Research On Seismic Design Method Of The Structural System Of The Steel Tower Built Atop High-rise Building

The structural system of steel tower built atop high-rise building has been applied in the practical engineering to a great extent. However, earthquake experiences reveal that the steel tower built atop building will have strong reaction under earthquake action even if the main structure have no or little damage. Nowadays the seismic design method of this structural system has no systematic research so that there is no practical design method for engineering design. The systematic research is applied to seismic design method of structural system of steel tower built atop high-rise building in this paper with respect to structural dynamic property, damping model, earthquake action calculation and seismic design method. The dynamic property of structural system of steel tower built atop high-rise building is studied by three-dimensional spatial finite element model in the case of Jiangsu Electricity-net Dispatcher Center. With respect to integral dynamic properties the steel tower will have secondary vibration under the vibrational stimulation of high-rise building under earthquake to have remarkable whiplash effect. According to the Rayleigh-Ritz principle, the simplified calculation method of dynamic properties of such structural system is presented. For such structural system composed of the main structure and steel tower, the integral dynamic properties can be solved approximately by Rayleigh-Ritz method with the natural period and vibration mode of the main structure and steel tower respectively. 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 studied. In the view of engineering practical application, the calculation method of equivalent viscous damping ratio of structural system of steel tower built atop high-rise RC building is studied to reflect the various energy dissipation properties of steel tower and the main structure. The analysis results reveal that the internal forces of steel tower need to be adjusted according to equivalent viscous damping ratio in the calculation of earthquake responses of such structural system. On the basis of summarization of calculation methods of structural earthquake action, the contributions of high-order vibration mode to seismic response of steel 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 steel tower and the influence of the seismic response of the main structure due to steel tower are studied with respect to damping property, field classification, design earthquake classification, mass and stiffness of the main structure and steel towers, on the basis of which the simplified calculation method of earthquake actions of steel tower and the main structure taken the steel tower into consideration 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 steel tower built atop high-rise building is summarized. The finite element analysis of the joint between the steel tower and the main structure is performed by three-dimensional spatial nonlinear finite element program.