CRITICAL MOMENT AND ROTATIONAL STIFFNESS OF STEEL COLUMN BASE CONNECTED TO CONCRETE FOOTING BY PRESTRESSING

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One of the typical steel column bases is formed by a set of base plate welded to the bottom of the column and anchor bolts embedded in cocrete footing by prestressing. Critical moment and rotational stiffness of column base have been examined by adopting various combination of the base plate rigidity and anchor bolts. Test and analytical results are as follows,(1) Critical moment depend on the rigidity of overhang of base plate.(2) Stiffnes of column base, if the active moment are under the critical moment, depend on the local deformation of cocrete footing and if the active moment are over the critical moment, depend on the deformation of base plate and anchor bolts.(3) The drawing method which estimate the hysteresis loops of the column base under cyclic loading is derived by use of the critical moment and stiffness of column base.(4) The empirical formuls for critical moment and stiffness of column base have been derived, which may enable a more reasonable earthquake resistant design of steel structure.