Keywords: fibre reinforced concrete, numerical simulation.

It is well known that concrete is a brittle material and has a low tensile strength. The addition of steel fibres in conventional reinforced concrete members greatly improves the tensile strength, the stiffness and the ductility, while the steel fibres restrict the growth of cracks [1]. Many studies on the behaviour of steel fibre reinforced concrete beams under many types of loading have occurred, mostly experimental in nature, but also analytical and numerical. In recent years, the simulation with the finite element method has become a really useful and powerful tool for the solution of many engineering problems, which allows a reduction in the number of the required experiments. However, every numerical model should be based on reliable test results. Therefore, experimental and numerical analyses can complement each other in the investigation of a particular phenomenon [2].

The aim of this paper is to understand the behaviour of concrete beams, mainly fibre-reinforced, with longitudinal and transverse reinforcement, under four-point bending. The response of these beams was studied under both static and one-direction cyclic loading (positive bending only). Conventionally reinforced concrete beams were also studied under static three-point bending and cyclic four-point bending, as well as fibre-reinforced concrete beams (with no conventional reinforcement) under static four-point bending and one-direction cyclic four-point bending (loading-unloading). Finally, the response of a conventional reinforced concrete beam, strengthened by a jacket of fibre-reinforced concrete with longitudinal and transverse reinforcement, was studied under static four-point bending. In order to investigate the behaviour of these beams, the respective finite element simulation models were formulated.

The simulation of all the models studied in this paper presented many numerical difficulties due to the complexity of the systems and the existence of various nonlinearities such as the cracking of concrete, plastification of steel, transfer of the tensile forces to the steel fibres after the exhaustion of the tensile strength of the cementitious matrix and the gradual pull-out of the fibres from the surrounding concrete. Another source of numerical instability is connected to the load application procedure.

The validity of each numerical model is established by comparing the numerical results with the corresponding experimental results [3]. Both the numerical and the experimental results show that the replacement of conventional concrete by high-tensile fibre-reinforced concrete, leads to beams with increased overall strength in the case of similar structural members.

1

Bentur A., Mindess S., "Concrete beams reinforced with conventional steel bars and steel fibres: properties in static loading", The International Journal of Cement Composites and Lightweight Concrete, Volume 5, Number 3, 1983. doi:10.1016/0262-5075(83)90007-6

2

Nethercot D.A., "The importance of combining experimental and numerical study in advancing structural engineering understanding", Journal of Constructional Steel Research, 58, 1283-1296, 2002. doi:10.1016/S0143-974X(02)00011-1

3

Papatheoharis T., Perdikaris P.C., Tzaros K., "Experimental Investigation of the Response of Fiber-Reinforced Concrete Beams under Static and Cyclic Bending", 3rd Greek National Conference of Seismic Engineering and Technology, Athens, Greece, November 5-7, 2008.

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