Comparative analysis of the cyclic behaviour of beam-column joints with plain and deformed reinforcing bars

Fernandes, C.; Melo, J.; Varum, H.; Costa, A.

doi:10.1590/S1983-41952011000100008

Abstracts

Damage reports after recent earthquakes proves that slippage between steel reinforcing bars and the surrounding concrete is one the common causes of damage and collapse of existing RC building structures. The bond-slip mechanism assumes particular importance in RC building structures built until the 70’s, with plain reinforcing bars, previously to the enforcement of modern seismic codes. This type of structures is usually characterized by poor reinforcement detailing, poor bond properties and inadequate concrete confinement. In RC buildings subjected to cyclic loads, as the induced by earthquakes, high stress concentration occurs at the beam-column joints, making this regions prone to the occurrence of severe damage. Beam-column joints are particularly sensitive to the bond-slip mechanism due to the stress concentration, but also due to the fact that anchorage of beam and column longitudinal reinforcing bars is typically made in the joint vicinity. In this paper are presented the main results of the cyclic tests performed on two full-scale beam-column joints with the same geometry and reinforcement detailing, representative of interior joints in RC building structures built until the mid-70’s, without adequate seismic detailing. One specimen was built with plain reinforcing bars (poor bond properties) and the other with deformed bars (good bond properties). For a better comprehension of the bond properties influence on the cyclic behavior of the beam-column joints, a comparison is established between the main experimental results obtained for the two specimens. The comparative analysis shows that the bond-slip mechanism has a strong influence in the cyclic response of RC structural elements.

Beam-column joints; Cyclic behaviour; Concrete-steel bond; Plain reinforcing bars; Experimental tests

Da observação dos danos provocados por diversos sismos recentes, verifica-se que o escorregamento aço-betão é uma das principais causas de dano e colapso de edifícios existentes de betão armado. Em muitos países, este fenómeno assume particular importância nos edifícios construídos até aos anos 70, com armadura lisa e anteriormente à introdução dos primeiros regulamentos que contemplam a acção sísmica com maior detalhe. Este tipo de estruturas apresenta, geralmente, pormenorização deficiente da armadura, fracas condições de aderência e confinamento inadequado do betão. As ligações viga-pilar nas estruturas de betão armado são pontos onde ocorrem danos significativos quando as estruturas estão sujeitas a carregamentos cíclicos, uma vez que nestas zonas ocorre a maior concentração de esforços. O fenómeno do escorregamento assume particular relevância nas ligações viga-pilar, devido aos maiores esforços que aqui se desenvolvem mas também ao facto de nestas zonas se realizar tipicamente a ancoragem dos varões longitudinais dos pilares e/ou vigas. Neste artigo são apresentados os principais resultados dos ensaios cíclicos de dois nós viga-pilar à escala real com igual geometria e igual pormenorização da armadura, representativos de nós interiores de edifícios de betão armado construídos até meados dos anos 70 sem pormenorização adequada para fazer face à acção sísmica. Um dos nós foi construído com armadura lisa (com fracas condições de aderência) e o outro nó com armadura nervurada (com boas condições de aderência). Faz-se também a comparação dos resultados obtidos para compreender a influência das condições de aderência na resposta cíclica de nós interiores viga-pilar deste tipo de estruturas de betão armado. Dos resultados obtidos, conclui-se que o fenómeno do escorregamento condiciona significativamente o desempenho das estruturas com armadura lisa quando solicitadas por acções cíclicas.

