- Author
- Abrams, M. S. | Gustaferro, A. H.
- Title
- Fire Endurance of Concrete Floors With Embedded Electrical Underfloor Ducts.
- Coporate
- Portland Cement Assoc., Skokie, IL
- Report
- Bulletin 216, October 1967, 32 p.
- Keywords
- floors | reinforced concretes | ducts | fire endurance tests | fire tests
- Identifiers
- embedded service ducts; pan-joist slabs
- Abstract
- This paper reports on the results of fire tests of 35 pilot specimens (3x3 ft) and 2 full-scale floor specimens (14x18 ft). In the pilot tests, one level of ducts was embedded in slabs, 5-, 6-, and 7-in. thick, and two levels of ducts in slabs 7-, 8.5-, and 10-in. thick. Full-scale specimens were pan-joist floors in which the slab was thckened 1.5 in. in the area where two levels of ducts were used. Nominal slab thicknesses were 5 and 5.5 in. The ducts caused no visible structural distress during the fire tests. Fire endurance was governed by the temperature rise of the unexposed surface. Where one level of ducts is used (without junction boxes), slab thicknesses of at least 5.3 in. and 6.6 in. are required for 2-, 3-hr fire endurance. For two levels with junction boxes, slab thickness requirements are approximately 6.5 and 7.5 in. for 2- and 3-hr fire endurance. Endurance periods were slightly greater for lightweight concrete, or if ducts contained wires during fire tests. States during the past 10 years and the attending wider use of precast, prestressed concrete structural shapes for building construction has created a nned for basic design information on the fire resistance of prestressed concrete. This paper is the first of a series of reports which have been planned as contributions to this need. The results of standard ASTM fire tests conducted on 18 pretensioned, prestressed, concrete "I" beams of 20-ft span are analyzed and discussed. the principal variable of the study was concrete covering thickness over the prestressing steel. The influence of concrete coverings in 1-, 2- and 3-inch thicknesses in normal weight and expanded shale lightweight concretes were investigated. Various other factors affecting the structural behavior of the beams and the results of the fire tests are described. Some observations are included relative to proper covering thickness, with qualifications which must be considered in choosing proper thickness.