Unreinforced masonry building
Encyclopedia
An Unreinforced masonry building (or UMB, URM building) 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. The term is used in Earthquake engineering
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
. 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
, construction of new unreinforced masonry buildings were prohibited in 1933, and state law (enacted in 1986) required seismic retrofiting
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, 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.
The California law left implementation and standards, up to local jurisdictions. Compliance took many years. As of 2008, most (but not all) of the unreinforced masonry buildings 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. 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
.
Building
In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...
where load bearing walls, non-load bearing walls or other structures, such as chimneys
Chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...
are made of brick
Brick
A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...
, cinderblock, tiles, adobe
Adobe
Adobe is a natural building material made from sand, clay, water, and some kind of fibrous or organic material , which the builders shape into bricks using frames and dry in the sun. Adobe buildings are similar to cob and mudbrick buildings. Adobe structures are extremely durable, and account for...
or other masonry
Masonry
Masonry is the building of structures from individual units laid in and bound together by mortar; the term masonry can also refer to the units themselves. The common materials of masonry construction are brick, stone, marble, granite, travertine, limestone; concrete block, glass block, stucco, and...
material, that is not braced by reinforcing
Reinforcement
Reinforcement is a term in operant conditioning and behavior analysis for the process of increasing the rate or probability of a behavior in the form of a "response" by the delivery or emergence of a stimulus Reinforcement is a term in operant conditioning and behavior analysis for the process of...
beams. The term is used in Earthquake engineering
Earthquake engineering
Earthquake engineering is the scientific field concerned with protecting society, the natural and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels...
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
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
. One problem is that most mortar
Mortar (masonry)
Mortar is a workable paste used to bind construction blocks together and fill the gaps between them. The blocks may be stone, brick, cinder blocks, etc. Mortar becomes hard when it sets, resulting in a rigid aggregate structure. Modern mortars are typically made from a mixture of sand, a binder...
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
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, construction of new unreinforced masonry buildings were prohibited in 1933, and state law (enacted in 1986) required seismic retrofiting
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 experiences with large earthquakes near urban centers,...
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, bracing or removing parapets
Parapet
A parapet is a wall-like barrier at the edge of a roof, terrace, balcony or other structure. Where extending above a roof, it may simply be the portion of an exterior wall that continues above the line of the roof surface, or may be a continuation of a vertical feature beneath the roof such as a...
and other unsecured decorative elements. Retrofits are generally intended to prevent injury and death to people, but not to protect the building itself.
The California law left implementation and standards, up to local jurisdictions. Compliance took many years. As of 2008, most (but not all) of the unreinforced masonry buildings 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
Wasatch Fault
The Wasatch Fault is an earthquake fault located primarily on the western edge of the Wasatch Mountains in the U.S. state of Utah. The fault is 240 miles long, stretching from southern Idaho, through northern Utah, before terminating in central Utah near the town of Fayette...
in the U.S. state of Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
closely parallels the state's most populous metropolitan area, the Wasatch Front
Wasatch Front
The Wasatch Front is a metropolitan region in the north-central part of the U.S. state of Utah. It consists of a chain of cities and towns stretched along the Wasatch Range from approximately Santaquin in the south to Brigham City in the north...
(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. 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
2010 Haiti earthquake
The 2010 Haiti earthquake was a catastrophic magnitude 7.0 Mw earthquake, with an epicentre near the town of Léogâne, approximately west of Port-au-Prince, Haiti's capital. The earthquake occurred at 16:53 local time on Tuesday, 12 January 2010.By 24 January, at least 52 aftershocks...
.