Analytical Prediction of Crack Width of FRC/RC Beams Under Short and Long Term Bending Condition (original) (raw)
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European Journal of Environmental and Civil Engineering, 2018
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2015
The main object of the research work presented in this paper is to establish design tools for concrete structures where main reinforcement is combined with addition of short discrete steel fibers. The work is concerned with calculating and measuring crack widths in structural elements subjected to bending load. Thus, the aim of the work is to enable engineers to calculate crack widths for flexural concrete members and analyze how different combinations of amounts of fibers and amounts of main reinforcement can meet a given maximum crack width requirement. A mathematical model including the ductility of the fiber reinforced concrete (FRC) is set up and experimental work is conducted in order to verify the crack width model. The ductility of the FRC is taken into account by using the stress crack width relation. The constitutive model for the FRC is based on the idea that the initial part of the stress crack width relation can be described by a linear relation between load and crack w...
Engineering Structures, 2020
The inclusion of fibres into concrete is now an accepted method of controlling crack widths. Several recently released design guidelines and codes of practice contain provisions which allow designers to predict the instantaneous crack widths in reinforced concrete members (containing fibre reinforcement) subjected to flexure. Most of these models have been developed for steel fibres, despite non-steel fibres representing a significant proportion of the fibres available in the marketplace. The current paper examines the results of flexural tests on 53 sets of beams reinforced with steel bars and fibre reinforced concrete. The specimens contained a wide range of fibre types, including steel, polypropylene, aramid, glass, basalt & PVA fibres. An assessment of available codified expressions for crack width estimation has been compared to measured crack widths presented herein. Despite satisfactory results, improved comparisons may be obtained by using the residual tensile strength of fibres at crack widths substantially smaller than is normally used, and by considering alternative expressions for the bond strength between steel reinforcing bars and fibre-concrete than are presently used in code models. 2. Experimental program The majority of test data used in this study were derived from tests
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The tensile behavior of concrete or mortar plays an important role for delaying the formation and propagation of cracks, and also for upgrading the bearing capacity of existing concrete and masonry constructions. Although the presence of steel fibers is known to improve, often considerably, the tensile capacity of concrete members, methods for the quantification of this improvement are still limited. For this reason, a model has been developed for the prediction of the tensile strength of steel fiber-reinforced concrete members, as crack opening occurs. Given the geometry and the physical characteristics of reinforced concrete member and fibers, the model predicts: (1) the number of fibers crossing a crack’s surface; (2) the distribution of these fibers in terms of (i) the angle a fiber forms with the crack surface (fiber inclination) and (ii) the embedded length of the fiber at both sides of the surface; (3) resistance to crack opening provided by each fiber, in relation to its pos...
Crack Model for Steel Fiber-Reinforced Concrete Members Containing Conventional Reinforcement
Aci Structural Journal, 2014
This paper proposes a new model for the calculation of crack spacings and crack widths in steel fiber-reinforced concrete members containing conventional steel reinforcing bars (R/SFRC). The model considers the effects of various fiber and conventional reinforcement parameters. Predictions are compared against the test results of 17 plain reinforced concrete (RC) and 53 large-scale R/SFRC specimens subjected to uniaxial tension available in the literature. It is found that the proposed model predicts the crack spacings and widths of R/SFRC with reasonable accuracy and outperforms other steel fiber-reinforced concrete (SFRC) crack spacing models currently available. The model is expanded to include biaxial stress conditions to facilitate the analysis of elements such as SFRC panels subjected to shear. Here, too, the model is found to give sufficiently accurate predictions of the average crack conditions.
