Ductile Behavior of Beam-Column Joints With High- and Low-Strength Concrete

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Title: Ductile Behavior of Beam-Column Joints With High- and Low-Strength Concrete

Author(s): S. W. Shin, J. M. Ahn, K. S. Lee, S. H. Lee, and S. K. Ghosh

Publication: Special Publication

Volume: 149

Issue:

Appears on pages(s): 331-346

Keywords: beams (supports); columns (supports); compressive strength; ductility; flexural strength; high-strength concretes; joints (junctions); loads (forces); low-strength concretes; shear properties; Structural Research

Date: 10/1/1994

Abstract:
In general, the structural member using high-strength concrete is accompanied by high brittleness, which may result in the unexpected dangerous failure. For economy and safety, high-strength concrete may be used for compressive members (vertical members) and low-strength concrete for flexural members (horizontal members). ACI 318-89 recommends that when the specified compressive strength of concrete in the column is greater than 1.4 times that specified for the floor system, the column concrete shall extend 600 mm into the slab from column face to avoid unexpected failure. The structural behavior of beam-column joints with two different compressive strengths of concrete for the beams and the columns has not been investigated adequately. ACI-ASCE Committee 352 recommends that for joints that are part of the primary system for resisting seismic lateral loads, the sum of nominal moment strengths of the column sections above and below the joint ( M c), calculated using the axial load, which gives the minimum column moment strength, should not be less than 1.4 times the sum of the nominal strengths of the beam sections at the joint ( M b). Thus, those recommended values should be examined before high-strength concrete can be used with confidence and convenience in structural members. The results showed that the ACI 318-89 extension distance of 600 mm is safe at least for members up to 300 mm in total depth, and the 2h (h is overall depth of the beam) extension distance was found to be safe also for members under flexural loading with a column-to-beam flexural strength ratio of 1.8.