AUGUST 2000
SELECTION OF STRUCTURAL STEEL BAY SIZES AND DESIGN LIVE LOADS
During the design phase, the key factor in minimizing construction costs is the use of repetitive members with fewer members. Selection of bay sizes and design live loads are design considerations addressed during the conceptual phase of a building project. Smaller bay sizes and minimum design live loads usually do not significantly reduce costs in steel-frame buildings. Alternatively, larger bay sizes and greater live loads increase the cost of materials. Fabrication and labor costs are usually more of a determining factor than material weight costs.
A 10% increase in steel construction cost translates to about a 1% increase in the total cost of the structural system. Larger bay sizes provide the Designer and Owner with greater flexibility in planning floor spaces. Potential interior partition layouts are increased by reducing the number of interior columns. The construction cost difference between a 25 x 25-ft. bay and a 30 x 40-ft. bay is about 10%. Bay spacing greater than 45 feet should be carefully evaluated to assure an economical structural system.
Using an increased design live load is more cost-effective than reinforcing existing members. Designers usually select design live loads based on the intended building use. During the life of a building, the Owner may want to change the building use resulting in the need for greater design live loads. Using an increased design live load during the original design phase increases the possible uses for a building, thus increasing the building’s value for sale or rent. Increased design live loads reduce the probability that existing structural members will have to be reinforced to support new live loads that were not accounted for in the original design.
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