Nós viga-pilar; Comportamento cíclico; Aderência aço-betão; Armadura lisa; Ensaios experimentais

Comparative analysis of the cyclic behaviour of beam-column joints with plain and deformed reinforcing bars

C. Fernandes^I; J. Melo^II; H. Varum^III; A. Costa^IV

^IUniversity of Aveiro, Civil Engineering Department, cfernandes@ua.pt, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal

^IIUniversity of Aveiro, Civil Engineering Department, josemelo@ua.pt, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal

^IIIUniversity of Aveiro, Civil Engineering Department, hvarum@ua.pt, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal

^IVUniversity of Aveiro, Civil Engineering Department, agc@ua.pt, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal

ABSTRACT

Damage reports after recent earthquakes proves that slippage between steel reinforcing bars and the surrounding concrete is one the common causes of damage and collapse of existing RC building structures. The bond-slip mechanism assumes particular importance in RC building structures built until the 70’s, with plain reinforcing bars, previously to the enforcement of modern seismic codes. This type of structures is usually characterized by poor reinforcement detailing, poor bond properties and inadequate concrete confinement. In RC buildings subjected to cyclic loads, as the induced by earthquakes, high stress concentration occurs at the beam-column joints, making this regions prone to the occurrence of severe damage. Beam-column joints are particularly sensitive to the bond-slip mechanism due to the stress concentration, but also due to the fact that anchorage of beam and column longitudinal reinforcing bars is typically made in the joint vicinity.

In this paper are presented the main results of the cyclic tests performed on two full-scale beam-column joints with the same geometry and reinforcement detailing, representative of interior joints in RC building structures built until the mid-70’s, without adequate seismic detailing. One specimen was built with plain reinforcing bars (poor bond properties) and the other with deformed bars (good bond properties). For a better comprehension of the bond properties influence on the cyclic behavior of the beam-column joints, a comparison is established between the main experimental results obtained for the two specimens. The comparative analysis shows that the bond-slip mechanism has a strong influence in the cyclic response of RC structural elements.

Keywords: Beam-column joints; Cyclic behaviour; Concrete-steel bond; Plain reinforcing bars; Experimental tests.

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References

[01] Varum, H. Seismic Assessment, Strengthening and Repair of Existing Buildings, Aveiro, Portugal, 2003, PhD Thesis - University of Aveiro, 508p.

[02] Berra, M.; Castellani, A.; Ciccotelli, S. Bond-slip effects on reinforced concrete elements under earthquake loading. European Earthquake Engineering, v. 8, n. 3, 1994; p.3-10.

[03] International Federation for Structural Concrete (CEB-FIB). Bulletin N.10 - Bond of reinforcement in concrete. State-of-art report prepared by Task Group Bond Models. Lausanne, Switzerland, 2000.

[04] Fabbrocino, G.; Verderame, G. M.; Manfredi, E.C. Structural models of critical regions in old-type r.c. frames with smooth rebars. Engineering Structures, v. 26, 2004; p.2137–2148.

[05] Fabbrocino, G.; Verderame, G. M.; Manfredi, G. Experimental behaviour of anchored smooth rebars in old type reinforced concrete buildings. Engineering Structures, v. 27, 2005; p.1575–1585.

[06] Feldman, L. R; Bartlett, F. M. Bond strength variability in pullout specimens with plain reinforcement. ACI Structural Journal, v. 102, n. 6, 2005; p. 860–867.

[07] Verderame, G. M.; Ricci, P.; Carlo, G. D.; Manfredi, G. Cyclic bond behaviour of plain bars. Part I: Experimental investigation. Construction and Building Materials, v. 23, 2009; p. 3499-3511.

[08] Liu, A.; Park, R. Seismic behaviour and retrofit of pre-1970’s as-built exterior beam-column joints reinforced by plain round bars. Bulletin of the New Zealand Society for Earthquake Engineering, v. 34, n.1, 2001; p.68-81.

[09] Pampanim, S.; Calvi, G. M.; Moratti, M. Seismic behaviour of RC beam-column joints designed for gravity loads. In: Proceedings of the 12th European Conference on Earthquake Engineering, London, 2002, Paper No. 726.

[10] Verderame, G. M.; Fabbrocino, G.; Manfredi, G. Seismic response of r.c. columns with smooth reinforcement. Part II: Cyclic tests. Engineering Structures, v. 30, 2008; p.2289-2300.

[11] Marefat, M. S.; Shirazi, S. M. H.; Rostamshirazi, R.; Khanmohammadi, M. Cyclic Response of Concrete Beams Reinforced by Plain Bars. Journal of Earthquake Engineering, v. 13, 2009; p.463-481.

