SmartLVL FR - Fire Rated LVL

Fireproof buildings do not exist. The contents of most buildings are combustible. As such, it is often a building’s contents, not its structural components, which pose the greatest potential fire hazard to life and property. Fire occurrences in the contents of so-called “fireproof ” buildings can be so severe that a building constructed with non-combustible framing can collapse.

The fire in Chicago, Illinois’ McCormick Place exhibition hall is a classic example. All structural members of this large exhibition hall, including interior non load bearing walls, were constructed of non-combustible materials. The fire quickly spread through the contents of the hall, generating temperatures so high that steel beams, girders and trusses buckled in the heat and the entire roof collapsed.

The building was a total loss at a cost of $150 million. With this lesson and others, the goal has become “fire safe” design, rather than “fireproof,” and it can be achieved with combustible structural materials as long as building code regulations are met.In addition to structural materials, considerations include the combustibility of contents and furnishings,interior finishes, the degree of protection provided by interior sprinklers, and the availability of adequate fire fighting equipment.

A reliable smoke detector with an alarm system and easily accessible exits are also vital in protecting a building and its occupants.Fire resistance is the length of time a structural member can support its load before collapsing. The goal of fire resistive construction is to provide adequate time for occupants to evacuate a building completely or to provide a safe haven during the passing of a bushfire.

Building fires, which normally reach temperatures of about 1000 oC, can affect the load bearing capacity of structural bearing elements in a number of ways. Apart from such obvious effects as charring and spalling of masonry/concrete products, there can be a permanent loss of strength in the remaining material and thermal expansion may cause damage in parts of the building not directly affected by the fire.

Many building materials except timber are likely to show significant loss of strength when heated above 250 ºC, strength that may not recover after cooling. 1.

There are also the well-known colour changes in concrete or mortar. The development of red or pink colouration in concrete or mortar containing natural sands or aggregates of appreciable iron oxide content occurs at 250 to 300 oC and normally, 300 oC may be taken as the transition temperature. The yield strength of steel is reduced to about 50% (half) at 550 oC and by 1000 oC, (normal temperature of building fires) the yield strength is 10 percent or less.

Apart from losing practically all of its load-bearing capacity, steelwork can undergo considerable expansion when sufficiently heated, potentially damaging or exposing gaps in cladding and plaster. The linear coefficient of expansion is 10.8 x 10-6 per degree Celsius.

The loss of strength of cold formed steel common in lightweight steel framed houses even exceeds that of hot rolled steel by between 10 and 20% .2. This means that lightweight steel framed houses are far more susceptible to the temperature effects of fire, and while they will not burn the rapid loss of strength may lead to significant structural deformation and even collapse.

References: 1. The Effects of Fire on Structural Systems by U.S. Department of Housing and Urban Development April 2007 2. Fire performance of light steel-framed buildings T Lennon, D Hopkin bre Trust Jun 1, 2011
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