Fire represents one of the extreme conditions during the lifetime of engineering structures. In order to fully understand the impact of fire on the load bearing function of structures, a fundamental research on material and structure behaviour including the fire phenomenon is needed. Reliable insight into the behaviour of structures during fire exposure is possible only through combined experimental research and numerical analysis of structural response during fire exposure. This thesis

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... the results of experimental tests obtained by testing fire behaviour of prestressed concrete structures (on material and structural level). In addition, this thesis presents newly developed numerical model for predicting fire behaviour of structures. Experimental research on material level consists of the determination of the mechanical properties of high strength concrete during and after the exposure to high temperatures. The tested mechanical properties in the study include: compressive strength, tensile strength, secant modulus, dynamic modulus and stress-strain curves up to the temperature of 800°C. Concrete samples were tested while heated to the maximum temperature (hot property), while cooled to the room temperature and 96 hours after initial cooling (residual property). Experimental research on structural level is comprised of a study of the fire behaviour of prestressed hollow core concrete slab with dimensions of 600/1200/200 mm. Concrete used for the tested slab was the concrete tested in the described material study. The tested slab was exposed to ISO fire curve and during the exposure, the temperature increase in the slab was measured in eleven measuring points; horizontal displacements were measured in two points and longitudinal deformations were measured in two points as well. In this thesis, a new numerical model for predicting fire behaviour of structures comprised of beam-column elements is developed. The developed model is comprised of three sub models: transient nonlinear heat transfer model, model for calculating nonlinear stress-strain distribution in composite cross-section and model for linear analysis of structures comprised of beam-column elements. Validity of the developed numerical model was tested on results of six different fire tests, including three fire tests of steel beams loaded with vertical force, two tests of steel beams loaded with vertical and horizontal compressive force and one test of prestressed concrete slab that is a part of this thesis. In this thesis, a new implicit model is developed for the inclusion of additional load dependent strains that occur during heating into structural analysis. Material stress-strain curves are implicitly modified so that the calculated additional load dependent strains are added to initial strain value of the stress-strain curves (strain modified curve). After the modification procedure, the strain modified curve has a reduced value of modulus of elasticity, thus influencing the structural stiffness during fire exposure.