An unreinforced masonry building (or UMB, URM building) is a type of

building A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). Buildings come in a variety of sizes, shapes, and fun ...

where load bearing walls, non-load bearing walls or other structures, such as

chimney A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gases or smoke produced by a boiler, stove, furnace, incinerator, or fireplace from human living areas. Chimneys are typic ...

s, are made of

brick A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a block composed of dried clay, but is now also used informally to denote other chemically cured cons ...

cinderblock A concrete masonry unit (CMU) is a standard-size rectangular block used in building construction. CMUs are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them. Tho ...

, tiles,

adobe Adobe ( ; ) is a building material made from earth and organic materials. is Spanish for ''mudbrick''. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is used to refer to any kind of e ...

or other

masonry Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...

material that is not braced by

reinforcing In behavioral psychology, reinforcement is a consequence applied that will strengthen an organism's future behavior whenever that behavior is preceded by a specific antecedent stimulus. This strengthening effect may be measured as a higher freq ...

material, such as rebar in a concrete or cinderblock. The term is used in

earthquake engineering Earthquake engineering is an interdisciplinary branch of engineering that designs and analyzes structures, such as buildings and bridges, with earthquakes in mind. Its overall goal is to make such structures more resistant to earthquakes. An earth ...

as a classification of certain structures for earthquake safety purposes, and is subject to minor variation from place to place. URM structures are vulnerable to collapse in an

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

. 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. In

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

, the

1933 Long Beach earthquake The 1933 Long Beach earthquake took place on March 10 at south of downtown Los Angeles. The epicenter was offshore, southeast of Long Beach, California, on the Newport–Inglewood Fault. The earthquake had a magnitude estimated at 6.4 , and a m ...

resulted in a near-immediate statewide ban on construction of new unreinforced masonry school buildings. A State law enacted in 1986 required

seismic retrofit Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent exp ...

ting of existing structures. Retrofits are relatively expensive, and may include the building being tied 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 shears during an earthquake, attaching walls more securely to underlying supports so that they do not buckle and collapse, and bracing or removing parapets and other unsecured decorative elements. Retrofits are generally intended to prevent injury and death to people, but not to protect the building itself. According to the 2006-04 California seismic safety commission report, there are still 7800 URM buildings with no retrofitting in the state, including 1100 in the city of Los Angeles. The California law left implementation and standards up to local jurisdictions. Compliance took many years, and as of 2008, most (but not all) of the unreinforced masonry buildings in San Francisco have undergone retrofitting. There is particular cause for concern in regions which can generate strong earthquakes, but only rarely. Such regions may not have regulations limiting the construction of UMBs, or have only implemented them recently. Public awareness of earthquake safety may be low. For example, the Wasatch Fault in the U.S. state of Utah closely parallels the state's most populous metropolitan area, the Wasatch Front (which includes the state capital Salt Lake City). The Wasatch Front has a population of 2 million, and contains 200,000 UMBs compared with the entire state of California's 25,000.Deseret News article
/ref> Utah has recently retrofitted many public UMBs to better withstand earthquakes, but most UMBs in the state are private homes. The lack of earthquake codes preventing the construction of UMBs was a major factor in the high death toll in the 2010 Haiti earthquake.

References

{{reflist Masonry buildings and structures Earthquake and seismic risk mitigation Earthquake engineering

See also

References