Experimental research has demonstrated the excellent performance of the near surface mounted (NSM) technique with carbon fibre reinforced polymer (CFRP) laminates for the shear strengthening of reinforced concrete (RC) beams. This paper presents a finite element analysis to evaluate the behaviour of RC beams shear strengthened with NSM CFRP laminates. To predict correctly the deformational and the cracking behaviour of RC elements failing in shear using a smeared crack approach, the strategy adopted to simulate the crack shear stress transfer is crucial. For this purpose, a strategy for modelling the fracture mode II was implemented in a smeared crack model already existing in the FEM-based computer program, FEMIX. This strategy is mainly based on a softening shear stress-shear strain diagram adopted for modelling the crack shear stress transfer. To assess the predictive performance of the developed model, the experimental tests carried out with a series of T cross section RC beams shear strengthened according to the NSM technique by using CFRP laminates were simulated. In this series of beams, three different percentages of CFRP laminates and, for each CFRP percentage, three inclinations for the laminates were tested: 90º, 60º and 45º. By using the properties obtained from the experimental program for the characterization of the relevant properties of the intervening materials, and deriving from inverse analysis the data for the crack shear softening diagram, the simulations carried out have fitted with high accuracy the deformational and cracking behaviour of the 2 tested beams, as well as the strain fields in the reinforcements. The constitutive model is briefly described, and the simulations are presented and analysed.
This paper present a design approach to predict the shear capacity of reinforced concrete (RC) beams strengthened with fiber reinforced polymer (FRP) laminates/rods applied according to the near surface mounted (NSM) technique. The new approach is based on the simplified modified compression field theory (SMCFT) and considers the relevant features of the interaction between NSM FRP systems and surrounding concrete, like debond and concrete fracture. In the SMCFT model, the shear strength of a RC element is a function of two parameters: the tensile stress factor in the cracked concrete (), and the inclination of the diagonal compressive stress in the web of the section (). However, this approach is not a straightforward design methodology due to its iterative nature. A sensitivity analysis is carried out to assess the relative importance of each input parameter that mostly affect the shear capacity of RC beams shear strengthened according to the NSM technique. Taking into account the obtained results, equations to determine and without recurring to an iterative procedure are derived. The experimental results of 112 beams shear strengthened with NSM FRP are used to appraise the predictive performance of the developed approach. By evaluating the ratio between the experimental results and the analytical predictions, an average value of 1.14 is obtained, with a coefficient of variation of 13.1%, being safe estimations 87% of the predictions.
The effectiveness of masonry infill wall on behavior of a Reinforced Concrete (RC) frame subjected to a column failure is studied experimentally. For this reason, one full scale RC frame designed according to Eurocode is statically tested to investigate the behavior of the frame with and without masonry infill wall. The obtained results show that infill wall can significantly increase the load carrying capacity of RC frame and thus serve as an important robustness reserve in the case of unpredictable extreme events (i.e. local impact, blast or earthquake). A photogrammetry analysis is carried out to study the behavior of the structure. Results give valuable information about the alternative load path, transfer of the applied load to the column and beams, and interaction forces between RC frame and infill wall. At the end, the experimental program is simulated by the OpenSees software to study the behavior of the frame. After having demonstrated that this model can predict the load deflection with good accuracy, a parametric study is conducted to evaluate the effect of the percentage of longitudinal reinforcement ratio of beams and columns on the load carrying capacity of the infilled RC frame.
Recently, Strain Hardening Cementitious Composite (SHCC) material has been used for the shear strengthening and the structural rehabilitation of reinforced concrete structures. However, the shear behavior of this material has not been yet fully understood due to lack of an appropriate and accurate direct shear test method. This paper aims to investigate the shear properties of the SHCC material. For this purpose, Iosipescu shear test was selected, where loads are applied in antisymmetric four points bending, assuring a pure shear section at the center of the specimen. A special geometry for the specimen was adopted in order to assure a uniform shear stress distribution in the pure shear section. This experimental test can characterize the shear behavior of SHCC material. The experimental test was simulated by the FEM-based computer program, FEMIX. To predict the average shear stress-sliding response, the shear crack softening diagram, available in the multi-directional fixed smeared crack model, was used. After demonstration the good predictive performance of the numerical model, a parametric study was carried out to evaluate the influence of shear retention factor, fracture energy of mode II, and crack shear strength on the average shear stress-sliding response of the SHCC. The advantage of SHCC instead of conventional mortar was also studied.
This paper aims to investigate the shear failure mechanisms in beams exclusively reinforced with longitudinal glass fiber reinforced polymer bars and to propose a design-based approach to predict the shear capacity of this type of beams. An experimental program composed of seven T cross section shaped concrete beams was executed to analyze the influence of the flexural reinforcement configuration on the shear capacity and deformability of the beams. Three values of the flexural reinforcement ratio (ρ l ), 1%, 1.4%, and 1.80% were adopted. Digital image correlation technique was used to better capture and analyze the cracking process up to the formation of the shear failure crack. Test results indicated that the shear capacity was not dependent of ρ l up to a limit of around 1.4%, but a tendency of the shear capacity to increase with ρ l was registered above this limit due to a more pronounced favorable contribution of aggregate interlock and dowel effect. K E Y W O R D S aggregate interlock, DIC, dowel effect, GFRP flexural reinforcement, shear capacity, shear failure, T-shaped RC beams 1 | INTRODUCTIONGenerally, the shear resistance of reinforced concrete (RC) beams or slabs is determined as a sum of the shear resistance attributed to the concrete V Rd,c and the shear resistance provided by the shear reinforcement V Rd,s . According to Eurocode 2 1 in regions of a member where V Ed ≤ V Rd,c no calculated shear reinforcement is necessary, where V Ed is the design shear force in the considered section, resulting from external loadings and prestressing force. In regions where V Ed > V Rd,c , sufficient shear reinforcement should be provided in order to satisfy the condition V Ed ≤ V Rd = V Rd,s , which means that the concrete contribution for the shear resistance of the member is not considered.Many structures constructed in 1960s have RC slabs without shear reinforcement. Since significant part of these slabs are still being used without any damage, a reasonable question that can be erased is about the reliability of actual existing codes on the prediction of the shear capacity of RC members without transverse reinforcement.On the other hand, intense research was carried out on RC members without shear reinforcement, by investigating the influence of several parameters on the shear capacity of this type of members (e.g., size effect, concrete strength, shear span-to-depth ratio, flexural reinforcement ratio). [2][3][4][5] Despite the strong research effort on the shear-transfer mechanisms in RC beams without stirrups, 3,4 this issue still raises many doubts and controversial opinions, due to the difficulties of isolating each mechanism and capture its influence on the shear capacity of an RC member, as well as the large scatter of results, even in members of same concrete strength and longitudinal reinforcement ratio.The shear capacity of RC beams without stirrups is governed by the following main shear-transfer mechanisms: aggregate interlock effect (V a ), 4 dowel action of the
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