Experimental Investigation of the Shear Strength of RC Beams Extracted from an Old Structure and Strengthened by Carbon FRP U-Strips

Abstract

Featured Application: This study presents the experimental results of the shear strength of reinforced concrete (RC) "real" beams extracted from an old RC building in Rome, built in 1929. The concrete strength is very small as in the case of many existing old RC structures. These results about "real" beams are innovative in the literature because the beams are usually built purposely to be retrofitted and tested. The data presented in this paper improve the literature database giving original data about the measured concrete strength variation along the beams, the stiffness, the deflections, and the strengths of the beams before and after retrofitting, and the Carbon FRP U-Strips strains. The shear strengths of these "real" beams, together with the ones obtained in other experimental studies, are in good agreement with the predicted strengths by design code equations.Abstract: In recent years, old reinforced concrete (RC) buildings have increasingly been protected as historic symbols in Italy. The conversion of these buildings can resolve the increasing need for new structures, reducing much social, economic, and environmental impact. Retrofitting solutions by carbon fiber reinforced polymer (CFRP) reinforcements are very common nowadays. Code predictions present uncertainties due to the brittle behavior and the debonding of CFRP strips resulting from concrete cracking. Therefore, especially in the case of old beams, experimental validation is necessary. This paper deals the experimental evaluation of the shear strength of two beams extracted from an old RC building in Rome built in 1929 with modest-quality concrete. Preliminary tests were carried out to evaluate the beam elastic response and the material characteristics. These beams were tested until failure (three-point load shear/bending tests) after strengthening for shear by CFRP U-jacketing and for bending by new steel rebars. The results obtained, together with the extensive data taken from the literature, were compared with the predictions by design code equations. The influence of construction details on beam shear strength and the experimental maximum CFRP strain were also analyzed. Code predictions can be effective to estimate the shear strength of the retrofitted beams.

Severely Damaged Reinforced Concrete Circular Columns Repaired by Turned Steel Rebar and High-Performance Concrete Jacketing with Steel or Polymer Fibers

“…Finally, the reduction factor (η) of the elastic demand (elastic response spectrum), which is used in many applications of structural engineering to estimate the force reduction for effect of damping [58,69], can be evaluated by Equation (18).…”

“…In seismic regions such as Italy, the evaluation of the capacity and fragility of structural and infrastructural systems subjected to seismic events [1][2][3][4][5][6][7][8][9], and implementing proper survey programs to monitor the evolution of their capabilities [10,11] are important for preventing severe seismic damage being observed in recent seismic events [12] by means of retrofitting interventions [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”

Post-Tensioning Steel Rod System for Flexural Strengthening in Damaged Reinforced Concrete (RC) Beams

“…where f'c is the compressive strength of the concrete; a is the Whitney stress block depth; b is the beam width; Es is the elastic modulus of the reinforcing bar; A's and As are the areas of the compressive and tensile reinforcements, respectively; εcu is the compressive strain of the concrete extreme fiber at the ultimate state; c is the neutral axis depth; d' is the distance from the beam top to the centroid of the compression steel; fy is the yield strength of the tension steel; Aps is the area of the external steel rod; fps is the stress acting on the external rod; α is the angle of the external rod with respect to the horizontal axis after deformation; εse and Δεps are the initial effective strain and increased strain on the external rod, respectively; and Ep and fpy are the elastic modulus and yield strength, respectively, of the external rod. Table 5 shows a comparison between the analytical and measured moment capacities for each f ps = ε se + ∆ε ps E p ≤ f py (9) where f' c is the compressive strength of the concrete; a is the Whitney stress block depth; b is the beam width; E s is the elastic modulus of the reinforcing bar; A' s and A s are the areas of the compressive and tensile reinforcements, respectively; ε cu is the compressive strain of the concrete extreme fiber at the ultimate state; c is the neutral axis depth; d' is the distance from the beam top to the centroid of the compression steel; f y is the yield strength of the tension steel; A ps is the area of the external steel rod; f ps is the stress acting on the external rod; α is the angle of the external rod with respect to the horizontal axis after deformation; ε se and ∆ε ps are the initial effective strain and increased strain on the external rod, respectively; and E p and f py are the elastic modulus and yield strength, respectively, of the external rod. The values of E s ε cu (c − d')/c and f ps are equal to those of f' y and f py , respectively, when the compressive reinforcing bar and external rod yield.…”

“…The most common strengthening techniques include new section enlargement [7][8][9][10], external plate bonding [11][12][13][14][15][16][17], and post-tensioning [18][19][20][21]. Sectional reinforcement involves the addition of an RC jacket section and the bonding of high-strength materials such as steel plate or carbon fiber.…”

A corrosion model for the interpretation of cyclic behavior of reinforced concrete sections

“…Structures subjected to repeated cyclic loads, as those located in earthquake-prone regions, are particularly vulnerable to corrosion, due to the smaller monotonic and cyclic ductility capacity resulting in a reduction of energy dissipation and equivalent damping, with possible crises due to lowcycle fatigue with member failure just after few cycles. 10 Based on the previous considerations, it is important to include corrosion effects to assess RC members and to evaluate properly the structural retrofitting [11][12][13][14][15][16] The paper at hand presents an analytical investigation of the hysteretic axial-bending behavior of RC sections in presence of corroded rebars. The analysis is carried out by means of CYRUS-M, a fiber program used to simulate the cyclic behavior of RC sections, developed using Matlab.…”