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member—the same result can be achieved using a single piece of metal with a greater number of bends in it. This principle can be easily understood

using a piece of paper. Hold your hands about 6 inches apart and have someone lay a sheet of paper across them. The paper buckles in the middle and slips between your hands. Now fold the paper once lengthwise, and open the fold so the paper forms a V-shaped channel. If you lay it across your hands now, it retains its shape better and does not buckle and slip through as readily. In fact, the more folds you put in it, the stiffer it gets within certain limits. Multi-bend technology takes advantage

of this effect by adding folded grooves, chan- nels and returns into the overall shape. Direct Strength Design—a new analysis method that is only practical using computers—has replaced traditional Effective Width Design and has made possible the evolution of simple shapes into re- lated, higher-performing configurations that get more strength from the steel. This trend can be seen in many CFSF systems currently available. Paired with higher-strength steel—57 ksi instead of the formerly industry standard 36 ksi—it increases the overall performance of a member without significantly changing its size, weight or steel thickness.

Image #5

In cold-forming steel, another factor comes

into play. Cold working of steel, such as making the bends, alters the properties of the steel itself. The portions of the steel that are worked gain in yield strength and in ultimate strength, and see a reduc- tion in ductility. The portions that are worked the most gain the most. Advances in rollforming have led to tighter bends, meaning that steel laying clos- est to the bent edge is worked more than in the older rollforming processes. The more bends and the tighter they are, the more of the steel within the member that is strengthened by cold working, raising the overall strength of the member. A conventional U-shaped track has two

bends. C-shaped studs have four bends. A pre- engineered header in a modifi ed W shape has 14 bends, located to maximize the portions of the metal that are actively engaged in resisting load. A single piece in this confi guration can be the entire header in a doorframe. For very wide openings—more than ap-

proximately 2 m (7 feet)—or situations with high loads, multi-bend headers can be stiffened even further by incorporating a mating W-shaped insert. It adds more metal and 14 more bends, increasing the total number of bends in the over- all shape to 28. The insert is placed inside the multi-bend header with the W inverted, so the two Ws together form a rough X-shape.

The legs of the W function as the top track

of the header. They receive the cripple studs above the rough opening, which are attached with screws. This works with or without the stiff- ening insert in place. The main benefi ts of such a pre-fabricated

header/clip system are speed, consistency and an improved fi nish. By selecting a manufac- tured header system that is code-approved, the designer can specify components according to load and wall type fi re requirements, and avoid having to design and detail each individual open- ing, saving time and resources. It ensures that the rough openings will be built as designed and have consistent structural soundness and quality, without variations introduced by fi eld-cutting and assembly. Consistency of installation is increased, too, since clips have pre-drilled screw holes that leave no doubt about the number and location of connections to the jamb stud. Metal-overlapping- metal connections on the wall plane are eliminat- ed, improving the fl atness of the gypsum board fi nish and avoiding bulges. Systems like this can be an environmental

plus, too. A single-piece header can use 40 per- cent less steel than built-up elements. It requires no welding and, therefore, eliminates toxic gas emissions associated with welding galvanized steel or special inspections for welding.

Cross sections of a manufactured multi-bend header system. From left to right: multi-bend header, multi-bend stiffening insert, header with insert in place, mating attachment clip. Two clips are installed fi rst, and then the multi-bend header snaps into place around them. The stiffening insert is added (if required), and the header assembly is secured with screws.


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Images from ICC-ES Evaluation Report ESR-1765

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