(a^ 



,)2 + (c 



:)' + (c^:^ 



where a^ = effective stress at an element per unit of applied pressure 



CT^.CTj.ag = principal stresses at each element per unit of applied 

 pressure 



Thus the relationship for yielding becomes 

 where 



KNOWN BY FINITE 

 ELEMENT SOLUTION 



KNOWN BY YIELD- 

 STRESS VS TIME 

 CURVES 



DESIGN 

 REQUIREMENT 



the maximum effective stress of all 

 elements with all the principal stresses 

 in compression 



the maximum effective stress of all 

 elements with any tension in the 

 principal stresses 



material yield strength in compression for 

 a particular loading duration 



material yield strength in tension for a 

 particular loading duration 



the maximum pressure that can be applied 

 to the viewport which initiates yielding in 

 any zone with all the principal stresses in 

 compression 



or 



the maximum pressure that can be applied 

 to the viewport which initiates yielding in 

 any zone with tension in the principal stresses 



