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This paper presents the efficiency of using prefabricated ultra‐high performance fiber reinforced concrete (UHPFRC) plates in shear strengthening of reinforced concrete (RC) beams experimentally and numerically using finite element method. In order to ensure high quality and facilitate the strengthening process on site applications, it has been considered to apply UHPFRC as a plate pasted on concrete surface using epoxy. Tested specimens included four strengthened beams besides three control beams. Strengthening the RC beams was based on the use of two different techniques; (a) one longitudinal side strengthening (b) two longitudinal sides strengthening. Moreover, strengthening RC beams with reinforced or non‐reinforced prefabricated UHPFRC plates was also investigated. Results show that UHPFRC plates significantly increased the maximum load capacity, ductility and mid span reinforcement strain of the strengthened RC beams comparing with reference beam failed in shear. Also, steel connectors used in reinforcement of UHPFRC plates prevented debonding failure mode. A three‐dimensional (3D) finite element model (FEM) of the tested beams was also developed to predict the behavior of these specimens strengthened in shear. The adhesive layer was simulated using cohesive surface model to consider the slippage between concrete surface and UHPFRC plates. Results of the FEM showed good agreement with experimental results, as they were able to predict the behavior of the beams with high accuracy. [ABSTRACT FROM AUTHOR]

• CFRP U-jacketing for the strengthening of exterior reinforced concrete beam-column (B-C) joints. • A two-dimensions finite element model is proposed for strengthened CFRP B-C joints. • Debonding existed on the contact surface of epoxy and concrete are considered. • Effects of concrete compressive strength and column axial load on the strengthened B-C joints shear strength were investigated. • New design equations of shear strength prediction of CFRP strengthened B-C joints. A key part of RC structure seismic performance is the effective distribution of earthquake forces across all resistance elements through reinforced concrete (RC) beam-column (B-C) joints. By virtue of their ease of implementation and convenient material properties, Carbon-Fiber-Reinforced Polymers (CFRP) are highly utilized for strengthening existing structures with inadequate reinforcement or insufficient confinement. Previous experimental research revealed that debonding failure widely occurs on CFRP shear-strengthened B-C joints. The experimental research as well showed the value of column axial load makes a great contribution to such joint's failure mode. Using CFRP U-jacketing to strengthen non-seismically B-C joints, this article presents a non-linear, two-dimensional FE model for investigating shear behavior. The developed FE model considered the adhesive layer between CFRP sheets and concrete to capture the debonding and a bond-slip model was implemented between concrete-to-CFRP sheets using connector elements. The FE results were verified versus experimental works from literature to prove the proposed FE model's accuracy with appreciate to load-deformation relation and failure modes. Depending on the verified FE model, a parametric study on shear-strengthened RC B-C joints with CFRP U-jacketing with free and fixed ends was performed below monotonic loading. In the existing study, several parameters, including column-to-beam flexural strength ratio (over strength ratio), concrete strength, and value of column axial load, were investigated on the structure's strength and ductility. Using the developed strut-and-tie model (STM), new design equations were proposed to calculate strengthened RC B-C joint's shear strength using CFRP. The proposed equations incorporate the interfacial bond among concrete and CFRP effect, as well CFRP sheet end boundary (free or fixed). The developed design equation's ability to estimate shear strengths of strengthened B-C joints with CFRP was verified through experimental works and FE results. It was evident from verification results that the produced design equations were compatible with experimental and FE model results. [ABSTRACT FROM AUTHOR]

This paper presents three‐dimensional (3D) and two‐dimensional (2D) finite element models to analyze strengthened reinforced concrete (RC) continuous beams with carbon fiber reinforced polymer (CFRP) which has become familiar technique in the last decade. Experimental results in the literature showed that two different debonding failure modes, either by interfacial debonding of fiber reinforced polymer (FRP) or by concrete cover separation may occur. This study takes the two possible debonding failure modes into account by considering two cohesive surfaces; the first is inserted in the adhesive layer, whereas the second is inserted between the reinforcing steel and the concrete cover. The proposed cohesive surfaces take the slippage into account considering the cohesive surface fracture energy. The numerical models are verified utilizing five symmetrical RC continuous beams available in the literature. The numerical results of 3D and 2D models for the plated beams (beams strengthened with FRP plates) agreed well with the experimental results. Additionally, the effect of the CFRP plate length, and the parameters of the cohesive surfaces on the behavior and debonding failure modes (in the adhesive layer and between the reinforcing steel and the concrete cover) of CFRP‐strengthened RC continuous beams are investigated. [ABSTRACT FROM AUTHOR]

