The effect of high temperature on reinforced concrete structures

The article represents the behaviour of reinforced concrete and its components (concrete and reinforcement) under high temperature. The comparing analysis of the experimentally and theoretically obtained results has been performed. The carried out experiment has disclosed that the mechanical properties of concrete alters differently in cases of temperature rise and theoretical reference. The most visible difference has been noticed at a temperature of 100 °C (Fig 4, Fig 5). The main fire resistance calculation basics are discussed. The temperature fields of the reinforced concrete element cross-section are calculated according to the standard fire curve using the program COSMOS/M of the finite element method. Concrete thermal properties, thermal conductivity and specific heat capacity dependence on temperature are taken into account in the model (Fig 10, Fig 11). By means of this model, the corresponding algorithm (Table 2) was made and can be used for obtaining temperature distribution for the reinforced concrete element of different cross-sections. According to the received temperature fields and applying the zone method, the influence of differences in theoretical and experimental results on element load bearing capacity is determined. The residual strength of the element considering the theoretical reduction curve of concrete strength is 5% larger than the results obtained in cases of 30 and 60 minutes heating. 90 and 120 minutes heating indicates that element strength is only 2% larger than the results calculated experimentally. The reduced zone dimension determined due to a decrease in the reduction coefficient at a temperature of 100 °C has affected residual element strength. Article in Lithuanian. Aukštos temperatūros įtakos betono ir armatūros savybėms bei jų bendrai elgsenai analizė. Santrauka. Nagrinėjama gelžbetonio ir jo komponentų (betono ir armatūros) elgsena aukštoje temperatūroje, tiriamos betono stiprumo ir deformatyvumo savybės kintant temperatūrai. Atliekama teorinių ir eksperimento būdu gautų rezultatų lyginamoji analizė. Aptariami pagrindiniai atsparumo ugniai skaičiavimo principai. Pasinaudojus baigtinių elementų metodo programa COSMOS/M, suskaičiuoti gelžbetoninio elemento skerspjūvio temperatūros pasiskirstymo laukai pagal standartinio gaisro kreivę. Pagal gautus temperatūrinius laukus zonų metodu nustatyta teorinių ir eksperimento rezultatų skirtumo įtaka elemento laikomajai galiai. Reikšminiai žodžiai: gelžbetonis, temperatūra, gaisras, temperatūrinės zonos, atsparumas ugniai. First Published Online: 16 May 201