Correlation of moment capacity with material properties of transformer bases
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Until the early 1970's, the light poles on the highways were directly fixed to the concrete foundation with the help of a base plate and bolts. Increasing fatality rates during vehicular impact on steel or concrete poles installed on the U.S. highways concerned the highway authorities. Out of this consideration evolved the concept of breakaway supports. The breakaway supports are placed between light poles and foundations, are made up of an aluminum alloy which has a certain strength, are brittle and can be molded. Since these bases house the transformers, they are also called transformer bases (t-bases). Initially, the t-bases had a height of 20 inches that was based on the 1975 American Association of State Highway and Transportation Officials (AASHTO) standard. In 1990, the Federal Highway Administration (FHWA) adopted a more stringent 1985 AASHTO light pole/t-base breakaway requirement, due to which t-bases of height 17 inches were manufactured. The new standard also required that the t-bases should be more fragile, but resist certain wind loads in addition to the breakaway requirements. Figure 1.1 shows an actual t-base installed in the field.