Seismic Behavior of Frames with Bolted End Plate Connections Rehabilitated by Welded Haunches Under Near- and Far-Fault Earthquakes

A retrofit method for bolted end plate connections is the use of haunches. This method needs no change or replacement of connection components. The optimum selection of rehabilitation parameters like thickness or haunch-beam angle is of great importance for designers. Besides, one of the important factors for designers to select this retrofit method, is the efficiency of retrofitting by haunches and the effectiveness of retrofit parameters on behavior of retrofitted frames in near- and far-field earthquakes. The results of 2D numerical modeling of the frames shows that rehabilitation of the weak end plate connections using haunch improves the seismic behavior of the weak frame relative to the reference frame with connections designed according to AISC code. For example, the roof displacements are reduced by 8% averagely and the maximum story drifts in near and far-field earthquakes are reduced by 22% and 12% in the rehabilitated frames compared to those of the reference frame. The results of 3D substructure numerical models, after verification by experimental results, showed that the increase of haunch thickness from 12 to 18 mm did not significantly increase the moment capacity and initial rotational stiffness. However, the pinching in moment-rotation hysteresis is decreased. The increase of haunch angle from 30 to 60 resulted in shift of plastic hinge to haunch internal area and 100% reduction of energy absorption and initial rotational stiffness compared to those of the reference specimen. Since the change of retrofit method parameters results in change of stiffness and natural time period of the structure and the affecting parameter on structure dynamic behavior is “the ratio between structure main time frequency to earthquake predominant time period”, the selection of the first haunch thickness with an angle of 30 degree toward the beam that satisfy the requirements of FEMA350 will be economic and optimized.