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Recently, ultra-high performance fiber reinforced concrete (UHPFRC) has been commonly used as a structural material. In this study, finite element (FE) model is constructed to investigate the behavior of ultra-high performance fiber reinforced concrete filled steel tube columns (UHPFRCFSTs) under axial or eccentric loading. The analysis included three-dimensional FE model using solid elements. The novelty of the suggested FE model is the consideration of the confinement of the UHPFRC in-filled material. Furthermore addition, the numerical model includes initial local and overall geometric imperfections, as well as the inelastic response of both UHPFRC and steel materials. The interaction between the steel tube and UHPFRC in-filled is modelled using surface to surface contact. Experimental results from the literature are used to validate the FE model. It is proved that the FE model can predict the ultimate capacities, failure modes, and post-cracking behavior accurately for both short and long UHPFRCFSTs. The FE interaction diagram agreed very well with the experimental results. Using the verified FE model, a parametric study on UHPFRCFSTs is carried out. Several parameters, including concrete strength material, steel yield strength, and aspect ratio of the columns (column diameter/tube thickness), are investigated. Eventually, comparisons are conducted between the results obtained from FE simulation and the existing design codes for predicting load-moment interaction diagram of UHPFRCFSTs. It has been found that the Eurocode 4 predictions in most analyzed cases are conservative for UHPFRCFSTs. [ABSTRACT FROM AUTHOR]

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]

• UHPFRC is eligible to enhance the performance of shear deficient RC shear walls. • Results indicated that a significant contribution of UHPFRC to the strength, ductility, and stiffness of the original wall. • Roughness and using steel shear connectors at the interface are crucial parameters. • A numerical study was carried out to provide a deeper understanding of the interfacial degradation. • A governing equation was derived to predict the shear strength capacity of UHPFRC strengthened walls. This paper presents an experimental and numerical investigation on the significant effect of the bond properties between Ultra-high performance fiber reinforced concrete (UHPFRC) layers and normal strength concrete (NSC) on the performance of strengthened composite squat shear walls through shear cyclic tests. Moreover, governing equation was derived to predict the shear strength capacity of UHPFRC strengthened walls considering tensile strength of UHPFRC, thickness of UHPFRC layers, surface roughness degree, ratio of steel shear connectors and its yield strength, concrete strength and thickness of original RC wall, and the axial normal force. A series of numerical analyses had been carried out, so proving the capabilities of the proposed formulation. The results indicated that the concrete substrate surface roughness, use of shear connectors, and UHPFRC layers thickness significantly affect the shear bond behaviour between UHPFRC layers and concrete. Installation of shear connectors at UHPFRC-concrete interfaces could significantly improve the post-peak shear behaviour as well as altered the failure mode from brittle due to debonding to ductile. The layer's thickness had a high influence on the shear behavior of specimens with properly roughened surfaces. [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]