Retrofitting RC Members with External Unbonded Rebars

  • A. Tinini
  • F. Minelli
  • G. A. Plizzari
Conference paper
Part of the Lecture Notes in Civil Engineering book series (LNCE, volume 10)


External unbonded rebars represents a suitable strengthening technique for the retrofitting of existing Reinforced Concrete (RC) members. Advantages regard the ease of installation, a minimum invasiveness and possibility of future inspections. Structurally, increment of flexural stiffness and bearing capacity and enhancement of shear-flexure behavior can be achieved. The presence of both bonded and unbonded bars introduces a change in the way the shear actions are resisted. Unbonded rebars develop an arch action component, with no bond present and constant force in the rebars, in addition to the beam action component, normally developing in presence of bonded bars. The present paper reports the results of four point loading tests on full-scale beam, with the aim of studying the influence of different bond condition. Moreover, the Double Harping Point technique, using external rebars and vertical deviators, is presented, with attention to the definition of the vertical equivalent stiffness of the deviators.


Shear strength Unbonded rebars Beam and arch action  Retrofitting 



The Authors gratefully acknowledge Engineers Esti Federica, Caldera Silvia and Migliarini Mauro for assistance in carrying out laboratory testing and data processing.

The fundamental contribution of the rebar provider (Priuli s.a.s. and Alfa Acciai S.P.A.) and the concrete provider (Italcementi Group) is also gratefully acknowledged.


  1. Abrams DA (1913) Test of Bond Between Concrete and Steel, University of Illinois Bulletin No. 71, University of Illinois, Urbana, IL, p 240Google Scholar
  2. Cairns J (1995) Strength in shear of concrete beams with exposed reinforcement. In: Proceedings of ICE structures & buildings, vol 110, May 1995, pp 176–185CrossRefGoogle Scholar
  3. Cairns J, Minelli F, Plizzari GA (2005) Strengthening RC beams by external reinforcement. In: Proceedings of the international conference on concrete repair, rehabilitation and retrofitting, Cape Town, South Africa, 21–23 November 2005Google Scholar
  4. Cairns J, Rafeeqi SFA (2003) Strengthening of reinforced concrete beams by external unbonded bars: experimental investigation: theoretical investigation. Proc Instit Civil Eng 156(1):27–48Google Scholar
  5. Cairns J, Zhao Z (1993) Structural behaviour of concrete beams with reinforcement exposed. Proc Instit Civil Eng Struct Build 99:141–154CrossRefGoogle Scholar
  6. EN 12350-2 (2009) Testing fresh concrete – Part 2: Slump TestGoogle Scholar
  7. EN 12390-13 (2013) Testing hardened concrete. Determination of secant modulus of elasticity in compressionGoogle Scholar
  8. EN 12390-3 (2009) Testing hardened concrete. Compressive strength of test specimensGoogle Scholar
  9. EN15630-1 (2004) Steel for the reinforcement and prestressing concrete – Part 1: Test methodsGoogle Scholar
  10. Feldman LR, Bartlett FM (2008) Bond in flexural members with plain steel reinforcement. ACI Struct J 105(5):552–560Google Scholar
  11. Giuriani E (2012) Consolidamento degli Edifici Storici. Utet Scienze Tecniche, Torino (in Italian)Google Scholar
  12. Minelli F, Plizzari GA, Cairns J (2008) Flexure and Shear behavior of RC beams strengthened by external reinforcement. In: Proceedings of the international conference on concrete repair, rehabilitation and retrofitting II, Cape Town, South Africa, 24–26 November 2008, pp 377–378Google Scholar
  13. Stoker MF, Sozen MA (1970) Investigation of Prestressed Reinforced Concrete for Highway Bridges. Part V: Bon Characteristic of Prestressing Strends, University of Illinois Bullettin No. 503, University of Illinois, Urbana, IL, pp 116–119Google Scholar
  14. Tassios TP (1979) Properties of Bond between Concrete and Steel under Load Cycles Idealizing Seismic Actions, Comité Euro-International du Béton, Bulletin No. 131, Paris, France, pp 67–121Google Scholar
  15. Tinini A (2016) Investigating Existing Beams and Slabs Experiencing Flexure and Shear deficiency, PhD thesis, University of Brescia, BresciaGoogle Scholar

Copyright information

© Springer International Publishing AG, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Department of Civil, Environmental, Architectural Engineering and MathematicsUniversity of BresciaBresciaItaly

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