VIBRATION OF CERTAIN SHELL STRUCTURES

Abstract

The present investigation covers the experimental study of a two-bay cylindrical shell and a hyperbolic para-boloid cooling tower. Free vibration, forced vibration, cyclic load-deflection and load-deflection tests upto ultimate were conducted on reinforced concrete models of both the structures. The cylindrical shell was monolithically cast with solid traverses along curved edges and narrow deep beams on the outer and inner longitudinal edges. The tests on cylindrical shell model were conducted in three stages: a) with a masonry wall panel built between _rintorced concrete columns, b) without such a wall, and, without the wall panel but with diagonal braces. The shell roof model was vibrated longitudinally, transversly as well as vertically. The experimental natural frequencies of the shell under rigid and flexible coniitions are comp-ared with the frequencies computed theoretically. Besides the free vibration test, the shell modelwas tested under cyclic horizontal loading with complete reversal of load and loaded upto ultimate. The cyclic load-deflection curve of the hyperbolic tower was obtained by loading and unloa3ing the structure (iv) from one side. The experimental frequency of tower is compared with the frequency obtained t..f theoretical analysis. Besides the above tests, a complete seismic analysis of a prototype cooling tower is also carried out by treating it as a bending - shear beam, finding its natural frequencies and modes, computing root-mean-square response to given ground motion and evaluating the mem-berane stresses induced in the shell