This report presents an experimental and computational study of two reinforced concrete beamcolumn assemblies, each comprising three columns and two beams. The two beam-column assemblies represent portions of the structural framing system of two ten-story reinforced concrete frame buildings, which were designed as part of the National Institute of Standards and Technology research program aimed at mitigating disproportionate structural collapse. One building was designed for Seismic Design Category C (SDC C) and the other for Seismic Design Category D (SDC D). The beam-column assemblies were taken from the exterior momentresisting frames of these buildings. The assembly from the SDC C building was part of an intermediate moment frame (IMF) and the assembly from the SDC D building was part of a special moment frame (SMF). The full-scale test assemblies were subjected to monotonically increasing vertical displacement of the center column to simulate a column removal scenario. The test was terminated when a collapse mechanism of each assembly was developed and the vertical load carrying capacity of the assembly was depleted. The primary test specimen response characteristics were measured. These included vertical and horizontal displacements at specific locations, rotations at beam ends, and strains in reinforcing bars at various locations. In addition, concrete surface strains were recorded by measuring the change in length between prepositioned targets at pre-selected critical zones of the beams. The failure of both the IMF and SMF assemblies was characterized by (1) crushing of concrete at the top of the beam near the center column, (2) development of major flexural cracks (deepening and widening), and (3) fracture of the bottom longitudinal beam reinforcing bars at a major crack opening near the center column.Computational analyses of the beam-column assembly tests were carried out using two levels of modeling: (1) detailed models with a large number of elements: solid elements for concrete and beam elements for both longitudinal and transverse reinforcement, and (2) reduced models with a limited number of elements: beam elements for beams and columns and rigid links connected by nonlinear rotational springs for the beam-column joints. The analyses conducted using these models provided insight into the overall behavior and failure modes of the test assemblies. Good agreement was observed between the experimental and computational results. Both detailed and reduced models were capable of capturing the primary response characteristics. The reduced models developed in this study will be valuable in the analysis of complete structural systems for assessing the reserve capacity and robustness of building structures. The analyses confirm that the ultimate loads under the column removal scenario are primarily resisted through catenary action, wherein axial tension develops in the beams. The tensile force increase is limited by the fracture strength of the tensile reinforcement of the beams.Keywords: buildings;...
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