Mechanism Research On "Whiplash Effect" Of The Tower Atop Tall Building Under Earthquake Action And Its Engineering Application

The prominent parts on the tops of tall buildings always damage or even break under strong earthquakes because of drastically vibration. Nowadays there is little systematic research on the seismic design method of this structural system, so that we have less practical design method for engineering design. The systematic research is applied to seismic design method of structural system of tower built atop high-rise building in this paper with respect to structural dynamic property, earthquake action calculation and seismic design method.The dynamic property of structural system of tower built atop high-rise building is studied by three-dimensional spatial finite element model in the case of the Second Long-distance Telecommunications Hub Tower of Hang Zhou. With respect to integral dynamic properties the tower will have secondary vibration under the vibration stimulation of high-rise building under earthquake to have remarkable whiplash effect.In this paper, the research progress on damping model in structural dynamic analysis is discussed in detail, on the basis of which the characteristics of dynamic responses of non-classical damping structural system are introduced. And on the basis of summarization of calculation methods of structural earthquake action, the contributions of high-order vibration mode to seismic response of tower are studied using the direct dynamic analysis method based on the mode-superposition. The principle of choosing vibration mode orders is presented with respect to the response spectrum method and the direct dynamic analysis method based on the mode-superposition.The whiplash effect of the tower built atop high-rise building under earthquake is discussed. The reason of the tower's whiplash effect is analyzed, which reveals that the whiplash effect will occur due to the co-vibration of the whole structure under earthquake and will not be strengthened when the vibration period of the tower equals to that of the main building. The basic principles of the tower's seismic conceptional design are presented.The influencing factors to earthquake action of tower are studied with respect to field classification, design earthquake classification, mass and stiffness of the main structure and towers, on the basis of which the simplified calculation method of earthquake actions of tower are presented. The computation results of the engineering example reveal the validity and applicability of the simplified calculation method. The seismic design method of structural system of tower built atop high-rise building is summarized. The finite element analysis of the joint between the tower and the main structure is performed by three-dimensional spatial nonlinear finite element program.