This research investigated experimentally the seismic performance of steel gravity framing with a concrete slab at the system level. Two half-story, two-by-three bay steel gravity frame specimens were tested under cyclic loading. Bolted-bolted double-angle connections were used for a beam-to-column gravity connection. Primary design variables and construction details include the orientation of the metal deck to the loading direction, the presence or absence of metal deck seams on secondary beams, and the contribution of additional reinforcement bars in the concrete slab. Concrete blocks were positioned at the midpoint of each bay to simulate gravity loads, and a quasi-static displacement-controlled cyclic loading protocol was applied to the specimen using three hydraulic actuators. These investigations confirmed general observations from previous subassembly testing programs that the composite steel gravity framing system can provide substantial flexural stiffness, strength, and ductility under cyclic loading. Further, the test findings showed that the primary design variables and construction details significantly affected the cyclic behavior of composite gravity connections. Comparing the test results from a multi-bay setup and a subassembly testing setup, the cyclic behavior showed remarkable differences, especially for cases with weak axis decking or strong axis decking with a seam. These large differences are attributed to a significant separation of the girder from the column in the subassembly testing setup, which may not be present in a real building. Virtually all previous cyclic loading tests on gravity connections have been conducted in subassembly test setups. These subassembly tests are therefore the basis for the models that are currently used to include gravity frame connections in the seismic performance assessment of buildings, and these models may be quite inaccurate in some cases. The data generated in this system-level testing program is intended to support efforts to develop improved models of gravity connections subject to seismic loading.
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Modeling of Composite MRFs with CFT Columns and WF Beams
A vast amount of experimental and analytical research has been conducted related to the seismic behavior and performance of concrete filled steel tubular (CFT) columns. This research has resulted in a wealth of information on the component behavior. However, analytical and experimental data for structural systems with CFT columns is limited, and the well known behavior of steel or concrete structures is assumed valid for designing these systems. This paper presents the development of an analytical model for nonlinear analysis of composite moment resisting frame (CFT MRF) systems with CFT columns and steel wide flange (WF) beams under seismic loading. The model integrates component models for steel WF beams, CFT columns, connections between CFT columns and WF beams, and CFT panel zones. These component models account for nonlinear behavior due to steel yielding and local buckling in the beams and columns, concrete cracking and crushing in the columns, and yielding of panel zones and connections. Component tests were used to validate the component models. The model for a CFT MRF considers second order geometric effects from the gravity load bearing system using a lean on column. The experimental results from the testing of a four story CFT MRF test structure are used as a benchmark to validate the modeling procedure. An analytical model of the test structure was created using the modeling procedure and imposed
displacement analyses were used to reproduce the tests with the analytical model of the test structure. Good agreement was found at the global and local level. The model reproduced reasonably well the story shear story drift response as well as the column, beam and connection moment rotation response, but overpredicted the inelastic deformation of the panel zone.
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- Award ID(s):
- 2037771
- NSF-PAR ID:
- 10344166
- Date Published:
- Journal Name:
- Steel And Composite Structures
- Volume:
- 43
- Issue:
- 3
- ISSN:
- 1229-9367
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Steel moment-resisting frames (MRFs) are widely used in the United States to resist seismic forces. MRFs have many advantages, including high ductility, architectural versatility, and vetted member and connection detailing requirements. However, MRFs require large members to meet story drift criteria. Moreover, strong-column-weak-beam requirements can result in significant member sizes, and – even in the cases where strong-column-weak-beam requirements are satisfied – MRFs can still be vulnerable to story mechanisms in one or a few stories. Recently, the concept of a strongback has been utilized successfully to delay or prevent story mechanism behavior in braced frames. The strongback is represented by a steel truss or column that is designed to remain essentially elastic, thus allowing the system to transfer inelastic demands across stories. Although systems including strongbacks exhibit more uniform story drift demands with building height and reduced peak drift response, the elastic nature of the strongback can also result in near-elastic higher-mode force demands. This study compares the dynamic response of a baseline MRF to that of a retrofit using a strongback column. Several ground motions are considered to determine which cases produce the largest drift, acceleration, and force demands.more » « less
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Summary Reinforced concrete structures that lack proper seismic detailing commonly have increased vulnerability to collapse during strong earthquake shaking. A major contributor to building collapse vulnerability is the prevalence of columns with widely spaced and poorly configured transverse reinforcement. Such columns are susceptible to shear failures, which can lead to axial failures and local or global building collapse. This study presents a laboratory test program that was designed to gain insight into the effects of column detailing on the dynamic response including collapse of concrete frames. Twelve concrete frames were tested on a shaking table and were subjected to two types of ground motions: one relatively short‐duration motion with strong velocity pulse and one relatively long‐duration motion with multiple cycles. The study also evaluates the effectiveness of modern analytical methods to simulate the nonlinear dynamic response of concrete structures. Two lumped plasticity models employing nonlinear rotational and shear springs at the column ends were used to simulate the collapse response of the tested specimens.
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.12989/scs.2022.43.3.000
