Size effect in concrete beams under bending – influence of the boundary layer and the numerical description of cracks

Ireneusz Marzec,Jerzy Bobiński,K Wilde,M Niedostatkiewicz

doi:10.1051/matecconf/201926210008

Ireneusz Marzec, Jerzy Bobiński + Show 2 more

Open Access

https://doi.org/10.1051/matecconf/201926210008

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Abstract

In the paper the size effect phenomenon in concrete is analysed. The results of numerical simulations of using FEM on geometrically similar un-notched and notched concrete beams under bending are presented. Concrete beams of four different sizes and five different notch heights under three-point bending test were simulated. In total 18 beams were analysed. Two approaches were used to describe cracks in concrete. First, eXtended Finite Element Method (XFEM) describing cracks as discrete cohesive ones with bilinear softening was chosen. Alternatively, an elasto-plastic constitutive law with Rankine criterion, associated flow rule and bilinear softening was defined. In order to ensure mesh-independent FE results, a non-local theory in an integral format as a regularisation technique was applied in the softening regime. In both approaches the influence of the decrease of the material parameters (mainly fracture energy) in the boundary layer on obtained maximum loads was studied. Additionally the influence of the averaging method in non-local plasticity was also examined. Obtained results were compared with experimental outcomes available in literature.

Highlights

The behaviour of heterogeneous quasi-brittle materials, like concrete, is very complex
The understanding and a proper description of the size effect is very important in extrapolating experimental results obtained on small specimens into bigger ones
Paper presents results of numerical simulations of experiments [1] using two different constitutive laws. In both approaches the influence of the decrease of the material parameters in the boundary layer on obtained maximum loads was studied

Summary

Introduction

The behaviour of heterogeneous quasi-brittle materials, like concrete, is very complex. Constitutive laws have to be equipped with a characteristic length of microstructure to preserve the well-posedness of the boundary value problem It can be done by means of e.g. a micro-polar, non-local or gradient theories. [3] studied the same problem by testing 12 beams with 4 different sizes and 3 notch heights These experiments were numerically simulated with cohesive elements [4] or non-local damage models [3, 5]. Paper presents results of numerical simulations of experiments [1] using two different constitutive laws In both approaches the influence of the decrease of the material parameters (mainly fracture energy) in the boundary layer on obtained maximum loads was studied. The influence of the averaging method in non-local plasticity was examined

Elasto-plasticity

Extended Finite Element Method

Problem data

Findings

Conclusions