[12] Pinto, A. V.; Varum, H.; Molina, J. Experimental Assessment and Retrofit of Full-Scale Models of Existing RC Frames. In: Proceedings of the 12th European Conference on Earthquake Engineering, London, 2002, Paper No. 855.

[13] Pinto, A. V.; Verzeletti, G.; Molina, J.; Varum, H.; Pinho, R.; Coelho, E. Pseudo-dynamic tests on non-seismic resisting RC frames (bare and selective retrofit frames). EUR Report No. 20244 EN, ELSA, JRC, EC, Ispra, Italy, 1999.

[14] COMITÉ EURO-INTERNATIONAL DU BETÓN (CEB). RC elements under cyclic loading. State-of-the-art report, London: Thomas Telford, 1996, 190 p.

[15] COMITÉ EURO-INTERNATIONAL DU BETÓN (CEB). Bulletin d’Information N. 217 - Selected justification notes, 1993.

[16] Eligehausen, R.; Popov, E. P.; Bertero, V.V. Local bond stress-slip relationships of deformed bars under generalized excitation. Report No. UCB/ EERC 82-23, Earthquake Engineering Research center, University of California, Berkeley, U.S.A., 1983.

[17] Verderame, G. M.; Ricci, P.; Carlo, G. D.; Fabbrocino, G. Cyclic bond behaviour of plain bars. Part II: Analytical investigation. Construction and Building Materials, v. 23, 2009; p.3512-3522.

[18] Prota, A.; Cicco, F.; Cosenza, E. Cyclic behavior of smooth steel reinforcing bars: experimental analysis and modeling issues. Journal of Earthquake Engineering, v. 13, 2009; p.500-519.

[19] Fernandes, C.; Melo, J.; Varum, H.; Costa, A. Comportamento cíclico de nós viga-pilar com armadura lisa. In: Proceedings of the CINPAR 2010 - 6th International Conference on Structural Defects and Repair, Córdoba, Argentina, Paper Ref. 042.

[20] INSTITUTO PORTUGUÊS DA QUALIDADE (IPQ). Portuguese Standard EN 206-1: Betão, Parte 1: Especificação, desempenho, produção e conformidade. Portugal, 2007.

[21] EUROPEAN COMMITTEE FOR STANDARDIZATION (CEN). Eurocode 2: Design of Concrete Structures – Part 1-1: General rules and rules for buildings. Bruxels, Belgium, 2004.

