Middle River Bridge Inspection and Evaluation, Wagmatcook, NS

 

The Lower Middle River Bridge (VIC004) is located in Cape Breton, Nova Scotia and spans over the Middle River.  The bridge has an overall span of approximately 106 meters and is comprised of two short, simple approach spans each approximately 9.5 meters long and two simple, steel truss spans of approximately 43.5 meters. The structure is founded on reinforced concrete abutments and piers, with a single in-water pier at mid-span of the bridge. The type of foundation (piles or spread footings) is unknown at this time. The bridge deck is cast-in-place reinforced concrete with two 4.04 meter wide lanes covered by an 80mm asphalt wearing surface. The driving lanes are flanked by two 0.92 meter wide sidewalks which support steel guardrail/concrete post barrier systems along the North and South sidewalk extents. 

Harbourside Engineering Consultants (HEC) was hired to complete a full structural assessment of the existing bridge including a site inspection followed by an analysis of the structure. The analysis was required to be completed in accordance with CHBDC CAN/CSA S6-06 (S6) Section 14 Evaluation and design live loadings were to be CL-625 Truck and Nova Scotia Transportation Infrastructure Renewal (NSTIR) B-train.

Documentation on the structure was limited, though it is evident that local strengthening of some supporting steel elements has occurred near each of the three expansion joints located at the ends of each truss span at the centerline of the structure. Additionally, repairs have been made to deteriorating concrete barrier posts and steel pipe extensions have been fitted to half of the original 16 deck drains along the outer edge of each driving lane.

The condition assessment of the Lower Middle River Bridge was conducted between November 4th & November 7th, 2013 by HEC. Elements and areas of the structure with limited access were inspected by representatives from Remote Access Technologies (RAT). Atlantic Sub-Sea Construction and Consulting Incorporated were also a sub-consultant of HEC for the project, performing below water inspections and providing dimensions for the center pier.

The inspection, confirmation of geometry of sections, member lengths and overall truss geometry for below deck elements on the truss spans were performed by RAT. Inspected elements included truss members, deck steel grillage, lateral bottom chord bracing, vertical bracing and the deck soffit. Atlantic Subsea conducted the dive inspection of the center pier.

As requested by NSTIR, HEC cut four 200mm x 300mm steel specimens from four locations on the existing structure. Samples were taken from batten plates on each of the four bottom chord segments closest to the east most and west most truss bearings, as they were easily accessible from land. Extracting the steel from batten plates on primary tension members also allowed for the acquisition of specimens without reducing the structural capacity of the members.

A high degree of overstress was found in many of the structural steel elements in both the deck grillage and the supporting steel trusses. All bridge barrier elements, were found to well exceed a demand to capacity value of 2.0 (100\\\\\\\% overstress).

In an effort to aid NSTIR, HEC provided four possible immediate options for review and consideration by NSTIR. HEC also prepared high order cost estimates for completing the additional scope and provided options and cost estimates for long term solutions for the structure including the development of several replacement options. Work on additional project scope set to begin in early spring 2014.

Client: Nova Scotia Transportation Infrastructure Renewal

Year: 2013 /2014

Role: Full inspection of Superstructure and Exposed Foundation Elements, Structural Analysis & Evaluation, Project Lead