3 Unreinforced masonry building


Unreinforced masonry building

An Unreinforced masonry building (or UMB) is a type of building where load bearing walls, non-load bearing walls, or other structures such as chimneys are made of brick, cinderblock, tiles, adobe, or other masonry material that is not braced by reinforcing beams.cite web|url=http://www.earthquakecountry.info/daretoprepare/building/urmwalls.html|title= Houses with Unreinforced Masonry Walls|publisher=Earthquake Country Alliance The term is used as a classification of certain structures for earthquake safety purposes, and is subject to some variation from place to place. [cite web|url=http://www.abag.ca.gov/bayarea/eqmaps/shelpop/typ2_f.html|title=Typical Unreinforced Masonry Building Damage |publisher=Association of Bay Area Governments]

UMB structures are vulnerable to collapse in an earthquake. One problem is that most mortar used to hold bricks together is not strong enough. Additionally, masonry elements may "peel" from the building and fall onto occupants or passersby outside.cite news|url=http://www.bizjournals.com/eastbay/stories/2004/02/23/focus5.html|publisher=East bay Business Times|date=2004-02-20|title=Quake shows danger of retrofit neglect|author=Broderick Perkins]

In California, construction of new unreinforced masonry buildings was prohibited in 1933, and state law enacted in 1986 required seismic retrofitting of existing structures. Retrofits are relatively expensive, and may include tying the building to its foundation, tying building elements (such as roof and walls) to each other so that the building moves as a single unit rather than creating internal shear during an earthquake, attaching walls more security to underlying supports so that they do not buckle and collapse, and bracing or removing parapets and other unsecured decorative elements. [cite web|url=http://www.sandiego.gov/development-services/industry/urmexamples.shtml|publisher=City of San Diego|title=Visual Examples of Seismic Retrofit Construction:Earthquake Caused Damage to Unreinforced Masonry Buildings] Retrofits are generally intended to prevent injury and death to people, not to protect the building itself.

The California law left implementation, and standards, up to local jurisdictions. Compliance took many years. [cite web |title=Unreinforced Masonry Building Law Update|date=1999-10-04|url=http://www.fema.gov/news/newsrelease.fema?id=10493|publisher=FEMA] As of 2008 most but not all unreinforced masonry buildings have undergone some retrofitting.cite news|url=http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/06/29/MNDD110U2E.DTL|title=S.F. leaders ignore weak buildings' quake risk|author=Robert Selna|publisher=San Francisco Chronicle|date=2008-06-29]

ee also

*Earthquake engineering

References


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