On The Effects Of The Circular Bolt Pattern On The Behavior Of The Extended End-plate Connection

Abstract

This study is pioneer in introducing the circular bolt pattern configuration in extended end-plate steel connections. Discovering the static and cyclic behavior of such connections is at the forefront of this research study. To accomplish this goal, full-scale experimental testing complemented with three dimensional non-linear finite element analysis were conducted. Due to the similarity between the behavior of T-Stubs under tension, and tension flange of the extended end-plate connection, experimental study was conducted on several T-Stub connections to study the effect of the bolt pattern configuration on the ductility, bolt force distribution, flange deformation, and overall performance of the connection. The specimens were fabricated in the laboratory and the bolts were strain gauged to monitor the bolt force during testing. This experimental study was coupled with nonlinear finite element modeling for further validation of the FEM results. Three dimensional non-linear finite element models were developed for each case using the corresponding geometric values. The steel plates were modeled with 8-noded linear brick, reduced integration, and hourglass control element. The 6-noded linear triangular prism elements were used to model the bolts, bolt head, nuts, and the washers. The combined hardening plasticity algorithm was used in order to model the behavior of the Grade-50 hot-rolled steel elements during the 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 by tie-contact algorithm. The frictional surfaces accompanied by tangential force were modeled by tangential-contact algorithm. The contact surfaces between the end-plate and column were modeled by the frictional contact using 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 conducted to include 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.