Seismic Resiliency of Repetitively Framed Mid-Rise Cold-Formed Steel Buildings

As a capstone to the multi-university-industry collaborative CFS-NHERI project, a full-scale 10-story CFS-framed building is planned for seismic testing under increasing, multi-directional earthquake motion intensity and subsequent live fire testing. This collaboration follows on successful prior system-level 2-story (CFS-NEES) and 6-story (CFS-HUD) efforts of the team.

Beyond-code, state-of-the-art CFS building

The CFS-NHERI capstone test building is designed with a height of 31.6 m (103 ft 9 in), exceeding the height limitation of 19.8 m (65 ft) set by the current ASCE 7-22 design standard. The design also advances lateral force resisting system (LFRS) details to provide for the increases in seismic shear and overturning moment demands associated with increases in building height. Data generated from this unique experimental program will shed light on the impact of architectural exterior and interior finishes, non-designated systems, such as gravity walls or window/door framing, that are along the same architectural line of the CFS-framed shear wall system. Another key factor, higher mode effects, which can significantly influence the structural and nonstructural seismic response of tall buildings, will also be studied for the first time for such repetitively framed structures. The experiments will provide vital full-scale system-level benchmark test data for a state-of-the-art CFS building under multidirectional seismic input. Furthermore, it will advance knowledge of the post-earthquake fire performance of mid-rise CFS construction, by incorporating a live fire test sequence following seismic test phase completion. 

Modular construction and resilient stair system

The test building will integrate conventional stick-framing, panelized (2D), and volumetric (3D) modular construction within one building specimen, allowing a unique opportunity to document and compare the efficiency of each construction method, and any differences in structural performance. The floor and roof diaphragm are also designed to embrace a modular stair system within the floor plan of the building. The seismically resilient stairs will provide safe egress/ingress to the building through the use of a variety of drift-compatible details, including following design and MCE level earthquake tests. Modular construction offers several benefits such as lower material waste, lower carbon footprint and embodied carbon, and greater energy efficiency through tighter building envelopes. However, it also requires creative engineering solutions to attain sufficient module strength and stiffness needs for handling-induced loads and to minimize damage during transportation without significantly modifying the seismic lateral force resisting system strength and stiffness, nor increasing the seismic weight. The CFS-NHERI project offers an exciting opportunity for collaboration between researchers and industry partners to bring forth new ideas to realize modular construction within CFS framing systems.

Functional recovery

Buildings utilizing lightweight CFS-framing have seen limited study for post-event functional performance. This test program will provide a valuable opportunity to examine the evolution of damage of different systems within a building and develop accurate fragility information, which can be used to improve loss and downtime predictions and evaluate the functional recovery performance. To support this effort, sensors will be installed at various locations throughout the building to capture critical engineering demand parameters for nonstructural components of interest to understand the system resiliency. The shake table tests also provide an opportunity to determine measurement accuracy and reliability of alternative sensing techniques such as laser-based optical sensing and vision-based sensing using camera-equipped unmanned aerial vehicles (UAVs). In addition, digital still, 360° panoramic/virtual reality media and video imagery will be captured throughout construction, testing and de-erection.

The CFS-NHERI capstone building test program will generate valuable knowledge, which accrues benefits not just for CFS-framed systems, but all systems, through improvements in design standards such as ASCE 7-22, AISI S400-20 and construction handbooks.

More information can be found at https://cfs10.ucsd.edu/.