Observations on Structural Damage

October 27, 2009 by  
Filed under Structural Observations

With funding from the U.S. National Science Foundation (NSF), EERI member and structural engineer Steven Baldridge, president of Baldridge and Associates in Honolulu, Hawaii, visited Pago Pago, American Samoa, to investigate structural damage associated with the M8 earthquake and the resulting tsunami of September 29, 2009.

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Figure 1: Within the inundation zone, most of the wood-framed residences were leveled down to the foundation.

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Figure 2: Many of the low-lying villages have churches near and facing the ocean. The typical construction is a combination of concrete frames and concrete masonry unit (CMU) infill. In several cases, the tsunami entered the churches through the front door and flowed out the windows along the sides of the church. While doors, windows, and interior furniture were damaged, the structures did not appear to have any distress from the hydrostatic loading. This picture shows the pews having been ripped from the slab as the tsunami flow rushed through the church.

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Figure 3: In addition to damage from the tsunami, floating debris such as vehicles and empty shipping containers caused large localized damage to buildings.

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Figure 4: While most CMU buildings withstood the tsunami, those that were poorly constructed did not fare well. The house in this picture was leveled to its foundation, while other nearby masonry buildings survived. Many of the block cells in the walls of this were not grouted, including many that had reinforcing steel in them.

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Figure 5: This CMU residence withstood most of the force of the tsunami except for an area at the back. It appears that some scouring of the foundation may have weakened the connection of the CMU walls at their base. The water passing through the house and trying to exit through small window openings would have created large forces on this wall.

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Figure 6: The seismic event did not appear to cause much, if any, damage. However, this school, located out of the inundation zone, exhibited some odd horizontal cracking along the top reinforcing steel in concrete frame members. This may be due to some pre-existing corrosion or construction issue that had been aggravated by the ground motion of the earthquake.