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Unreinforced Masonry Buildings: A Hidden Danger

July 23, 2014

Did you know that almost 1,000 buildings in Seattle are unreinforced, and only about 15% of those buildings have had the necessary seismic upgrades to make them earthquake safe?

Many buildings are constructed of unreinforced masonry (URM) and prone to collapse in an earthquake.

A Bit of Background

During the early to mid-19th century, wood was plentiful, and cities all over America were booming, especially on the West Coast. Gold fever struck, and Seattle became a major stopping point for those heading to Alaska, while Californians were discovering gold up and down their state. Many cities needed a cheap, easy-to-acquire material to accommodate huge amounts of growth as quickly as possible.

Forests were cleared, and wood was the obvious choice for building. By the end of the 19th and beginning of the 20th century, many large cities in America experienced huge fires, sometimes more than one, that devastated city centers. Even Seattle had its own massive fire, joining Chicago and other cities — including Washington state cities Ellensburg and Spokane — which then had to rebuild.

Many builders switched to joisted masonry construction because masonry, whether it’s concrete, adobe, brick, stone or another material, is relatively noncombustible, especially in comparison to wood. While the contents and combustible flooring within these buildings are susceptible to fire, the external structures themselves tend not to be.

Buildings severely damaged by an earthquakeThough unreinforced masonry buildings are somewhat resistant to fire,
they are prone to severe earthquake damage

 

Related:
Do You Know Your Earthquake Classifications for Buildings?

 

These buildings are still susceptible to fire due to combustible roofing and combustible floors in multi-story structures, but they’re designed to fall in on themselves when they collapse and don’t spread fire to other buildings quite so easily. Masonry also helps contain a fire  within a structure for longer, whereas fire easily spreads between wooden buildings.

Problem solved, right? Unfortunately, that's not the case. Unreinforced masonry is notoriously brittle and lacks tensile strength, a measure of how much stretching or pulling a material can withstand before it falls apart. Earthquakes move the earth in all different kinds of waves, causing structures standing on top of it to oscillate; that is, earthquakes cause structures to move and bend. When you combine a rigid, brittle structure with a moving, fluid foundation, you have a recipe for building safety problems.

In fact, looking at a long string of earthquakes from the 1906 San Francisco earthquake to the 1994 Northridge quake reveals examples of URM buildings suffering from complete collapse. 

The Nisqually Earthquake was a magnitude 6.8 with an epicenter located near Anderson Island, about an hour and a half south of Seattle. Had the earthquake been located closer to the city, many more URM buildings would likely have collapsed. 

What can we do? Going back to cities built from wood is not practical, and URM buildings are obviously unsafe. The solution, it ends up, is reinforcing buildings.

The Case for Reinforced Masonry Buildings

The entire West Coast of the United States, and some states across the South, require builders to use reinforcing structures (check out this publication by FEMA to learn more). Buildings can be reinforced using pre- or post-stressed concrete (sometimes referred to as pre- and post-tensioned) during the construction process. Existing URM structures can be retrofitted to give them the strength and stability they need. Indeed, modern reinforced masonry buildings are proving to be safer and more reliable in earthquakes while helping to prevent massive fires in most major U.S. cities.

 

Related:
To Educate Customers about Earthquake Risk, Look Beyond Fault Lines

 

Retrofitting — Costly but Worthwhile

Fortunately, these URM buildings all over Washington state, and the country, are not just sitting ducks. Retrofitting, even 100 years after the building was constructed, is possible and effective. Many major U.S. cities are undergoing retrofitting programs or are working with building owners to address these issues.

The process is slow and requires careful consideration because retrofitting a building is often prohibitively expensive. After the Nisqually Earthquake in 2001, the City of Seattle passed a ballot measure to retrofit 32 of the city’s fire stations that were not properly reinforced. Over $197 million in tax dollars were collected to upgrade these structures. Some building owners in Seattle have said that it may cost as much as $1.5 million to update a single building.

Why spend the money to retrofit? If URM buildings are not reinforced prior to a quake, much of them may need to be rebuilt after. More importantly, however, is life safety. Retrofitting a building helps prevent damage or collapse, and keeping the structure sound means the people living or working inside have a much higher chance of surviving the shake.

What Does This Mean For Your Insurance?

Earthquake coverage is not included on a standard insurance policy in Washington state and must be bought separately. If you live in or own a business in a URM building and an earthquake completely or even partially collapses your business, home or apartment, your regular policy will not cover you or your belongings for the earthquake damage. That’s pretty scary.

Talk with your agent about purchasing earthquake insurance, and make sure you understand how it works. It’s always best to understand the coverage you’re buying and what it means before disaster strikes.


Robert Lacy, WSRB's Vice President, Inspection Services & Professional Development, oversees our team of commercial property analysts as they produce advisory loss costs, commercial property reports and evaluate automatic fire sprinkler systems. He is involved in the annual evaluation of our loss cost levels and ensuring we are current on coding and rating issues for commercial property. He also works to encourage continual professional development for all WSRB employees.

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