The postcracking capacity of fiber reinforced concrete (FRC) mainly depends on the content, material, and geometry of the fibers considered. Even though the general influence of these factors on FRC behavior has been extensively addressed, the uncertainty of the FRC performance prediction along with the variability of the results still poses a challenging issue that needs to be solved to encourage the use of FRC for design and construction purposes. In this line, a database including the results of the flexural residual strength obtained from different experimental programs combined with the results of previous studies has been gathered and analyzed herein to obtain general correlations and trends providing additional information about the influence of the fibers in FRC behavior, these meant to serve for initial design stages (e.g., make decisions on the type and amount of fibers based on technical and economical requirements). The results are analyzed distinguishing between the fiber material, the fiber shape, the aspect ratio and tensile strength. The results presented herein may provide valuable information on the initial prediction of the residual strength of FRC to fully take advantage of the mechanical properties of the material.
Tensile strength constitutive laws for fibre reinforced concrete (FRC) are commonly defined through the parameters of flexural tests conducted on standard prismatic specimens. However, there are no specific criteria to determine such parameters using small specimens that could simplify the testing procedure and provide more representative results of slender structural FRC elements. In this line, the influence of size effect becomes an issue particularly relevant during the characterisation stage given that the residual strength decreases while increasing the size of the element. The objective of this document is to propose a methodology to obtain the parameters of the constitutive law using small specimens. For this, FRC residual strength was determined through three-point bending tests on prismatic notched beams of 40x40x160,
The investigation on flexural creep of high performance fibre reinforced concrete (HPFRC) is still scarce. Even though the presence of fibres in concrete help to control the deformations, these may increase under the effect of a sustained load. To analyse the effect of creep in pre-cracked HPFRC elements, twelve beams reinforced with either glass or steel fibres with dimensions 40 x 80 x 1200 mm were tested under a three-point configuration. For that, a new type of frame was designed and constructed to test the HPFRC beams under flexural load in a climate-controlled room with constant temperature and relative humidity. The loading mechanism was based on a lever system, applying sustained load ranging between 25% and 50% of the load at which the first crack appeared. The deflection at the mid-span was registered by means of LVDT transducers. Additionally, the influence of the curing procedure (with or without aluminium tape wrap) was assessed. In general, glass fibre reinforced beams presented higher deflections than steel fibres, even though at low load levels the type of fibre did not have significant influence on the deformation.
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.
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