Collapse behavior and connection effects of an LRFD-designed 345 kV strain-type transmission tower: Full-scale testing and multiscale analysis

This study investigates the ultimate behavior of a 345-kV strain-type transmission tower designed according to South Korea’s revised LRFD provisions using full-scale testing, global geometrically and materially nonlinear analysis, and detailed local connection analysis. Repeated service-level loading produced stable structural responses. The tower reached 135% of the design load in the ultimate test, compared with 129% predicted by the global model. Both approaches identified main-post buckling within Panels 12–13 as the governing collapse response, although the buckling-initiation location differed slightly. To examine this discrepancy, a detailed model explicitly representing the connection plates, bolts, bolt holes, and contact interactions was developed. The detailed model predicted approximately 5% higher local resistance than the simplified single-member model, indicating a modest effect of connection representation on local resistance and force redistribution. Parametric analyses showed stage-dependent effects of bolt-hole clearance, pretension, and interface friction. Using a nominal diametral clearance of 2 mm as the reference, idealized enlarged clearances of 4, 6, 8, and 10 mm exhibited an initial slip-related transition near a load proportionality factor (LPF) of 0.48. The 4 and 6 mm cases recovered to LPFs of 0.94 and 1.12, whereas the 8 and 10 mm cases showed no comparable recovery. Increasing pretension from 60% to 90% delayed the first transition from LPF 0.29–0.43 without a monotonic increase in resistance. Friction coefficients of 0.25–0.35 produced maximum LPFs of 1.14–1.18, while coefficients of 0.20 or lower caused an early peak near LPF 0.48 followed by a descending response. The global model reasonably captured the ultimate resistance and governing failure region, while the detailed model provided complementary insight into local load transfer, slip initiation, contact redistribution, and buckling development.