FO UNDATIONS, GAS WORKS BUILDINGS, ETC.
45
disposition of the bars is such that thcy are called upon to relieve the concrete of the greater part of the tensional and shear stresses. In the case shown the founda-tion was required to support several rows of columns, each carrying a load of approxi-mately £0 tons ; accordingly the maximum reinforcement occurred in open squares in alignment with the columns, whilst the remaining portions of the slab were pro-vided with considerably less reinforcement. When foimdations of the floating type are employecl on the more easily compressible soils, care is necessary to see that no derangement takes place, otherwise adjacent buildings may sufier disturbance. Foundations to-day, liowever, are not of the massive character employed in the past, owing to the tendency to erect light steel-framed buildings with a comparatively thin. filling.
When dealing with reinforced concrete work it is essential that due consideration
Fig. 4.—Reinforced Raft Foundation for Vertical Retort Bench, showing Indented Bars in position before concreting-up.
should be given to the avoidance of those influences which. tend to promote corrosion of the iron. and steelwork employed. Dr. Newton Friend has stated that preserva-tion of the metalwork in concrete may be effected in one or more of three ways:— (1) By complete exclusion of air; (2) by complete exclusion of water, and (3) by rendering the concrete sufficiently alkaline. If tlie engineer can make bis concrete conform perfectly to any one of these conditions he will achieve his purpose, for the reinforcing metal will not rüst. Unfortunately in practice materials cannot be re-lied upon to yield perfect results, but by conforming as nearly as is reasonably possible to all three conditions lie may hope so to reduce the tendency to corrosion as to render it negligibly small within finite time.
The following considerations are, therefore, put forward as worthy of careful study :—
1. None of the concrete material should be too coarse, otherwise thorough