An unreinforced masonry (URM) building is a structure with at least one wall made of brick or blocks joined by mortar with no steel reinforcing bars. URM buildings were constructed in Portland between about 1870 and 1960. Many have aged handsomely. They include historic churches, schools, and theaters, breweries, dance halls, and other landmarks that Portlanders know and love. URM buildings define the character of many Portland neighborhoods and business districts. More than 7,000 Portland households reside in multi-family URM buildings.
URM Building Risks
In an earthquake, URM buildings pose a life-safety risk to building occupants and people nearby. According to the Federal Emergency Management Agency (FEMA), “More than any other kind of construction, they can be singled out as being seismically vulnerable.” Masonry walls are heavy and brittle. When the ground shakes, the roof and floors pull away from URM building walls, which crack and crumble. Typical earthquake damage to URM buildings includes the collapse of the walls, roofs, and upper floors. Mortar weakens with age, so the risks increase in older buildings. With even light shaking, chimneys, parapets, and architectural ornaments may break off and fall. It is for all these reasons that URM buildings pose a great risk for human injury, property damage, and loss of economic use after an earthquake.y have aged handsomely. They include historic churches, schools, and theaters, breweries, dance halls, and other landmarks that Portlanders know and love. URM buildings define the character of many Portland neighborhoods and business districts. More than 7,000 Portland households reside in multi-family URM buildings.
Examples from across the world, including earthquakes in Washington, California, New Zealand, and Chile, illustrate potentially tragic outcomes for URM building occupants and others nearby during an earthquake. Fortunately, URM buildings can be retrofitted using a variety of strategies: walls can be braced; roofs, floors, chimneys, and parapets can be more strongly anchored to the walls; and building diaphragms (floors) can be strengthened. Evidence from earthquakes in other states and countries shows that URM building retrofits work. Seismically strengthened URM buildings have survived in earthquakes while adjacent un-retrofitted structures were lost.
Existing City Code
Earthquake risk in the Pacific Northwest was not well-understood by scientists until the late 1980s. In 1995, the City of Portland updated City Code (Title 24.85) to partially address the specific seismic risks of URM buildings. This code was updated again in 2004. Current code requires building owners to seismically retrofit their buildings when at least 1/3 of the building is changed to a more intensive use, the occupancy increases by 150 or more people, or the owner spends more than about $43 (FY 2016) per square foot on other improvements. A partial upgrade, to brace the parapets and tie the walls to the roof, is required when more than half of the building is re-roofed. In all cases, seismic improvements are required only when the building owner approaches the City to make other changes; structures that continue in the same use without major upgrades will never be required to be retrofitted under the current code.
Code Effectiveness Concerns
Since the City’s requirement to retrofit URM buildings was put in place in 1995, about 8% of Portland URM buildings have been demolished. Of those that remain, about 5% have been fully retrofitted, and about 9% have been at least partially upgraded. An estimated 85% of existing URM buildings have had no retrofits at all. The current regulations have not proven to be as effective in reducing the risk posed by URM buildings as had been hoped. In June 2014, the Portland City Council held a work session on Portland’s URM building risk. Based on information presented at the session, Council directed the Portland Bureau of Emergency Management (PBEM), Bureau of Development Services (BDS), and Prosper Portland to work together to propose a strategy to reduce Portland’s URM building risk. This report represents the work of these bureaus and the advisory body of engineering experts, building owners, and community stakeholders they assembled to support the effort.