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Smarter Design Creates Saving on Primary and Secondary Framing

Mcn  Kyp  Varco Pruden  July17 2

Reduce metal building costs with a few simple steps

There are numerous ways to take big chunks of money out of a steel building price just by doing a few smart yet simple things. First it is important to understand a few basics about steel design and building systems in general.

The term pre-engineered building is a bit misleading. In today's market no one pulls a building off the shelf and ships it. The preferred term, systems construction, is much more accurate as panels, purlins, bracing and frames all work together. Knowing the various components helps when putting together the most cost-efficient project for a customer's needs. Basically, systems construction is sold by the pound. To reduce steel, designers can use smart options like reducing the tributary area (loading area of a member) by:

• Adding interior columns to support the rafter on wider buildings. Typically, when a building width exceeds 80 feet, adding an interior column will reduce the rafter weight, and the price. The savings can be considerable even when including the additional cost of foundation and erection labor for the extra columns. Remember, columns may impact the customer's needs for clear interior space.

Beyond tributary loading, components in building systems have cross-sectional area (thickness, depth, amount of steel) and how this is used in a building can greatly impact overall cost.

• Reducing end-bay spacing on wide buildings saves money on the roof secondary (purlins) costs. If a project has heavier loads, costs can be reduced by cutting down the tributary area on the end bays. For example, if a building is 100 feet in length designed with 25-foot bays, price an alternate with 23-foot end bays and 27-foot interior bays. The wider the building and the more end bay purlins, the greater the price difference.

• Another tip regarding purlins: If the design reduces the purlin spacing from the typical 5-foot intermediate space used by many manufactures, at some point erection labor will impact total cost. A better option for large buildings with lots of purlins is if purlin spacing goes to 3-feet, 6-inches or closer, try increasing the purlin depth and go back to standard 5-foot spacing. Many manufacturers can provide a 10-inch-, 11 1/2-inch- or even 12-inch-deep member.

 

Primary Framing

Considering the cross sectional area of columns and rafters, engineers have a saying, "deeper is cheaper." By tapering primary framing members, systems manufacturers can provide the most cost-effective member. Tapering allows building systems to be very competitive against the conventional market. Where conventional members are straight, systems construction optimizes design by putting the steel where it is required and removing it where it is not.

A similar principle applies when restricting the depth of a member (to finish around it or hide it behind a wall or roof, for example), if the cross-sectional area cannot be achieved in the depth, it must be made up in flange size, which can greatly increase the cost of the member.

If requested to hold to strict depth requirements, showing the customer how much is saved by going from 10 inches straight to 12 inches straight may convince them. If nothing else, it shows concern and smarts in looking for the best possible solution.

When depth restrictions are required but only to a certain height, try straight-then-tapered columns (often called supermarket columns). Design them, for example, 12 inches straight to 12 feet, 6 inches and then taper, perhaps above a ceiling where they are concealed.

Lastly, consider open web rafter frames for large spans and heavy loads. The open web members are economical compared to solid web frames. Open web also provides benefits including running pipe, wiring and sprinklers through the open area. Open web members are typically more rigid and easier to erect-a benefit for all involved with the project. Meeting the customer's project needs is first priority. However, if using smarter design techniques available with systems construction offers the customer money-saving options, it's a win-win!

Stephen Hudak is training/education coordinator at Varco Pruden Buildings, Memphis, Tenn. To learn more, visit www.vp.com.