Elongation in Ductile Seismic-Resistant Reinforced Concrete Frames

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Title: Elongation in Ductile Seismic-Resistant Reinforced Concrete Frames

Author(s): R. C. Fenwick and B. J. Davidson

Publication: Special Publication

Volume: 157

Issue:

Appears on pages(s): 143-170

Keywords: axial loads; beams (supports); earthquake-resistant structures; ductility; frames; hinges (structural); reinforced concrete; shear properties; Structural Research

Date: 10/1/1995

Abstract:
To survive a major earthquake, current practice requires seismic resistant frames to be designed to be ductile. To achieve the required level of ductility in multistory frames, the majority of the potential plastic hinge zones are located in the beams. The inelastic rotation, which may develop in these zones, arises predominately from the tensile yielding of the reinforcement. The associated compressive strains are small and, as a consequence, elongation occurs. Test results show that elongation on the order of two to four percent of the member depth develop in plastic hinge zones of beams subjected to cyclic loading before strength degradation occurs. The factors influencing elongation are reviewed in this paper. The results of a time history analysis, in which elongation effects are modeled, shows that this action, which is neglected in current design practice, has important implications for the detailing of columns and the design of supports for precast components and external cladding.