PRECAST CONCRETE STAY-IN-PLACE FORMWORK TO PREVENT LOSS OF SEISMIC RESISTANCE DUE TO CORROSION

This paper describes how probabilities of seismic damage of reinforced concrete bridge columns change due to environmental deterioration and whether a precast, fibre-reinforced concrete cover can slow down corrosion and improve seismic performance. The fibre-reinforced concrete selected was an engineered cementitious composite known for their high tensile ductility, and narrow, well-distributed cracking. The fibre-reinforced concrete cover serves as stay-in-place formwork and can accelerate construction of bridge columns. Reinforcement corrosion process was simulated for bridge columns, considering pitting corrosion, unique crack distribution characteristics of ductile fibre-reinforced concretes and their influence on corrosion rate, and environmental exposure conditions. Loss of reinforcement area was calculated for bridge columns with conventional concrete covers and those with precast fibre-reinforced concrete covers as a function of time in service. Bridge columns were modeled using the open-source analysis software, OpenSees, and using fibre-based beam-column elements. Loss of reinforcing bar mass was incorporated into the structural models. Nonlinear response history analyses were performed on the columns to build seismic fragility functions that consider uncertainties in ground motion characteristics. Fragility functions were generated for bridge columns across their service life, and the seismic damage probabilities for columns with and without the precast concrete cover were compared. These analyses indicated that the precast fibre-reinforced concrete cover improved durability, reduced loss of reinforcing bar area, and resulted in a lower probability of seismic damage over time compared to the pier with a conventional concrete cover. Fibre-reinforced precast concrete columns can, therefore, be used both to accelerate construction by serving as a stay-in-place formwork and to protect reinforcement from deterioration.