Steel mechanical properties evaluated at room temperature after being submitted at fire conditions
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abstract
Several researchers have already studied the effect of temperature increase in steel structures regarding load-bearing capacity and some material models have been developed in fire conditions, based on experimental results. The mechanical properties of a S275 JR steel construction material has been tested at elevated temperatures after a natural and forced cooling. The major focus has been made on yield and ultimate strength behavior, hardness material and residual stress relief. Experimental results will be presented for each temperature level, dwell time and cooling rate. Test results were compared with the normal room temperature condition. The material specimens were cutted from the web of each unit length IPE 100 profiles, after being heated by means of electro ceramic mat resistance and tested at the universal machine, according to NP EN 10002-1 standard. Microstructure analysis has been done regarding each different steel state, based on the standard NP-1467. The hardness tests has been determined for some steel specimen conditions over the entire cross section, according to NP 4072 standard. The results shown that material yield strength from the tested heated specimens are smaller and grater when compared with the yield strength of the used material at room temperature, depending on the temperature level during fire and respective cooling rate. Residual stresses were measured as closed as possible to ASTM E837-01. A stress relief was thermally induced and the final stress state measured and compared with the initial state.
