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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 91
PROCEEDINGS OF THE TWELFTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by: B.H.V. Topping, L.F. Costa Neves and R.C. Barros
Paper 125

Concrete Stability Achieved by Confinement in a Reinforced Concrete Column

P.G. Papadopoulos1, H. Xenidis1, D. Plasatis1, P.D. Kiousis2, C. Karayannis3 and A. Diamantopoulos1

1Department of Civil Engineering, Aristotle University of Thessaloniki, Greece
2Colorado School of Mines, Golden CO, United States of America
3Department of Civil Engineering, Democritus University of Thrace, Xanthi, Greece

Full Bibliographic Reference for this paper
P.G. Papadopoulos, H. Xenidis, D. Plasatis, P.D. Kiousis, C. Karayannis, A. Diamantopoulos, "Concrete Stability Achieved by Confinement in a Reinforced Concrete Column", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 125, 2009. doi:10.4203/ccp.91.125
Keywords: reinforced concrete column, transverse reinforcement, confinement, truss model, geometric stiffness, global instability.

Summary
In a reinforced concrete (RC) column, the transverse reinforcement plays the following roles:

  1. It transfers shear forces.
  2. It reduces spalling of outer concrete.
  3. It prevents buckling of longitudinal reinforcement.
  4. It enhances axial and flexural strength, stiffness and ductility of the confined concrete core.

Ductility is particularly needed in potential plastic hinge regions at the ends of column.

The aim of the present work is to examine the confinement of a RC column from another point of view, that of structural stability of the concrete. It is observed in experiments that, for a quite large axial compressive strains in a RC column, the axial compressive stress suddenly drops to zero, which is a mark of structural instability. Here, in order to study the instability of the concrete, a part of the RC column, between two successive sets of transverse reinforcement, is simulated by a plane truss [1], with bars obeying nonlinear stress-strain laws of concrete or steel including tensile cracking for concrete and plastic yield for steel. The equilibrium conditions are written with respect to the deformed truss and the simple global stiffness matrix of the truss is updated, within each step of an incremental loading procedure, to take into account geometric nonlinearities.

A local instability mode of concrete (spalling) and a global one for the RC column are revealed by the proposed truss model. Based on the global instability mode, a simple method is developed, to calculate by hand the required amount of transverse reinforcement, which prevents the global instability of the column. This method is applied to a typical RC column and the results are compared with corresponding code requirements (Greek RC Code, Eurocode, UBC, NZS).

References
1
P.G. Papadopoulos, H.C. Xenidis, "A truss model with structural instability for the confinement of concrete columns", Journal of EEE (European Earthquake Engineering), Vol. 13 II, pp. 57-80, 1999.

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