COLUMNS 179 



"4. From the behavior under test of the columns reinforced 

 with spirals and vertical steel and the results computed, it would 

 seem that a static load equal to from 35 to 40 per cent of the 

 yield point would be a safe working load. 



"5. The results obtained from tests of columns reinforced with 

 structural steel indicate that such columns have considerable 

 strength and toughness, and that the steel and concrete core 

 act in unison up to the yield point of the former. The shell 

 concrete will remain intact until the yield point of the steel 

 is reached, but no allowance should be made for its strength or 

 stiffness. 



"6. As many of the blotters on the tops and bottoms of columns 

 bore imprints of the vertical steel after failure, it would seem a 

 safe precaution to use bed plates at the foundations for such 

 columns, and thus prevent any possiblity of the steel punching 

 through the concrete under an excessive load." 



Further experiments made in 1910 at The University of Wis- 

 consin were for the purpose of making a detailed study of the 

 strength and elastic properties of columns reinforced with spirals 

 and longitudinal rods. To quote from Bulletin No. 466 of the 



University written by Prof. Withey: " The tests were 



made to obtain some data relating to 1, the effect of varying the 

 percentage of spiral reinforcement; 2, the effect of varying the 

 percentage of longitudinal reinforcement; 3, the effect of varying 

 the richness of the mixture; 4, the effect of a small number of 

 repeated loadings; 5, the effect of maintaining a constant load for 

 different time intervals; 6, the behavior of columns eccentrically 

 loaded; 7, the relative value of plain and deformed bars for longi- 

 tudinal reinforcement; 8, the effects of differences in end condi- 

 tions. All told, 66 columns of commercial size were made and 

 tested. 



"It is customary in good practice to encase all column rein- 

 forcement in a shell of concrete about 2 in. thick. This 

 shell is provided to protect the reinforcement against fire and 

 rusting. Since this coating is liable to be injured or destroyed 

 in various ways its strength should not be considered in structural 

 design. Consequently, the core, or portion of the column inside 

 the spiral, should be proportioned to carry the entire load. It, 

 therefore, seemed desirable to make the protective shell on these 

 columns as thin as possible in order that the properties of the 

 core might be more readily observed." 



