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During extreme events such as earthquakes, stairs are the primary means of egress in and out of buildings. Therefore, understanding the seismic response of this non-structural system is essential. Past earthquake events have shown that stairs with a flight to landing fixed connection are prone to damage due to the large interstory drift demand they are subjected to. To address this, resilient stair systems with drift-compatible connections have been proposed. These stair systems include stairs with fixed-free connections, sliding-slotted connections, and related drift-compatible detailing. Despite the availability of such details in design practice, they have yet to be implemented into full-scale, multi-floor building test programs. To conduct a system-level experimental study using true-to-field boundary conditions of these stair systems, several stair configurations are planned for integration within the NHERI TallWood 10-story mass timber building test program. The building is currently under construction at the UC San Diego 6-DOF Large High-Performance Outdoor Shake Table (LHPOST6). To facilitate pre-test investigation of the installed stair systems a comprehensive finite element model of stairs with various boundary conditions has been proposed and validated via comparison with experimental data available on like-detailed single-story specimens tested at the University of Nevada, Reno (UNR). The proposed modelling approach was used to develop the finite element model of a single-story, scissor-type, stair system with drift-compatible connections to be implemented in the NHERI TallWood building. This paper provides an overview, and pre-test numerical evaluation of the planned stair testing program within the mass timber shake table testing effort. 

Mass timber is a sustainable option for building design compared to traditional steel and concrete building systems. A shake table test of a full-scale 10-story mass timber building with post-tensioned mass timber rocking walls will be conducted as part of the NHERI TallWood project. The rocking wall system is inherently flexible and is expected to sustain large interstory drifts. Thus, the building’s vertically oriented non-structural components, which include cold-formed steel (CFS) framed exterior skin subassemblies that use platform, bypass, and spandrel framing, a stick-built glass curtain wall subassembly with mechanically captured glazing, and CFS framed interior walls, will be built with a variety of innovative details to accommodate the large drift demands. This paper will describe these innovative details and the mechanisms by which they mitigate damage, provide an overview of the shake table test protocol, and present performance predictions for the non-structural walls. 

Studies of recorded ground motions and simulations have shown that deep sedimentary basins can greatly increase the damage expected during earthquakes. Unlike past earthquake design provisions, future ones are likely to consider basin effects, but the consequences of accounting for these effects are uncertain. This article quantifies the impacts of basin amplification on the collapse risk of 4- to 24-story reinforced concrete wall building archetypes in the uncoupled direction. These buildings were designed for the seismic hazard level in Seattle according to the ASCE 7-16 design provisions, which neglect basin effects. For ground motion map frameworks that do consider basin effects (2018 USGS National Seismic Hazard Model), the average collapse risk for these structures would be 2.1% in 50 years, which exceeds the target value of 1%. It is shown that this 1% target could be achieved by: (1) increasing the design forces by 25%, (2) decreasing the drift limits from 2.0% to 1.25%, or (3) increasing the median drift capacity of the gravity systems to exceed 9%. The implications for these design changes are quantified in terms of the cross-sectional area of the walls, longitudinal reinforcement, and usable floor space. It is also shown that the collapse risk increases to 2.8% when the results of physics-based ground motion simulations are used for the large-magnitude Cascadia subduction interface earthquake contribution to the hazard. In this case, it is necessary to combine large changes in the drift capacities, design forces, and/or drift limits to meet the collapse risk target.