Experimental and analytical study of galloping forces on support structures
Mardith A. Baenziger
Until recently, the design of the transmission lines and the structures supporting the lines have been primarily based on static loads with a conservative safety factor. The project seeks to improve the design by determining realistic forces for dynamic forces due to galloping. Therefore, a base-excitation test was performed experimentally to simulate galloping and then to measure the dynamic forces on support structures directly. The single-span wire, symmetrical with respect to midspan, was subjected to support motion at both ends by hydraulic actuators to excite galloping motion. Two hundred and twenty-one tests have been performed on a variety of wire lengths, areas, unit weights, modulus of elasticity, and span length. Results of the experimental study include the description of the test model's vibrating behavior, time of occurrence of galloping, and the relationships between support force and unit weight/area/length of the wire;The project also seeks to develop the equations of galloping motion for linear and nonlinear cases. An algorithm based on the physical interpretation of the equations was developed to obtain the solution numerically. Results of analytical study confirm the experimental observation of the wire's galloping characteristic. It also provides the support force in correspondence with a given amplitude.