Modified SpeedCore Adapts Game-Changing Construction System

An innovative, seismically resistant construction system known as SpeedCore has been emerging as a viable alternative to the traditional, reinforced-concrete shear wall system, and the development of a modified version is now gaining attention as a competitive alternative.

SpeedCore offers many advantages for buildings that use structural steel as a primary construction material in areas of higher seismic activity, but the expense for this enhanced system has made it less desirable for regions of low to moderate seismicity, such as the East Coast.

“We intend to simplify the on-site construction, reduce field work and deliver better value to our clients,” said Ahmad Rahimian, Ph.D., PE, SE, F.ASCE, executive vice president and director of building structures at WSP in the U.S.

WSP patented the original modified system but has since partnered with the American Institute of Steel Construction (AISC), who agreed to cosponsor the second phase of this research, Rahimian said.

Working with AISC and the University at Buffalo (UB), WSP is performing testing validation and is developing industry design guidelines for Modified SpeedCore.

SpeedCore is a composite steel-concrete system, featuring wall modules that are composed of two steel faceplates, tie bars connecting the faceplates and concrete infill. Steel plate modules are fabricated off-site, transported to a construction site, erected into final position, connected to each other and then filled with concrete in-situ.

Compared to conventional reinforced concrete shear walls, SpeedCore eliminates temporary formwork and the need for labor-intensive field placement of reinforcement bars. The system also has a competitive advantage in structural steel or hybrid buildings because the steel modules are fabricated and erected by the same contractor.

This avoids complications arising from different trades coordinating schedules, interface points, logistics and site access. These complications often lead to delays and disputes in buildings where structural steel framing is built around reinforced concrete cores.

“With SpeedCore, there’s no traditional, shear wall construction to sequence before or after steel framing installation,” Rahimian said. “A steel contractor can build an entire story at the same time, shaving weeks and possibly months off the construction schedule.”

Backed by research supported by the Charles Pankow Foundation and its industry partners, SpeedCore has been successfully used in several projects located in high-seismic urban sites on the West Coast. These studies have demonstrated that SpeedCore can significantly reduce the project’s overall construction time, with many advantages over other systems in high-seismic areas, according to David Odeh, senior vice president and national director of building structures at WSP.

Recognizing the successful experience with the SpeedCore system in earthquake-prone regions, the WSP team led by Rahimian decided to adopt the system, specifically for tall-building projects where wind loading is the governing lateral load consideration.

“We spoke to national steel erectors and fabricators to find out what can be done to make SpeedCore more cost-effective for use throughout the USA,” said Jeffrey Smilow, PE, F.ASCE, executive vice president and U.S. managing director of building structures at WSP. “They told us reducing the amount of field welding is key to increased erection speed and improved economics.”

Rahimian and his WSP team developed a jointing approach that reduces the amount of field-welding and simplifies the connections between wall modules. The new approach is to orient prefabricated steel modules in a way that lends itself to easier fabrication, transportation and field erection.

Rahimian’s team recognized that vertical and horizontal joints between modules have different function and levels of stresses and can be differentiated. The horizontal joints can be field-welded, while vertical joints that experience lower structural demand can be joined without welding.

In the modified SpeedCore system developed by WSP, vertical joints are constructed using specially designed reinforcement bars that “stitch” adjacent modules through concrete fill. Using a vertical orientation of the prefabricated module, the system also minimizes the horizontal field-welded joints.

“This approach gives steel contractors the option of fabricating narrower modules, allowing them more control over fabrication, transportation and erection in projects where wide modules may otherwise present challenges,” said Konstantin Udilovich, PE, associate, building structures at WSP.

The increased tolerance in the vertical joints between modules offered by this jointing strategy allows the steel erectors to move faster and assemble more steel modules in reduced timeframes. By reducing the amount of time spent on joining steel modules at the construction site, this approach minimizes disruptions that come from major construction projects in dense urban areas. It also improves safety for construction workers by minimizing field operations.

Another crucial aspect of the Modified SpeedCore system is an alternative design of coupling beams over openings in steel modules. These beams, also known as “link-beams,” are often some of the most critical elements of a tall building lateral force resisting system. Instead of extending the wall module face plates over the openings, WSP proposed to use conventional I-beams (rolled or built up from plates) to construct the link-beams. The I-beams can then be embedded into concrete fill between face plates.

“We use embedded steel I-beams for link-beams on many projects,” said Ilya Shleykov, Ph.D., PE, vice president of building structures at WSP. “We have a good understanding of their behavior and contractors are comfortable using them.”

I-beams also allow for openings for piping and ductwork and are easier to fabricate and construct. Both the vertical joints and the modified link-beams can be designed using provisions already covered by steel and concrete design specifications. Certain aspects of the modified system, such as embedded I-beams, have been utilized in both moderate and high earthquake hazard regions and are known to exhibit the desired seismic performance.

WSP is in the final stages of the first phase of testing of the proposed jointing system. In collaboration with AISC, this testing is taking place at the UB Structural Engineering and Earthquake Simulation Laboratory, where different configurations of reinforcement were subjected to multiple monotonic tests.

The first phase results will be reported to the industry review panel assembled by the AISC. After the completion of peer review and additional numerical studies, WSP plans to proceed to the next phase, in which joints will be subjected to cyclic testing, which will improve understanding about the seismic performance of Modified SpeedCore system.

The modified system builds upon the SpeedCore system benefits envisioned by AISC and has the potential to further increase speed and economy of structural steel building construction. It is a contractor-friendly system that has the potential to be competitive with a conventional reinforced concrete shear wall system, particularly in low- to moderate-seismicity regions.

“It is critical for the structural engineering profession to lead in developing new and innovative systems like this in order to respond to the changing construction market conditions,” Rahimian said. “By utilizing the latest research we can deliver cost savings to the steel industry and our clients.”