ON THE EFFECTS OF CIRCULAR BOLT PATTERNS ON THE ...

elements during monotonic and cyclic loading. Isotropic hardening was used to model the
material properties for the high strength steel bolts. Small sliding surface-to-surface contact
algorithm was considered for all the contacts. The welds were modeled by a tie-contact algorithm.
The frictional surfaces accompanied by tangential forces were modeled by a tangential-contact
algorithm. The contact surfaces between the end-plate and column were modeled by the frictional
contact using the penalty method.
One hundred eighty two numerical models with circular and square bolt patterns were
developed and analyzed by using the developed FEM. A comprehensive test matrix was used to
investigate the effectiveness of the various geometric parameters on the overall behavior of the
connections. The parametric study included seven bolt diameters, six values of end-plate
thickness, three beam sizes, and two different bolt pattern configurations based on the most
commonly used range of variables. The numerical results of the connections with circular bolt
pattern were compared with that of the connections with traditional square bolt pattern. Also, the
effects of these parameters on the moment-rotation characteristics and energy dissipation of the
connection were investigated.
To simulate the hysteresis behavior of the connection (i.e. energy dissipation), four parameter
tri-linear hysteresis models were used to fit the outer loops of the moment-rotation hysteresis
loops obtained from the FEM experiments. Comprehensive regression analyses were conducted
to obtain equations for dependent variables (tri-linear model parameters) in terms of independent
geometric variables.)
The results of this study show that the circular bolt pattern can enhance the moment capacity,
reduce pinching, and ultimately increase energy dissipation of the connections depending on their
geometric parameters.
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