Title:
Confined Concrete Columns With Stubs
Author(s):
Shamim A. Sheikh and Shafik S. Khoury
Publication:
Structural Journal
Volume:
90
Issue:
4
Appears on pages(s):
414-431
Keywords:
axial loads; columns (supports); elasto-plastic behavior; confined concrete; earthquakes; energy absorption; hinges (structural); Structural Research
DOI:
10.14359/3960
Date:
7/1/1993
Abstract:
The critical sections of columns in a framed structure subjected to earthquake loads are invariably adjacent to the beam-column/slab joints or the footings. External restraint provided by the heavy elements alters the behavior of the adjacent sections and may not always prove conservative. To simulate this behavior, six reinforced concrete columns 12 x 12 x 58 in. (305 x 305 x 1473 mm), each cast integrally with a 20 x 30 x 32-in. (508 x 762 x 813-mm) stub, were tested under cyclic flexure and shear while simultaneously subjected to a constant axial load. The variables in the test program were the amount of lateral steel, steel configuration, and level of axial load. From a comparison of the results from this test series with those from similar prismatic specimens tested earlier, it was concluded that the stub enhanced the adjacent section's flexural strength by more than 20 percent. Increase in the amount of lateral steel, reduction to axial load, and increased effectiveness of the lateral support provided to the longitudinal bars result in an increase in ductility and energy-absorbing capacity of the columns. The maximum usable compressive strain for confined concrete was found to be in the range of 0.025 to 0.042, and the equivalent plastic hinge length was approximately equal to the section size, irrespective of the variables examined.