Solutions in Steel

Understanding the overall concepts of each structural steel system can strengthen decisions made during the design process and allow for productive discussion and collaboration with the project team. The choice of structural system is not just based on material costs, but also accounts for the methods of construction, amount of on-site labor, and complexity of design. Systems that are efficient in design often prove to be economical in the construction phase.

Thin Floor Systems

Architects are frequently faced with solving the owner’s desire to maximize the number of residential stories in a limited building height allowance. Specialized steel beam and precast hollow-core plank systems can help the building industry to address this need. Reducing the floor plate thickness in a building provides many benefits: lower floor-to-floor heights, savings on overall building energy, and a lighter structural weight, to name a few. Steel systems are available that allow the top and bottom planes to include both the structural floor and the structural beams in an 8-inch or 10-inch-deep system. Lightweight floor systems as slim as 8 inches span 30 feet without the need for beams projecting below the slab. The equivalent flat plate system in an all-concrete solution requires rebar and formwork, adding to the on-site labor requirements. Wood framing typically requires deep joists to meet the average spans for mid-rise and high-rise apartments and condominiums. Buildings implementing a structural steel thin floor system have saved enough overall height in some applications to add additional floors and maximize the building total square footage.

In an efficient and economical thin floor system scenario, steel beams support precast hollow-core planks. Grout fill is used to lock the beam and plank together and create composite action on-site. The underside of the plank is commonly used as a finished ceiling that is smooth and regular. Savings in both time and material are achieved by exposing the underside of the structure. Compared to an all-concrete framing solution, a structural steel system utilizing a thin-floor system is 50 percent lighter in weight. Reducing the loads supported by foundations leads to reduced project costs. The thin floor system allows for a rapid speed of erection due to the prefabrication of plank and steel. Reduction in on-site labor and the elimination of formwork are major benefits in saving time and costs. Other trades are able to access floors faster to complete their work, condensing the overall construction schedule. In a market where speed governs, architects must factor in the time for building completion in their overall design services to meet the owner’s schedule. A number of buildings have implemented specialized thin floor systems in North America.

Image courtesy of Stantec Architecture

THIN FLOOR SYSTEM: GLASSHOUSE

In 2014, the GlassHouse project broke ground in Winnipeg, Canada, using the Deltabeam thin floor system developed by the Peikko® Group. Designed locally by the international practice Stantec Architecture, this high-end 21-story residential building promises floor-to-ceiling glass in a cool modern aesthetic for 196 condominium units. To meet the need for speed, the project team implemented a thin floor structural steel system to advance the erection process in the most economical way. The modified beams, known as Deltabeams, have been UL tested to achieve 2-hour, 3-hour, and 4-hour ratings without the need for additional fire protection on the beam itself. The underside of each exposed beam is painted black in contrast with the exposed hollow core plank ceilings, stark white walls, and warm walnut flooring. Steel columns are architecturally exposed and coated with a black intumescent paint to meet the required fire protection. The typical floor-to-floor height is 9 feet 10 inches separated by thin 10-inch horizontal bands on the facade. Architect and Senior Associate Michael Banman along with Fletcher Noonan, design leads of GlassHouse at Stantec, are well-versed in the Deltabeam system. Banman elaborates, “In our practice, it is vital to consider concept, construction, and structure simultaneously, holistically. The organization, clarity, repetition, and rhythm of the exposed structural steel and of the construction assembly facilitate the construction schedule. This in turn lowers construction costs and reduces the cost of owning while providing a more sophisticated space in which to dwell.” The steel is tracking on schedule and the building is set for completion in 2016.