MFG Construction Products Co. (div. of Molded Fiber Glass Cos., Ashtabula, Ohio) manufactures fiberglass forms for cast-in-place concrete construction. The company has recently been involved with demanding applications at historic locations, including a $59 million (USD) library expansion at the U.S. Military Academy at West Point, N.Y.
Designer STV Inc.'s (New York, N.Y.) complex entryway concept for the buildingï¿½s first-floor faï¿½ade included two vertical columns with arches spanning 25 ft/7.7m (column to column), adorned with cloverleaf-shaped cast reliefs. Though a decorative feature, the exposed concrete columns also had to support a portion of the buildingï¿½s dead load.
Rick Rohrer, senior project manager for formwork subcontractor Ceco Concrete Construction (Gladstone, Mo.), notes that the complexity and compound radii of the arches and columns made site-built wooden forms impractical. Ceco contracted with MFG to design and build custom fiberglass forms. MFG's engineering manager Eric Brace converted the architectï¿½s design data to shop drawings and built a three-dimensional digital model. This allowed the CNC machining of a series of male plugs for the arches and columns. Because only two arch plugs were needed (two of the three arches are identical), low-cost wood and masonite were cut to form the plugs, says Brace. MFG then hand-layed chopped strand mat (CSM) reinforcement wet out with isophthalic polyester resin supplied by AOC Resins (Collierville, Tenn.) over the plugs to create the forms, adding reinforcing ribs of standard 2x lumber on the reverse side to stiffen the large mold surfaces. A total of 16 subforms were pulled from the plugs for the two columns and three arches. Flanges were integrally molded into each subform to facilitate assembly, and finished forms were wet-sanded and buffed to meet requirements for a smooth concrete finish. The finished subforms were assembled at MFG's facility to ensure accurate fit, then disassembled and shipped to the job site on July 17 this year.
At the site, the forms were bolted together through the flanges. The seams at mating edges were filled with silicone caulk. With rebar in place, forms were filled with self-compacting concrete, which chemically optimizes air release to ensure a smooth finish.
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