AISC funds research to streamline structural steel design and construction

Raineir Square Tower in Seattle has a novel, steel-concrete composite core, part of AISC’s SpeedCore initiative that aims to speed the construction process. Magnusson Klemencic Associates

Years ago, leaders at the American Institute of Steel Construction (AISC) met to discuss ways the steel construction industry, including structural steel fabricators, could innovate. Structural fabricators deal with continual pricing pressures, and cutting costs below margin obviously isn’t sustainable.

“We soon realized that speed was the key to meaningful innovation.”

That was Chris Raebel, PhD, vice president of engineering and research at AISC. The Fabricator spoke with Raebel about the association’s research efforts around streamlining not just structural fabrication, but the entire design and construction process. He also clarified that “speed” meant more than just accelerating workflow through the fab shop, though that’s certainly one piece of the puzzle.

More significant pieces can be found elsewhere in the construction value chain—especially at the building job site. AISC’s Need for Speed initiative aims to shorten the steel construction cycle. It’s already achieved a 50% reduction, and the organization now is focusing on increasing the speed of construction even more. This sometimes can mean more work in the shop, but less time in the field usually pays for that shop work and then some. Speed the flow throughout the value chain, overall cost plummets, and everyone wins.

SpeedCore and the Bolted Connection

A prime example of this is SpeedCore, a construction method that replaces a building’s reinforced-concrete core with a steel plate wall sandwich that’s filled with concrete. Comprising that wall are sections with two hot-rolled plates connected with a series of spacer rods, which can be welded or bolted. Concrete is poured in between the plates after each section is installed on the job site. Workers on-site install the core wall, then pour concrete between the plates.

After the concrete cures, the core wall becomes a composite system. All this tie-rod bolting and welding does take time and resources at the structural fabricator. But again, the time saved on-site pays for that and then some.

“If the building goes up faster and the structural steel goes up faster, that tower crane comes down sooner,” Raebel said. “That saves time and money. The same applies to mechanical aspects, like plumbing, heating, and cooling. If the steel goes up faster, because it doesn’t have to follow the concrete core, the mechanical trades can get in the building faster.”

The system has some less obvious benefits that impact the speed of construction. Consider steel fabrication rework that often comes from tolerance issues. As Raebel explained, “Concrete core walls have a tolerance of 1 in. plus or minus, while steel fabrication has a tolerance of 1/8 in. over 30 ft. There’s a disconnect between those two sets of tolerances, and that’s where problems arise. Framing the core in steel and filling with concrete makes that incompatibility go away entirely, and you get a system that is built to tighter tolerances as well.”

SpeedCore’s first uses have been in high-seismic applications, which call for more welding, but the method applies to lower-seismic applications, too, many of which rely more on bolting.

Researchers at the University at Buffalo are designing ways to utilize bolted splice connections, including one method that uses Atlas Tube’s Shuriken pre-tensioned, blind anchor system (see Figure 1). Each nut is located on its bolt, after which a unique sheath is slid over the nut and tack-welded in place. The bolt then is removed, leaving the sheath and nut in place.

FIGURE 1. The SpeedCore wall is a composite system of steel and concrete. Plates connected by tie-rods are shipped to the job site, installed, and filled with concrete. The use of Atlas Tube’s Shuriken blind nut system is being researched to replace welded connections, reducing costs and speeding on-site construction even further. AISC

After that, the section is sent to the job site, then lifted and bolted in place, with the bolts reinserted into the nuts. Again, the arrangement can require significant bolting and tack welding time in the fab shop—but like before, money saved with faster construction on-site more than pays for that extra fabrication work.

Hit the (Metal) Deck

Structural fabricators process girders and beams, but when it comes to decking, their involvement isn’t so heavy. They might supply the decking, and the erectors would install it and any shear connectors. “But after that, it’s all concrete,” Raebel said.

The FastFloor System for commercial applications could change this scenario. Like SpeedCore, FastFloor accelerates tasks on the job site and moves more work inside to the controlled environment of the fab shop floor. “[The commercial-construction version of FastFloor] is an all-steel system, with steel plates and beams,” Raebel said.

