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A Tale of Two Cities: A Cautionary Tale



by Garrett Hagen, SE
     Design Engineer

The February 6th Mei-Nong earthquake with a magnitude 6.4, caused 117 deaths and 551 injuries. The earthquake triggered at least $100 million direct loss, left over 900 families homeless, several hundreds of buildings were red tagged and at least 11 buildings completely collapsed.

Degenkolb Engineers sent a team including myself to investigate the damage. Quite a few of the buildings we investigated were constructed with non-ductile concrete and unreinforced masonry partitions, similar to numerous building constructed in pre-1970s Los Angeles. Most of the buildings that suffered major failures had a dangerous combination of non-ductile concrete and critical seismic deficiencies. 

Thanks to a seismic retrofit program for their schools and an emergency response program for their acute care facilities, the city of Tainan, Taiwan prevented many more potential deaths and injuries: 

1. Just prior to the earthquake Taiwan had completed its K-12 school building retrofit program, in which over 400 buildings were analyzed and retrofitted if needed. The retrofit solutions addressed the major seismic deficiencies including unreinforced masonry walls (URM), soft/weak stories and torsion. Out of 334 designated “safe” buildings, only 1 building was damaged.

2. A 1200 bed hospital responsible for first-response after the earthquake had virtually no structural damage or operational disruption during the event. Lessons learned from the 1999 Chi Chi earthquake showed that many of the injured could be treated by experienced medical professionals at collapsed building sites rather than sending all of the injured to the hospital. This way, the injuries could be attended to in the most expeditious manner rather than inundating the hospital with patients and delaying treatment. Operations ran surprisingly smoothly, despite the large number of injuries at one time. 

The Taiwanese people demonstrated impressive resiliency in the city of Tainan. Los Angeles has approved an ordinance for similar non-ductile concrete structures, however our major cities could still learn a lot from the Tainan quake and there’s much preparation to be done.

Guayaquil, Ecuador

by Alvaro Celestino, SE

Degenkolb Engineers sent a team to Ecuador following the devastating magnitude 7.8 earthquake on April 16th.  The quake struck at 7:00 pm and resulted in 648 deaths, 12,492 injuries and left 130 missing. Close to 7,000 buildings were destroyed in the severely damaged northern coastal regions of the country.

As a member of the team, we visited the city of Guayaquil which is located 175 miles from the coastal cities. One would have expected that ground shaking in the Guayaquil area would have been negligible, however, the city sits on ‘soft’ soils, which tend to amplify weak seismic shaking coming from miles away. This same phenomenon can be observed in the Los Angeles basin.  Damage in the city mainly occurred to non-structural elements and a few very weak buildings.

We also visited the coastal cities where very serious damage was observed. The strong shaking resulted in the collapse of many buildings, leaving hundreds dead and thousands displaced from their homes. The method of construction in the coastal cities was similar to that of Guayaquil, confirming that the potential for severe damage is very high if (or when) an earthquake of similar magnitude occurs closer to Guayaquil. Large magnitude earthquakes seem to occur in Ecuador in intervals of 20 to 40 years.

Structural damage is often the focus of earthquakes, but non-structural damage to architectural finishes, contents, and mechanical systems is more likely to disrupt operations, result in higher losses, and be a threat to life. Non-structural damage was prevalent in the city of Guayaquil, even at low levels of shaking, which reinforces the fact that serious measures need to be taken to enhance the seismic behavior of non-structural elements. Closer to home, the California Seismic Safety Commission reported after the Northridge earthquake of 1994 that the repair cost for non-structural elements, such as suspended ceilings, mechanical and electrical equipment, and partition walls was between 50 and 80% of the total repair cost. In the US, a great deal of work has been done in the last decades to reduce this gap for new buildings, but more work needs to be done with our existing structures in large populated areas of the country.

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Posted by onayarghandiwal on June 30, 2016 9:29 AM
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