continued

These units were typically supported by steel beams over which top reinforcement was positioned in the continuous member pockets to provide continuity of the floor slab system. This precast system was capable of spans from 10 to 25 feet.

Tee Stone System

This precast member could be used as a floor beam, roof beam, or wall panel, and was originally manufactured in New York. The T-section was 8 inches deep, with a 16-inch-wide flange and a one-inch-wide stem, and was manufactured in standard lengths of 8 and 16 feet. For floor construction, the T could be installed in either a flange-up or flange-down position. The units were placed in the field with a one-inch gap between the edges of the flanges, which was filled with grout. The flange mesh reinforcement extended into these continuous gaps to produce a monolithic slab.

Pyrobar Precast Roof System

This cast gypsum system was manufactured for use as a roof slab and was available in both 3-inch-deep solid and 4-inch-deep hollow-core sections for short-span applications, as well as 5- and 6-inch hollow-core sections for long-span applications. The short-span sections were made in 12-inch widths and 30-inch lengths. The long-span sections were made in 18-inch widths and lengths from 4.0 feet to 6.5 feet. The short-span members were typically supported by steel bulb tees, while the long-span members were supported by underslung steel wide flange and channel beams.

All of the above precast systems were designed based on the basic reinforced concrete beam analysis theories of their era. Load tables were also commonly developed and published by most of the manufacturers.

The problem with all of the above systems, when one encounters them in a building, is that in the absence of existing drawings, it is difficult to determine the internal reinforcement and, consequently, the load-carrying capacity of the system. However, it is hoped that this article, by identifying the many different types of products that were in use at one time or other, will facilitate research of antiquated or archaic systems when they are encountered in existing structures.

D. Matthew Stuart, P.E., S.E., F.ASCE, SECB, is a licensed structural engineer in 20 states. He currently works as a senior project manager at the main office of CMX, located in New Jersey, and also serves as an adjunct professor for the master's of structural engineering program at Lehigh University in Bethlehem, Pennsylvania.   More by D. Matthew Stuart

This article is reprinted from the September 2008 issue of STRUCTURE magazine, with permission of the publisher, the National Council of Structural Engineers Associations (NCSEA).

References

Kidder, Frank E., and Harry Parker. Architects' and Builders' Handbook, 18th ed. John Wiley & Sons, Inc., 1956.

Specification and Load Table Archives. Nitterhouse Concrete Products, Inc., Chambersburg, Pennsylvania.

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SUBSCRIPTION SAMPLE The Watson precast concrete system, type A. Source: Architects' and Builders' Handbook by Frank E. Kidder and Harry Parker Extra Large Image The Miller precast concrete system. Source: Architects' and Builders' Handbook by Frank E. Kidder and Harry Parker Extra Large Image SUBSCRIPTION SAMPLE The Lith-I-Bar precast concrete system. Source: Architects' and Builders' Handbook by Frank E. Kidder and Harry Parker Extra Large Image The Tee Stone precast concrete system. Source: Architects' and Builders' Handbook by Frank E. Kidder and Harry Parker Extra Large Image The Pyrobar precast concrete roof system. Source: Architects' and Builders' Handbook by Frank E. Kidder and Harry Parker Extra Large Image Prefabricated and site-cast concrete elements combine to form the shells of the Sydney Opera House. Photo: Amanda Slater Extra Large Image   Click on thumbnail images to view full-size pictures.