Optimal Design of Latticed Towers Subjected to Earthquake Loading

Abstract

The problem of optimal design of latticed transmission towers subjected to normal operating loads and an earthquake load is formulated. A time history analysis of the structure is performed. The constraints given in a design code are imposed. Many of the constraints are time dependent; therefore methods to treat them are incorporated in the solution process. All members are treated as equal- ~unequal-! legged angle sections. The members are selected from the sections available in a manufacturer's catalog. Two methods are presented and evaluated for such discrete variable optimization problems. The first method, called the two-phase method, uses a combi- nation of continuous and discrete optimization algorithms, and the second one, called an adaptive discrete assignment method ~ADAM!, uses only a continuous optimization algorithm. The proposed methods are applicable to any discrete variable problem that can be formulated as a continuous problem. In addition, the problem is solved using a genetic algorithm ~GA!. The efficiency and practicality of the proposed methods are compared to those of the GA. From the results, it is concluded that the GA is a very straightforward method to use for discrete problems; however, it requires a significant amount of Central Processing Unit time. On the other hand, the two-phase method and the ADAM do not require as much computational effort but the discrete designs found with them are slightly more expensive. Also, numerical implementation of the two methods requires more effort.