STUDY OF THE STEEL BEAM WITH FIRE-PROTECTIVE MINERAL WOOL CLADDING BEHAVIOR IN CASE OF FIRE
Abstract
The article considers the processes of loss of integrity of fire-protective mineral wool cladding of the steel beam. Computer model of steel beam with fire-protective mineral wool cladding, which takes into account its own weight, current mechanical load and temperature mode of heating under the conditions of heat-insulating effect of the lining was developed using a computer system LS-DYNA. It is shown that fire-retardant cladding loses its integrity under the thermal influence of fire long before the onset of the limit state of loss of fire resistance by bearing capacity. The conditions under which fire-retardant cladding loses its integrity and fire-retardant ability are investigated. During the calculation, it was assumed that the probable separation of the fire-retardant cladding is not on the adhesive seam but on the adjacent layers of mineral wool, i.e. the destruction is cohesive. This assumption is made taking into account the fact that the strength of the adhesive seam is much higher than the tensile strength and shear strength of the mineral wool. This assumption is taken into account by means of the software environment LS-DYNA when describing the contact interaction between the elements of the model.
According to the results of the work it was found that during the 60 minutes of fire at a temperature of 433 °С there are detachments of mineral wool fasteners, and at a temperature of 967 °С there are signs of local loss of stability in the form of folds in the shelves and I-beam in the middle and at its fixed ends. The onset of the state of loss of fire resistance on the bearing capacity of the investigated steel beam with mineral wool fire-retardant cladding occurs at the 117th minute of exposure to the standard temperature of the fire. 25 mm opening of the gap between the beam and the mineral wool fire-retardant cladding is observed at the 44.5 minute at a heating temperature of the steel beam 425 °С. The loss of fire-retardant capacity of mineral wool on the basis of the 25 mm opening of the gap between the beam and the cladding occurs 73 minutes earlier at the onset of the limit state of loss of fire resistance by load-bearing capacity, which must be taken into account.
