ABSTRACT
A unique network tied-arch bridge with free-standing, unbraced arch ribs was designed to carry the 2nd Avenue traffic over the Interstate Highway (I-94) in Detroit, Michigan. This 96.5 ft wide and 18° skew bridge with a 245 ft span is the first unbraced network arch bridge in Michigan, the fourth in the U.S., and the only unbraced and skewed network tied-arch bridge in the world. The bridge superstructure was assembled at a nearby staging area and moved into place on the permanent abutments using Self-Propelled Modular Transporters (SPMTs) and launching techniques. This design and construction method was selected for this site to minimize traffic disruption, improve safety, and allow 2nd Avenue to completely span over I-94 without intermediate supports to facilitate future widening and alignment shift of I-94 freeway and the adjacent interchange. Several alternative designs were considered; a) the use of post-tensioned concrete tie girders, (b) the use of internally redundant steel tie girders and (c) a multi-span bridge with a movable pier. During preconstruction planning, the contractor submitted a Value Engineering Change Proposal to erect the bridge in place by using a combination of cast-in-place concrete and spliced precast segmental tie girders. The paper describes the project and the technical basis for the selection and implementation of the post-tensioned concrete tie girders.
