Experimental and numerical study on the stable bearing capacity of steel tubular cross bracing of a transmission tower

Taking the 1000 kV ultra-high voltage (UHV) steel tube transmission tower as the engineering research subject, the ultimate bearing capacity of the X-cross bracing was experimentally studied. The main tube was manufactured together to add the end constraint on the cross bracing used in the design, with six types of X-cross bracing specimens under two horizontal loading cases to study its ultimate bearing capacity and failure mode in the steel tube transmission tower. Under two loading cases as described, the two inclined tubes of the cross bracing are simultaneously compressed. One is in compression, the other is in tension. The magnitude of the force applied to the tubes remain the same. And then, the results show that the bearing capacities of the common U-joint and C-joint cross bracing specimens are low, especially the bearing capacity of the C-joint with diaphragm is insufficient as the inclined tubes of cross bracing is compressed simultaneously, while the bearing capacities of the intersecting joint and the cross-insert joint are excellent under both cases. Moreover, the corresponding ABAQUS finite element model with imperfection was verified using the test results. As a result, the stress distribution, failure mode and ultimate bearing capacity of the numerical simulation are in good agreement with the experimental results, which shows that results obtained from the subsequent numerical analysis are reasonable. The simplified finite element model is used to analyze the bearing capacity of the intersecting joint cross bracing with the different cross positions and the slenderness ratios under two loading cases. For the calculation according to the Technical Specification for Design of Steel Tube Towers for Overhead Transmission Lines, combined with the calculation results from 60 finite element models, the calculation formula of the slenderness ratio correction factor under two loading cases is elaborated. Compared with the existing formula, the improved formula is closer to the finite element calculation results, which helps reduce material waste during the stage of design.