of concrete by a factor of about 1.25 f (Ref 10). Therefore, k values 

 J c c 



for the cylinder test specimen of this program should show a value on 



the order of 1.25. As a miniirium, k should be 1.0. 



c 



Figure 1 shows that short cylinders, those of L/D ^ 1, had a k 

 around 1.25. However, longer cylinders showed a k on the order of 

 1.0. The decrease in k was probably due to specimen imperfection . 

 The short specimens were also imperfect, but end-closure effects 

 restrained the cylinder wall. At L/D of 2.0 the end-closure effects 

 were diminished. 



An average k value of 0.89 was observed at L/D =4. It was 

 speculated that some unknown fabrication or testing problem existed for 

 the cylinders of this length in comparison to the other specimens.* 



For design purposes, a k =1.0 was selected for cylinders of 



L/D ^ 2. The reader is reminded that this k includes the effect of 

 o c 



out-of-roundness and experimental error. The reduction in k from 

 1.25 to 1.0, a 20% change, is difficult to assign solely to out-of- 

 roundness effect because thick-walled structures are usually insensitive 

 to small geometric out-of-roundness. Hence, k =1.0 should be a 

 conservative strength factor for design purposes . 



*Much attention was given to why k should be as low as 0.89. If 

 out-of-roundness was the sole cause, then the specimens showed a 

 decrease in strength of 29% due to out-of-roundness, which was too 

 large an effect for thick-walled cylinders . There appeared to be no 

 reason based on engineering mechanics to cause cylinders with L/D of 

 4 to fail at lower pressures than those at, say, L/D of 8. It is oe- 

 lieved that some problem related to specimen fabrication or test was 

 responsible for the low strengths . The author personally participated 

 in the fabrication and testing of some of the specimens under consid- 

 eration. He discussed this topic with others involved in the test pro- 

 gram, and no procedure was singled out as suspicious. One procedure 

 that was distinctly different for specimens of L/D of 4 and 8 from 

 that of the shorter specimens related to the interior mold. The inter- 

 ior mold was made in segments having a length of L/D = 2. Cylinders 

 longer than L/D of 2 used multiple segments . During mold removal 

 operations it was quite difficult to disassemble the multiple segments to 

 extract the interior mold. If harm was done to the specimens during 

 this operation, it was not recognized at the time. 



