Estimation of bearing capacity and serviceability of a floor slab after high-temperature exposure

Introduction. Reinforced concrete structures of buildings have significant fire resistance, but high-temperature effects lead to changes in strength and deformation characteristics of concrete and reinforcement of structures. In addition, for prestressed reinforced concrete structures, fire impacts can be associated with partial or even complete loss of prestress. At the same time, it is the prestress of the reinforcement that makes it possible to limit the width of the crack opening and the deflection of reinforced concrete structures within acceptable limits.Materials and methods. The paper presents and analyzes the results of analytical calculations of the bearing capacity and serviceability of a prestressed reinforced concrete ribbed floor slab before and after high-temperature fire impact on it. After fire exposure, the calculations are carried out with a complete loss of pre-stressing by the reinforcement. The heating temperature of the concrete in the compressed zone and tension reinforcement in the calculated cross section of the floor slab is taken according to the results of experimental studies.Results. The comparison of the floor slab deflections obtained by calculation and experimentally indicates the presence of additional factors (temperature expansion of concrete and reinforcement, high-temperature creep of reinforcement) that determine the increased value of the experimental floor slab deflection compared to the calculated one. The structural solution of the floor slab is analyzed, the feasibility of increasing the area of longitudinal tensile reinforcement to increase the bearing capacity and reduce the crack opening width in the slab is considered. The effect of fire protection on the heating temperature of the concrete in the compressed zone and the tensile reinforcement of the slab is shown.Conclusions. An analysis of the results of calculating a prestressed concrete ribbed floor slab before and after a fire showed a slight decrease in its bearing capacity after fire impact, an increase in the width of the crack opening and a significant increase in the deflection of the slab.

reinforced concrete building structures, ribbed floor slab, prestress, experimental and analytical studies, fire effects, warm-up temperature, strength and deformation characteristics of materials, load bearing capacity, operational characteristics of structures