Mechanical behavior of thermally activated building structures

Abstract

This paper focus on two low energy systems, thermo-active building systems (TABS) and energy foundations, both with the common use of building concrete elements, that are already required for structural reasons, but which simultaneously work as heat exchangers. The aim of this paper is study the mechanical behaviour of these concrete elements due to the inclusion of polyethylene pipe heat exchangers cast directly in their concrete core and the influence of fluids flowing inside at a moderate temperature. Cylindrical and cubic specimens have been manufactured in order to study the influence of temperature through compression and pull-out tests and the influence the embedded pipes in different positions using compression tests. The analysis of results shows that mechanical properties decrease when the temperature increases in both types of concrete (H-25 and H-30), with a sharper decline in H-30 specimens. The layout of the pipes reduces the mechanical resistance of the structural elements regardless of the type of concrete used, being the most damaging position the one perpendicular to the load. Therefore, thermo-active reinforced concrete elements best behaviour occurs when polyethylene pipes are placed in parallel to the load, and the temperature of the fluids in the pipes is lower than 70ºC.