This paper presents an evaluation of the bearing capacity of cross-bracing in steel transmission tower structures. Design guidelines (ASCE 10-15, BS EN 50341-1, GB 50017-2017, and DL/T 5486-2020) related to the buckling capacity of the cross-bracing are summarized and compared with the experimental results. The current design provisions obtained the bearing capacity from the equivalent slenderness ratio, and then the stability coefficient and buckling capacity were derived. The calculated bearing capacity based on the design code tends to be overly progressive for smaller slenderness ratios (particularly those below 100), except for EN 50341-1-2012. Conversely, for larger slenderness ratios, ASCE 10-15 and DL/T 5486-2020 Class A design codes lean towards being overly progressive, while GB 50017-2017 and EN 50341-1-2012 codes tend to be more conservative. The design standard appears to exhibit unsafe predictions for Class A and B connections with low slenderness ratios and Class C connections. It needs to be noted that the effects of torsional stiffness and joint connection type are not considered in the current design codes, which are proved to be nonnegligible by the test results. In this paper, the bearing capacity calculation formula is proposed by introducing a modified effective length coefficient (K), and both the torsional stiffness and joint connection type are taken into account. The modified bearing capacity is verified with the test results; the correlation coefficient is 0.997, and the coefficient of variation is 0.04. It can provide a reference for the engineering design of steel lattice transmission tower structures.

Steel angles connected by bolts have been commonly used in transmission towers. Due to the limited length of steel angles, double-shear splice connections are generally adopted to connect steel angles in main members. The stability of this type of members remains unclear as a result of the presence of discontinuity and is difficult to evaluate using existing design methods. This study presents numerical simulations of steel angles with double-shear splice connections under axial compression. Numerical models are established for discontinuous steel angles and validated against published experimental results. Parameters including splice steel ratio, discontinuity location, slenderness ratio, and width-to-thickness ratio on the axial compression load capacity of steel angles are evaluated. A design equation is proposed based on numerical results to quantify the axial load capacity of discontinuous steel angles. Comparisons with experimental data and values calculated using Chinese design code demonstrate that the proposed equation can predict the ultimate load capacity of discontinuity steel angles with better accuracy than the design method in the Chinese code. Finally, a design equation is further simplified by eliminating the effect of parameters with limited influence on ultimate load under axial compression.

Structural safety of transmission towers is directly influenced by the behavior of bolted connections at discontinuity joints in the main steel angles. Thus, it is essential to investigate the axial compression behavior of double-shear splice connections of main steel angles. In this study, a total of 10 groups of discontinuous steel angle specimens with double-shear splice connections, comprising eight groups of specimens with the same upper and lower angles and two groups of specimens with different upper and lower angles, were designed and tested in compression. The axial deformation, out-of-plane deflection, and strain at the mid-height of steel angles were measured to analyze the influence of double-shear splice connections on the compression behavior of steel angles. Moreover, comparisons were made among discontinuous steel angles in terms of the ultimate load and the associated deformation to investigate the effects of splice steel ratio, slenderness, bolt spacing, and bolt torque, respectively. Based on the experimental results of steel angles in compression, comparisons with the values calculated using Chinese design codes suggest that present design methods show limited accuracy in calculating the axial compressive load capacity of steel angles with double-shear spliced connections, indicating the necessity for revising the design methods in relevant codes.