Column-base connections in steel moment-resisting frames (SMFs) in seismic regions are commonly designed to develop the capacity of adjoining column with an intent to develop a plastic hinge in the column member, rather than in the connection (i.e., a strong-base design). Recent research has shown base connections to possess high ductility, indicating that this practice may be not only expensive but also unnecessary. This suggests that concentrating inelastic rotations in the base connection may result in acceptable performance. Motivated by this finding, the performance of steel moment resisting frames with a weak-base design is investigated to examine the relationships between base-connection strength, deformation capacity, and structural performance. The main scientific basis of this study is nonlinear static pushover and nonlinear time history simulations on SMFs designed for high seismicity. These simulations interrogate parameters including frame height (4-, 8-, 12-, and 20-story), base-connection strength, base flexibility, and base rotation capacity, resulting in a total of 160 parametric combinations. The performance of each of these is assessed to estimate the probabilities of failure or collapse corresponding to a 2/50 (2% probability of exceedance in 50 years) intensity of shaking. The key finding is that for all frames, acceptable performance (i.e., comparable to current practice with capacity-designed bases) may be obtained by designing the base connections for overstrength seismic loads (i.e., based on the Ω factor) rather than based on column capacity; this has the potential to offer significant cost savings. For a low-rise (i.e., four-story) frame, acceptable performance is achieved even without significant rotational demands in the base connection. For the other frames, a base-connection rotation capacity of approximately 0.05 rad is necessary to achieve acceptable performance. Implications of these findings for prospective design practices, as well as future research, are outlined, and limitations are discussed.

Due to their potential to reduce greenhouse gas emissions, light-frame timber buildings (LFTBs) are widely used in seismically active regions. However, their construction in these areas remains limited, primarily due to the high costs associated with continuous anchor tie systems (ATSs), which are required to withstand significant seismic forces. To address this challenge, frictional seismic isolation offers an alternative by enhancing seismic protection. Although frictional base isolation is an effective mitigation strategy, its performance can be compromised by extreme ground motions that induce large lateral displacements, resulting in impacts between the sliders and the perimeter protection ring. The effects of these internal lateral impacts on base-isolated LFTBs remain largely unexplored. To fill this knowledge gap, this study evaluates the collapse capacity of a set of base-isolated LFTBs representative of Chilean real estate developments. Nonlinear numerical models were developed in the OpenSeesPy platform to capture the nonlinear behavior of the superstructure, including the impact effects within the frictional isolation system. Incremental dynamic analyses following the FEMA P695 methodology were performed using subduction ground motions. Collapse margin ratios (CMRs) and fragility curves were derived to quantify seismic performance. Results indicate that frictional base-isolated LFTBs can achieve acceptable collapse safety without ATS, even with compact-size bearings. Code-conforming archetypes achieved CMRs ranging from 1.24 to 1.55, indicating sufficient safety margins. These findings support the cost-effective implementation of frictional base isolation in mid-rise timber construction for high-seismic regions.