Issue 30

O. Sucharda et alii, Frattura ed Integrità Strutturale, 30 (2014) 375-382; DOI: 10.3221/IGF-ESIS.30.45 376 M ATERIAL MODELS OF THE CONCRETE n order to choose the model of the concrete correctly, it is necessary to consider the purpose and area where the concrete should be used because the concrete models require different data and accuracies of the models are different. This is, for instance, the case of details in the computational model. In most of advanced models the following is true: the more precise is the model, the higher are the demands in terms of quantity and quality of the complex data, this making, in turn, the computational process more demanding. A non-linear analysis of the concrete and reinforced concrete structures is often combined with other types of the task. Such tasks could, for instance, simulate dynamic loads or earthquakes [14]. Constitutive models of the concrete are implemented in several software applications [10], [18] and [21]. [1] and [21] deal also with the modelling and analysing of the concrete structures - they describe possible approaches to the behaviour of concrete elements and concrete models. [5] and [22] provide a good summary of the topic under study. One of advanced models - Fracture Plastic Material [9] in ATENA [6] - has been chosen for numerical modelling of the behaviour of the reinforced concrete beam. A predecessor of this concrete model is SBETA which is among widely-used models. The numerical analysis of stress and deformation in concrete structures uses the Finite Element Method [20]. S TOCHASTIC MODELLING n numerical analyses it is recommended to consider, in some cases, the random character of input data. The most common random inputs are material properties of the concrete. This is, for instance, the compression strength, tensile strength or modulus of elasticity of the concrete. In those cases, it is possible to use the stochastic modelling. Responses of the structure are calculated for individual sets of stochastic input parameters which describe uncertainty of input data [7] and [8]. The input values should be properly described, e.g. with a mean value, standard deviation, or type of distribution. The analysis output are processed typically in histograms. Stochastic modelling is performed in FReET [17] which is a LHS software application. LHS (Latin Hypercube Sampling) and possible use are described in an theoretical manual [7] and user manual [8]. FReET is compatible with ATENA. The both software applications are supplied together as SARA. When selecting the random variables, it is recommended to follow JCSS [12] and ISO [11] and use a correlation matrix. The number of simulations depends on complexity of the task. Typically, it takes tens of hours to calculate the task. E XPERIMENTS ore than sixty years ago one of the first important scientific work focused on the concrete appeared. The authors was Bresler-Scordelis [2] and his works has been supported by several experiments which have been properly documented. These were three-point bending tests of the reinforced concrete beams. The beam span and reinforcement were different. The work dealt with shear failures and total bearing capacity of the beams. The tests were used later for validation of several papers and recommendations. Twelve beams in four series were tested. Each series had a specific reinforcement and span. The shape was rectangular. The basic length of the beam was 3.66, 4.57 or 6.4 mm. Each beam was ca. 552 mm long. Fig. 1 shows principles of the experiment. More details about the test and numerical calculations are provided in [2]. Figure 1 : Scheme of the experiment. I I M