COLUMNS 175 



employed connected by riveted latticing. (Fig. 82.) Tests of 

 columns of this character generally show lower ultimate strength 

 than similar columns reinforced with the same quantity of steel 

 in the form of vertical rods. This is most likely due to the 

 difficulty of properly placing the concrete around the steel, 

 and, furthermore, to the fact that the adhesion of concrete 

 to steel where the latter presents broad flat surfaces is not 

 good. 



It is often advantageous to employ steel columns for reinforce- 

 ment and arrange them to carry the false work and dead load of 

 two or more floors, thus enabling the placing of concrete to 

 proceed simultaneously on several floors. The initial dead load 

 stress applied to the steel of the column in this way enables 

 higher steel stresses to be used. In other words, this initial 

 stress need not be counted with respect to the stress in the 

 concrete, but the total stress in the steel must be looked to in 

 order to make sure that the allowable stress per square inch 

 is not exceeded. 



To be able to count upon the concrete in columns reinforced 

 with structural forms, the concrete should be well enclosed either 

 by the steel form itself or by means of bands or hooping. However 

 when the amount of steel becomes very large, the relative value 

 of the concrete becomes more uncertain, and it would be good 

 design to neglect its element of strength. 



69. Tests on Plain and Reinforced Concrete Columns. 

 Important tests have been made on plain and reinforced concrete 

 columns at the Watertown Arsenal, the Massachusetts Institute 

 of Technology, the University of Illinois, and the University of 

 Wisconsin. Similar conclusions have been reached in each case. 

 Some of the tests made at The University of Wisconsin will be 

 described as indicating in general what results may be expected 

 from any series of tests. 



All columns of the series to be described were 10 ft. long with 

 a 1:2:4 concrete mix throughout. Columns were reinforced 

 (Fig. 83) as follows: 



A l} A 2) A 3 , A 4 . none. 



B lt B 2 , B 3} B 4 reinforcement shown in Fig. 82. 



C l} C 2 , C 3 , C 4 reinforcement shown in Fig. 80. 



D lt Z) 2 , Z) 3 , D 4 reinforcement shown in Fig. 81. 



E lt E 2) E 3 reinforcement shown in Fig. 79. 



