Experimental Investigation On The Residual Mechanical Properties Of FRP Bars In The Structure During And After Exposure To High Temperatures

Fiber Reinforced Polymer(FRP)or fiber-reinforced plastics,advanced composites materials(ACMs)has the excellent mechanical performance of high specific stiffness and specific strength,superior fatigue endurance,and has the physical advantages of low density and excellent corrosion resistance.Its application in the civil engineering structure can be divided in two major fields: one is to apply FRP as a structural restoration material to strengthen existing structures,and the other is to use FRP as a structural reinforced material to replace a part of traditional steel bars in a new structure.Although the application of FRP is increasing,there is a lack of research under high temperatures,and more attention has been focused on the performance indicators of FRP directly exposed to high temperatures,which is not suitable in paractical structures.Morevoer,the performance indicators mentioned above are not optimistic and discrete.These aspects have impeded the wide acceptance and use of these materials.Thus the experimental study of the residual mechanical properties of BFRP bars with cladding layer,which is to get close to the practical situation,during and after temperatures,is more reasonable and practical.Firstly,the cladding layer with good resistance to crack was selected.Results from the tests indicates that cement mortar reinforced with chopped basalt fiber can avoid cracks under the heating rate of 100?/min up to 400?.Based on that,the influence of prefabricated crack width on the temperature filed of the cladding layer member was investigated.Through the comparison of the results,the effect of crack width is less important.Secondly,to solve the difficulty of acquiring the strain of BFRP bars with cladding layer,an optical sensing technology,i.e.,BOTDA(brillouin optical time domain analysis),is utilized.And the two key parameters,i.e.,the temperature coefficient and the strain coefficient,are calibrated under different conditions,which provides guarantee for the reliability of the subsequent data.Then,the mechanical properties of BFRP bars with cladding layer,during or after high temperatures,were investigated.For the experiment during high temperatures,the results indicated that the influence of crack width(up to 2.0mm)on the FRP mechanical properties is not significant.And compared with bare BFRP bars after the same high temperatures,its strength and modulus is higher.For the experiment after high tempertures,the results indicated that the influence of crack width(<2.0mm)is less important.And compared with bare BFRP bars at 400?,its strength and modulus is obviously higher.Finally,data from the experiments was utilized to proposed empirical relations for variation of tensile strength and modulus of BFRP bars that with cladding layer with temperatures.