Engineers from the American Midwest have developed a new form of fibre-reinforced concrete that promises to enhance the seismic resistance of high-rises relatively easily and inexpensively.
University of Wisconsin-Madison (UWM) engineers are lending their expertise to the construction of a new skyscraper in the West Coast tech-hub of Seattle by trialling an innovative form of concrete that provides an easier solution to earthquake resistance.
The Lincoln Square Expansion, situated in the centre of the Seattle suburb of Bellevue, is comprised of two towers that will rise to a height of more than 137 metres upon completion. The 1.5 million square foot mixed-use development will house a hotel and luxury condos, as well as retail, office and dining facilities.
Key to the success of the high-rise project will be its ability to resist the seismic impacts that so frequently plague the Pacific northwest. In order to shore up the the ability of the towers to weather any earthquake shocks, the engineers are using their new fibre-reinforced concrete for all of the coupling beams that span the myriad doorways and windows throughout the multi-storey development.
Coupling beams play a critical role in heightening the seismic resistance of buildings, as they reinforce the cohesive structural integrity of walls that contain openings. This in turn enhances the strength of the the overall structure.
While adding a tangle of rebar is the standard method for augmenting the strength of coupling beams in seismic prone areas, engineers involved in the project point out that this is a costly and time-consuming approach that can slow down the construction process.
“Placement of the rebar in these link beams can sometimes control the construction schedule,” said Cary Kopczynski, head of the structural engineering firm for the development.
“Most of the west coast of the US, of course, is a highly seismic area, so when you’re building concrete structures, they require a lot of intricate rebar to carry the seismic loads.”
The alternative solution developed by UW-Madison professor of civil and environmental engineering Gustavo Parra-Montesinos involves the incorporation of steel fibres into the concrete mix as opposed to rebar. This produces beams which have a seismic performance commensurate with or better than those of rebar-based coupling beams, yet it takes less time and hassle to produce and install them.
According to Kopczynski, the adoption of fibre-concrete coupling beams for the Lincoln Square Expansion is significantly streamlining the construction process for the project.
“The reason we’re using the new coupling beams is that they’re faster, less expensive and reduce the potential for field mistakes,” he said. “With traditional coupling beams, it’s very common to have placing mistakes in the field because of all of the intricacy.
“Now, not only can we build the building faster and more simply, but we can reduce the potential for field errors.”
The fibre-reinforced concrete has already been used for the coupling beams of a 23-storey apartment complex in Seattle that was built in 2013, with plans in motion to included the new material in the building code of the American Concrete Institute.