Most recent edit on 2005-10-29 16:31:07 by EschaTon

Additions:
The truss is an engineered structural member that uses a rigid geometric form – usually the triangle – to provide a load caring [either "bearing" or "carrying"] capacity greater than the sum of its parts. A truss is typically made of wood, steel, a combination of wood and steel, or aluminum.

The lightweight wood truss industry has known for some time of the dangers there [their] product represents in fire situations. According to the Wood Truss Council of America’s online time line, the use of fire retardant treated lumber in truss construction was first introduced in 1981 (Industry Timeline). Mainly due to cost, and without building code legislation that requires it, this practice has not take hold in the industry. Today, most all [either most or all, but not both] trusses are produced with untreated lumber. Even if the industry used treated lumber, the third vulnerability still exists. The gang-nail is still prone to warping and pulling out under fire conditions.
In order to remedy these problems, a number of things must happen. First and foremost, fire personnel must be trained in how to identify the presence of lightweight trusses in buildings. According to the NIOSH Alert, this is best done during pre-incident planning and inspections and in turn the fire department should enact stander [standard] operating procedures to fight fires in the buildings with known lightweight trusses. NIOSH also suggests that the fire department get involved in writing building codes and enforcement procedures regarding truss use in buildings (NIOSH, pp. 6-7).

Some of the building considerations that may limit the vulnerability of the truss include requiring fire sprinklers in truss voids to extinguish fires before they compromise the truss’s integrity. Building codes may also require the addition of a locking screw on each side of the gain[gang]-nail to keep it from warping and pulling out when exposed to the heat of a fire. Both of these solutions would take time to implement, all the while, more building will be erected using lightweight trusses [this last clause is a little confusing. There has to be a better way to coordinate your ideas here]. To better inform the firefighter about already existing buildings with lightweight truss construction, code can require the use of identifying stickers at the entrance to all commercial or public buildings that utilize truss construction. The State Of New Jersey already requires such stickers:
[This is a great paper. It is well researched, clearly written, and informative. You still have some proofreading issues and a few messy sentences, but, overall, this was both an interesting and informative read.]

Deletions:
The truss is an engineered structural member that uses a rigid geometric form – usually the triangle – to provide a load caring capacity greater than the sum of its parts. A truss is typically made of wood, steel, a combination of wood and steel, or aluminum.

The lightweight wood truss industry has known for some time of the dangers there product represents in fire situations. According to the Wood Truss Council of America’s online time line, the use of fire retardant treated lumber in truss construction was first introduced in 1981 (Industry Timeline). Mainly due to cost, and without building code legislation that requires it, this practice has not take hold in the industry. Today, most all trusses are produced with untreated lumber. Even if the industry used treated lumber, the third vulnerability still exists. The gang-nail is still prone to warping and pulling out under fire conditions.
In order to remedy these problems, a number of things must happen. First and foremost, fire personnel must be trained in how to identify the presence of lightweight trusses in buildings. According to the NIOSH Alert, this is best done during pre-incident planning and inspections and in turn the fire department should enact stander operating procedures to fight fires in the buildings with known lightweight trusses. NIOSH also suggests that the fire department get involved in writing building codes and enforcement procedures regarding truss use in buildings (NIOSH, pp. 6-7).

Some of the building considerations that may limit the vulnerability of the truss include requiring fire sprinklers in truss voids to extinguish fires before they compromise the truss’s integrity. Building codes may also require the addition of a locking screw on each side of the gain-nail to keep it from warping and pulling out when exposed to the heat of a fire. Both of these solutions would take time to implement, all the while, more building will be erected using lightweight trusses. To better inform the firefighter about already existing buildings with lightweight truss construction, code can require the use of identifying stickers at the entrance to all commercial or public buildings that utilize truss construction. The State Of New Jersey already requires such stickers:

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Edited on 2005-10-29 16:23:10 by EschaTon

Additions:
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Edited on 2005-10-29 16:20:46 by EschaTon

Additions:

