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- Jerry Grana - Chicago, IL
- Jerry Grana - Chicago, IL
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Alternative Purlin Applications for Steel Buildings
There are a number of alternative types of purlins that can be used in steel building systems effectively. Two of the most popular are discussed thoroughly in this article.
A purlin style that is used in many systems is that of hot-rolled steel beams. Steel building systems came into widespread use only after many years of the introduction date for hot-rolled steel purlins. Roof framing design for industrial applications in the early twentieth century consisted of the roof trusses being spanned by hot-rolled channel and I-beam purlins.
A purlin style that is used in many systems is that of hot-rolled steel beams. Steel building systems came into widespread use only after many years of the introduction date for hot-rolled steel purlins. Roof framing design for industrial applications in the early twentieth century consisted of the roof trusses being spanned by hot-rolled channel and I-beam purlins.
Today, this approach can still be used in pre-engineered steel buildings, especially in production facilities needing substantial interior support. The popularity of hot-rolled steel beams is due to their great gauged designs. These beams can be used for spans above thirty feet.
Hot-rolled purlins are also supportive of heavy overhead loads in the interior. This design, although substantially robust, can be very expensive.
The shape of hot-rolled roof purlins are determined by the wide flanges and channels design. Their use atop the primary frame rafters is normally quite economical. Hot-rolled purlins can be used with steel decking which allows for excellent bracing and can span long distances. The load carrying ability of the deck determines the purlins' spacing. Forces acting on the purlins can be adjusted for by use of a roof-deck diaphragm or sag rod bracing. If sag rods are utilized they can be placed up to three inches below the top of the steel. This helps to reduce torsional factors.
"C" and "Z" cold-formed framing are not immediately adaptable for uplift, however, braced or unbraced hot-rolled steel purlins are easily adapted to this force.
The use of open-web steel joists is another alternative purlin design to consider. These are also known as bar joists and can span longer areas than hot-rolled or cold-formed purlins. Open web joists are very economical to use in steel building systems that are over thirty feet in span and/.or buildings requiring wider bays.
In steel building systems utilizing open-web joists, a standing-seam roof can be readily attached and the diaphragm function is supplied by cable or horizontal rod bracing. A negative to the use of bar joists is their inability to withstand substantial torsion forces as they do not have solid webs to aid in transfer of this stress.
In successful design applications utilizing bar joists to support standing-seam roofing there are two proven approaches. One is to use a steel deck and to add light gauge hat channels which run atop the steel deck perpendicular to its flutes. Another roof design procedure is to not employ the steel deck in the configuration but introduce tightly spaced cross bridging instead. The stabilization is provided by the cross bridging at the tight intervals with the entire assembly helping to resist any force applications that are present.
The shape of hot-rolled roof purlins are determined by the wide flanges and channels design. Their use atop the primary frame rafters is normally quite economical. Hot-rolled purlins can be used with steel decking which allows for excellent bracing and can span long distances. The load carrying ability of the deck determines the purlins' spacing. Forces acting on the purlins can be adjusted for by use of a roof-deck diaphragm or sag rod bracing. If sag rods are utilized they can be placed up to three inches below the top of the steel. This helps to reduce torsional factors.
"C" and "Z" cold-formed framing are not immediately adaptable for uplift, however, braced or unbraced hot-rolled steel purlins are easily adapted to this force.
The use of open-web steel joists is another alternative purlin design to consider. These are also known as bar joists and can span longer areas than hot-rolled or cold-formed purlins. Open web joists are very economical to use in steel building systems that are over thirty feet in span and/.or buildings requiring wider bays.
In steel building systems utilizing open-web joists, a standing-seam roof can be readily attached and the diaphragm function is supplied by cable or horizontal rod bracing. A negative to the use of bar joists is their inability to withstand substantial torsion forces as they do not have solid webs to aid in transfer of this stress.
In successful design applications utilizing bar joists to support standing-seam roofing there are two proven approaches. One is to use a steel deck and to add light gauge hat channels which run atop the steel deck perpendicular to its flutes. Another roof design procedure is to not employ the steel deck in the configuration but introduce tightly spaced cross bridging instead. The stabilization is provided by the cross bridging at the tight intervals with the entire assembly helping to resist any force applications that are present.