Full strength design of column base connections accounting for random material variability

The seismic design of moment resisting steel frames, classically, is carried out by adopting full strength joints. In this approach, the dissipation of the seismic input energy is obtained relying on the plastic hinges developed at beam ends and at the base of columns preventing from plasticization the elements composing the connections. Currently, the design of full strength joints can be led in the framework of Eurocode 8, which proposes to design joints adequately overstrengthened with respect to the flexural resistance of the connected beam/column. This overstrength depends on two factors: the first one accounting for the strain-hardening of the steel composing the beam/column, the second one depending on the materials’ random variability. In this work, the attention is focused on the evaluation of the accuracy of the code approach for the case of exposed column base plate joints. In order to reach this goal four steps are developed. First, a wide set of full strength column base joints is designed according to the component method codified in last version of EC3. Then, a Monte Carlo simulation accounting for the statistical distribution of the material composing the elements of the base plate (i.e. concrete, steel of plate, steel of anchors, steel of column) is set up and the accuracy of the approach provided by Eurocode 8 is analyzed. Finally, a criterion accounting for both the material random variability and the overstrength of the connected member due to the strain hardening is proposed and its accuracy is evaluated on the base of the collected statistical data.

► In this paper available criteria for designing full strength column base joints are analyzed. ► To this scope a Monte Carlo simulation is developed. ► The results point out that EC8 approach needs an improvement for the case of stiffened joints. ► A calibration of the coefficient accounting for the materials’ random variability has been made. ► An enhancement to the EC8 criterion for designing full strength base plate joints is proposed.