Received: 24 Jun 2010

Accepted: 08 Nov 2010

Avaiable Online: 04 Mar 2011

[01] Varum, H. Seismic Assessment, Strengthening and Repair of Existing Buildings, Aveiro, Portugal, 2003, PhD Thesis - University of Aveiro, 508p.
[02] Berra, M.; Castellani, A.; Ciccotelli, S. Bond-slip effects on reinforced concrete elements under earthquake loading. European Earthquake Engineering, v. 8, n. 3, 1994; p.3-10.
[03] International Federation for Structural Concrete (CEB-FIB). Bulletin N.10 - Bond of reinforcement in concrete. State-of-art report prepared by Task Group Bond Models. Lausanne, Switzerland, 2000.
[04] Fabbrocino, G.; Verderame, G. M.; Manfredi, E.C. Structural models of critical regions in old-type r.c. frames with smooth rebars. Engineering Structures, v. 26, 2004; p.2137–2148.
[05] Fabbrocino, G.; Verderame, G. M.; Manfredi, G. Experimental behaviour of anchored smooth rebars in old type reinforced concrete buildings. Engineering Structures, v. 27, 2005; p.1575–1585.
[06] Feldman, L. R; Bartlett, F. M. Bond strength variability in pullout specimens with plain reinforcement. ACI Structural Journal, v. 102, n. 6, 2005; p. 860–867.
[07] Verderame, G. M.; Ricci, P.; Carlo, G. D.; Manfredi, G. Cyclic bond behaviour of plain bars. Part I: Experimental investigation. Construction and Building Materials, v. 23, 2009; p. 3499-3511.
[09] Pampanim, S.; Calvi, G. M.; Moratti, M. Seismic behaviour of RC beam-column joints designed for gravity loads. In: Proceedings of the 12th European Conference on Earthquake Engineering, London, 2002, Paper No. 726.
[10] Verderame, G. M.; Fabbrocino, G.; Manfredi, G. Seismic response of r.c. columns with smooth reinforcement. Part II: Cyclic tests. Engineering Structures, v. 30, 2008; p.2289-2300.
[11] Marefat, M. S.; Shirazi, S. M. H.; Rostamshirazi, R.; Khanmohammadi, M. Cyclic Response of Concrete Beams Reinforced by Plain Bars. Journal of Earthquake Engineering, v. 13, 2009; p.463-481.
[12] Pinto, A. V.; Varum, H.; Molina, J. Experimental Assessment and Retrofit of Full-Scale Models of Existing RC Frames. In: Proceedings of the 12th European Conference on Earthquake Engineering, London, 2002, Paper No. 855.
[13] Pinto, A. V.; Verzeletti, G.; Molina, J.; Varum, H.; Pinho, R.; Coelho, E. Pseudo-dynamic tests on non-seismic resisting RC frames (bare and selective retrofit frames). EUR Report No. 20244 EN, ELSA, JRC, EC, Ispra, Italy, 1999.
[14] COMITÉ EURO-INTERNATIONAL DU BETÓN (CEB). RC elements under cyclic loading. State-of-the-art report, London: Thomas Telford, 1996, 190 p.
[16] Eligehausen, R.; Popov, E. P.; Bertero, V.V. Local bond stress-slip relationships of deformed bars under generalized excitation. Report No. UCB/ EERC 82-23, Earthquake Engineering Research center, University of California, Berkeley, U.S.A., 1983.
[17] Verderame, G. M.; Ricci, P.; Carlo, G. D.; Fabbrocino, G. Cyclic bond behaviour of plain bars. Part II: Analytical investigation. Construction and Building Materials, v. 23, 2009; p.3512-3522.
[18] Prota, A.; Cicco, F.; Cosenza, E. Cyclic behavior of smooth steel reinforcing bars: experimental analysis and modeling issues. Journal of Earthquake Engineering, v. 13, 2009; p.500-519.
[19] Fernandes, C.; Melo, J.; Varum, H.; Costa, A. Comportamento cíclico de nós viga-pilar com armadura lisa. In: Proceedings of the CINPAR 2010 - 6th International Conference on Structural Defects and Repair, Córdoba, Argentina, Paper Ref. 042.
[20] INSTITUTO PORTUGUÊS DA QUALIDADE (IPQ). Portuguese Standard EN 206-1: Betão, Parte 1: Especificação, desempenho, produção e conformidade. Portugal, 2007.
[21] EUROPEAN COMMITTEE FOR STANDARDIZATION (CEN). Eurocode 2: Design of Concrete Structures – Part 1-1: General rules and rules for buildings. Bruxels, Belgium, 2004.

Publication Dates

Publication in this collection
21 Aug 2014
Date of issue
Mar 2011

History

Received
24 June 2010
Accepted
08 Nov 2010

This work is licensed under a Creative Commons Attribution 4.0 International License.

[1] [01] Varum, H. Seismic Assessment, Strengthening and Repair of Existing Buildings, Aveiro, Portugal, 2003, PhD Thesis - University of Aveiro, 508p.

[2] [02] Berra, M.; Castellani, A.; Ciccotelli, S. Bond-slip effects on reinforced concrete elements under earthquake loading. European Earthquake Engineering, v. 8, n. 3, 1994; p.3-10.

[3] [03] International Federation for Structural Concrete (CEB-FIB). Bulletin N.10 - Bond of reinforcement in concrete. State-of-art report prepared by Task Group Bond Models. Lausanne, Switzerland, 2000.

