###### Abstract  
As the stress amplitude in the anchorage zone of cable-stayed bridges vary considerably, it is essential to study the fatigue-load-bearing capacity of the anchorage structures of cable-stayed-bridge girders. In this study, the mechanical properties and force-transmission mechanism of a built-in double-fixed steel anchor box, as well as the influence of the geometric design parameters of the main pressure plates and support plates on its stress performance, were studied. A PSO-BP built-in double-fixed steel anchor box mechanical-performance-prediction-and-evaluation system was established, with the geometric design parameters of the important plates of the main body of the anchor box as the input variables and the mechanical properties of the main stress-transmitting welds of the steel anchor box as the output-evaluation variables. The results were as follows: the cable force was mainly transmitted in the form of shear force through the welds between the support plate and the web of the main beam; the transmission ratio of the four main welds was generally maintained at about 23%, and the stress distribution of each plate was relatively uniform, with most of the stresses in the range of 10-50 MPa. The shear-stress-inhomogeneity coefficient of the transmission weld was sensitive to the changes in the thickness of the support plate and the pressure plate, and the transmission ratio of the main weld was sensitive to the changes in the thickness and length of the support plate. The PSO-BP-based mechanical-performance-prediction-and-evaluation system can be used to explore the intrinsic relationship between the designed cable force, important plate-geometry parameters, and the force performance of steel anchor boxes during the iterative process, and to generate more accurate prediction and evaluation values. cable-beam anchorage structure; force characteristics; force-transmission mechanism; parameter analysis; predictive evaluation system +
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anchor-plate cable-girder anchorage structure of a large-span-railroad cable-stayed bridge, and the test results showed that the new anchor plate without ribs had a fairly uniformly lower stress distribution near the butt weld compared with the traditional ribbed-tension-anchor plate, and the fatigue performance of this anchorage structure met the design requirements of the bridge within the design's service life. [PERSON] et al. [5] conducted a full-scale static-load-fatigue-model test on an anchor-plate cable-beam anchorage structure, and studied its structural characteristics, the stress-concentration degree, and the fatigue performance of key structural features. The research showed that the anchor-plate cable-beam anchorage structure had a simple structure, clear force, and convenient maintenance. When the structural parameters were reasonable, it had good fatigue resistance and met the design requirements. [PERSON] et al. [6] conducted a fatigue test on a full-scale test model of an externally anchored box-girder anchorage structure, and analyzed the fatigue performance of the structure under cyclic loading on the basis of a theoretical analysis and experimental research results, which showed that the test model was reasonable and that the structure had a large fatigue-resistance safety reserve. [PERSON] et al. [7] conducted static-load tests on and a comparative analysis of four common cable-stayed bridge-girder anchorage structures, investigating the force-transfer mechanism, stress distribution, and stress-concentration phenomena of the four configurations and also proposing measures to improve the stress concentration. Due to the excellent self-learning ability of artificial neural networks [8; 9], they are increasingly used in research on steel properties. [PERSON] et al. [10] established a feed-forward multilayer perceptron (FF-MLP) thermal-flow-stress regression model with steel temperature, strain rate, and strain as the input variables. The results showed that the model can effectively predict the thermal-flow stress of steel.