Numerical Investigation of Removing Horizontal Continuity Plate in Beam to Column Connection in the Box Columns in Moment Resisting Frame Systems (MRFs)

Continuity plates in box columns play a crucial role in transferring loads from beams to columns. According to seismic code requirements, these plates are often connected to the column flange using full penetration groove welds. Full penetration groove welding of continuity plates to columns presents challenges such as incomplete penetration at corners, difficulty in repairing defective welds, the necessity of using the fourth face or electroslag welding, potential delamination in the column plate, and more. These issues can lead to reduced structural efficiency and safety. In this paper, to address the challenges of embedding and installing horizontal continuity plates inside box columns, which in some cases, due to difficult access and specific geometry and layout, make it very challenging to properly and adequately satisfy seismic design criteria, new and strategic connections are proposed using numerical analysis. These analyses were performed using advanced finite element software, and their results were compared with conventional connections. To achieve a suitable load transfer path from the beam to the column in the connection region and to facilitate the assembly and execution of the frame elements in the connection region, the use of internal vertical stiffeners instead of conventional horizontal continuity plates and widening the beam flanges as a suitable solution has been proposed and examined. These solutions not only help improve structural performance but also simplify the construction and installation process. Additionally, to complement this connection approach, the use of external vertical stiffeners on the beam flange in the beam-to-column connection region, along with the use of internal vertical stiffeners instead of horizontal continuity plates in the connection region, has been proposed. Furthermore, the simultaneous use of widened beam flanges, the presence of external vertical stiffeners on the beam flange, and replacing internal vertical stiffeners instead of horizontal continuity plates in the connection region has also been investigated. The investigations were carried out using finite element analysis on the proposed samples. The results obtained from the numerical analysis of the proposed connections indicate adequate performance compared to conventional moment connections. Connections made using widened beam flanges exhibited an 18% higher energy absorption capacity than conventional moment connections up to a maximum displacement of 6% radians, without showing significant strength degradation. This percentage was reported to be 14% and 28% higher than the conventional moment connection for connections using external vertical stiffeners on the beam flange and connections made using the simultaneous presence of widened beam flanges and external vertical stiffeners on the beam flanges, respectively. Moreover, the rupture index of weld was evaluated in different scenarios. The final results indicate that the simultaneous use of widened beam flanges and external vertical stiffeners on the beam flange along the beam web leads to the creation of a suitable load transfer path from the beam to the column in the connection region. Additionally, the mechanism of moving the plastic hinge away from the column face in this idea has been well achieved, reducing the possibility of brittle fracture of the penetration weld at the beam-to-column connection. These findings highlight the potential for improved structural integrity and safety in seismic design.