My client thanks you for saving his life. However, your well educated, split second, heroic actions caused him under discomfort and harm-Thus...
Dead load is the weight of the building itself and any equipment permanently attached to it or built in.
A more accurate term is self-weight. Years ago, dead load was often piled on the building without regard for the consequences.
The modern designer more clearly understands that dead weight breeds dead weight.
Consequently, efforts are now made to lighten all parts of a building.
Removing a pound of dead weight at the top of a building enables the builder to reduce ounces at many points in the supporting structure.
As proof of the criticality of this consideration, advertisements for building materials such as gypsum shaft liners now emphasize their weight saving over the traditional masonry enclosures.
Today, buildings can be considered as being bought “by the pound.”
Fire resistance is closely related to mass.
All other things being equal, a heavier steel beam will take longer to fail due to heating than a lighter beam.
A 4- by 10-inch (102- by 254mm) wooden beam will support its load longer while burning than will a 2- by 10-inch (51- by 254-mm) beam.
This point highlights a valid general principle: Any substitute structural element that is of less mass than the element previously used to carry an equivalent load is inherently less fire resistant.
Added Dead Loads
A structure’s dead load is often increased during alteration of a building.
For example, the addition of air conditioners to the roof of a building previously without air conditioning may mean that its dead load is increased without any strengthening of the structure.
At one fire in a large city, fire fighters were overhauling a fire in a restaurant, seeking out hidden pockets of fire in the overhead.
They attacked the fire-weakened supports of the building. Above them, added-on air-conditioning units fell, causing several fatalities.
Even when a structure is strengthened to cope with the added load, the modifications may not prove adequate to avoid collapse in a fire.
For instance, if lightweight trusses are strengthened by additional trusses, there is no improvement to resistance from fire collapse because all the trusses will burn and lose strength at the same time.
In one case, a supermarket was converted to a Japanese restaurant with many grills.
Each grill required a heavy fume hood. These hoods were hung from the roof.
When the building was a supermarket, the roof did not have to support such a dead load. Now the same roof must carry the hoods—and safety has been greatly reduced.
Dead loads can be deadly—especially dead loads for which the building has not been designed.
It is critical that your local building department be notified and that a structural engineer assess the situation when you suspect a dead load is a catastrophe waiting to happen or you see dead loads on a building.
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