Load Tests of Transmission Line Structures and Structural Components

Structural load tests of most transmission line structural components are currently not highly regulated. For typical structural materials, users must expand the few pages of generalized information provided by ASCE documents in order to develop a more project specific test plan. These documents may include the ASCE Standard 10-97, Standard 48-11, or the new ASCE concrete pole design manual. For major structural types, such as a latticed tower or steel pole, there is often enough background information available from collective past experience within this industry to develop a representative test program. Other less common components, such as hardware or insulators, do not have such clear-cut testing practices. Granted, most of these structural components are proof-tested by manufacturers based on load cases defined by the Owner’s engineer. Test procedures will then be developed, most likely by the manufacturer based on its facility limitations, to address (in all likelihood) only the maximum load required. To cover uncertainties, a safety factor is commonly assigned. As the electrical transmission industry pushes the limits on all design parameters, is this traditional approach still adequate to ensure structural integrity? How to determine that sufficient capacity has truly been achieved? What if material nonlinearity behavior exists? Do the selected test and test plan accurately represent inservice conditions? Are most test programs satisfactory enough to find potential problems? What exactly are these ‘potential problems’? How to guarantee structural reliability in today’s demanding environment? This article attempts to provide basic background on the mechanical load test, and hopes to stimulate further studies and discussions in this area from the utility industry. Mechanical Load Test The mechanical load test is a dependable way to confirm structural integrity. With good planning and execution, the test results can present unquestionable and undisputable evidence of structural performance within the limits of defined scopes.