Introduction to the Girder-Slab® system and design tool V3.4

What the Girder-Slab system is and why it was developed

The Girder-Slab system came out of a collaboration between an engineer, a general contractor, and a fabricator who were looking for a viable alternative to conventional cast-in-place concrete construction. The problems they wanted to solve were practical ones: lengthy curing times, the cost and coordination burden of shoring and falsework, multiple trade sequencing conflicts, heavier structures that drove up foundation costs, and the difficulty of winter construction in cold climates. The resulting system is a shallow floor profile method that relies on the chemical and mechanical bond between the steel D-beam girder, the grout, and the hollow core plank.

Girder-Slab Technologies was founded in 1997 and has completed roughly 300 projects, primarily in the US, with growing activity in Canada, India, the Middle East, and Australia. The project type list covers hotels, apartments, condominiums, mixed-use, assisted living, student housing, self-storage, correctional facilities, and office buildings across a height range of 4 to 40 stories. More than 70 percent of the company's business comes from repeat clients.

How the system is constructed

A single trade, ironworkers, handles both the steel framing and the precast hollow core plank installation. This is a significant scheduling advantage over conventional construction, where concrete forming, reinforcement, and placing crews operate in sequence. Because shoring is not required, follow-up trades can access completed floors immediately rather than waiting for the structure to clear.

The D-beam girder is a fabricated element made from standard wide flange shapes using a castellated cutting pattern, with zero waste in the production process. Two identical castellated tees are produced from a single wide flange and welded together with a narrower, thicker top flange. Two families of D-beam exist: an eight-inch series and a nine-inch series. The eight-inch series is used with eight-inch hollow core plank, and the nine-inch series with ten-inch plank. A variable topping, up to two inches, is placed using lightweight leveling compound, normal weight concrete, or lightweight concrete.

Year-round construction is possible without heating and hoarding costs because the grouting step can be scheduled to favorable weather windows rather than being a continuous cast.

Technical design and the D-beam calculator

The design tool is a sophisticated Excel-based calculator provided at no cost by Girder-Slab Technologies to engineers and architects. It covers D-beam selection for a given span and tributary width, incorporating composite section analysis that normalizes concrete and grout components into an equivalent steel stress analysis. The neutral axis positions for both the non-composite and composite sections are computed, and the results display strength and serviceability checks against current code requirements.

A worked example shown during the webinar used a 16-foot-plus span with a 16-foot tributary width and an eight-inch D-beam with eight-inch hollow core. Input included 64 PSF self-weight, 140 PSF grout density, 35 PSF superimposed dead load (25 PSF two-inch topping plus 10 PSF for MEP and finishes), 15 PSF partitions, and 40 PSF reducible live load. The output confirmed that all strength and serviceability checks were satisfied for that section selection.

Design tools are available in US AISC LRFD Imperial format, metric, Canadian CSA, and Australian and New Zealand standards. Additional free resources include a downloadable design guide, typical sections in DWG format, Revit Structure families, and cutting patterns in DXF format for fabricator plasma cutting tables.

Fire rating, acoustics, and MEP coordination

The system is listed under UL K912 for two-hour and three-hour fire ratings, with Canadian recognition under BX UV 7. Fire protection is applied to the D-beam bottom flange, which is the only exposed steel surface, because the remainder of the girder is encased in grout and plank. Methods include cementitious spray or gypsum board boxing. In some configurations, drywall finishing that extends past the bottom flange, or fire-rated walls that automatically enclose the framing, provides the required rating without supplemental protection.

Acoustically, hollow core floor systems with topping achieve STC ratings above 50, which is a primary reason hotel owners favor the system. From an MEP standpoint, the completed floor platform gives mechanical and electrical trades a clean, shoring-free working surface, allowing horizontal service runs without structural interference.

Project outcomes and construction speed

The Edmonton International Airport Renaissance Hotel is a frequently cited project. Originally designed as an eight-story cast-in-place concrete building with a tight deadline and liquidated damages provisions, the project was fully redesigned using the Girder-Slab system. All eight stories were retained within the height restriction, winter construction proceeded without heating and hoarding costs, and the project saved six months off the construction schedule and 15 percent off the capital cost. The owner subsequently upgraded the project to Renaissance branding.

At 400 West Elm in Conshohocken, Pennsylvania, a 12-story, 400,000 square foot apartment building set a record installation pace of 23,500 square feet of steel framing and hollow core per week. That pace became the fabricator's new baseline for comparable projects.

Two projects in Massachusetts by separate design teams using different fabricators demonstrated that supply and design competition exist in the market. An NYU Manhattan project used conventional steel for the lower six levels and the Girder-Slab system for the residential towers above, successfully combining the two approaches. A Calgary East Village Hilton Hotel replicated the Edmonton result: six months saved off the construction schedule and 15 percent off the capital cost.

Diaphragm performance, seismic applications, and system limits

For lateral load resistance, the structural engineer selects the vertical system: cast-in-place shear walls, steel braced frames, or shear cores. The hollow core diaphragm transfers wind and seismic shear to those elements following conventional design rules or PCI guidance. The integrated steel grillage in the Girder-Slab system provides diaphragm performance superior to conventional steel framing with Nelson studs. Some engineers increase topping thickness to two or three inches specifically to improve diaphragm chord performance in high-seismic zones.

Diaphragm frame values are still being quantified. Auburn University is conducting push-out tests on variable conditions, with component and full-scale system tests planned.

The system handles live loads of 100 to 125 PSF using heavier D-beam sizes at reduced spans, which has opened up self-storage as a growing market segment. For elevated parking and podium applications, the system is used regularly, with conventional framing placed above the GSS podium level.