Oregon is earthquake territory. Researchers and officials are urging the public to prepare for a Cascadia earthquake as more tremors are noted off the southern Oregon coast. While they’re common along the Blanco Fracture Zone, there’s more activity just off the Cascadia subduction zone near the trench, which could result in a quake with an 8.5 to 9 magnitude.
Portland city officials are aware of the dangers and are requiring the owners of unreinforced masonry buildings to retrofit the structures within the next 10 to 20 years. Because unreinforced masonry buildings are among the most likely to topple during a quake, demolition companies in Oregon are preparing to assist first responders when the Big One hits.
Why the Concern for Unreinforced Masonry Buildings?
The City of Portland has 1,650 unreinforced masonry buildings—more than any city on the West Coast. The aging brick buildings are schools, apartment buildings, offices, auditoriums, churches, hospitals, fire stations and community centers. A report commissioned by the city noted that Portland’s unreinforced masonry buildings not only pose a risk to those within them, but also to those on surrounding streets and sidewalks.
Portland officials have known the risks unreinforced masonry buildings pose for more than 20 years. In 2014, officials began writing new policies that would force building owners to upgrade the structures to prevent collapses. The retrofits would require the work of Portland demolition crews to complete. The primary motivation for Portland’s consideration of the mandatory retrofits is the safety of its populace. Historical preservation and economic vitality are also motivating factors.
Unreinforced masonry buildings are old brick buildings typically built before 1945. They were designed to withstand fires. Bricks were cheap and simple to acquire, making it easy to accommodate the large growth Portland experienced. Because the buildings weren’t constructed using modern building codes, they’re more likely to collapse during an earthquake. This is particularly true considering unreinforced masonry lacks tensile strength and is brittle. Combining a rigid, brittle structure with a fluid, moving foundation is a recipe for destruction.
The buildings in question typically have brick walls and wood-frame roofs and floors. Portland demolition contractors are well aware that unreinforced masonry buildings are vulnerable to collapses and damage during an earthquake because walls and parapets aren’t secured to floors and roofs. Incidentally, a brick parapet wall and chimney could break away from the floor and topple onto the street, putting pedestrians and nearby buildings in danger.
Making Unreinforced Masonry Buildings Safer
Upgrading an old brick building so it’s safer during an earthquake may involve:
- Bracing parapets: The areas of a wall that extend past the roof, or parapet, may need steel diagonal bracing
- Using diaphragm anchors to secure walls to the roof: Contractors secure a brick wall to the roof using steel bolts
- Using diaphragm anchors to secure walls to floors: Brick walls are tied to floors with steel bolts
In some cases, a building may require:
- Diaphragm strengthening using plywood sheathing
- Overall building bracing using steel beams
- Out-of-plane wall bracing using steel beams to connect walls to floors to keep walls from bending
While the financial cost to retrofit unreinforced masonry buildings may be high for some owners, taking the steps to secure a structure gives those living or working in and around them a greater chance of surviving an earthquake. If a building owner chooses to retrofit a structure, Portland demolition contractors can salvage the bricks for reuse during construction to retain its character. Talk to a green Portland demolition specialist today to learn about the steps Elder Demolition takes to help you save money on building retrofits.