Experimental study of transformer bases
Haque, Mohammed M.
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Cast aluminum transformer bases (t-bases) are used as breakaway supports for luminaire poles to protect occupants during vehicular collisions. Following the crash requirements of t-bases upon vehicular collision provided by Federal Highway Administration, 1975 standard 20 inch t-bases were replaced by 1985 standard 17 inch t-bases. These transformer bases must also resist an applied moment caused by lateral wind forces on the luminaire pole. Although a large amount of experimental data regarding the ultimate moment capacity of t-bases is available from the manufacturer, all these data are scattered and could not be used to determine the ultimate moment capacity of the new t-bases. Thus concerns have arisen about the moment capacities of the new transformer bases. The problem also arises when an old 20 inch t-base needs to be replaced by a new 17 inch t-base for maintenance purpose or as a permanent fixture. An experimental program was conducted at Texas Tech University to determine the moment capacity of the transformer bases and the influence of different variable parameters which appear to control the ultimate moment capacity of the transformer bases was experimentally determined. Results of this study indicated that the moment capacity increases with the increase of parameters, such as, top bolt circle diameter, bottom bolt circle diameter, and base plate thickness. The results also indicated that the magnitude of the increase in moment capacity due to increase in one of the parameters depended on the other variable parameters as well. The interaction between the base plate and t-base top during the loading is complex and depends on the base plate deformation. Furthermore, the pole diameter seemed to have a insignificant effect on the strength oft-base/light pole system when it was changed from 7 in. to 8 in. Above all, material properties significantly affected the moment capacities of transformer bases. Moment capacities of'75 standard t-bases were found to be slightly higher when compared to '85 standard t-bases for a particular set of parameters. Based on the results of this experimental program and the experimental data published by the manufacturer, it was concluded that direct replacement of'75 standard t-bases with '85 standard t-bases is possible provided good quality t-bases are substituted.