Experimentally based mechanical model of sandwich pipes with a strain-hardening cementitious composite core

Abstract

The thesis aims to build a comprehensive mechanical model for Sandwich pipes (SPs), which mainly consists of the concrete damage plasticity (CDP) model for the SHCC core and the actual interlayer behavior model. The thesis proposes a particular CDP model for the SHCC core based both on experimental data and on the continuum damage mechanics (CDM) theory. The fundamentals of the CDP model can be divided into three major issues, namely, damage evolution, yield criterion, and plastic flow rule. For the damage evolution, two models of damage variables, under tension and compression, respectively are built based on uniaxial experimental data available and the fracture energy theory. For the yield criterion, the parameters for the Lubliner model are fitted according to available experimental data from uniaxial and biaxial compressive tests. For the plastic flow rule, the dilation angle is deduced from the results of triaxial compressive tests combined with the Drucker-Prager type plastic flow rule. Then, the thesis investigates the actual interlayers behavior through push-out and self-stress tests, and a bond-slip layer numerical model is proposed. The finite element model of the actual interlayer behavior is modeled in three parts as the surface-based cohesive model for the bond-debonded behavior, the Coulomb friction model for the frictional behavior in the tangential direction, and the pressure over closure contact model in the normal direction. Finally, to verify the whole mechanical model of SPs, the results from collapse and bending numerical simulations are correlated to full-scale tests, presenting good agreement. A parametric study is then performed to investigate the influence of geometric parameters and initial ovality on the ultimate bending strength.