The design features pre-fabricated cold-formed steel joists, rim track and structural blocking. The cold-formed steel joist roof structure at Convent Hill has the strength and stiffness to support five terraces each filled with a variety of greenery.įigure 3. The roof membrane is a screw fastened 1½-inch B deck with tapered insulation and ballasted EPDM roofing. Double C-sections 12-inch deep x 2-inch flange x 97 mil thickness where used for the longer 24-foot spans and 8-inch deep x 1-5/8-inch wide flanges x 43 mil thickness were used to span the corridors. Joist bridging was typically at 6 to 7 feet on center. The roof joists are cold-formed steel C-sections, 10-inch deep x 2-inch wide flange x 54 mil thickness, spaced at 24 inches on center for the 15-foot spans. The perimeter of the web holes had rolled edge stiffeners to add web strength and stiffness over the entire span of the joist. These joists leverage the strength and formability of cold-formed steel with punched web holes to accommodate HVAC, mechanical, plumbing and sprinkler runs. From the second floor upward, the structure features cold-formed steel joists that were prefabricated into panels to shorten construction times and eliminate on-site labor. The combination of concrete and some structural steel with cold-formed steel supports 120 senior apartments and five rooftop garden terraces. The main lateral resisting system is cast-in-place reinforced concrete stairs and elevator cores. Cast-in-place concrete was used for the foundation walls, lower slab and shallow footings. Design Solution and Special ConsiderationsĬold-formed steel framing is the primary load-carrying structure for the upper residential stories. The structure, which features 12,000 square feet of green roofs, represents “a new level of sustainable and green technology,” states the Milwaukee Journal Sentinel.īut how could the structure support the green roofs without a large and significant use of structural steel? Matsen Ford Design Associates, Waukesha, Wisconsin, engineered the project’s cold-formed steel system, which comprises the majority of the structure’s support system. For the present redevelopment, the city wanted to take advantage of the latest environmentally friendly building designs. The City of Milwaukee had the Convent Hill complex built in 1959. The concrete core also aided in detailing and fire rating of the shafts. The concrete core was chosen over discrete bracing or cold-formed steel shear walls due to building height restrictions. The cast-in-place concrete cores served to resist the lateral loads resulting from both wind load and seismic load. The main lateral resisting systems are cast-in-place reinforced concrete stairs and elevator cores. The foundation walls, lower slab and footings are cast-in-place concrete. Hot-rolled steel with cold-formed steel joists were used strategically for only the first two floors.