FOUR-ELEMENT HYBRID SIMULATION OF A STEEL FRAME WITH CAST STEEL YIELDING CONNECTORS

Cast steel structural components, and in particular, cast steel energy dissipative components have been developed and used in order to enhance the seismic performance of structures due to their reliable energy dissipation capacity, improved ductility, and highly increased low-cycle fatigue life. One such device is the Cast Steel Yielding Connector (YC); an innovative cast steel energy dissipative hysteretic brace connector. Cast steel yielding connectors have a unique and desirably symmetrical hysteretic response, demonstrating increased post-yield stiffness at large deformations due to geometric second order effects. This behaviour makes numerical modelling of these systems more challenging than typical yielding systems under earthquake excitations. In the present study, a set of full-scale four-element pseudo-dynamic hybrid simulations are carried out on a four-story steel frame equipped with cast steel YCs. The pseudo dynamic hybrid simulations are followed by cyclic tests on two YC elements using the ASCE-SEI 41-13 protocol to evaluate the remaining low cycle fatigue capacity of the elements after the seismic events. The results of the hybrid simulations indicate that available numerical models for YCs tend to over-predict their maximum deformations under earthquake excitations. The over-prediction is within acceptable margins for the first floor; however, the numerical results tend to further deviate from the experiments at upper floors. In addition, cast steel YCs were shown to have a very reliable low-cycle fatigue life; being able to sustain most of the cyclic loading protocol even after several major earthquakes. The study is then extended to a numerical study where the response of the four-story reference steel structure with the Yielding Brace System (YBS) is evaluated under a suite of 40 ground motions, selected and scaled to match the Uniform Hazard Spectrum and to be representative of the seismological characteristics of the site. The YBS, in the reference structure, is replaced with a Buckling-Restrained braced Frame (BRBFs) and the study is repeated to underline the advantages of each system. The results of this preliminary numerical study indicate that mid-rise Steel Frames with the YBS manifest a more uniform inelastic response along the structures’ height and are less prone to soft-story mechanism formation on the first floor, when compared to their BRBF counterparts.