• UHPFRC was effective for strengthening shear-deficient squat‎ RC shear ‎walls‎. • Strengthening techniques increased resistance, ductility, and fracture toughness. • Roughness and using steel shear connectors at the interface are crucial ‎parameters. • Cracks pattern can be accurately tracing using the DIC technique. Ultra-high performance fiber reinforced concrete (UHPFRC) is now available as an advanced building material for strengthening applications. It is characterized by high strength, ductility, fracture toughness, and good durability. This paper presents an experimental investigation conducted on seismically shear-deficient squat reinforced concrete (RC) shear walls strengthened with casting UHPFRC layers/jacket subjected to lateral quasi-static reversed cyclic loading and a constant axial load. The experiment was conducted on four identical rectangular RC shear walls with a scale of ⅓, an aspect ratio of 1.5 and having low concrete strength. As a reference sample, one of the shear walls was not strengthened with UHPFRC while the other three were strengthened with UHPFRC using different configurations as (i) one layer only on one long side, (ii) two layers on the long sides, (iii) all sides of the wall (jacket). Digital image correlation (DIC) technique was utilized for assessment of the damage mechanism of all specimens. According to the results, the strengthening techniques significantly improved the lateral load strength, ductility, and energy dissipation capacities especially for RC walls strengthened with UHPFRC jacketing. Results indicated the occurrence of debonding failure for the wall strengthened with two UHPFRC layers. The shear and flexural strength capacities of identical wall specimens strengthened with reference concrete were evaluated according to ACI 318 code and their efficiency was compared with test results of UHPFRC strengthened walls. The UHPFRC strengthened techniques increased the lateral load carrying capacities by 70% to 227% of the original wall. [ABSTRACT FROM AUTHOR]

• A 2D FEM conducted to predict the behavior of RC and UHPFRC shear walls subjected to lateral loading. • The strengthening by UHPFRC jacket improved diagonal tension shear strength of the RC wall having poor concrete quality. • Using steel mesh in the UHPFRC jacket bound both shear and flexural and limit their opening. • Addition of dowel bars between footing-jacketing could be able to effectively restrain the sliding mechanism. Reinforced concrete (RC) shear walls are considered one of the main lateral resisting members in RC buildings. Recently, ultra-high performance fiber reinforced concrete (UHPFRC) is an advanced cement composite material, which is characterized by high tensile and compressive strength, ductility, durability and fracture toughness. Nevertheless, while extensive studies have shown the superior mechanical of UHPFRC at the material scale, there remain very few studies on the application of UHPFRC for retrofit/strengthening structural elements especially under lateral loading like earthquake. This paper numerically analyzed the behavior of strengthened RC shear walls by a UHPFRC and reinforced UHPFRC (R-UHPFRC) jacketing under lateral loading using a two-dimensional (2D) model and the bond stress-slip model was incorporated to the analysis to simulate the interfacial concrete-to-concrete bond. First, behavior of RC and UHPFRC shear walls subjected to lateral loading is investigated using the proposed 2D model. Validation of the model is done using the available experimental results. The validated model is utilized to study the behavior of RC shear walls strengthened by UHPFRC and R-UHPFRC jacketing under lateral loading. It is stated that the strengthening procedure improved diagonal tension shear strength of the reference weak RC wall. Finally, the effectiveness of the proposed procedure is shown by performing a comparison with the outcomes of numerical analysis of RC shear wall strengthened by external CFRP sheets available in the literature. [ABSTRACT FROM AUTHOR]