ОПРЕДЕЛЕНИЕ ПРЕДЕЛЬНЫХ СОСТОЯНИЙ ПУСТОТНЫХ ПРЕДНАПРЯЖЕННЫХ ЖЕЛЕЗОБЕТОННЫХ ПЛИТ ПЕРЕКРЫТИЙ ПРИ ОГНЕВОМ ВОЗДЕЙСТВИИ ПОД НАГРУЗКОЙ

Abstract

Experimental dependences of limit states of the hollow core floor slabs under fire exposure and specified load are presented in this work. It have been defined that the main advantages of hollow core slabs are the cost effectiveness, wide application in construction of various objects, high durability and insulating characteristics. The important advantage of floor slabs is presence of tubular voids that allow reducing material consumption, mass of slabs and load on foundation consequently. Air-filled tubular voids increase thermal and noise insulation of floor slabs and also can be used for laying the service lines. Application of prestressed reinforcing cage raises strengthening and operational indices of the slabs. Dependences of heating up of the slab reinforcing elements (ropes) under standard fire conditions have been determined. Dependences of heating up of slabs at the depth of 150 and 200 mm during the time of fire exposure as well as dependence of their deflection on exposure time and specified load are shown. As a result of fire load tests it was established that time until limit state, when slab losses bearing and thermal insulating capacities, is more than 65 min. During 65 min of the test bearing capacity wasn't loss; deflection and deflection rate of the slab were 156 mm and 2,5 mm/min accordingly, and these values weren’t critical. The reversed strain (deflection) didn't become during 12 hours after fire exposure was finished. The number of cracks on a sample and their sizes haven't exceeded standard. Heating of a slab to the critical temperature of 140 °C haven't detected.