In a beam string structure, the failure of a cable unit may trigger severe progressive collapse. To address the tension cables located failure at critical positions in the lower chord of traditional suspendome structures, a novel variable stiffness cable (VSC) component composed of a weakened origin cable and two slack cables is designed and developed. The load-bearing mechanism of the component is analyzed, and the working state curve is formulated based on the mechanical response. The component can reestablish an effective load-transfer path at the location of cable failure, leading to an internal force redistribution, and it provides the structure with a higher safety reserve and enhances its resistance to progressive collapse. Subsequently, the component is introduced into a planar beam string structure, and a finite element model is established. A novel planar beam string structure test model based on VSC is also designed and fabricated. The failure of the lower-chord tension cable is simulated using a cable failure triggering device, and static and progressive collapse tests are performed to validate the finite element model. A parametric study is carried out with component length ratio γ , the origin cable cross-sectional area ratio α 1 , the slack cable cross-sectional area ratio α 2 and the slackness β as the key parameters to analyze the static and dynamic performance of the beam string structure, and reasonable parameter ranges are recommended. The research results indicate that the introduction of VSC leads to a slight reduction in the overall stiffness of the beam string structure, approximately 1.96%. During the engagement of the variable-stiffness cable, the structure exhibits a certain dynamic response, which gradually stabilizes thereafter. Comparison between the test results and FEM simulations shows that the cable force error during the static test is within 10%, while the maximum vertical displacement error during the vibration stage is 12.37%. These results indicate that the FEM can accurately capture the structural state transition process. In practice, it is recommended that the component length γ be 40%–50% of the original cable length, the origin cable cross-sectional area ratio α 1 be 80%, the slack cable cross-sectional area ratio α 2 be 1–2, and the slackness β be 5%.
Lu et al. (Thu,) studied this question.