Interest in the effects of geometrical imperfections and cracks on the stresses in reinforced concrete shells has been stimulated by the failure of the Ardeer cooling tower. Due to the extreme difficulties of testing doubly curved, reinforced concrete shell models, a programme of experiments on an axially loaded aluminium cylinder containing controlled axisymmetric geometric imperfections has been carried out to show the nature of the stress distributions that occur when meridional cracking passes across the imperfection. Results over a wide range of crack configurations, for which the discrete cracks have both partial and complete loss of stiffness in the circumferential direction, are found to be in close agreement with predictions from an appropriate finite element numerical modelling. It is shown how the concentration of membrane hoop stresses associated with the imperfections are redistributed to cause substantial changes in meridional bending and membrane stresses only when a complete loss of stiffness occurs at the cracks. With the thin reinforced concrete shells used in cooling towers having only limited flexural capacity, the combination of geometric imperfections and cracks could, as a consequence, readily lead to failure once yield or fracture of the hoop reinforcement occurs.
Design and verification of reinforced concrete shell elements
