RELIABILITY-BASED STRENGTH REDUCTION FACTOR FOR BOND

The formulation of a reliability-based strength-reduction (phi) factor for developed and spliced bars is described. Conventional and high relative rib area bars, both with and without confining reinforcement, are considered. The phi-factor is determined using statistically based expressions for development/splice strength and Monte Carlo simulations of a range of beams. The overall approach is applicable to the calculation of phi-factors for all types of loading on reinforced concrete. A strength-reduction factor of 0.9 is obtained for the design expressions for development/splice length, based on a probability of failure in bond equal to approximately one-fifth of the probability of failure in bending or combined bending and compression. The value phi=0.9 is incorporated into two expressions for development/splice length in a manner that is transparent to the user. A major advantage of each of the final expressions is that they provide identical values for development and splice length, removing the need to multiply development length by 1.3 or 1.7 to obtain the length of most splices.

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