[4] [04] Fabbrocino, G.; Verderame, G. M.; Manfredi, E.C. Structural models of critical regions in old-type r.c. frames with smooth rebars. Engineering Structures, v. 26, 2004; p.2137–2148.

[5] [05] Fabbrocino, G.; Verderame, G. M.; Manfredi, G. Experimental behaviour of anchored smooth rebars in old type reinforced concrete buildings. Engineering Structures, v. 27, 2005; p.1575–1585.

[6] [06] Feldman, L. R; Bartlett, F. M. Bond strength variability in pullout specimens with plain reinforcement. ACI Structural Journal, v. 102, n. 6, 2005; p. 860–867.

[7] [07] Verderame, G. M.; Ricci, P.; Carlo, G. D.; Manfredi, G. Cyclic bond behaviour of plain bars. Part I: Experimental investigation. Construction and Building Materials, v. 23, 2009; p. 3499-3511.

[9] [09] Pampanim, S.; Calvi, G. M.; Moratti, M. Seismic behaviour of RC beam-column joints designed for gravity loads. In: Proceedings of the 12th European Conference on Earthquake Engineering, London, 2002, Paper No. 726.

[10] [10] Verderame, G. M.; Fabbrocino, G.; Manfredi, G. Seismic response of r.c. columns with smooth reinforcement. Part II: Cyclic tests. Engineering Structures, v. 30, 2008; p.2289-2300.

[11] [11] Marefat, M. S.; Shirazi, S. M. H.; Rostamshirazi, R.; Khanmohammadi, M. Cyclic Response of Concrete Beams Reinforced by Plain Bars. Journal of Earthquake Engineering, v. 13, 2009; p.463-481.

[12] [12] Pinto, A. V.; Varum, H.; Molina, J. Experimental Assessment and Retrofit of Full-Scale Models of Existing RC Frames. In: Proceedings of the 12th European Conference on Earthquake Engineering, London, 2002, Paper No. 855.

[13] [13] Pinto, A. V.; Verzeletti, G.; Molina, J.; Varum, H.; Pinho, R.; Coelho, E. Pseudo-dynamic tests on non-seismic resisting RC frames (bare and selective retrofit frames). EUR Report No. 20244 EN, ELSA, JRC, EC, Ispra, Italy, 1999.

[14] [14] COMITÉ EURO-INTERNATIONAL DU BETÓN (CEB). RC elements under cyclic loading. State-of-the-art report, London: Thomas Telford, 1996, 190 p.

[16] [16] Eligehausen, R.; Popov, E. P.; Bertero, V.V. Local bond stress-slip relationships of deformed bars under generalized excitation. Report No. UCB/ EERC 82-23, Earthquake Engineering Research center, University of California, Berkeley, U.S.A., 1983.

[17] [17] Verderame, G. M.; Ricci, P.; Carlo, G. D.; Fabbrocino, G. Cyclic bond behaviour of plain bars. Part II: Analytical investigation. Construction and Building Materials, v. 23, 2009; p.3512-3522.

[18] [18] Prota, A.; Cicco, F.; Cosenza, E. Cyclic behavior of smooth steel reinforcing bars: experimental analysis and modeling issues. Journal of Earthquake Engineering, v. 13, 2009; p.500-519.

[19] [19] Fernandes, C.; Melo, J.; Varum, H.; Costa, A. Comportamento cíclico de nós viga-pilar com armadura lisa. In: Proceedings of the CINPAR 2010 - 6th International Conference on Structural Defects and Repair, Córdoba, Argentina, Paper Ref. 042.

[20] [20] INSTITUTO PORTUGUÊS DA QUALIDADE (IPQ). Portuguese Standard EN 206-1: Betão, Parte 1: Especificação, desempenho, produção e conformidade. Portugal, 2007.

[21] [21] EUROPEAN COMMITTEE FOR STANDARDIZATION (CEN). Eurocode 2: Design of Concrete Structures – Part 1-1: General rules and rules for buildings. Bruxels, Belgium, 2004.

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Comparative analysis of the cyclic behaviour of beam-column joints with plain and deformed reinforcing bars

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