Analysis Of Seismic Resistance Of The Steel Tower Atop Concrete Frame

In terms of the structure of steel tower that built atop tall buildings, as the quality and stiffness on roof of building abruptly changes on roof of building, when the earthquake occurred, the steel tower is stimulated through the strenghed and enlarged vibration of the main structure, consequently, an obvious "whiplash effect" may exist. Several earthquake experiences reveal that under the situation of "whiplash effect", the steel tower still suffers strong reaction even resulting in-collapsing, although the main structure brings little damage. Currently, the systematic research on such function of earthquake prevention has seldom touched, as a consequence, no design code or rules can be applied. Therefore, it is necessary to do some research systematically, in which concerns the steel tower atop buildings structure and gives the simplified calculation of these towers under earthquakes.The research adopts general finite element software ANSYS to build such three-dimensional space model with steel tower built atop concrete frame building, using Lanczos to analyze the characteristic of the model when the system and steel tower are operating respectively. From the entire dynamic characteristics aspect, it is can be seen when the concrete framework incurring vibration under earthquake, the roof of steel tower will have secondary vibration due to stimulation on the vibration of the housetop framework, which is the "whiplash effect" stated above.There are two types of material making up the roof of steel tower construction, with the different characteristics of extent to damp energy cost. To overcome the damping problem, the essay uses material damping to demonstrate the characteristic of steel tower and major structure, this method is more exacted than equivalent viscous damping. While using material damping and integral damping ratio to proceed the analysis concerning the structure of steel tower on roof of building, the result revealed that it should not be neglected on the effect of reducing power on the floor of steel tower by non-proportional damping, yet it has no obvious effect on the framework structure. It has been discussed that the effect of steel tower under earthquake in different position on roof of building, as well as the effect of steel tower and major structure under earthquake with regard to the major structure's height. Generally speaking, from the aspect of framework structure, the steel tower on roof of building can be seen as the TMD system, thus, the function of steel tower on roof of building might not be considered while designing structural program; from the aspect of steel tower, since the stiffness of steel tower in X-directed are stronger than in Z-directed, so the "whiplash effect" of steel tower is more obvious in X-directed when earthquake occurring. Consequently, the checking computations should focus on the steel tower on roof of building in X-directed earthquake.On the basis of elastic time-history analysis, adjusting the steel tower's stiffness, then making use of a composite parameter "Comparative Cycle" to discuss the incremental coefficient of steel tower on roof of building, and finally providing simplified method of earthquake on roof of steel tower. According to the calculation in practice, the correctivity and suitability of the calculation can be approved. At last, some advices are raised relating to the design of earthquake prevention in such structure.