Copyright Goodheart-Willcox Co., Inc. 404 Section 5 Concrete Prestressed Panels Standard-shaped concrete panels that are prestressed have brought a new concept to architec- tural precast concrete. These units are crack-free and highly resistant to deterioration. Common designs include double-tee units, single-tee units, and hollow-core panels. Figure 18-51 shows a structure with double-tee roof units. Double-tees are the most widely used prestressed, precast units. Widths are generally 4′, 5′, 6′, 8′, and 10′. The 4′ and 6′ widths are the most popular sizes. Depths range from 6″ to 36″. Spans up to 60′ are possible with the 4′ wide unit. Greater spans are possible with wider units since they usually have a deeper web. Single-tee units are generally used where long spans, beginning at about 30′, are needed. They can be placed flange to flange, as shown in Figure 18-52, or spread apart with concrete planks or cast-in-place concrete completing the enclosure. Flange widths range from 4′ to 10′ with depths from 12″ to over 36″ in 4″ increments. Spans of 30′ to 100′ are common with single-tee units. Goodheart-Willcox Publisher Figure 18-50. Crane lifting panels in place. As more panels are erected, the final building structure becomes more identifiable. Gage Brothers in Sioux Falls, SD Figure 18-51. Double-tee concrete units are the most widely used prestressed concrete product for medium range spans. Four foot wide double-tees are commonly used for spans up to 60′. Goodheart-Willcox Publisher Figure 18-52. Single-tee precast, prestressed concrete units are generally used for very long spans. Typical spans are from 30′ to 100′.