Dr. Nuñez-Castellanos, Eduardo

The study of moment connections in steel structures subjected to cyclic loads has been extensively studied, providing a great number of requirements, including the strong column-weak beam relationship, to guarantee a satisfactory cyclic performance. However, investigations on the cyclic performance of moment connections considering the bidirectional and axial load effects simultaneously with tubular columns are limited. This study aims to assess and validate the strong column-weak beam relationship of 3D steel moment connections using reduced order models. The simplified model (reduced order model) approach was employed to extend the range of beam and column elements sizes and reduce the experimental and computational costs. These models were calibrated from full-scale experimental studies. A great number of configurations with different beam and column sizes without loss of reliability and structural representativeness of the studied phenomenon were studied. A total of 13640 simplified models were developed. Results show a cyclic behavior controlled by the strong column-weak beam relationship to modify the joint’s failure mechanism. The increasing of strong column-weak beam relationship and the biaxial effect caused degradation of the strength and stiffness as well as in dissipated energy. An optimal strong column-weak beam relationship was obtained for all joint configurations analyzed. Finally, a robust design procedure is proposed, ensuring the cyclic behavior of end-plate moment connection with built-up box column including biaxial effect and axial load. Therefore, the use of this type of moment connection can be used in special and intermediate moment frames designed according to Seismic provisions.

This paper presents an experimental research to assess the cyclic behavior of a bolted moment connection with the use of optimized end-plate connected to built-up box column subassemblies subjected to bidirectional and unidirectional loading. Seven real scale specimens were tested: three specimens with four beams connected to column as interior joint, two specimens with two beams connected as corner joint configuration and two specimens with two beams connected to column as interior joint, according the protocol established in AISC Seismic provisions. The seismic performance was evaluated in terms of hysteretic behavior, failure mechanism, stiffness and dissipated energy. The joints studied were manufactured from of hot-rolled I-beams and square built-up box columns. The elements of connection such as bolts, welding, outer stiffeners and end-plates were designed to remain in elastic range from the flexural expected capacity of beams. The results showed that the required minimum moment of 0.8Mp at 0.04 rad of drift angle was achieved for all specimens tested. However, a higher stiffness and resistance was reached in configuration with unidirectional load (interior joint) in comparison to joint subjected to bidirectional load (corner joint). The damage was concentrated uniquely in beams, while an elastic behavior in columns and connection components was reached for 0.04 rad of drift angle. Finally, this moment connection configuration can be used as an alternative to design buildings with special moment frames under bidirectional loading considering the cyclic behavior of joints evaluated.

In this numerical research, the variation of cyclic behavior of beam-to-box column connection was studied. Dimensional and load conditions were parametrically evaluated with the goal of assessing the applicability and use of this biaxial moment connection according to the Seismic Provisions, such as bending strength and rotation capacity, secant and tangent stiffness, dissipated energy and strong column-weak beam relationship. A total of 83 different models of 3D connections were developed using in ANSYS software with the load at the top of the column. Results show a cyclic behavior not controlled by axial load. However, the variations of clear span to depth beam ratio caused degradation of the strength, secant and tangent stiffness as well as in dissipated energy. The 80% of plastic moment of beam and rotation at 4% interstory drift were reached for all models analyzed according to criteria established in AISC 341. Finally, the configurations designed with low levels of axial load are controlled by the design of the web panel zone shear, while configurations designed for high levels of axial load are controlled by the strong column-weak beam criterion.