at implosion. Near implosion, the inelastic behavior of concrete along 

 with plasticity and creep impart a stress distribution across the wall 

 that is more closely modeled by a uniform stress distribution than by an 

 elastic (Lame) stress distribution. A uniform stress at implosion is 

 expressed by 



o. = F. -^ (1) 



im im t 



where o. = wall stress at implosion 

 im 



p. = implosion pressure 



im '^ ^ 



R = outside radius 

 o 



t - average wall thickness 



The wall stress at implosion, a. , can be expressed as the ultimate 

 compressive strength of concrete multiplied by a strength factor. 



a. = k f (2) 



im c c 



where k = strength factor for cylinder structures under 

 hydrostatic loading 



f - uniaxial compressive strength of concrete 



The term k was determined empirically. Figure 1 shows k as a 



function of length-to-outside- diameter ratio, L/D , for cylinders of 



various wall-thickness-to-outside-diameter ratios, t/D . 



' o 



For cylinders under hydrostatic loading, the wall is stressed 

 biaxially in compression on the inside surface and triaxially in compres- 

 sion at all other locations. The two major stresses are in the hoop and 

 axial direction where the hoop stress is about twice the magnitude of 

 the axial stress. The third, and smallest, component of stress acts 

 radially. If the concrete is considered biaxially loaded, then the hoop- 

 to-axial stress ratio of 2 is known to increase the compressive strength 



