A Notion in Modeling Concrete Members

In this paper, the influence of aggregate size on width of fracture process zone wc is considered. Some researchers observed that the greater the grains of aggregate, the wider the fracture process zone (FPZ). The average value of the FPZ width taken from tests performed by Woliński was 26.6 mm and it did not depend on maximum aggregate size Dmax. There are no consistent conclusions as to whether the width of FPZ depends on aggregate size, and there are no standard methods of FPZ width measurement. The problem arises how to choose the width of FPZ in numerical modeling of concrete structures. For example, Bažant and Oh proposed to take wc = 3Dmax in numerical calculations. To discuss this problem, the authors’ own numerical simulations concerning bent concrete members with different widths of FPZ: 5, 10, 20, 26.5, 50 and 100 mm were performed. On the basis of the comparison of obtained results, significant differences dependent on wc have been observed. Taking into account the minimum potential energy in a member, it can be said that the most rational thing to do is to take the smallest elongation within the localized microcracking. This condition takes place in the analyzed beam when wc = 50 mm. The assumption wc = 3Dmax does not fit this criterion. Also, the width from the experiment performed by Woliński is not in good relation to obtained numerical results. The main conclusion from this paper is that the width of FPZ does have an influence on obtained numerical results performed by crack band model. The problem of estimating the width of FPZ in numerical simulations exists and requires further research.