USEFUL DATA 



k 



panels, the numerical sura of the positive moment and the negative moment at the 

 two sections named is given quite closely by the equation 



In this formula and in those which follow relating to oblong panels: 



w =sum of the live and dead load per unit of area; 



I =side-of a square panel measured from center to center of columns; 



li =one side of the oblong panel measured from center to center of columns; 



h = other side of oblong panel measured in the same way; 



c = diameter of the column capital; 



3/x = numerical sum of positive moment and negative moment in one direction. 

 My — numerical sum of positive moment and negative moment in the other direction. 



(See paper and closure, Statical Limitations upon the Steel Requirement in Rein- 

 forced Concrete Flat Slab Floors, by John R. Nichols, Jun. Am. Soc. C. E., Transac- 

 tions Am. Soc. C. E, Vol. LXXVII.) 



For oblong panels, the equations for the numerical sums of the positive moment 

 and the negative moment at the two sections named become. 



Where 3/x = is the numerical sum of the positive moment and the negative moment 

 for the sections parallel to the dimensions h, and My is the numerical sum of the 

 positive moment and the negative moment for the sections parallel to the 

 dimensions U. 



What proportion of the total resistance exists as positive moment and what as 

 negative moment is not readily determined. The amount of the positive moment 

 and that of the negative moment may be expected to vary somewhat with the design 

 of the slab. It seems proper, however, to make the division of total resisting moment 

 in the ratio of three-eighths for the positive moment to five-eighths for the negative 

 moment. 



With reference to variations in stress along the sections, it is evident from condi- 

 tions of flexure that the resisting moment is not distributed uniformly along either 

 the section of positive moment or that of negative moment. As the law of the distri- 

 bution is not known definitely, it will be necessary to make an empirical apportion- 

 ment along the sections; and it will be considered sufficiently accurate generally to 

 divide the sections into two parts and to use an average value over each part of the 

 panel section. 



The relatively large breadth of structure in a flat slab makes the eflFect of local 

 variations in the concrete less than would be the case for narrow members like beams. 

 The tensile resistance of the concrete is less affected by cracks. Measurements of 

 deformations in buildings under heavy load indicate the presence of considerable 

 tensile resistance in the concrete, and the presence of this tensile resistance acts to 

 decrease the intensity of the compressive stresses. It is believed that the use of moment 

 co-efficients somewhat less than those given in a preceding paragraph as derived by 

 analysis is warranted, the calculations of resisting moment and stresses in concrete 



205 



