Mechanical behaviour of masonry walls subjected to fire action

This dissertation deals with an experimental campaign executed to determine the effect of high temperature to the mechanical properties of several materials for masonry walls (blocks, mortars), testing a series of cylindrical specimen (diameter 100 mm – height 200 mm). After compression tests at 20°C, an experimental procedure has been designed for high temperatures testing. The cylindrical elements are inserted on a muffle furnace, to reach the required temperature, and then subjected to mechanical compression after entering in a specific apparatus (called “thermos”) to maintain the prescribed temperature. The results show variation in strength and ultimate strainy and correspondingly of the modulus of elasticity, with increasing temperature: specific diagrams are performed for each material. Moreover, stress-strain curves in function of temperature are proposed and compared with those drown by European regulations. A methodology for the prediction of equivalent masonry parameters is also proposed with a model of layered elastic wall panels. The out-of-plane mechanical behaviour is also investigated. The method proposed herein aims to define such interaction diagrams for walls subjected to the eccentric normal force applied on various types of blocks exposed to fire on one side. To this end, the temperature distributions across the wall thickness are first determined. Then, as the laws governing the decay of the material resistance and axial stiffness as a function of the temperature are known, the wall crushing strain fields are calculated as a function of the curvature. Lastly, based on the isotherms already calculated and the stress–strain–temperature constitutive relation, we determine the crushing surfaces on the plane N–e (in which "N" is the axial force and "e" is the out-of-plane eccentricity) for increasing exposure time to nominal fire.