CONSOLIDATED STEEL CORPORATION 165 



GRILLAGE BEAMS IN FOUNDATIONS 



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Grillages of steel beams imbedded in concrete are used in column footings 

 to distribute the load over the desired area on yielding soil, thereby avoiding 

 large masses of masonry and deep excavations. The beams should not be 

 less than 3 inches apart in the clear between flanges so that the space between 

 beams can be thoroughly filled with concrete. Separators should be used 

 to keep the beams properly spaced. 



The load supported by each beam in a layer equals the total load on the 

 foundation divided by the number of beams in the layer. Loading is uniformly 

 distributed over the length on which ft is applied and the beam is uniformly 

 supported from below over its entire length. Maximum bending occurs at c, 

 the center of length of the beam. 



W=load supported by each beam, in pounds. 



L = length of beam, in feet. 



TV = length, in feet, on which load is applied. 



C = coefficient of strength for the beam. 

 Maximum bending moment in foot-pounds = ^W(L-N). 



This formula for bending moment is the same as that for a simple beam 

 of the length (L-N) supporting a uniformly distributed load of W. By using 

 the length (L-N) as the span the size or safe load of grillage beams may be 

 obtained directly from the tables of safe loads for I-beams and girder beams 

 If (Lr-N] is less than the spans given in these tables the size or safe load must 

 be obtained by means of the coefficient of strength or section modulus. When 

 W is in pounds and L and TV are in feet, the safe load on a given grillage beam 

 is found by the formula 



and the coefficient of strength required by a beam for a given loading from 

 the formula 



C=W(Lr-N). (2) 



