Seismic Performance of Circular High-Strength Concrete Columns by ProQuest


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									 ACI STRUCTURAL JOURNAL                                                                                      TECHNICAL PAPER
Title no. 106-S37

Seismic Performance of Circular High-Strength
Concrete Columns
by Patrick Paultre, Rami Eid, Hugo Ita Robles, and Najib Bouaanani

This paper presents results from tests of six large-scale high-                performance-based equations depend on ductility demand
strength concrete (HSC) circular columns under reverse cyclic-                 and account for the level of axial load; the concrete compressive
flexure and constant axial loads. The objectives of the tests                  strength; and the transverse reinforcement configuration,
presented in this paper were to examine the post-elastic behavior              spacing, and yield strength. These equations are the basis of
and the ductility level reached by HSC circular columns designed               the prescriptive design confinement reinforcement requirements
according to the 2004 CSA A23.3 requirements for transverse steel
                                                                               in the 2004 CSA A23.3 Standard.16
reinforcement. The columns were subjected to constant axial loads
and a cyclic horizontal load-inducing reversed bending moment. It                 A large database of concentric axial compression tests on
is shown that columns designed according to the confinement                    confined HSC columns is available in the literature. Only a
reinforcement requirements of the Canadian standard behave in a                small number of experimental test results, however, are
ductile manner regardless of transverse steel reinforcement yield              available for HSC columns under combined cyclic flexure
strength or axial load level.                                                  and axial load,17 predominantly for square (or rectangular)
                                                                               columns. Furthermore, the authors considered that there is
Keywords: confined concrete; ductility; high-strength concrete; tied column.   a lack of test data on HSC circular columns subjected to
                                                                               such loading, except for the tests performed by Saatcioglu
                       INTRODUCTION                                            and Baingo.18
   In recent years, the use of high-strength concrete (HSC)                       This paper presents tests on circular HSC columns
has been steadily increasing due to its many advantages over                   subjected to combined constant axial load and reversed
normal-strength concrete (NSC). HSC is used primarily in                       cyclic flexure simulating earthquake loading. The objectives
high-rise buildings to significantly decrease the dimensions                   of the tests presented herein are to examine the post-elastic
of the columns in lower stories, thereby reducing the volume                   behavior and the ductility level reached by HSC circular
of concrete. Studies have shown, however, that HSC is more                     columns designed according to the 2004 CSA A23.3
brittle than NSC1,2 in compressive behavior. These studies                     Standard’s16 transverse steel reinforcement requirement.
show that when the concrete strength increases, the amount
of confinement reinforcement has to be increased to reach a                                   RESEARCH SIGNIFICANCE
constant level of ductility for columns subjected to the same                     There is an urgent need for test data on spirally reinforced
level of axial load.                                                           circular HSC columns subjected to combined constant axial
   While the ACI Code3 does not limit the concrete compressive                 load and reversed cyclic flexure. This paper presents new
strength, the 1995 New Zealand Standard NZS 31014 and the                      experimental results obtained from six HSC circular
1994 CSA A23.3 Standard5 limited the maximum strength                          columns subjected to constant axial load and reversed cyclic
that can be used for seismic design to 70 MPa and 55 MPa                       flexure. The targeted concrete strength was 100 MPa (14.5 ksi).
(10.15 ksi and 7.98 ksi), respectively. These limits were due                  The amount of transverse steel reinforcement was determined
in part to a lack of test results when the latter standards were               according to the confinement reinforcement requirements
published. Légeron and Paultre6 and Azizinamini et al.7 have                   of the 2004 CSA A23.3 Standard.16 The post-elastic
shown that the axial load level has a significant influence on                 behavior and the level of ductility of the test specimens are
the ductility of concrete columns subjected to cyclic flexure                  used to evaluate the new confinement steel requirement of
and constant axial loads. Moreover, studies have shown that                    the CSA Standard16 as well as the requirements of the ACI
HSC columns reinforced according to the current ACI Code                       Code3 and the New Zealand Standard.4
confinement requirements behave in a ductile manner if the
axial load is less than 0.20Ag fc′ ,6-11 where Ag is the gross                                 DESIGN EQUATIONS FOR
area of column section and fc′ is the concrete compressive                            CONFINING SPIRAL REINFORCEMENT
strength. The New Zealand Standard4 is the only one of the                        Confinement of concrete columns is required by design
three standards examined that take the axial load level into                   codes to provide ductile behavior to con
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