270 



PRACTICAL STRUCTURAL DESIGN 



Cast iron brackets are cast on the side of cast iron columns. 

 There is really no rational method for designing them. They 

 should be at least as thick as the shell of the column. For light 

 loads one bracket is used under the shelf and for wide beams two, 

 or more, brackets are used to avoid eccentricity in the loading. 



The depth of the brackets at the face 

 of the column must be enough to pre- 

 vent shearing. There is of course a 

 bending moment created by the reac- 

 tion from the beam. This bending 

 moment divided by the depth of the 

 bracket gives the tension in the shelf 

 where it is attached to the shell of 

 the column. This tension must be 

 divided by the length of the edges of 

 the shelf and multiplied by the thick- 

 ness of the metal in the shell to de- 

 termine the shearing stress which acts 

 to tear the shelf away from the shell. 

 This shearing stress divided by the 

 safe allowable shear in the metal 



Bolt Holes 

 K---Ot6"mm. >1 



Fig. 174 Cast Iron, or Steel, 

 Ribbed Column Base 



must be less than the tension, or the thickness of the shelf must 

 be increased. Such computations are merely checks but should 

 not be neglected. 



In Fig. 174 is illustrated a ribbed cast iron base cap for a 

 column. No known rational method exists for determining the 

 stresses, so these bases are made according to empirical rules. 

 The thickness of all the parts should be not less than the thick- 

 ness of the shell of the column. All parts should have the same 

 thickness to avoid danger of casting cracks. A small fillet should 

 be used in every angle. 



The projection at the top should be not less than three inches 

 wide, so bolts can be used with plenty of clearance for the heads. 

 When the bottom projection P is greater than six inches, ribs should 

 be used. The height H should never be less than the projecting P 

 and the diameter of the base under the column should be equal to 

 that of the column. The number of ribs should never be less than 

 eight, and an empirical rule for fixing the number of ribs is that 

 the space between ribs at the circumference of the column should 

 never be greater than twice the thickness of the shell. 



