Unreinforced Masonry Building Retrofit Project
The City of Seattle is considering the possibility of mandating retrofits for buildings with unreinforced masonry (URM) bearing walls to help mitigate the losses that could result from earthquakes, such as injuries to people and damage to buildings. The objective of the program is to reduce the risk of collapse of URMs without resulting in demolition or vacation of buildings.
The City of Seattle established a high-level URM Policy Committee to help determine the answers to the issues noted below. Draft Recommendations are available now. The Committee will re-evaluate the recommendations once a cost-benefit analysis of program alternatives is complete mid-2013. Final Recommendations will then be presented to City Council with legislation anticipated by the end of 2013.
Why Retrofit Unreinforced Masonry Buildings?
Unreinforced masonry buildings have proven over the years and around the world to be the most vulnerable buildings in an earthquake. Following the Nisqually Quake in 2001, two-thirds of the buildings that were determined to be unsafe to immediately enter were URMs.
URMs are the brick buildings commonly seen in Seattle’s older neighborhood commercial cores, such as in Pioneer Square, Chinatown/International District, Columbia City, Capitol Hill and Ballard. These buildings were built without steel reinforcement and with inadequate ties and connections between building elements.
The primary reason for requiring retrofits of URMs is public safety. However, there are also concerns about retaining important buildings that are the heart of the historic and cultural character of many neighborhoods. An additional byproduct of increasing public safety in URM buildings is an improvement in the ability of businesses to reopen in a timely manner following a smaller earthquake—a city’s resiliency is key to recovery.
What Are the Current Requirement for URMs?
Seattle currently requires seismic upgrades when an owner is making a substantial investment in remodeling a building and extending the building’s life. Such upgrades generally do not bring the building up to the current code for new buildings, but help to stabilize the building enough to reduce the chance of collapse during a seismic event. URM buildings that are not undergoing remodeling are not currently required to make seismic upgrades.
The URM Survey and Study
Based on a “sidewalk survey” of buildings in the city, DPD estimates there are around 800 URM structures in Seattle. It is not known which of these have been retrofitted, but 10-15% may have been retrofitted to some degree.
URM Retrofit Standard
In 2008, DPD established a Technical Advisory Committee, which consisted of engineers, architects, building owners, and other stakeholders. This group, which worked closely with the Structural Engineers Association of Washington (SEAW), drafted a proposed standard for URM retrofits. The Technical Committee proposed a standard similar to San Francisco’s “bolts plus” minimum standard. The main feature of the standard is to tie the masonry walls to the floors and roofs with bolts. Such a standard would reduce risk of injuries and building collapse during an earthquake. However, the building itself could still be heavily damaged.
The challenging policy issues discussed included::
- Threshold for Retrofit Requirement: We anticipate single family will not be included; should other building types or sizes be excluded?
- Timeline for Compliance: What is a reasonable time period for compliance?
- Penalties and Incentives: What are appropriate penalties for non-compliance? Are there incentives that would encourage upgrades?
- Financing Options: What types of assistance might be available?
January 30, 2013