FastFloor uses steel plates supported by beams and can be used with a raised-floor system. Being developed by a variety of industry partners—including the Charles Pankow Foundation, researchers from several universities, and several fabricator partners—the project still is in the experimental stages. Researchers continue to optimize the system, focusing on details like acoustic and vibration performance (see Figure 2).

When implemented, though, the fab shop could see some dramatic benefits. The first, and most obvious, is the additional need for fabricated steel, with every floor calling for cut plates welded to beams. Another benefit is the system’s modular, repetitive nature, ripe for automation.

“Efficient delivery is another benefit,” Raebel said. “These 10-ft.-wide, 40-ft.-modules can nest on top of each other on a flatbed. And they can eliminate the need for laydown space. They can pick these pieces right off the truck and drop them right into the structure. It’s relatively easy to install and panelized just like the SpeedCore system.”

Connecting Fast

“Along with the walls and floors, we want to see if we can speed up connections so they’re easier to install on-site and have fewer parts,” Raebel said, adding that this is the central idea behind AISC’s SpeedConnection initiative.

Among other things, the initiative involves research into two novel connection techniques. One is a drop-in flange connection being developed by researchers at Auburn University. The drop-in flange connection consists of a wide-flange beam with a coped section at the bottom flange and two angle pieces that are shop-welded to a column, girder, or other connecting section. Once the steel is in the field, erectors simply slide the beam’s web in between the two angle sections on the column (see Figure 3). The beam’s top flange sits on the angles, and erectors bolt it in place. It’s similar to building flat-pack furniture, where dowels hold parts in place until cam screws secure the connection. If research proves that the new flange connection is safe and effective, it could speed the erection process significantly. And in this case, the time savings in the fab shop could be just as significant.

“Fabricators aren’t drilling as many holes,” Raebel said. “They’re not putting in as many bolts, and they’re not welding plates. They just need a few angles cut to shape and that cope at the bottom flange, which you’d have at a column anyway. The only bolts needed are from the top flange to the angle.”

Another project involves the development of what researchers at the University of Washington call the SnapLocX column connection (see Figure 4). It’s designed specifically for axial splices in gravity columns, with one column stacked on top of the other. In this case, the structural fabricator would connect two plates on each flange in such a way that they’re splayed out slightly. When ironworkers butt the top column against the bottom column, the splayed plates on the bottom column are forced inward and clamp the top column in place. In some cases, no field bolting or welding would be required.

FIGURE 2. The FastFloor system comprises steel beams under a steel plate. A raised floor system can be placed on top. Magnusson Klemencic Associates

Raebel emphasized that this is only for gravity columns, including gravity columns in seismic frames, as long as the requirements for those frames are met. And, of course, the connection method is still in the research phase. But considering the connection method reduces or outright eliminates both on-site welding and bolting, the results could be profound.

A Holistic Look at Speed

SpeedCore, FastFloor, and SpeedConnection are just three AISC-supported research projects, but plenty of other speed-related initiatives are in the works. For instance, the organization also has a broad initiative dedicated to streamlined bridge fabrication. Raebel recently visited a bridge fabricator that has invested heavily in cobot welding.

“They realized cobots don’t need to stop, lift up their hood, and take a second to rest,” he said. “The cobot can continue laying the weld,” adding that the shop’s cobots were set up in a way that allowed them to do large-scale connection fabrication of structural plate—not your typical tabletop welding cell. “This is just one small [improvement] that, together with other projects in the value chain, add up to a much bigger increase in speed.”

Then there’s augmented reality (AR). Researchers at the University of Wisconsin-Madison, for instance, aim to use AR to accelerate construction, especially when it comes to worker training and quality assurance.

These research areas share common goals: to accelerate the project timeline; simplify fabrication and erection; and, ultimately, make the entire construction industry safer, more profitable, and more attractive to the next generation of workers. The idea is to reduce costs across the construction supply chain in a sustainable way—and not by eating into a fabricator’s margins.