Reliability based design of RC beams with recycled aggregate and steel fibres

This study proposes a reliability analysis framework for the design of secondary beams fabricated with steel fibre reinforced recycled aggregate concrete (SFRRAC). The use of SFRRAC in fabrication of structural members is proposed due to its optimal combination of recycled aggregate concrete (RAC) and steel fibre (SF), to gain advantages in terms of environmental effects, production costs, and structural properties. However, structural members composed of new materials should be used for practical structural design according to proper design equations and safety factors determined via test-aided reliability analysis. The current international provisions are applicable only to natural aggregate concrete (NAC) beams, and cannot be directly applied to SFRRAC beams. This study adopts a safety factor calibration method based on the first-order reliability method (FORM) to evaluate the relation between the safety factor and the target reliability level for SFRRAC beams designed using the existing models for RC beams provided in Australian, American, and European design codes. This evaluation is based on the proposed improved prediction model for the flexural capacity of RAC due to the addition of SF. Furthermore, the optimal contents of SF in SFRRAC beams with 100% recycled aggregates (RA) to make the beams equivalent to NAC beams, in terms of moment carrying capacity are estimated using a proposed inverse analysis. The optimal contents are estimated to be around 0.015% of SF (by volume).