CORRUGATED BARS 



THE question of using plain or deformed bars for reinforced concrete construction 

 has been answered in the United States where the volume of such construction 

 is probably greater than in all the rest of the world. Fifteen years ago about 80% 

 of the reinforcement used was plain bars, to-day 80% is deformed bars. 



Nearly all building codes, architects' and engineers' specifications and committee 

 recommendations of technical societies allow larger working values for the bond stress 

 of deformed than for plain bars. 



A review of available test data on bond shows clearly that American practice is on 

 a very sound basis. Diagram 1 is the average resulting from the tabulation and 



analysis of the thousands of bond tests 



made by recognized authorities in the 



United States and Europe on both plain 



CORRUGATED ROUNDS and Corrugated Bars. The variation in 



the case of plain bars, from a very low 

 value for a minimum to a maximum value which approximates only the average of 

 Corrugated Bars, is due entirely to the fact that the bond of a plain bar is a function 

 of accidental surface condition. A smooth bar has a very low bond value; a rusty, 

 pitted, rough bar may have a high value. 



An important difference in behavior between plain and Corrugated Bars is shown in 

 Diagram 2. This diagram is a composite of load slip curves taken from University of 

 Illinois tests where conditions were practically identical, and illustrates clearly that 

 plain bars reach a maximum bond value at about 0.01 inch slip and then decrease while 

 Corrugated Bars have much higher bond at the same slip and increase in resistance 

 until a final value several times that of plain bars is reached. 



It is not good engineering practice to leave the bond — the most important function 

 of the reinforcement — to chance, while all the other physical properties of the material 

 are required to conform to rigid specifi- 

 cations within narrow limits. 



To realize the highest efficiency of 

 bond value, a deformed bar of proper corrugated sqhAHt.^ 



design is required; merely roughening the 



surface of a bar by haphazard projections may actually decrease its bond value. The 

 twisted bar, for example, for years considered a standard deformed bar, has been found 

 on careful examination to have lower bond resistance than a plain bar. 



The conditions governing the design of a satisfactory deformed bar are clearly stated 

 in Bulletin No. 71, University of Illinois, Engineering Experiment Station, as follows: 

 **In a* deformed bar of good design the projections should present bearing faces as 

 nearly as possible at right angles to the axis of the bar. The areas of the projections 

 should be such as to preserve the proper ratio between the bearing stress against the 

 concrete ahead of the projections and the shearing stress over the surroimding en- 

 velope." 



Of all the deformed bars on the market the Corrugated Bar is the only one that 

 substantially fulfills these requirements. 



