Seismic Behavior Of Steel Moment Frames By Considering The Effect Of Exposed Column Base Connections

In steel moment frames, column base is the key connection of the upper structure and the foundation, transferring loads to the foundation. The column base affects the internal force distribution and building deformations. Exposed column bases are mainly used in light steel structure and low-rise buildings, with advantages of convenient installation, short construction period and low cost. In engineering practice, taking base-connection as perfectly pinned or rigid, without considering the exist rotational stiffness, thiswill increase the uncertainty in the predicted structural response and contribute to both economy and safety. Exposed column base and its effects on the seismic behavior of the upper steel moment frame are investigated by finite element method.The main research contents are as follows:First of all, the current design of exposed column bases in China, US, Japan and Europe are summarized, including moment resistance, shear resistance, and rotational stiffness. Based on the comparison, the deficiency of the current design methods is pointed out which needs a further study to estimate. This conclusion offers a relevant suggestion on associative study in our country.Based on the research introduced above, a 4-story 3-bay steel moment frame is studied with the nonlinear time history analysis, using Opensees. In the numerical analysis, the rotational stiffness and hysteretic performance of exposed column base were considered. The characteristics of structural deformation, hysteretic loops and plastic energy dissipation of components were compared. To explore the possibility of semi-rigid connections used in the practice, and provide a reference for the application of exposed column base in engineering. Gain the following major conclusions:(1) In design, it is prefer to consider the contribution of rotational stiffness of exposed column base, rather than a pinned one. As a result, the structure has larger potential to avoid structural damage.(2) As the rotational stiffness of exposed column base is two times that of column, it is possible to consider the column base connection as rigid for the nonlinear time history analysis.(3) Modelling the hysterestic characteristics of column base connection in simulations will simulate the behavior of the structure under earthquake more accurately. Furthernore, its influence on the whole structure increases with the increase of the rotational stiffness.Hence, it is necessary to consider the rotational stiffness of exposed column base for application in engineering, so as to make the design more reasonable close to a real one, reduce total steel mass and the economic cost, moreover, promote the development of structural optimization design.