Design criteria of FRP Reinforced Concrete Flexural Members

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The compressive strength and the stiffness of some FRP reinforcements are reduced by the repeated tensile load. The fatigue life is affected by the environmental temperature and the time interval of repeated load. These characteristics should be taken into consideration of design criteris.The resistance factor for flexural capacity was calculated to be 0.8 approximately. However, there still remains the discussion of safety margin against the failure. In this study, not considered are the smaller compressive strength of FRP reinforcement than the tensile strength, the reduction of compressive strength by the repeated tensile load, etc. Specially the resistance factor should be calculated, considering the compressive strength of FRP reinforcement, when the structure would be subjected to earthquake load.The short term loading test and the long term loading test of flexural members with grid type FRP reinforcement were conducted to obtain the design criteria for serviceability limit. As a result of evaluation of measured deflection and crack width, the prediction formulae, that could well reproduce the experimental results, could be postulated.When the stiffness degrades much after cracking, the working stress would be limited under the cracking moment level. In this case, the increase of long term deflection is proportional to the stress level of FRP reinforcement. However, the total deflection is not large comparing the span length. The increase of crack width is also proportional to the stress level of FRP reinforcement. However, the crack width immediately after cracking is considerably large. So, the design criteria should be needed such as no more increase of crack width could be permitted under the working stress level. In this case, We have to know that the stress level of FRP reinforcement would be limited to a considerably low stress level when the crack width would be a serviceability limit.