Research On Dynamic Performance Of Wheel-spoke Cable-membrane Structure In Damaging Condition

Wheel-spoke cable-membrane structures have the advantages of light quality, reasonableforce and increasing the span etc, which is composed of the inside pull cables, radial cables,and external pressure rings. Prestressing force level of cables and its distribution plays a vitalrole in the system stiffness and performance. Because of the effect of construction errors,external loads and environmental factors, the cables are likely to be led to the relaxation ofprestressing force, unevenly distributed level stress, and the corrosion on the surface ofcables’ joints. The structure’s behavior will be changed significantly and potential danger maybe caused under Accidental loads, such as earthquake, cyclone, and so on. Therefore, it’s verynecessary to carry out the research of dynamic performance for these damaged structures.Engineering background with Century Lotus Stadium, based on experimental test ofqualitative model and finite element analysis, wind-induced vibration, seismic performance,and collapse-resistant performance of Wheel-spoke cable-membrane structure were subjectedto intensive studies when it was damaged. The following new results were obtained.(1) Based on wind tunnel tests, according to inverse Fourier Transform, and the conceptof frequency double index, and harmonic synthesis method, time history of turbulent windspeed of120joints of the structure were gained by using Matlab program. And then, adoptingANSYS program, wind-induced vibration of the structure were analyzed under these timehistory of turbulent wind speed when prestressing force of the structure’s cables were slacked.The fundamental law of the dynamic response and the sensitive wind direction of the structure,63°angle and135°angle, were gained under wind loads when the structure was damaged.The distribution law of the dynamic magnification factor of the whole structure was obtained.To deter the dynamic amplifying caused by the relaxation of prestressing force or unevenlydistributed level stress of cable system, the pressure distribution coefficient and the winddynamic coefficient gained from wind tunnel tests should be multiplied by adjustingcoefficient of structure’s dynamic damage, equaling1.1. The calculation method of thedynamic coefficient was proposed.(2) Based on the above FEM model, the structure’s dynamic characteristics and itsseismic performance were analyzed. The results show that natural frequencies of the structureare all lower and concentrate in a small range, and its jumping phenomenon isn’t in evidence.Its dynamic characteristics are very complicated. The mode mass participating coefficient isrelated to the mode order. To ensure that the mode mass participating coefficient is not less than90%, the contribution of the former140modes should be considered when the analysisof response spectrum is done. The seismic responses have only a little difference underdifferent types of seismic waves. So we should only calculate one type seismic waves inseismic analysis. Because the harming degree of the seismic loading to the structure is notsimilar when the directions of the earthquake waves are different, the effects of the waves’direction and their combination should be considered. Because the structure’s internal forceand displacement are bigger under designing seismic loads than under designing wind loadswhen the prestressing force of the cable system is released, the internal force should berespectively calculated under seismic loads and wind loads.(3) The qualitative model was made with1:60scales. And then, its static testing andnumerical analysis were done. Mechanics responses and its law were obtained when themodel was damaged. The results shows that the relaxation of prestressing force of cablesystem has only a low impact on the whole stiffness and yield load, but it has a stronginfluence on the limit load and energy dissipating capacity of the structure. The stiffness ofthe compression ring and the truss web also has a strong influence on the limit load andenergy dissipating capacity of the structure. Based on quasi-static analysis of the model, theappropriate stiffness ratio of the upper compression ring, the truss web, the lower compressionring, and the column was obtained, which was1:1.2:1.3:4.8.(4) Dynamic damage test of the qualitative model was done, and the influence of localcables failure on the whole structure was researched based on the collapse-resistant analysis.The results shows that because of the dense natural frequencies and the low impact of cables’damage on the structure’s frequencies, dynamic test equipments couldn’t collect the densenatural frequencies with neat exactitude. It is very difficulty to watch the structure’s damage,judge the degree of structure’s damage and the damage location by testing the dynamiccharacteristics. The importance degree of main components of structure from the little to thegreat is the hanging cables, the truss web, the lower compression ring, the upper compressionring, the column, the divaricating cable, the upper radial cable, the lower radial cable, and theinside pull cables. The degree of the damage caused by the important members breaking fromthe little to the great is the breaking of one lower radial cable, one upper radial cable, twoneighboring lower radial cables, two neighboring upper radial cables, column, twoneighboring radial cables, three neighboring radial cables, the inside pull cables. The structurehas good collapse-resistant performance. After the breaking of important members, their loadscould be rapidly transferred to the neighboring members. And the collapse range was preferably restricted in limited region. Double cables system, zone-design, and multi-columnstyle pier could improve the collapse-resistant performance of the structure.