With the progress of construction technology and the application of high-performance materials, arch bridges are constantly breaking the span records. This study conducts parametric design and numerical analysis on upper-support thrust-bearing concrete arch bridges (UTCAB) with spans ranging from 450 to 2000 m, utilizing concrete of different strengths to explore the feasibility limits of spans. Through parameter sensitivity analysis, the study determines the reasonable parametric design of UTCAB with different spans. The results of static wind response analysis indicate that as the span increases, wind load gradually becomes the control load, but after comprehensive consideration, it is unnecessary to install installing tuyeres on the main arch to reduce the wind load. Ultimate bearing capacity analysis is conducted, and the results confirms that all parametric designs meet the requirements. Research on the impact of nonlinearity reveals that material nonlinearity has a much greater impact on ultimate bearing capacity than geometric nonlinearity. Considering the construction feasibility, the recommended feasible maximum span is 1200 m. This study can provide valuable reference for the future design of super long span upper-support thrust-bearing concrete arch bridges.
The second-order blind identification (SOBI) and its variants have been extensively explored for output-only modal identification of civil structures under varied excitations. At the core of these methods is the matrix joint approximate diagonalization (JAD) technique, while their efficiency and accuracy are largely determined by how the target-matrices for JAD are constructed from multi-channel structural responses. This study first formulates the JAD framework for structural identification, where different techniques in formulating the target-matrices are summarized and mathematical tools to conduct JAD are also presented. Then two novel ways stemming from conventional identification methods are presented as alternatives to construct the target-matrices for ambient identification, to maintain a low-order formulation and even avoiding the formation of covariance matrix. Subsequently, in view of the large number of candidate target-matrices which are analytically usable, a guiding principle is proposed for selecting reliable target-matrices, where the closeness of the eigenvectors of the target-matrices are compared beforehand, therefore eliminating of distorted target-matrices and also improving the efficiency of the subsequent JAD. The proposed techniques are applied to modal identification of the Donghai Bridge from monitoring data and the proposed JAD-based methods are compared in this context. The results suggest the effectiveness of the proposed techniques and also provide a performance evaluation of these methods.
The significant load disparity between the two decks of a cable-stayed bridge with separated unequal-width decks results in complex asymmetric static effects in the jointed dual-pylon. To investigate the structural behaviour and reliability of the jointed dual-pylon under asymmetric loads, a 1:30 scaled model test and numerical simulation were conducted based on the world's first road-railway same-level cable-stayed bridge with jointed pylons. The test results indicate when the unbalanced horizontal force of the jointed dual-pylon structure reaches its maximum during the service phase, the stress at the dual-pylon connectivity node remains relatively low, indicating good shear resistance of the dual-pylon connectivity node. Structural failure occurs when the load reaches 1.82 times the maximum shear stress at the tower column merging section, and the railway beam will experience severe cracking and stiffness degradation, ultimately leading to loss of bearing capacity. The calculation results further reveal that under the combined action of dead load, full-span moving load, and lateral wind load, the minimum calculated nonlinear stability coefficient of the dual-pylon connectivity node is 1.65. Moving load and longitudinal wind load have minimal impact on the nonlinear stability coefficient, and the dead load and lateral wind load primarily govern the failure of the dual-pylon connectivity node.