Surigao, Philippines: Examining Damages after the 6.7-magnitude Earthquake on February 10, 2017
Linnel examining the soft story collapse of a building in Surigao
From February 23 to February 25, 2017, Carl and Linnel from our engineering team in the Philippines performed post-earthquake reconnaissance following the 6.7 earthquake in Surigao Del Norte, on the north side of the island Mindinao. The team investigated and documented the response of rural school buildings and informal urban housing in the area, which will help inform our retrofit efforts in Manila and further our understanding of the seismic vulnerability of school buildings. The highest concentration of damaged housing exists in Surigao City, and San Francisco has experienced the most significant damage to schools. Unfortunately, San Francisco is inaccessible due to collapsed bridges and damaged roadways, and the team’s efforts have therefore been focused in Surigao City.
In plane wall cracking and out of plane wall failure due to lack of ring beam
Soft story collapse in Surigao, Philippines
Surigao City is a moderately dense city with a population of about 160,000 people. The team flew into Butuan on Thursday, about 4 hours south of Surigao City as the Surigao airport was closed (the runway sustained substantial damage requiring the suspension of service). Many large scale commercial buildings, hotels, and hospitals of masonry construction in the city area have been closed due to sustained damage.
Soft story collapse of 3 story mixed use residential and commercial building
Masonry gable wall failure.
The Build Change team coordinated with the Provincial Disaster Risk Response Management Office to locate the most heavily impacted areas. They have observed and encountered a wide range of housing typologies including unreinforced masonry, infill masonry, masonry skirt wall, timber post with masonry infill, lightweight timber, and masonry ground story with timber upper-story construction. The majority of homes are limited to 2 stories or less.
2 story masonry infill construction experiencing permanent tilt due to settlement of foundation. Example of good construction above grade but inadequate foundations.
Minor wall cracking on 2 story masonry infill construction. Neighboring buildings were heavily damaged and ground ruptures were visible, although building foundation did not exhibit damage. Example of good construction and good building response.
Wall out of plane failure of school building due to lack of a ring beam
The team observed damage in all building typologies, however only in buildings that exhibited noticeably substandard construction were severely damaged or collapsed. Encouragingly, buildings that used common Philippines construction practices either experienced minor damage or no damage at all, even when neighboring homes were completely destroyed.
The most common failures for masonry construction were out of plane wall failure. The most common for timber was soft story failure and a lack of complete lateral system.
The team completed their reconnaissance on Saturday, February 25 and returned to Manila. The results and observations will be used to continue development of retrofit manuals for urban environments such as those in Metro Manila.
This work may be cited as follows: The Build Change Guide to Resilient Housing: An Essential Handbook for Governments and Practitioners. Denver, CO: Build Change, 2021.
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