Construction Concerns: Expansion of Metals

Article and photos by Gregory Havel

"Steel will expand from 0.06 percent to 0.07 percent in length for each 100oF rise in temperature. The expansion rate increases as the temperature rises. Heated to 1,000oF, a steel member will expand 9½ inches over 100 feet of length….If steel beams are restrained, as by a masonry structure, and the temperature of the fire is sustained at around 1,000oF, the expansion of the steel may cause the displacement of the masonry, resulting in a partial or total collapse." (Brannigan's Building Construction for the Fire Service, Fourth Edition, page 206) If the masonry or concrete walls restraining the beam are massive enough that they are not displaced, the increasing length of the beam and its weakening from the heat will cause it to buckle and fail in the middle of the span. This information has been passed on to us beginning with our Firefighter I and II courses.

Photo 1 shows an assembly of masonry and concrete walls, steel columns, steel girder trusses, and bar joists. The girder trusses and bar joists are restrained either by connection to the walls, or by welds and bolts to each other. There is no allowance in the design for expansion of the structural steel, since the temperature change between day and night or winter and summer is considered insignificant. In an air-conditioned building, the normal temperature range might be less than 20oF. In an unheated building in a cold climate, the temperature range is likely to be less than 100oF. The expansion and contraction of the steel does become a concern when there is a fire inside the building.

In any large building, metal pipes supported by structural steel may be hundreds of feet long. When these pipes carry heated or chilled water for heating and air conditioning, their internal temperatures can range from 40oF to 200oF. When they carry steam, their internal temperatures can range from room temperature to more than 300oF. When they carry domestic hot and cold water, their internal temperatures can range from 40oF to 150oF. Building and other codes require that these pipes be insulated to conserve energy.

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Steel pipes expand when heated at the same rate as structural steel. Copper pipes expand when heated at a rate about 40 percent higher than steel. Although the expansion and contraction within the pipe's normal operating temperature range may not be high enough to cause the walls to fail or the pipe to buckle, it can be noisy, and will eventually cause leaks at pipe joints if it is not controlled.

One way to control the expansion of pipes is the use of expansion joints. One type uses a section of flexible corrugated metal pipe or rubber tubing at intervals in the long run of pipe. Another type is a slip-joint fitting with a mechanical seal or O-rings. Both of these work well when they are new, but both will eventually leak and need replacement.

Another method is the use of expansion loops, which have been in use for more than 100 years. Photo 2 shows expansion loops in two steel pipes, which will carry hot water for heat in the winter and chilled water for air conditioning in the summer. This installation uses Victaulic® fittings with gaskets of a higher-temperature rubber than those used in automatic fire sprinkler systems. In this building, the runs of pipe will be restrained in the middle of the run between the expansion loops.

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Photo 3 shows expansion loops in a group of insulated pipes carrying hot and cold domestic water, hot water for heating, and steam. In this system, the restraints are at the center of the expansion loops rather than in the middle of the runs of pipe.

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Today, expansion joints are usually used where there is no space for expansion loops. Although they require less labor to install than expansion loops, they often cost more than the materials for expansion loops. In addition, they require replacement periodically.

Expansion loops are more expensive to install than expansion joints because of the labor required, but usually have a much longer life between failures. When repairs are necessary, they require less labor and less expensive materials than replacement of expansion joints, especially if the expansion loops use Victaulic® fittings.

A pipe full of water can be a significant load on the building structure.

A group of expansion loops like those shown in Photo 3 can load a structure like a rooftop air conditioner, especially if the pipes are large like those shown in Photo 2. We must keep in mind that structural steel supporting a heavier load will fail sooner under fire conditions than a similar structural member with a lighter load.

Subjects: Expansion of structural metals, building construction for firefigher operations, construction hazards