serious, the widespread damage most likely resulted from the lack of ductility and the brittleness of exterior infill walls and interior partitions. There were also isolated cases of RC frame damage due to shear failures that led to soft-story mechanisms.
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