Size Effect on Post-cracking Strength of High Performance Fibre-Reinforced Concrete
High Tech Concrete: Where Technology and Engineering Meet, 2017
The size effect is a well-known phenomenon in the design of reinforced concrete structures. Although it has been studied extensively for conventional concrete with or without traditional reinforcement, its influence on the post-cracking behaviour of fibrereinforced composites is scarcely reported in literature. This is particularly true in the case of high performance fibre-reinforced concrete (HPFRC), which allows the design of very thin elements and whose behaviour may be highly influenced by their size. The aim of this research was to evaluate the influence of the size of HPFRC beams on the mechanical performance at a cross-sectional level. An experimental program involving three-point bending tests of HPFRC on beams of dimensions 40 x 40 x 160, 100 x 100 x 400 and 150 x 150 x 600 mm was conducted. Three steel fibre contents were investigated: 90, 140 and 190 kg/m 3. These bending tests were also simulated via a sectional analysis model, taking as a reference the constitutive law described in the fib Model Code for Concrete Structures 2010. The results suggest that the values of stress in the constitutive model should depend upon the cross-sectional size of the beam. This is reflected when adjusting the parameters of the MC2010 to fit the experimental values, resulting in a coefficient of determination above 0.88 when comparing the ratio between these two parameters and the size of the cross section.
Experimental Study and Modelling on the Structural Response of Fiber Reinforced Concrete Beams
Applied Sciences
In many structural applications, concretes reinforced with short metal or synthetic fibers (fiber-reinforced concrete (FRC)) have a number of advantages over traditional concretes reinforced with steel rebars reinforcement, such as easier and more economical production, wear resistance, impact resistance, integrity, etc. In the present study, several concrete mixes were developed and prismatic FRC specimens were fabricated. Their structural behaviors were studied using bending tests until prisms were fractured. Two types of fibers, namely, steel and polypropylene (PP) and three different concrete matrixes were investigated, testing in total 12 FRC prismatic specimens. Every group of FRC had the same concrete matrix, but different internal fiber architecture. All specimens were tested by Four-Point Bending (4PBT). The analysis was carried out with a goal to determine the workability and flexural tensile strength of all FRC groups, comparing these parameters with fracture modelling re...
Structural Concrete, 2020
The use of fibers in reinforced concrete (RC) beams mainly improves both the bearing capacity and the cracking control. In this way, positive effects on the service life of RC structures can be expected. In this paper, the fiber influence on the flexural behavior of RC beams with different longitudinal reinforcement ratios (0.5% ≤ ρ s ≤ 1.2%) is analyzed by testing small-scale RC beams. Concretes incorporating 0, 25 and 50 kg/m 3 of steel, 6 and 12 kg/m 3 of glass macrofibers, and 5 and 10 kg/m 3 of polymer macrofibers were studied. Crack and deflection control, as well as bearing capacity and crack localization were evaluated for a broad range of fiber-reinforced concrete (FRC) toughness. It is verified that fibers, in the longitudinal reinforcement ratio considered, improve the bending behavior at serviceability limit state (SLS) and ultimate limit state (ULS) of RC beams, without limiting the structure ductility. It was also confirmed the philosophy of the fib Model Code 2010, such that FRC can be considered as a composite material where performance parameters govern its mechanical behavior. Finally, the several data available allowed to deeply analyze fib Model Code 2010 formulations (mean crack spacing and flexural bearing capacity) and to propose modifications where needed.
2016
Although fibre reinforcement is known to reduce the crack width and crack spacing of conventionally reinforced concrete elements, the impact of fibres on the crack width profile and crack morphology has not received as much attention. This paper presents experimental results of the crack width profile and internal crack pattern obtained from three-point bending test of conventionally reinforced concrete notched beams made of plain concrete and fibre reinforced concrete at low fibre dosages. The induced cracks were, under loaded conditions, injected with a fluorescent epoxy-resin. From each beam, two pieces were extracted and subjected to a second impregnation. Digital images were taken using a microscope and were then processed and analysed to extract quantitative information. The results revealed that the accumulated crack width was similar for all mixes. However, in the samples with fibres the main crack branched off into several narrower cracks compared to plain concrete, which g...