Dynamic analysis of tapered thin-walled masts

Three methods are used to investigate the behaviour of cantilevered and linearly tapered thin-walled high masts under different kinds of dynamic loadings. First, the mast is represented as a single degree of freedom system with a prescribed shape function defining the mast deformation. Second, the finite element approach utilizing beam elements is used. Third, the governing partial differential equation of motion is solved using the finite difference approach. The effect of mesh density, load pattern, tapering ratio and height of masts on the behaviour of these masts is investigated. Results indicate that the finite difference method provides a better solution than the single degree of freedom and finite element methods. An increase in the taper ratio results in a decrease in the lateral displacements for both the concentrated and the distributed dynamic loadings. However, the increase in the taper ratio results in an increase in the lateral displacements during base motion. Masts with a high taper ratio experience lower natural frequencies than masts with a low taper ratio for the same material properties and height.