Lightweight truss may cause Firefighter Death

One hallmark of today’s economic growth is the availability of relatively inexpensive building techniques. These techniques, such as lightweight trusses, may not always be the safest. An example would be the Foxdale Village auto port fire. Only minutes after the first fire apparatus arrived on scene, a fire in one of the auto port’s 14 two car bays caused the entire roof structure to collapse: a structure built using lightweight wood trusses. A survey of the scene after the fire found that the lightweight wood trusses failed. Without training and building codes that specifically address the fire hazards and threats caused by the use of lightweight truss construction, many civilian and fire fighter lives may be lost due to early structural collapse during fire situations.
The truss is an engineered structural member that uses a rigid geometric form – usually the triangle – to provide a load caring capacity greater than the sum of its parts. A truss is typically made of wood, steel, a combination of wood and steel, or aluminum.
Italian architect Ande Palladio (1860 – 1880) is credited with developing the three forms of the basic truss. In 1955, the gang-nail (gusset plate), a mechanical fastener that simplified truss construction, was invented by J. C. Jureit. His company, Gang-Nail Systems Inc (now MiTek Industries) revolutionized lightweight truss construction to the point that all mechanical fasteners are now generically called gang-nails (Industry Timeline).
First utilized in the home building boom of the 1950s, the lightweight truss uses less lumber and can span further openings than roof rafters of similar strength. These benefits, in addition to the inexpensive cost of production, have led to lightweight truss use in more than 60% of all building roofs in the United States. In recent years, with the development of the parallel wood chord truss, lightweight truss systems can now be found as the structural support for floors as well (NIOSH, pp2-3).

According to the NIOSH Alert, “Engineered building components,” like the lightweight truss, “may provide adequate strength under normal loading; but under fire conditions, these truss systems can become weakened and fail, leading to the collapse of roofs, floors, and possibly the entire structure” (NIOSH, p3). Lightweight truss systems provide three avenue of vulnerability to fire. The first vulnerability is that trusses are structural components of the building and are usually hidden from public site. As such, a fire in a truss system may go unnoticed for long periods of time. This allows the fire to grow in size as it weakens the wooden members of the truss. Secondly, the truss has

more wooden surface area that can be exposed to fire. All three components of the truss, the top and bottom chords as well as the web members, may be made from 2x4s, whereas the rafter it replaced may have been a single 2x6 or 2x8. Therefore, the truss provides more wooden surface area exposed to the fire. The third, and sometimes overlooked, fire vulnerability of the truss is the gang-nails used to hold the members together. One of two things will happen to the gang-nail when exposed to the heat of a fire. The heat may cause the plate of the gang-nail to buckle and bend, popping the teeth out of the wood destroying the structural integrity of the truss. Or, the gang-nail may transfer the heat of the fire down its teeth to the soft pine wood of the cord or web member. The gang-nail will do this because it resembles a heat sink. It has a large flat metal surface area, commonly 3 by 5 inchs, which can collect heat and then transmit it down its 3/8th inch teeth into the pine wood that comprises the truss members. This heat transfer will hasten the charring of the wood covered by the gang-nail leading to the point of early structural failure.

The lightweight wood truss industry has known for some time of the dangers there product represents in fire situations. According to the Wood Truss Council of America’s online time line, the use of fire retardant treated lumber in truss construction was first introduced in 1981 (Industry Timeline). Mainly due to cost, and without building code legislation that requires it, this practice has not take hold in the industry. Today, most all trusses are produced with untreated lumber. Even if the industry used treated lumber, the third vulnerability still exists. The gang-nail is still prone to warping and pulling out under fire conditions.

These vulnerabilities were born true in a series of tests conducted by the Los Angeles City Fire Department in May of 1982. One of the tests utilized parallel chord lightweight wood trusses in a floor system. According to the test, the time of failure was one minute and twenty seconds after fire involvement. The study concluded that failure was caused by two factors. First, once the 2x4s were charred to a depth of 1/4th inch, the gang-nails pulled out. And second, once the gang-nails pull out, the truss looses its structural integrity (Mittendorf, pp. B 15-16).

In order to remedy these problems, a number of things must happen. First and foremost, fire personnel must be trained in how to identify the presence of lightweight trusses in buildings. According to the NIOSH Alert, this is best done during pre-incident planning and inspections and in turn the fire department should enact stander operating procedures to fight fires in the buildings with known lightweight trusses. NIOSH also suggests that the fire department get involved in writing building codes and enforcement procedures regarding truss use in buildings (NIOSH, pp. 6-7).

