ABSTRACTS: DESIGN FOR EARTHQUAKE-RESISTANT REINFORCED CONCRETE STRUCTURAL WALLS
DESIGN FOR EARTHQUAKE-RESISTANT REINFORCED CONCRETE STRUCTURAL WALLS 1
Dr D.M.Cotsovos1, N. Zygouris2 Institute of Infrastructure and Environment, School of the Built Environment, Heriot-Watt University, Edinburgh, EH14 4AS, UK, e-mail:
[email protected] 2 Laboratory of Concrete Structures, National Technical University of Athens, Athens, Greece, e-mail:
[email protected]
Abstract: The work is concerned with the application of an alternative (to the current codes of practice) method for the design of earthquake resistant RC walls. The results presented show that although both methods adopted lead to solutions which satisfy structural performance requirements, the application of the alternative method led to a significant reduction in transverse reinforcement within the concealed-columns of the walls.
1.
Introduction
In order to safeguard against brittle types of failure and to enhance ductility and load-carrying capacity, current codes of practice [1],3] specify the use of dense arrangements of shear links forming concealed column (CC) elements along the wall edges throughout their height. This dense arrangement can result in reinforcement congestion which in turn can cause difficulties during concreting and incomplete compaction. Previous work [6,7,8] indicates that, as the ultimate-limit state is approached, concrete in the compressive zone of linear RC elements is subjected to a triaxial state of stress developing for purposes of deformation compatibility, irrespective of the presence of confining reinforcement. In localized regions, this triaxial state of stress is characterized by the presence of transverse tensile stresses that may lead to an abrupt loss of load-carrying capacity, if the compressive zone is not properly reinforced; the reinforcement required for this purpose may be calculated by using the “Compressive Force Path (CFP)” method [8], and, as it was shown [1], it is significantly less than the code specified amount for providing confinement to concrete. In view of the above, it was argued that although it is widely recognized that there may be a need for specifying transverse reinforcement within the compressive zone in order to increase ductility, such reinforcement is not necessarily required for providing confinement to concrete, but in order to sustain the transverse tensile stresses that invariably develop in the compressive zone when the ultimate limit state is approached. In fact, sustaining these stresses by specifying an appropriate amount of transverse reinforcement has already been found to significantly improve the ductility of one-dimensional structural elements [7, 8]. From the above it appears that the manner in which the stirrup reinforcement of the CC elements is linked with the ductility of structural walls is of primary importance in attempting to reduce the amount of such reinforcement below that specified by current code design methods. Moreover, a comparison of the predicted response via finite-element analysis (FEA) of RC walls [1] with similar geometric characteristics and flexural reinforcement, but different amount and arrangement of 8th German-Greek-Polish Symposium Recent Advances in Mechanics September, 09-13, 2013, Goslar, Germany
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ABSTRACTS: DESIGN FOR EARTHQUAKE-RESISTANT REINFORCED CONCRETE STRUCTURAL WALLS
transverse reinforcement, designed in accordance with either the current code provisions [2,3] or the CFP method [8] (the adoption of latter method leading to significant savings in horizontal reinforcement) has shown that wall behaviour is essentially independent of the method used to design the transverse reinforcement. The work herein is concerned with the application of the CFP method for the design of earthquake resistant RC structural walls. It is based on a comparative study of the results obtained from tests on structural walls under cyclic loading [4,5]. These walls have been designed in accordance with either the CFP method or the provisions of EC2 [2] and EC8 [3]. The results obtained show that both methods of design adopted lead to solutions which satisfy the requirements of current codes for structural performance in all cases investigated. Moreover, the solutions obtained from the application of the CFP method result in a significant reduction of transverse reinforcement within the critical lengths of the walls. In fact, such reinforcement is not specified by the latter method for the case of walls with a spanto-depth ratio smaller than 2.5, whereas for the case of walls with a shear span-todepth ratio larger than 2.5 the amount specified is significantly smaller and extends over a considerably smaller length that the code specified values. 2.
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References
[1]
Cotsovos D.M. and Kotsovos M.D., “Seismic design of structural concrete walls: an attempt to reduce reinforcement congestion” Magazine of Concrete Research, Vol. 59, Issue 9, November, 2007, pp. 627-637.
[2]
Eurocode 2 (EC2) 2004, Design of concrete structures. Part 1-1: General rules and rules of building, British Standards.
[3]
Eurocode 8 (EC8) 2004, Design of structures for earthquake resistance. Part 1: General rules, seismic actions and rules for buildings, British Standards.
[4]
Zygouris N.St., Kotsovos G.M., Kotsovos M.D. “Effect of transverse reinforcement on short structural wall behavior” Magazine of Concrete Research (proofing stage, to appear in 2013).
[5]
Kotsovos G.M., Cotosvos D.M., Kotsovos M.D. and Kounadis A.N. “Seismic behaviour of RC walls: An Attempt to reduce reinforcement congestion”. Magazine of Concrete Research, Vol. 63, Issue 4, 2011, pp. 235–246.
[6]
Kotsovos G.M. and Kotsovos M.D. “Criteria for structural failure of RC beams without transverse reinforcement” The Structural Engineer, Vol. 86, No. 23/24, Dec. 2008, pp.55-61.
[7]
Kotsovos M.D. and Pavlovic M.N. “Structural Concrete: Finite-element analysis for limit-state design”. Thomas Telford (London), 1995, 550 pp.
[8]
Kotsovos M.D. and Pavlovic M.N. “Ultimate Limit-State Design of Concrete Structures: A New Approach”. Thomas Telford (London), 1999, 164 pp.
8th German-Greek-Polish Symposium Recent Advances in Mechanics September, 09-13, 2013, Goslar, Germany
