CHAPTER VI 

 COLUMNS 



Concrete columns may be divided into five classes, as follows: 



1. Plain concrete columns. 



2. Columns reinforced with longitudinal rods only. 



3. Columns reinforced with bands or spirally wound metal, 



called hooped columns. 



4. Columns reinforced with both hoops and longitudinal rods. 



5. Columns reinforced with structural steel shapes. 



It is generally conceded that long columns should be avoided 

 because of the fact that any variation in the quality of concrete 

 affects the strength more seriously than in any other structural 

 form, and also because of the fact that for such columns very 

 little data is available from tests. The use of reinforced columns 

 should be limited to a length of about 15 diameters (see recom- 

 mendations of the Joint Committee, Art. 40) and for this reason 

 the strength of longer columns will not be considered in the 

 discussion which follows. 



64. Plain Concrete Columns. In the testing of plain concrete 

 columns, two distinct forms of failure have been observed: (1) 

 a diagonal shearing failure, and (2) a failure by gradual crushing. 

 The failure by diagonal shearing is sudden, the columns breaking 

 suddenly with a loud report and without warning. The failure 

 by gradual crushing may be considered as due to simple com- 

 pression, the breaking down not being discovered until the 

 weighed load begins to decrease and the point of failure not being 

 determined until the machine produces a further shortening of 

 the column. For both forms of failure, however, the ultimate 

 strength of a column could be predicted if a stress-deformation 

 diagram were developed with the progress of the test. It has 

 been found that rich mixtures tend to give the diagonal shearing 

 type of failure, and columns with lean mixtures generally give a 

 failure of the simple compression type. 



But few comparative tests of cylinders and columns are avail- 

 able, but these indicate that the strength of the column and of 

 the cylinder very nearly agree. (For the relation of crushing 

 12 167 



