Termisk och mekanisk påverkan av komposita bjälklag utsatta för ambulerande bränder : Med hjälp av finita elementmetoden

Modern structural systems and contemporary architectural features increase the complexity of buildings while structural fire design is still based on traditional methods. The methods assume uniform burning and homogeneous temperature conditions throughout the whole compartment. This methodology might be considered acceptable and gives a valid representation for smaller environments but is not a realistic definition of a fire in large compartments. Instead of burning locally and simultaneously throughout a compartment the fires in large compartments tend to move. This happens as flames spread, ventilation changes due to glazing failure and walls or ceilings break and the fire move across the floor area. This is called travelling fires.In January 2015, a full-scale test entailing travelling fire was performed in Tisova, outside Karlovy Vary in Czech Republic. The fire was centered on the ground floor of a four story building where wood cribs represented the fuel.The main purpose of this master thesis has been to determine the thermal and mechanical impact on the structural parts in a concrete and steel frame building exposed to a travelling fire. The work is based on an extensive literature review and calculations presenting the response of the partly composite slab on the ground floor using the Finite Element Method software Abaqus. User subroutines (US) were used to prevent the concrete from regaining its old material properties when the fire cooled.Performed calculations represent three different fires; ISO-834 (ISO), temperatures measured in the full-scale test (TFT) and temperature measured from a prior study in FDS representing a travelling fire (FDS). Presented result from Abaqus consisted of nodal temperatures, mid-span deflections, stresses and strains.The results show that it might not be necessary to use US when the main interest is in temperature. However, if the main interest is in the mechanical response, the comparison depicts significant differences. The results also show that the geometry of the structure is of importance. A slender construction covering a large area deflect more than a stubbier and smaller structure since it is carrying more weight on its own.In the conclusions it is stated that large temperature differences, between fire exposed and non-exposed surfaces, lead to great temperature gradients. Large gradients lead to large deflections. Validerat; 20151225 (global_studentproject_submitter)