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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:

It transfers shear forces.
It reduces spalling of outer concrete.
It prevents buckling of longitudinal reinforcement.
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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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	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 doi:10.4203/ccp.91.125 purchase the full-text of this paper 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: It transfers shear forces. It reduces spalling of outer concrete. It prevents buckling of longitudinal reinforcement. 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. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £140 +P&P)
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