Investigation of changes in steel frames stress state in fire and influence on its vitality

Modern studies of the multi-storey buildings load-bearing structures vitality are analyzed. The shortcomings of the previously studied measures to increase the steel multi-storey frames vitality are identified. The need to study more effective and cost-effective measures have been identified. The change of 2d steel frame various elements loading during a fire is investigated. The dependence of the frame load-bearing capacity on the location of the fire source on different floors and spans is analyzed. 4 scenarios of fire source location in 2d multi-storey frame are considered. The influence of the distribution of the internal forces in the heated beams on the frame stress state, in particular on the local buckling of the I-beam flange and the web is analyzed. It was found that due to temperature expansions due to fire, not only heated elements are can be the first to be damaged in the frame. It is established that during a fire the first destruction occurs faster in the outside span of the frame than in the middle. When comparing the fire scenarios on the lower and upper frame floors, it was determined that on the lower floor the columns are more prone to damage earlier than the beam on the upper floor. When comparing the fire scenarios in the middle and outside frame spans, it was determined that in the middle span the beams are more prone to collapse earlier than the column than in the outside. It has been confirmed that, depending on the fire source location on different floors and spans, both the beam and the column of the frame may be the first to collapse. It is established that depending on the fire source location there may be different mechanisms of multi-storey frame collapse. It is established that the frame structures' stress state is significantly influenced by the distribution of internal forces at temperature loads, and not only fire protection and steel structures fire resistance.