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Earthquake reconnaissance trip: Chile

As part of our ongoing series on earthquake reconnaissance and education, the Reid Middleton team wanted to share some notes from our reconnaissance trip to Chile following the February, 2010 earthquake.  The report is below.

The Earthquake

Reconnaissance Team

On Saturday, February 27, 2010 at 3:34 AM (local time), the Maule region of Chile was struck by an 8.8-magnitude earthquake as the boundary between the Nazca and the South American plates ruptured along an offshore section. The area of rupture extended over 60 miles in width and nearly 300 miles in length along the Chilean cost. A similar event along the Cascadia Subduction Zone would extend from Vancouver, B.C. to Portland, OR, and from the coast to the I-5 corridor.

The M8.8 earthquake and series of 21 aftershocks greater than 6.0 in magnitude affected an area populated by approximately two million people and generated a tsunami that severely impacted Chile’s west coast and was felt across the Pacific Ocean. The earthquake and tsunami resulted in over 500 fatalities, damaged approximately 200,000 houses, and caused an estimated $30 billion in direct losses.

Our Team

Recognizing the impacts this earthquake may have on the Pacific Northwest, we had the opportunity to participate with the Structural Engineers Association of Washington (SEAW) reconnaissance team of engineers to observe and evaluate damage in the affected areas.  We traveled to the metropolitan cities of Concepción and Santiago, the coastal towns of Talcahuano and Constitución, and inland towns including Talca, Chillán, and Maipu to observe the earthquake/tsunami damage, document our observations, and learn from the behavior of high and low performance structures.

Damage Summary

The following is a brief overview of some of the damage we observed:

Alto Rio Building Collapse: The collapsed 13 -story residential building appeared to have overturned onto its side. The structure consisted of reinforced concrete shear walls for its lateral system and reinforced concrete slabs, walls, and columns for its gravity system.
Torre Higgins Building: The 20-story office building in Concepcion’s city center had significant damage, including four stories that collapsed starting on the 12th floor. Significant damage was also observed in the walls and concrete piers in the stories below the collapsed floors. It appeared that the building experienced unique dynamic effects resulting from the building’s irregularities and torsional movement.
Rio Bio Bio Vehicular Bridge: Soil liquefaction features including sand boils, ground surface settlement, and lateral spread displacements were plentiful along the east shore of the Bio Bio river. The two vehicular bridges that connected the cities of Concepcion and San Pedro were damaged because of ground deformation. The Leacolon bridge was re-opened after replacing an unseated span with a temporary truss structure, but the Juan Palo bridge remained closed because of pier damage.
Puente Viejo Pedestrian Bridge: The Veijo bridge was restricted to pedestrian traffic two years before the earthquake. Several spans collapsed during the main shock because of lateral spreading and spans continued to fall during large aftershocks.
Talcahuano Tsunami Damage: Three distinct episodes of sea level rise occurred in Talcahuano at approximately ¾, 4, and 5 hours after the main shock. The typical maximum sea level rise was 5 feet above street grade. Bridge structures, well-constructed buildings, and many nonengineered residential buildings withstood the loading, but debris (including ships) damaged many of the residences.
Constitución: The tsunami damage in Constitucion, and other coastal towns near the epicenter, was devastating. Building and industrial (e.g., pulp and paper) structures were knocked from their foundations and destroyed. Bridge structures, partly due to their low profile, did not collapse and could be navigated during our reconnaissance. Run-up heights above the ground surface were at least 10 feet along the shore, and increased considerably in narrow waterways. Many of the single-family residences near the waterfront were completely destroyed, while the residences that were protected had significant water damage resulting front the surge run-up. However, little or no structural damage was observed at the four 5-story governmental housing buildings along the waterfront, although the first-floor units had water damage up to the height of the door frame. A 2-story concrete moment frame restaurant building along the waterfront was also found to be structurally intact, although the wood façade was significantly damaged. It appeared the building was designed to allow the water to surge through the building’s first floor.
Talca City Center: Talca is located 65 miles east of the epicenter on soft rock and firm ground conditions (NEHRP site classes B and C). The stiff site conditions correlated well with damage to short period structures compared to our observations in Concepcion. Many of the single family residences were constructed with adobe rather than URM, timber, or concrete, which may have skewed this conclusion, but the performance of mid-and hi-rise buildings in Chillán and Talca supports the conclusion. Damage to the 1-3 story adobe and URM buildings in Talca was significant and widespread. This included the collapse of countless residential and commercial building in the city center. A historic cathedral in the city center also had significant damage to its URM exterior walls and towers.

Conclusion

As a design engineer, it was a humbling once-in-a-lifetime opportunity to participate in this post-earthquake reconnaissance, particularly for an earthquake with many characteristics that parallel the Pacific Northwest.

Center Tilt Up Warehouse: Damage was observed at a “Home Depot”-like store constructed with concrete tilt-up walls and steel truss roof system. A large section of the wall along the storefront had fallen out of plane, while multiple panels remained in an unstable and unbraced condition. The portion of the roof system along this wall collapsed as well after losing its gravity system.
Urban Buildings Near Central Plaza: Rocking of mid-rise and high-rise buildings was apparent based on localized damage of walkways adjacent to building columns. Damage was observed in the lower floor shear walls of these high-rise buildings. A 3-story steel braced frame shopping center had significant damage to the URM facade.
Ciudad Empresial: This office park in Santiago included 30-50 mid-rise office buildings and hotels. In general, these 4-10 story office buildings were constructed in the last 10 years and had RC shear walls, columns, and floors with masonry or glass facades. Relative to comparable buildings in Santiago, the buildings in Cuidad Empresial experienced significant structural and non-structural damage, many of which were non-operational.

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