We are presently designing a flat plate reinforced concrete building in which the lowest suspended floor overlies an unheated parking garage. The mechanical engineer is contemplating the use of a bonded steel mesh embedded in the 8-inch thick slab (between the top and bottom reinforcing) and coupled up to a low-voltage source of electric power.We have been unable to secure information on the effect such an installation may have on the performance of the slab (bays 20 feet x 20 feet) with special reference to thermal expansion, warpage and miscellaneous factors affecting long-term deflection.Can you direct us to some authoritative unbiased literature on such installations. We are particularly interested in reports on the field performance of such installations in suspended slabs.

Unfortunately there is no written unbiased literature available on this subject, although many structures have been built using such type of heating. In Chicago, a large project for the elderly designed some years ago by Bertrand Goldberg & Associates used this type of heating. However, we are not aware of the results of its performance.The following are structural points we would like to bring out in conjunction with the design of such slabs: By considering the surface temperatures of the top (inside) and the bottom of the slab (outside) and the heat source, gradients through the slab can be determined. With these gradients the moments and deflection for such conditions can be computed. It is important that the maximum temperature of the heating element be limited in order to avoid problems. By judicious placement of the heating element within the slab section a condition can be arrived at which does not create warping and moments in the slab.The Portland Cement Association, Old Orchard Road, Skokie, Illinois 60076, could provide a brief study on this subject on a consultant basis. In the framework of its fire research, PCA has recently developed a computer program for slab deflections due to gradients.