Xueyuan Yan

A bidirectional OpenFAST–OpenSees method is developed to examine dynamic interaction between a jacket-supported offshore wind turbine and its pile group. Pile-head motions and reactions connect the turbine model to a shared three-dimensional displacement–pore-pressure soil domain. Static-reference mapping and state isolation coordinate the initial states and loading histories. A nonlinear elastic-support benchmark using the actual solvers checks nonzero reaction feedback, closed-loop response, and time-step sensitivity. Responses are then examined for a 60-s marine case and a 20-s case with concurrent marine loading and three-component earthquake excitation. In the marine case, startup governs the peaks of the horizontal pile-head displacement-increment magnitude and the dynamic mudline bending-moment resultant. With earthquake excitation, these peaks occur at approximately 12.3 and 8.8 s, respectively, and are governed by different piles. Global motion and local foundation demand therefore require separate assessment. The findings are conditional on the specified cases; discretization error and the effects of contact residuals in the complete soil model remain to be assessed.

Ferronickel slag and ground granulated blast-furnace slag (GGBFS) are solid waste by-products from the metallurgical industry. When incorporated into concrete, they help promote resource utilization, reduce hydration heat, and lower both solid waste emissions and the carbon footprint. To facilitate the application of ferronickel slag–GGBFS concrete in 3D printing, this study examines how aggregate size and nozzle diameter affect its performance. The investigation involves in situ printing, rheological characterization, mechanical testing, and scanning electron microscopy (SEM) analysis. Results indicate that excessively large average aggregate size negatively impacts the smooth extrusion of concrete strips, resulting in a cross-sectional width that exceeds the preset dimension. Excessively small average aggregate size results in insufficient yield stress, leading to a narrow cross-section of the extruded strip that fails to meet printing specifications. The extrusion performance is closely related to both the average aggregate size and nozzle diameter, which can significantly influence the normal extrusion stability and print quality of 3D printed concrete strips. The thixotropic performance improves with an increase in the aggregate size. Both compressive and flexural strengths improve with increasing aggregate size but decrease with an increase in the printing nozzle size. Anisotropy in mechanical behavior decreases progressively as both parameters mentioned increase. By examining the cracks and pores at the interlayer interface, this study elucidates the influence mechanism of aggregate size as well as printing nozzle parameters on the mechanical properties of 3D printed ferronickel slag–GGBFS concrete. This study also recommends the following ranges. When the maximum aggregate size exceeds 50% of the nozzle diameter, smooth extrusion is not achievable. If it falls between 30% and 50%, extrusion is possible but shaping remains unstable. When it is below 30%, both stable extrusion and good shaping can be achieved.

In order to improve the seismic and energy dissipation capacity of the whole structure, a friction-oval section mild steel rod composite damper (FOSRCD) was proposed, and its working principle was clarified. The finite element analysis of FOSRCD was carried out, and the effects of friction, frequency and displacement on the damper performance were studied. Considering the structural characteristics of FOSRCD and the mechanical models of friction dampers and mild steel rod dampers, the restoring force model of the composite dampers was proposed and compared with the numerical simulation results. The results showed that the FOSRCDs had good performance and could provide stable energy dissipation capacities in both directions, with the energy dissipation coefficient exceeding 2.3 and the equivalent damping ratio exceeding 0.37. The theoretical analysis results were in good agreement with the numerical simulation results, which verified the theoretical restoring force model; the FOSRCDs make full use of the friction energy dissipation and the shear and bending energy dissipations of the mild steel rod. It enables the two dampers to work together to achieve the purpose of multi-stage energy dissipation. FOSRCD’s structure allows it to dissipate energy in both the X- and Y-directions. The composite dampers have a variety of restoring force models and can be utilized in a wide range of practical applications.

A structure may be exposed to a range of unexpected loads throughout its full life cycle. Partially precast concrete (PC) beams refer to the process of manufacturing concrete beams in which one part of the component is pre−fabricated in a factory and the other part is completed at the construction site. Through the test, it is possible to better ensure the safety and dependability of the PC composite beams under impact load by examining the reinforcement effect, structural toughness, and damage mode of PC composite beams with bonded steel. Additionally, a scientific basis and practical guidance are provided for the actual project. Their impact resistance can significantly affect the overall safety of a structure when subjected to an impact load. Three of the four PC beams used in this investigation were strengthened with steel plates. Residual flexural bearing capacity tests and drop weight impact tests were then conducted. The impacts of steel plate thickness and U−shaped steel plate hoops on the failure mechanism and dynamic response of the component were investigated. The dynamic responses obtained from the experiments included the displacement–time history curve, impact force, and support reaction force. In order to explore the failure mechanism of the partially precast beam during the impact process, a staged analysis was conducted based on the failure mode and dynamic response characteristic values of each curve. Residual flexural bearing capacity tests were used to examine the residual flexural bearing capacity of PC beams strengthened with bonded steel plates. The results of the research reveal that the failure mechanisms of each test beam are bending–shear failures. With the increase in bonded steel thickness, the peak mid−span displacement reduced by 6.55%, the residual mid−span displacement decreased by 29.53%, and the residual flexural bearing capacity improved by 25.02%. With the adoption of U−shaped steel plate hoops, the residual flexural bearing capacity significantly increased while the peak mid−span and residual mid−span displacements both decreased.

A building may be subjected to a variety of accidental loads during its service life. Partially precast concrete (PC) beams are a primary structural component. Their impact resistance can have a substantial impact on the overall safety of a structure when it is subjected to an impact load. In this study, numerical analyses were performed on the dynamic response of PC beams strengthened with bonded steel plates subjected to impact loading. The model was verified from four aspects: energy conversion, failure form, impact force–time history curve, and midspan displacement–time history curve. The dynamic response eigenvalues of the peak impact force, peak midspan displacement, and residual midspan displacement were compared between the numerical simulations and experimental tests. The relative inaccuracy of the peak impact force ranged from 9.51% to 14.0%, with an average value of 11.9%. The average relative error for the midspan displacement was −0.09%, with the greatest relative errors varying between −0.64% and 0.3%. The residual value errors of the midspan displacement ranged from −0.95% to 2.38%, with an average relative error of 0.94%. On this basis, the effects of the impact mass, impact height, width, and length of the bonded steel plate on the impact resistance of the components were evaluated. Furthermore, the differences in the equivalent plastic strain contours, impact force–time history curves, and midspan displacement–time history curves under different parameters were compared. The results demonstrated that the failure modes and flexural deformations of the test beams were influenced by the impact mass and impact height. The increase in the length and width of the steel plate had no effect on the impact force response, but the peak and residual values of the midspan displacement decreased, which could significantly increase the impact resistance of the beams. Lastly, the impact mass m, the impact height h, the thickness t of the bonded steel plate, the length of the bonded steel plate h_s, and the width of the bonded steel plate b_s were all taken into account in the fitting formula. These five parameters were used to predict the peak impact force response, the peak value of the midspan displacement, and the residual value of the midspan displacement. The results demonstrated that the fitting formula had small errors and could accurately reflect the dynamic responses of the PC beams strengthened with bonded steel plates under impact loading.