WOOD AND CAST-IRON COLUMNS 191 



metal of 1.5 1.25 = .25 in. gives an increase in strength of 

 454,000-386,000 = 68,000 Ib. 



The table may also be used for calculating the strength 

 of columns when a factor of safety other than 8 is to be used. 



Let W be safe load given in the table; W\ the safe load 

 corresponding to another factor of safety; and /, the new- 

 factor of safety. Then, 



W : Wi=f:S, 



SW 

 and Wi= 



8 



EXAMPLE. A hollow, cast-iron column of 13-in. external 

 diameter and l}-in. metal is 18 ft. long. Assuming that the 

 factor of safety is 6, find the safe load. 



SOLUTION. From the table W = 343,000; hence, accord- 

 ing to the formula, 



6 



Many concerns have their own standard designs for column 

 connections and brackets. These are usually embodied in 

 tables that give the required dimensions. The accompany- 

 ing table gives the standard dimensions of brackets on 

 cast-iron columns for I-beam connections, both for double 

 and for single beams. The top surface of the shelf should 

 have a pitch away from the column of J in. to the foot to 

 allow for the deflection of the beam. The top surface of 

 the shelf should have a pitch away from the column of J in. 

 to the foot to allow for the deflection of the beam. As the 

 holes in the column are cored, it will usually be necessary 

 to have the beams drilled in the field in order to insure 

 alinement. 



In this table the values given in the columns marked 

 A, B, C, etc. are the various dimensions for brackets, these 

 dimensions being represented by corresponding letters in the 

 figures accompanying the table. Thus, for a 12-in. I-beam 

 connection, the distance from the bottom of the beam flange 



