Interplay of sources of size effects in concrete specimens

conference paper

English

We study well published results on direct tensile tests of dog-bone specimens with rotating boundary conditions performed by van Vliet and van Mier. There are several papers presenting the experimental results and naming various sources of experimentally observed size effect on nominal strength. We model the experiments by methods stochastic nonlinear fracture mechanics attempting at capturing the size effects. We first model the specimens by microplane material law to show that a large portion of the dependence of nominal strength can be explained deterministically. However, it is clear that more sources of size effect take part and we consider two of them. Namely, we model the local material strength by an autocorrelated random field attempting at capturing statistical part of the complex size effect, scatter inclusive. A noticeable fact already shown by Vořechovský is that such an approach has the large size asymptotic behavior coinciding with the classical Weibull power law while the small size asymptote deviates strongly from the Weibull size effect. The strength drop of the smallest specimen reported in experiments is explained by weak surface layer of constant thickness (caused e.g. by drying, surface damage, aggregate size limitation at the boundary or other irregularities). All three named sources are believed to be the most contributing sources of the observed strength size effect and the model combining all of them is capable of reproducing the measured data. The computational approach represents a marriage of advanced computational nonlinear fracture mechanics with simulation techniques for random fields representing spatially varying material properties. Using the numerical example we document how different sources of size effect on strength can interact and result in relatively complex processes in quasibrittle failure. The presented study documents the well known fact that an experimental determination of material parameters (needed for rational and safe design of structures) is very difficult for quasibrittle material such as concrete.

Size effects, concrete, specimens, fracture mechanics

VOŘECHOVSKÝ, M.; MATESOVÁ, D.

2006

3. 7. 2006

Alexandropoulis, Greece

1-4020-4971-4

Fracture of Nano and Engineering Materials and Structures

1365

1374

10