Some of the building considerations that may limit the vulnerability of the truss include requiring fire sprinklers in truss voids to extinguish fires before they compromise the truss’s integrity. Building codes may also require the addition of a locking screw on each side of the gain-nail to keep it from warping and pulling out when exposed to the heat of a fire. Both of these solutions would take time to implement, all the while, more building will be erected using lightweight trusses. To better inform the firefighter about already existing buildings with lightweight truss construction, code can require the use of identifying stickers at the entrance to all commercial or public buildings that utilize truss construction. The State Of New Jersey already requires such stickers:
Truss Placard-State of New Jersey; NJAC 5:70-2.20(a) 1 and 2 [NJAC 1992]
Until the threat that lightweight wood trusses pose the fire service and the public is brought to light, expect an increase in their use as unprotected structural element, in new buildings. Even after building codes have been adopted to lessen the threat from new truss construction, the threat from buildings already built will still exist. Therefore the firefighter must, through training and planning, become aware of building conditions that my fail due to fire conditions. Without that knowledge, the safety of civilians and firefighters may continue be to be compromised.
WORK CITED:
“Industry Timeline,” Wood Truss Council of America, On Line

<www.woodtruss.com/timeline.php>

“NIOSH Alert: Preventing Injuries and Deaths of Fire Fighters due to Truss System

Failures.” National Institute for Occupational Safety and Health, 2005.

NIOSH Publication No. 2055-132
<www.cdc.gov/niosh/docs/205-132/>
Mittendorf , Capt. John, “Building Construction for the Fire Suppression Forces:
Principles, Wood and Ordinary Construction.” National Fire Academy, June, 1986, Appendices B: “Lightweight Construction: Tests Open Fire Service Eyes to Special Hazards,” Excerpted from Western Fire Journal, January 1982
By Captain John Mittendorf, LACFD

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The truss is an engineered structural member that uses a rigid geometric form – usually the triangle – to provide a load caring capacity greater than the sum of its parts. A truss is typically made of wood, steal [steel], a combination of wood and steal, or aluminum [I would word this: "wood, steel, aluminum, or some combination of these materials." Should make your meaning clearer].

Deletions:
The truss is an engineered structural member that uses a rigid geometric form – usually the triangle – to provide a load caring capacity greater than the sum of its parts. A truss is typically made of wood, steal, a combination of wood and steal, or aluminum.

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Oldest known version of this page was edited on 2005-10-19 02:17:06 by Squad514 []
DRAFT
10-18



The lightweight wood truss may be helping more people afford their first home, but without training and building codes that specifically address the fire hazards and threats caused by this building material, many civilian and fire fighter lives may be lost due to early structural collapse.


The truss is an engineered structural member that uses a rigid geometric form – usually the triangle – to provide a load caring capacity greater than the sum of its parts. A truss is typically made of wood, steal, a combination of wood and steal, or aluminum.


IMAGE)

Triangular truss
(Image courtesy of NIOSH)

Italian architect Ande Palladio (1860 – 1880) is credited with developing the three forms of the basic truss. In 1955, the “Gang-Nail” – a mechanical fastener that simplified truss construction – was invented by J. C. Jureit. His company, Gang-Nail Systems Inc (now MiTek Industries) revolutionized lightweight truss construction to the point that all mechanical fasteners are now generically called gang-nails (Industry Timeline).

(image)

A gang-nail with exposed teeth
(Photo courtesy of NIOSH)



First utilized in the home building boom of the 1950s, the lightweight truss uses less lumber and can span further openings than roof rafters of similar strength. These benefits, in addition to the inexpensive cost of production, have led to lightweight trusses being used in more than 60% of all building roofs in the United States. In recent years, with the development of the wood parallel chord truss, lightweight truss systems can now be found as the structural support for floors as well (NIOSH, pp2-3).


image)
A gang-nail with exposed teeth
(Photo courtesy of NIOSH)

size as it weakens the wooden members of the truss. Second, there is more wooden surface area on the truss to be exposed to fire. A truss may be made from multiple 2x4s as both the top and bottom cord and as the web members where as the rafter it replaced may have been a single 2x6 or 2x8. This provides more surface area of wood to become involved in fire. The third, and sometimes overlooked, fire vulnerability of the truss is (ARE?) the gang-nails (gusset plates) used to hold the members together. The gang-nail most resembles a heat sink. It has a large flat metal surface area that can collect heat and then transmit it down it’s three-eighths inch teeth into the pine wood that comprises the truss members. This heat transfer will hasten the charring of the wood covered by the gang-nail leading to the point of early structural failure.

These observations were born true in a series of tests conducted by the Las Angeles City Fire Department in May of 1982. One of the tests utilized parallel chord lightweight wood trusses in a floor system. According to the test, the time of failure was one minute and twenty seconds after fire involvement. The study concludes that failure was caused by two factors. First, once the 2x4s were charred to a depth of 1/4th inch, the gang-nails pulled out. And second, once the gang-nails pull out, the truss looses its structural integrity (Mittendorf, pp. B 15-16).




Work Cited to follow.