Finite element crack width computations with a thermo-hygro-mechanical-hydration model for concrete structures

Abstract

The paper presents an overview of a finite element approach for the analysis of the thermohygro-mechanical-hydration behaviour of concrete structures. The thermo-hygro component considers the mass balance equation of moisture as well as the enthalpy balance equation, and uses two primary variables, namely the capillary pressure and temperature. Heat of hydration is simulated using the approach of Schlinder and Folliard. The basic mechanical model simulates directional cracking, rough crack closure and crushing using a plastic-damage-contact approach. Hydration dependency is introduced into the mechanical constitutive model. The material data from the Concrack benchmark (CEOS.fr,2013) are considered with the model. This includes data on adiabatic temperature changes during curing, changing elastic properties during curing, shrinkage and creep. The model, as implemented in the finite element program LUSAS, is used to analyse the Concrack benchmark beam RL1. Particular attention is paid to crack openings and the difference between predicted crack openings from analyses with and without time dependent effects. It is concluded that ignoring time dependent effects can result in a significant underestimate of crack openings in the working load range.

CEOS.fr experimental programme and reference specimen tests results

“…But, for RL1, microcracks at core developed during the cooling phase should have influence on the crack pattern obtained during pure mechanical loading. European Journal of Environmental and Civil Engineering 747 Jefferson et al (2014, in this special issue) obtained such numerical prediction for RL1 using a model that takes into account hydratation, temperature variation and the time dependent effects of creep and shrinkage. This author used theoretical outdoors temperatures gave for benchmark ConCrack that are closed to RL1 experimental conditions.…”

A Continuum Coupled Thermo-Hygro Mechanical Time-Dependent Model for Concrete

“…The basis of the expressions adopted is the work of de Schutter (2002), although it is noted that the definition used here for the relative degree of hydration (Γ r ) differs from that used by de Schutter for reasons explained in Jefferson et al (2014);…”

“…This results in a formulation in which capillary pressure (P c ) and temperature (T) are the primary variables. The HT model requires a set of standard constitutive equations (Gawin et al 2006, Lewis andSchrefler 1998) which are given in full in Jefferson et al (2014).…”

“…The FE mesh showing crack widths is given in Figure 3. More details of the analysis and results may be found in Jefferson et al (2014).…”

“…This subject of the paper is a finite element model for the thermo-hygromechanical behaviour of concrete that was applied to the international benchmarking exercise Concrack (Jefferson et al, 2014). The particular focus of the work was on the computation of crack patterns for a beam in which the full casting, curing and loading history was available.…”