The existing functionally obsolete steel arch bridge is being replaced with a new concrete arch bridge along the same alignment and traffic must be maintained during construction.

The existing bridge is to be partially demolished with part of the deck and stringers removed from its West side. The partially demolished bridge will support one lane of traffic and SAFWAY Scaffolding. The new bridge is to be partially constructed with the arch ribs, the spandrels, and the Stage 1 cap beams, girders, and deck constructed. Falsework and temporary arch struts are installed. The partially constructed bridge will support one lane of traffic and SAFWAY Scaffolding.

The designer of this project is FHWA and the contractor is Flatiron Construction Inc (FCI). VAK Construction Engineers (VAK) is tasked with the design of the temporary works for construction. OPAC is engaged by FCI to support VAK by performing the following tasks:

• Perform a strength and stability check of the partially demolished existing steel arch bridge for the critical stage identified by FCI.
• Perform a strength and stability check of the partially constructed concrete arch bridge for theoretical stage identified by FCI.

The scope of work for OPAC included the followings:

1. Review the stage-by-stage construction sequence by the contractor.
2. Prepare a time-dependent structural analysis model that incorporating the existing steel bridge, temporary structures and the new concrete arch bridge.
3. Incorporate design modifications for strength or stability.
4. Verify the strength and stability of the modified structure at each construction stage.
5. Prepare a report with findings and calculations.