THE FEATURES AND BENEFITS OF STEEL JOISTS
This specific steel structures are widely used in USA for building construction, stadium, warehouse etc. But, apart from USA, including India, it is not so popular choice of engineers while they do design buildings or other structures. Here, we will discuss few benefits and features of Open Web Steel Joist.
R. Donald Murphy (Managing Director of Steel Joist Institute) wrote an article, where he described the benefits and features of using open web steel Joist.
- Strength-to-Weight and Multi-Directional Strength
More and more engineers are weighing the benefits of steel and steel joist construction. One reason is the amazing strength-to-weight ratio of steel joists which typically runs 25 to 1. And, steel can perform in both tension and compression,unlike concrete which must be steel reinforced to resist tensile forces.With their high strength-to-weight ratio, steel joists can support greater loads. Steel itself is a wonderfully ductile material. This ductility means that steel can be more forgiving than concrete in situations such as the recent earthquakes in California. Steel can take uplift and gravity loading because steel has inherent strength in each direction.
A high strength-to-weight ratio coupled with low price per pound of steel joists contributes significantly to lower building costs. An additional economy stemming from joistsâ€™ light weight is that structural supports such as beams, columns and foundations can be lighter in many cases. This further reduces material cost.
- Cost-Saving Ease of Erection
Steel erection is faster than concrete. You donâ€™t have the expensive labor costs for setting custom-fitting forms and installing reinforcing rods at the job site. You can work with steel in almost any weather, whereas concrete pouring is limited below 40Â° F. and, in some cases, is not recommended when
the temperature exceeds 90Â° F. And, you donâ€™t have to wait for curing and stripping forms because, once
the steel joists are properly erected and the deck installed, youâ€™ve immediately created a permanent
working platform to begin construction of the next level.
Naturally, steel joists are subject to corrosion if left unprotected and exposed to hostile environments.
Concrete can be affected in a similar way. It can crack and crumble when subjected to moisture and temperature extremes. However, steel joists have proven to be extremely durable in enclosed construction. Many years ago a bank building in New York City was tom down. The steel joists used in the construction had not suffered any deterioration despite being over 80 years old. And, the shop marks were still visible on the joists.
- Infinite Flexibility
There is infinite flexibility in the design of a steel joist building because each joist is custom fabricated
to the designerâ€™s specifications. A variable number of depths, spans and load-carrying capacities can be
custom specified and produced at the factory avoiding expensive onsite labor. One example of the low cost and infinite flexibility of a steel joist is cantilevering. Cantilevering in concrete is an expensive, labor-intensive procedure. This involves considerable form set-up and carpentry to build the supporting structure to hold the concrete until it cures. With steel joists, cantilevering can be done by specifying an
extended end or a full-depth cantilever. All of this work is done at the factory. The design flexibility of long spans can also be achieved by using steel joists. Spans of over 100 feet are not uncommon. This is not only a factor in new construction, but the greater number of support-columns needed in concrete construction often limits the designerâ€™s ability to move walls and partitions when buildings are remodeled.
- What You See Is What You Get
In an age of increasing liability and fault-finding, steel joist construction is much easier to inspect because itâ€™s exposed. The specifier can see whatâ€™s been used and whatâ€™s been done for himself. He can check the design, measure every member of the joist and review connections and fastening methods. Once concrete is poured the reinforcing bars are hidden from view. The specifier must then rely solely on the integrity of his contractor and the construction crew to assure that the job has been done properly.