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Box-columns are suitable members for structures with moment frames in two directions but performing the internal continuity plate in them causes some practical troubles. Details of the new proposal to alleviate this problem in box-columns is CONXL connection. This connection includes a set of Collar Flange Top (CFT), Collar Flange Bottom (CFB), Collar Corner Top (CCT), Collar Corner Bottom (CCB) and when the depth of the beams is more than 460 mm, Collar Corner Middle (CCM), Collar Web Extension (CWX) (only in the face of beam to column connection) and also a set of diagonal pre-tensioned high strength bolts (45 degrees angle), which collectively make up CONXL node. The bolts and collars performance make up a rigid diaphragm around the column. All collar flanges top and bottom are connected to the beam by means of groove welding with complete joint penetration, and the connection of collar web extension to the beams and that of collars corner to the column walls is made by fillet weld; collar corners are connected to each other through groove weld in factory and the pieces are just assembled in worksite. The objectives of presenting these details are industrializing, removing weld in workplace, removing continuity plate, enhancing quality, speeding up the construction, and simplifying the inspection. Through the distribution of force among collar systems, forces are transmitted from beams to the columns. The aim of this study is to numerically study the seismic behavior of CONXL connection without filler concrete of columns and to reduce the number of collar bolts with different arrangements. In order to reach this purpose, the numerical results of specimens; RBS and Kaiser bolted bracket (KBB) connection are compared to experimental results to verify the modeling and analyzing and good agreement is observed between numerical and experimental data. Afterward nine specimens of CONXL moment connections in box-columns not filled with concrete whit axial force in single, planer and bi-axial loading conditions with different arrangement of bolts are studied and their performances are evaluated. Results showed that seismic behavior of specimens with beam section depths equal or less than W30 series under cyclic loading, even with reducing the number of bolts to 16 numbers, is suitable in the over 0.04 radian rotations. Also, use of 16 numbers of bolts in connections with W30 series of beams, when it would be appropriate that use for corner connections (Single sided loading), and the specifications of ASTM-A36 for beams material to be used. Also, whatever the position of bolts to be outer than in collar flanges, axial strain in the bolts shank is bigger and its slip is less. The optimal position of the bolts is near the middle of the collar flanges. The results also showed that seismic behavior of all specimens with columns without concrete filling is appropriate and the column will remain without any remarkable local buckling in over 0.04 radian inter-story drift angle.

Keywords: CONXL moment connection, Seismic behavior, Bolt, Box-column, Collar system

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