Copyright Goodheart-Willcox Co., Inc. 398 Section 5 Concrete A few such materials are wood, corrugated metal sheets, plastic form liners, fiberglass sheets, formed plastic, and tempered fiberboard. Plaster waste molds can be used for fine sculpturing. Cast-in-Place Concrete Roof and Floor Systems There are four basic cast-in-place concrete roof and floor structural systems. They are pan joists, waffles, flat plates, and flat slabs. Pan Joist Roof and Floor System Pan joist construction is a one-way structural system using a ribbed slab formed with pans. See Figure 18-40. This system is economical because the standard forming pans may be reused. Standard pan forms produce inside dimensions of 20″ to 30″ and depths from 6″ to 20″. Waffle Roof and Floor System Waffle pans or forming domes are normally used to form the ceiling between levels of one floor and another. The pans or domes are placed between structural members to form the ceiling in the lower level and the floor directly above. Concrete is placed on top of the pans or domes. After the concrete cures, the pans or domes are removed. Waffle and forming domes are available in standard sizes but may be custom made for a particular job. Like pan joist construction, the forms can be reused. Figure 18-41 shows a structure built with the waffle technique. Standard 30″ × 30″ square domes have a depth of 8″, 10″, 12″, 14″, 16″, or 20″. They have 3″ flanges that provide for 6″ wide joist ribs on 36″ centers. Standard domes 19″ × 19″ square have a depth of 6″, 8″, 10″, 12″, or 14″ and form 5″ wide joist ribs on 24″ centers using 2 1/2″ flanges. Spans from 25′ to 60′ are possible using waffles. Flat Plate Roof and Floor System The main features of a flat plate system are minimum depth and architectural simplicity. See Figure 18-42. A flat plate is a two-way reinforced concrete framing system that uses the simplest structural shape—a slab of uniform thickness. Goodheart-Willcox Publisher Figure 18-40. Pan joist roof construction is a one-way structural system using a ribbed slab formed with pans. Spans of up to 50′ are common in this type of construction. Goodheart-Willcox Publisher Figure 18-41. Waffle plate construction used to form the roof slab. Spans of up to 60′ are possible. Goodheart-Willcox Publisher Figure 18-42. A flat plate roof is a two-way reinforced concrete framing system having a slab of uniform thickness.