Avoiding Disproportionate Collapse
Full Session with Abstracts
339808-4 - Strategies for Enhancing the Robustness of Precast Concrete Frame Structures
Friday, April 20
3:30 PM - 5:00 PM
Joseph Main, PhD
Research Structural Engineer
National Institute of Standards and Technology
A recent experimental and computational study of two precast concrete moment-frame subassemblies under an interior column removal scenario revealed vulnerabilities in the moment connections arising from (a) localized bending of reinforcing bars due to eccentricity in the tensile load path between components, and (b) a reduction in the ductility of the deformed bar reinforcement due to welding. The tested subassemblies exhibited performance that may be insufficient to effectively resist disproportionate collapse, when compared to the applicable loading on a building.
To overcome the vulnerabilities stemming from connection eccentricities and welding of the anchorage reinforcing bars, three new alternative connections, which incorporate welded link plates, threaded bars, and grouted bars, respectively, were proposed to enhance the robustness of precast concrete frame structures. Computational analyses conducted on subassemblies that were geometrically identical to one of the tested subassemblies, but that incorporated the three alternative connection details, demonstrated that the frames with the alternative connections had increased peak vertical load and displacement capacities, in comparison to the tested subassembly. For example, the subassembly with the proposed threaded bar connections had a 124 % larger peak vertical load and a 232 % larger vertical displacement capacity when subjected to loads simulating a column removal scenario.
Component and subassembly testing of the alternative connections is underway. These tests are meant to validate key features of the models and to refine the connection detailing in preparation for planned full-scale connection testing. Communication with stakeholders in the precast concrete industry has already led to improvements to the alternative connection concepts to increase their constructability and economy. The goal of this experimental and computational work is to develop a suite of precast concrete connections that are constructible and economical, yet provide adequate robustness under column loss and other extreme loading scenarios. This paper describes the three proposed precast concrete connection concepts, presents results from modeling and component testing, and outlines plans for full-scale connection testing.
This paper targets both researchers and practicing engineers who work with precast concrete structures, including those who are interested in recent developments in the field of disproportionate collapse mitigation. At the conclusion of the presentation, the audience should understand (1) why new connections are needed for precast concrete frame structures and (2) the precast concrete connection details that are currently being investigated at the National Institute of Standards and Technology to provide enhanced robustness under column loss.