Effect of Climatic Actions On Buildings with Internal Insulation and Thermal Breaks: Multi-Scale Approach and Thermo-Hydro-Mechanical Modeling

Abstract

For buildings designed with internal insulation, thermal bridges at the junction between slabs and walls are a common issue, since they create heat loss from inside of the building. Thermal break systems (TBS), which are composed of structural elements (rebars and steel profiles) and insulation material, are used to reduce this heat loss and to transfer shear forces from the slab to the walls. Insulation system of TBS generates a temperature gap from wall to slab. As a consequence, while the wall is exposed to climatic actions and is repeatedly dilated and contracted, whereas the slab pertains a constant temperature and does not present any volumetric variation, thus the TBSs are submitted to large displacement constrains. The paper illustrates the effect of the thermal dilatation and contraction of the walls, which create a supplemental force in the TBSs, and consequently cracking of the walls. A numerical model of a quarter of a building's storey is submitted to the climatic actions computed at the location of Embrun city, in France. One side of the L-shape wall is supposed to face to the south, and the other one to the west. The thermal and mechanical analysis are performed with the software CASTEM. In thermal analysis, air temperature and flux of solar radiation signal are defined from databases of METEO FRANCE, and are applied on the exterior surface of the walls. The results of the first calculation, by thermo-hydro-mechanical analysis (THM) with elasticity behavior, confirm that a significant stress level in tension occurs in the concrete at the corner of the walls and the nearby interface elements of the TBS. Furthermore, the TBSs that are close to the corner of the walls pertain the highest horizontal and axial forces, and are at risk to exceed the limit strength. Based on those results, a second calculation, which includes the coupling of damage with shrinkage and creep model from the THM analysis, is made for determining more realistic forces in the TBSs, and analyzing the cracking pattern of the walls.

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