SOLUTION

WJE engineers performed a two-part analysis to evaluate the ability of the bridge substructure to carry the loads from the proposed shoring towers. First, the bridge superstructure was analyzed to determine the forces that would be applied to the substructure from lifting and live loads. Then, the substructure was analyzed for the effects of these loads and in situ loads from the surrounding soil and water. As part of the superstructure analysis, a two-dimensional finite element model was constructed of one of the main bridge trusses to facilitate determining the reactions at the bridge supports. A three-dimensional finite element model was used to analyze the bridge substructure. Loads obtained from the superstructure analysis were applied to the substructure model at the proposed shoring tower locations and superstructure bearing points. The capacity of the substructure was assessed based on the guidance of the ACI code. Evaluation showed the existing pit slab not capable of resisting the heavy concentrated loads applied from the showing towers because there is no reliable load path from the slab into the caissons. WJE engineers provided several alternate shoring options with installing new micropiles recommended to be the most advantageous. Also suggested was consideration to repairing the existing steel elements in place.