After experiencing the damages caused by the 1994 Northridge and 1995 Kobe earthquakes, several solutions were proposed to strengthen the seismic beam-to-column connections of moment frames, which are considered a crucial factor in the stability of structures. The behavior of connections in nonlinear models can greatly influence the response of structures. Several studies have investigated the nonlinear behavior of structures and the impact of connections. However, there is limited research on diverse connection modeling under different structural analysis methods. Analyzing connections in frames with varying ductility, seismicity levels, and adherence to seismic design principles can lead to diverse results. The importance of connections in the seismic performance of moment frames prompts questions: How do different nonlinear modeling parameters, compliance with regulations, or laboratory hysteresis curves in various analyses affect structures? To what extent does neglecting seismic design principles, such as the strong column-weak beam concept in special moment frames, affect connection seismic performance?
According to the linear evaluation approach, force-based regulations often view RBS connections as amplifying drift. An unresolved question is the impact of these connections, using strengthening and weakening methods, on non-linear lateral displacements. Additionally, how much can RBS serve as a seismic fuse, altering drift distribution and values? This factor might aid in managing non-structural component deformation. Thus, assessing non-linear structural behavior through various connections and deformations can utilize non-linear drift evaluation in performance-based analyses like pushover. A non-linear drift curve, devoid of sudden shifts, could help prevent non-structural component damage.
In this study, the seismic performance of different beam-to-column moment connections in low- and mid-rise structures is investigated. Three types of connections, including RBS, WUF-W, and rigid connections, are analyzed in 5- and 10-story buildings. Initially, 3D models were evaluated using nonlinear static analysis following the ASCE41-17 guidelines. Criteria such as capacity curve, nonlinear drift, plastic rotation, and the performance of plastic hinges are scrutinized. Subsequently, a two-dimensional internal frame of each building is selected for further seismic investigation through nonlinear dynamic analysis using 11 earthquake records with varying characteristics. A 5-story structure is specifically examined to evaluate the impact of the strong column-weak beam principle on connection and frame effectiveness. The modeling includes hysteresis deterioration based on laboratory data, with the ductility demand index serving as a critical control criterion. After assessing the average structural responses in accordance with regulations, the most critical scenario is identified among the 11 earthquake records. Moreover, the amplification of plastic rotation is monitored by considering the increase in the ductility demand index as a measure to identify design parameters affecting structural behavior. The results show that incorporating connections into performance-based assessment can yield more conservative outcomes and alter the non-linear drift distribution. Applying RBS connections has notably decreased abrupt changes in the drift curve, consequently mitigating local damage risks, particularly crucial for mid-rise structures. Furthermore, RBS connections have enhanced plastic hinge performance up to IO-LS levels consistently across analyses. The findings highlight the importance of implementing seismic design principles like the strong column-weak beam concept to facilitate ductile behavior through mechanisms such as RBS connections and special frames. Neglecting this principle in the results can lead to reduced plastic hinge performance and increased structural response. The ductility demand index escalates by 1.25 and 1.66 on average and in peak response mode, respectively, when this principle is not adhered to.
The change of connections has significantly impacted the response of the structures. On average, the ductility demand index of the structures has increased by 2.23 times. Considering this, it's important to give special consideration to the use of RBS in structures that are more sensitive, such as those with smaller sections or high-rise structures.