Retrofitting RC Members with External Unbonded Rebars
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.
KeywordsShear 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.
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