Structural modeling and characterization of steel fiber reinforced concrete beams under bending shear

Abstract

As the need for the adoption of improved structural materials emerge, so does the need for experimental, analysis and design methods that can account for the technical benefit inherent in these materials. In the case of structural application of SFRC in shear strengthening, the methods should be able to provide realistic and accurate assessment of the shear strength, stiffness and ductility characteristics. Literature survey informs a limited understating and lack of transparency in existing information on steel fiber reinforced concrete (SFRC) as a structural material, particularly in shear strengthening. Moreover, there is no universally accepted design guideline for structural applications of SFRC which limits further, its wider application such as in shear strengthening. In this research, strength and deformation behavior in steel fiber reinforced concrete (SFRC) beams, under bending-shear, is investigated by analytical and experimental methods. For clarity on the shear strength merit offered by steel fibers, the experimentation process also employed a comparative fiber and stirrup reinforced beam evaluations. In practice, steel fibres are discretely and randomly constituted in the concrete volume of a structural member. They bridge cracks and transfer stress, thereby enhancing the post cracking strength which indeed is responsible for improvement in structural capacity such as shear strength and deformation. It is therefore imperative to investigate and clarify these influencing factors in detail. However, limitations of conventional measurements techniques and the difficulty associated with measurement of strain fields as well as visualisation and identification of the cracking behaviour hinders the full potential of evaluating and quantifying the performance of SFRC as structural material. To overcome this difficulty, optical full-field electronic speckle pattern interferometry (ESPI) and digital image correlation method (DICM) measurement techniques have been applied in this research to supplement conventional measurement methods in the experimentation process. Design requires predictive methods for gauging the performance of structural

elements without the need of a practical test at the design stage. Currently there is no information on shear strength-deformation evolution prediction model for SFRC beams. This research proposes a unified theoretical model capable of predicting the shear load deflection and shear stress-strain response to failure in SFRC beams. Parametric analysis was undertaken to gauge the performance of the model and the variables that influence shear capacity of SFRC beams. FEM simulation of SFRC beams under bending shear was also undertaken with application of an experimentally derived material model for the SFRC. Results from the experimental investigations and the FEM analysis were further applied to validate the proposed theoretical model. By applying these techniques as discussed above, structural characteristics of SFRC beams under bending shear are clarified, quantified and a practical design case for shear strengthening using steel fibers in which the proposed Equivalent Shear Design Method (ESDM) for SFRC beams is applied is illustrated.