Shao-Bo Kang

Bent angle-steel joints embedded in concrete foundations are commonly used as load-transfer components between transmission tower legs and foundations. Due to their bent geometry and bolted connections, these joints are subjected to complex stress states under vertical loads and auxiliary inclined or horizontal loads. To investigate the structural behaviour of bent angle-steel joints embedded in concrete foundations of transmission towers, full-scale tension and compression tests were conducted on Q420 high-strength steel joints. The specimens were subjected to vertical loads together with auxiliary inclined or horizontal loads, and the corresponding load-strain responses, stress development and failure modes were recorded. Finite element models were also developed to evaluate the stress distribution of the joint and the strength reserve of the gusset plate. The test results showed that, under tensile loading, the joint ultimately failed at a vertical tensile load of 1100 kN after local yielding developed near the upper loaded end of the angle member and tearing of steel occurred in the top loading plate. Under compressive loading, local bending first occurred on the compressive side of the angle member, and the joint eventually failed by flexural yielding at a vertical compressive load of 1989 kN. The numerical results indicated that the maximum von Mises equivalent stresses under tensile and compressive loading were 254.2 MPa and 264.1 MPa, respectively, both lower than the nominal yield stress of Q420 steel. The observed failures were mainly associated with yielding or bending of the angle member rather than yielding of the gusset plate. Under the investigated loading conditions, the joint satisfied the required load-transfer capacity.

This study investigates the behaviour of normal-strength concrete (NSC)–ultra-high-performance concrete (UHPC) composite slabs under four-point bending through experimental tests, finite element simulations, and analytical modelling. A total of 12 slabs were tested under static loading to examine the effects of UHPC layer position, UHPC thickness, reinforcement ratio in the UHPC layer, and shear span ratio on load-deflection behaviour, crack development, strain evolution, and failure mode. The test results showed that, when UHPC was placed in the tension zone, the slabs generally exhibited higher post-cracking stiffness and load capacity. The specimens with the longitudinal reinforcement spacing in the UHPC layer reduced from 100 mm to 50 mm exhibited an approximately 16% increase in ultimate load, but they were more prone to develop localised cracks and shear failure with a high reinforcement ratio in the UHPC layer and a small shear span ratio. When UHPC was placed in the compression zone, the specimens showed greater deformation capacities. With the same UHPC thickness, reinforcement ratio, and shear span ratio, their failure deflections were approximately 1.5–4.8 times those of the corresponding specimens with UHPC in the tension zone, whereas their failure was mainly governed by interface debonding. Finite element models were also developed and validated against the test results, followed by parametric analyses. The numerical results indicate that interface bond strength plays a dominant role in failure mode and deformation capacity, particularly for slabs with UHPC cast in the compression zone. Increasing the UHPC thickness generally improves the stiffness and load capacity, whereas insufficient thickness increases the risk of shear failure or interface debonding. Finally, an analytical model was proposed for composite slabs with different UHPC layer positions, and the model was shown to provide a reasonable prediction of the load-deflection curve of flexure-dominated slabs.

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.

Precast concrete segmental bridges (PCSBs) have become a widely adopted solution in bridge construction due to their construction efficiency and reduced on‐site time. This study investigates the structural behavior of tri‐segment precast concrete T‐girders (TCTGs) with internally bonded tendons, combining full‐scale experimental testing and numerical modeling. Experimental results showed that the TCTG exhibited localized deformation at the joint, with a 23‐mm‐wide major crack forming at 1880 kN. The cracking loads were 720 and 760 kN for the segmental girder, compared to 950 kN for the monolithic one, representing a reduction of approximately 20%–24%. Finite element model (FEM) revealed that the mid‐span section of the TCTG exhibited enhanced flexural capacity due to the contribution of ordinary steel reinforcement, with moment capacity increasing from 13,676 to 15,949 kN·m, representing a 16.6% improvement. Grouted (bonded) conditions significantly improved joint flexural performance: the ultimate load increased from 1484 kN (unbonded) to 1974 kN (bonded), reflecting a 33% improvement. Effective prestress had limited influence on ultimate flexural capacity but significantly increased cracking loads. When the prestress level was varied from 600 to 1400 MPa, the maximum difference in ultimate moment at the joint was only 0.6%. The amount of ordinary steel reinforcement had minimal effect on flexural capacity near the joints, whereas under mid‐span loading, flexural capacity increased with higher reinforcement ratios. Increasing girder height led to a near‐linear increase in flexural capacity for both joint and mid‐span loading conditions. Comparison with AASHTO 2020 provisions showed that FEM‐predicted capacities consistently exceeded code‐based predictions, indicating a conservative bias in the current design specifications. This study provides valuable insights for improving the design and analysis of segmental concrete bridge girders.