CAMBKIA STEEL. 



FIREPROOFING REINFORCED CONCRETE. 



The actual fire tests of reinforced concrete have been limited, 

 but experience, together with the results of tests so far made, 

 indicates that concrete may be safely used for fireproofing pur- 

 poses. It is in itself incombustible and proof against ordinary 

 fire when composed of the best materials properly mixed, applied 

 and anchored in place. For a fireproof filling or deadening layer 

 in floors, these same materials without reinforcement may be 

 used or clean hard burned cinders may be substituted for this pur- 

 pose. The low rate of heat conductivity is one reason of its 

 value for fireproofing and the concrete actually affected by fire, 

 remains in position and affords protection to the concrete be- 

 neath it. The thickness of protective coating required, depends 

 upon the probable duration of a fire, which is likely to occur in 

 the structure. However, for ordinary conditions, it is recom- 

 mended, as a general rule, that the metal in girders and col- 

 umns be protected by a minimum of 2 inches, beams 1| inches, 

 and floor slabs, the different minimum values, as indicated in the 

 accompanying table. 



A properly designed combination of protected steel framework 

 with reinforced concrete floor slabs, if well executed is particu- 

 larly safe and effective in fireproof building construction, and 

 the use of concrete and steel in the floor slab is especially advan- 

 tageous, affording both strength and rigidity. 



In reinforced concrete design, the following assumptions are 

 recommended and considered by almost all authorities, and are, 

 therefore, used as the basis for the formulae and tables of pages 

 92 and 93, but it must be noted that all these ideal conditions 

 cannot be had in practice and if possible allowance should be 

 made accordingly. 



(1) Calculations should be made with reference to working 

 stresses and safe loads, rather than to ultimate strengths and 

 ultimate loads. 



(2) A section, plane before bending remains plane after bending. 



(3) The modulus of concrete in compression within the usual 

 limits of working stresses is constant. The distribution of com- 

 pressive forces in slabs is therefore rectilinear. 



(4) The tensile stresses in the concrete shall be neglected in 

 calculating the reinforced slab resistance. 



(5) Perfect adhesion between concrete and reinforcement is 

 assumed. 



(6) Initial stresses in the reinforcement due to contraction 

 or expansion in the concrete may be neglected. 



These above assumptions, while not entirely borne out by 

 experimental data, are recommended and used by various 

 authorities on this subject in the interest of simplicity and 

 uniformity. 



