COLUMNS AND STRl'CTrHKS 



261 



causes no bending in the columns but does add a direct load. It 

 adds a direct load to the floor beams or girders, which must be 

 investigated. The forces may be ascertained analytically or 

 graphically. It is usually best to put in counters, as indicated 

 by the dotted lines. 



Loads on Columns in Buildings 



The dead weight of a building is a constant matter. Live 

 loads vary from time to time. Just what proportion of live load 

 should be carried to columns is not settled, but it is common prac- 

 tice to design the columns supporting the roof for the full dead 

 and live roof load. The columns supporting the floor next to the 

 roof are designed to carry the load transmitted to them by the 

 roof columns together with the dead load of the floor and part 

 of the live load. In Chicago only 85 per cent of the live load on 

 the top floor is carried to the columns. In other cities 90 per cent 

 is used and some engineers use 95 per cent of the live load. It 

 is only on the top floor columns that any difference of opinion 

 exists. On all columns below the top floor the live load is reduced 

 progressively 5 per cent per floor until the reduction amounts 

 to 50 per cent of the live load. From this floor, only 50 per cent 

 of the live load on each floor is carried to the column, together 

 with the total dead load. Using Chicago requirements and 

 assuming a ten-story building with 100 Ibs. per sq. ft. live load 

 on each floor; roof live load 30 Ibs., etc., the load per square foot 

 carried to the columns will be as follows: 



