Force Finding Optimization And Cable-Strut Rupture For Kiewitt Cable Domes

Cable dome is a self-balanced tensile system with great structural efficiency,which at present,has become one of many focuses for the research and application in engineering.Research on the force-finding method,optimization of prestress and local cable-strut rupture for Kiewitt domes is conducted in this thesis,and the main contents are summarized as follows:(1)Taking Kiewitt cable domes that contain multiple overall self-stress modes as the research project,improvements are made upon ratio-updating method,which has not been proved applicable for cable domes with multiple overall self-stress modes.By using error analysis method based on least-squares,precision of the method has been assessed in comparison with the singular value decomposition method.Studies show that unlike the singular value decomposition method,the results of the method are all overall feasible self-stress modes,which is clearer in mechanic concept,and accurate with small error.Further research also indicates the obvious difference when gravity is considered in force-finding analysis,and it is suggested that additional prestress distribution be included during force-finding.(2)After the rationality analysis of different prestress level,half-span distribution of live loads and slack of cables,with the objective funtion of minimizing initial strain energy of the structure and the original constraint of slack cables,contrastive analysis is conducted upon the optimizations of the prestress for a cable dome using basic genetic algorithm and niche genetic algorithm based on group exclusion mechanism respectively.On this basis,an improved constraint of slack cables is proposed.Research shows that improvement of structural rigidity is not obvious,and half-span live loads are worse for the vertical displacement of nodes that are not central,in addition to a greater tendency to slack for ridge-cables under whole-span live loads.In contrast to the optimization of basic genetic algorithm,better results and better local search capability are shown in niche genetic algorithm.To prevent cables from slacking in load state,proper restriction on the sag of cables during the optimization is able to meet the requirements of structural safety and serviceability.(3)Using the method of transient dynamic analysis,further investigation is conducted on the problem of local cable-strut ruptures,and the influences on internal forces of other cable-struts,support reaction and greatest vertical displacement of nodes are discussed.With the mechanisms of structural collapses caused by the failure of different cable-struts revealed,destruction patterns caused by different cable-strut ruptures are classified,after which the indicator of sensitivity using strain-energy is verified applicable to the case of sequential cable-struts ruptures.Research indicates that dynamic amplification of forces for cable-struts during vibration is much greater than that of equilibrium,and the ignoration of dynamic magnification is unsafe.Under the self-weight of the dome alone,the rupture of a center brace or an outer hoop-cable would result in the large-scaled slack of cables.By contrast,under the live load,the damage of an outer hoop cable causes progressive collapse of the entire structure catastrophically,while the failure of a few braces would lead to the sequential ruptures of conjoint ridge-cables and local collapse of the structure.On the foundation of damage patterns described above,suggestions are made that internal tensile ring be adopted instead of a center brace,and safety margin of local ridge-cables be adjusted accordingly,in addition to the increment of sections for outer stay-cables to resist continuous collapse.The sensitivity coefficient based on strain-energy is capable of evaluating the sensitivity for the case of sequential cable-strut ruptures,but the energy release becomes smaller due to sequential cable-strut ruptures,hence it is more advisable to use the results calculated based on elastic constitutive relation hypothetically.As the most sensitive member in cable domes,outer hoop-cable deserves the most margin capacity and adequate protection to avoid inception rupture,as well as the necessary attention to the impact from its own separate damage.