Post-tensioning tendon force estimation using eddy currents at various temperature conditions

This study proposes an eddy current-based tensile force estimation technique for a post-tensioning (PT) tendon under varying temperature conditions. The tensile force in the internal PT tendon is inferred by measuring the compressive stress on the external anchor head. A dual-coil probe consisting of two identical eddy current coils with orthogonal orientations measures the unidirectional loading level based on the piezoresistive effect. The temperature effect is eliminated using identical eddy current signal alternations in the coils under temperature variation. The performance of the proposed technique was evaluated by estimating the tensile force of a PT tendon under various loading and temperature conditions. The uniqueness of this study lies in the (1) design and fabrication of a dual-coil probe for unidirectional loading level estimation, (2) elimination of the effect of temperature on tensile force estimation, and (3) experimental validation under various loading and temperature conditions.