Differentiation Analysis of Vertial Stiffnees and Cable Force Sensitivity of Double-Layer Cable Net and Beam String Structure

Due to the introduction of cable element, the mechanical performance of long-span flexible and semi-rigid structures is significantly improved, so that more structures meeting the requirements of architectural innovation can be realized. In recent years, the above two kinds of structures are widely used in large stadiums and gymnasiums. Scholars at home and abroad have done a lot of theoretical research on them, and the research results have been well used in practical engineering. Due to the difference of the dependence of flexible and semi-rigid structures on cable elements, there are great differences in the vertical stiffness and the sensitivity of cable forces between the two structures, which makes large effects on the actual design and construction.In order to explore the above problems, large-span spoke double-layer cable net and radial beam string structures with the same size were established by using the general finite element software ANSYS, and the corresponding contrast parameters were set for the vertical stiffness and cable force sensitivity, including the equivalent vertical stiffness coefficient G, the cable force sensitivity value TS₁ and the cable force sensitivity relative value TS₂. Comparative analysis was carried out to guide the design of similar projects.The results showed that: in the process of increasing the external load, the vertical stiffness of the cable net structure had the phenomenon of mutation and slow enhancement. Through tracking and recording the internal force of the circumferential cable (structural cable), it was found that the internal force of the circumferential cable gradually decreased from positive value to 0 (relaxation) at the point of stiffness mutation, which indicated that the relaxation of the circumferential cable led to the mutation of the vertical stiffness of the structure. According to the data analysis, compared with the initial stiffness of the load, the final stiffness of the cable net structure increased by about 3.2%, which could be ignored in the actual analysis because of the small increase. The vertical stiffness of beam string structure was basically unchanged and there was no sudden change of stiffness. When the span was small, the equivalent vertical stiffness G of cable net structure and beam string structure was close. With the increase of span, the equivalent vertical stiffness G of both structures decreased, but the decline rate of cable net structure was much faster than that of beam string structure. Under the same plane layout, the cable force sensitivity TS₁ and the relative value TS₂ of the cable net structure were greater than that of the beam string structure, which indicated that the cable net structure was less sensitive to the cable force, while the overall stiffness of the beam string structure had been formed in the case of small cable force due to the existence of upper rigid members, which made the structure more sensitive to the cable force. In the process of increasing prestress or reducing span, the sensitivity of cable net and beam string structure to cable force decreased. After comparing the cable force sensitivity value TS₁ of cable net and beam string structure, it was found that the TS₁ ratio of the two structures was stable between 2.43 and 2.55, which could provide reference for similar projects.