Metal pan stairs filled with concrete must meet minimum strength requirements. Pan stairs have a usually steel framework, or stringers, with steel horizontal plates that have a lip a the front and back. Inside each plate or pan, concrete is poured after the framework is installed to fill the empty space in the top of the step, creating the tread. Concrete provides solid footing on the stairs.
No universal requirements exist as far as the pounds-per-square-inch load or PSI load of cast-in-place concrete stairs. Various proposals on architectural firm websites indicate that requirements usually relate to specific city code in the municipality in which the firm intends to complete its work. In most cases, firms submit their proposals with these specifications in mind.
Some firms recommend the use of concrete-filled metal pan stairs with a 33,000-lbs.-per-square-inch load minimum yield point. This is the requirement made by the San Francisco Bay Area Rapid Transit District as well. The authority indicates that 14 gauge steel should be used to build metal pan stairs. In some cases, recommendations are made in terms of pounds of pressure. Noble Building and Development in Angleton, Texas, recommends concrete that supports 300 lbs. per 4 square inches of step surface.
The concrete generally needs to meet minimum strength requirements also. For instance, the Bay Area Rapid Transit District indicates that concrete should weigh no less than 120 lbs. per cubic foot. The required strength of the concrete is 4,000 lbs. per square inch after 28 days of curing. Additional particles are usually added to ensure that the concrete has a nonslip surface.
Fabrication of concrete-filled metal pan stairs is generally performed by shops or firms that specialize in the creation of such architectural structures. Railings and stairs of this type generally have no protruding bolts or screws of any type. They are usually fabricated as one piece or as several smaller pieces that are welded at the site of construction. Concrete is usually set in place on-site as well, although there can be exceptions to this practice. If the stairs are moved with the concrete in place, caution has to be taken to avoid vibrating the stairs, which causes cracking and splitting.
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