Proceedings home preface contents authors keywords copyright reference ©2012 Civil-Comp Ltd				Paper 5 Numerical Evaluation of Column Base Rigidity J. Razzaghi and A. Khoshbakht Department of Civil Engineering, University of Guilan, Rasht, Iran Keywords: base connection, degree of rigidity, rotational stiffness, steel structures, numerical analysis, finite element. full paper (pdf) - reference Determination of column base rigidity in steel structures has been a major challenge for civil engineers. In reality, the majority of column base connections show relatively semi rigid behaviour. Nonetheless, due to difficulties in assessment of the degree of rigidity, it is a common practice to assume a fully rigid or fully pinned behaviour when a column base is being designed. It is worth mentioning that any difference between the actual behaviour of the column base and the presumed rigidity of the connection may affect overall behaviour of the whole frame. Hence structural engineers use a wide range of detailing to assure the degrees of rigidity assumed in the design of structure. Despite the importance of the problem, enough attention has not been paid to it, so the current investigation evaluates the effects of some of the most commonly used components of base connections, including base plate thickness, anchor bolts and stiffeners.. A nonlinear three dimensional finite element model has been utilized to simulate the column base connection. Several types of connections with different configurations of anchor bolts and stiffeners have been used for modelling. The thickness of the base plate and stiffeners and also sizes of anchor bolts were also changed in a number of models. After assessing the accuracy of the numerical model by comparison with the results of an experimental study, a series of tests were carried out and the relative rigidities of each set of connection were derived. The upper and lower bounds for rotational stiffness and ultimate strength of the column base connections were obtained and categorized. It was observed that in the models with initially fully pinned base connections, the column bases exhibit considerable rotational stiffness. By contrast, relatively high amount of rotations were obtained from the models consisted of connections which were initially designed to be fully rigid. This behaviour sheds doubt over the accuracy of the typical assumptions made during the current design practice. Therefore, degrees of semi-rigidity of the column base were derived from moment rotation curves and appropriate recommendations were made for their use for analytical modelling of steel structures and the achievement of a more realistic and accurate design.