Influence of corrosion on reliability-based design of steel grid MSE walls

Design for internal limit states of steel grid reinforcement in mechanically stabilized earth (MSE) walls must provide for loss of steel thickness due to corrosion. The paper combines key features of zinc and steel corrosion models used in North American practice with corrosion rate statistics reported in the literature for the zinc coating on buried galvanized steel strips and for steel rebar. Examples of loss of strength and pullout capacity of steel grid elements constructed with different member diameters and up to 120 years after construction are presented in probabilistic terms. Results of reliability-based analysis for the tensile strength and pullout limit state at design lives of 75 and 120 years are demonstrated for a typical wall under operational conditions using tensile load and resistance models in combination with non-aggressive soils recommended in North American design codes. The results of calculations show that for the wall example the influence of different zinc cover thickness on probability of tensile failure of longitudinal members is detectable at the end of design life. However, the typical minimum specified zinc thickness of 0.086 mm recommended in North American practice is likely sufficient to keep probabilities of failure to 1% or less (i.e., reliability index of 2.33 or greater). The influence of a range of initial zinc thickness reported in the literature on probability of pullout failure of the same steel grid elements was found to be negligible.