Nondestructive Load Predictions of Concrete Shell Buckling

Nondestructive test methods are evaluted for predicting the buckling capacity and buckling location of fabric‐reinforced concrete shells. The load‐deformation methods consist of measuring vertical deflections of 10—20 points on the shell surface under increasing vacuum pressures, curve fitting of the deflectionpressure response at each point, calculating a characteristic pressure on each curve, and using the lowest such calculated pressure as a predictor of shell buckling capacity. The curve fits are updated at each pressure increment and the test is continued to a pressure equal to a safe fraction of predicted buckling load, based on prior testing experience. Predicted and actual buckling pressures are compared for six experimental shells. The chosen method was selected from a comparison of four extrapolation methods, based on its least standard deviation between predicted and actual buckling pressures for the six shells. Vacuum tests can also indicate approximate buckling locations, for installing reinforcing arches before placing shells in service, and provide an inexpensive means for proof loading shells to any specified overload factor.