East River - Sydney River Arch Bridges, Cape Breton County, NS

 

The East River Bridge is a 213 meter long multiple span bridge featuring a 140 meter long arch main span over the East River in Sheet Harbour, NS. The arch structure is a half through, two-hinge type arch made up of two parallel steel ribs with a built up box cross section. The deck is hung from the arch by vertical steel wide flange shape hangers. The bridge was opened for traffic in 1956. The arch ribs were heavily reinforced 1988.

The Sydney River Bridge is a 160 meter long span bridge featuring a 130 meter long arch main span over the Sydney River in North Sydney, NS. The arch structure is a half through, two-hinge type arch made up of two parallel steel ribs with a built up box cross section. The deck is hung from the arch by vertical steel wide flange shape hangers.

Under Phase 1 of the project HEC was engaged by NSTIR to conduct a full assessment of both structures including a detailed field inspection, through thickness testing of steel elements, ambient vibration measurements, full structural analysis including considerations of dynamic response of the structure, and sub-structure assessment.

The structural assessment included the development of full finite element models for both structures, calibration of the models with ambient vibrations in the field, a review of the dynamic response of the hanger elements under buffeting winds, and a full in-plane and out-of plane buckling analysis of the arch ribs using non-linear buckling analysis to determine the critical buckling of load of the arch ribs giving full consideration to locked in dead loads.

Phase 2 of the assignment was to include a detailed design of rehabilitation or upgrades for the structure as well as the detailed design and generation of a tender package to re-deck the bridges while maintaining traffic across the structures.

HEC completed a full Phase 1 report for both structures including a summary of findings, concept level repairs (where applicable) and recommendations as to the suitability of a rehabilitation program versus a full structure replacement including full capital cost estimates.

As a result of the Phase 1 inspection emergency repairs on both bridges were designed and detailed by HEC in order to ensure the immediate safety of the travelling public.

The results of the Phase 1 assessment indicated that the extensive reinforcing previously completed on the East River Bridge arch ribs provided sufficient capacity to resist loading prescribed by CAN/CSA S6-06. Full replacement of the approach spans, rehabilitation of the arch thrust blocks and main pin assemblies, full replacement of the concrete deck and longitudinal stringers with minor reinforcing of the transvers floor beams were required in order to sufficiently upgrade the structure. The capital cost estimate to complete the upgrade work is significantly less than that to replace the structure.

The Sydney River Bridge required most of the same rehabilitation measures described above for the East River Bridge except that significant reinforcing of the arch ribs was also required. The capital cost estimate to complete the upgrades work exceeded the capital cost estimate to replace the structure.

NSTIR has decided to replace both structures. HEC is currently finalizing the detailed design of replacement structures for both sites consisting of twin trapezoidal steel box girders with composite concrete decks. It is intended that both structures will be launched from one approach into the final position.

HEC will also endeavour to provide construction engineering services to local contractors for the demolition of both existing arch bridges. Due to potential restrictions on in-water work, the concept being developed includes a phased demolition approach that would include the use of PSS cables to provide a tie for the arch, transforming the structure from an externally restrained fixed end arch into a tied two pin arch. The whole structure could then be floated clear of the navigation channel and demolished near land. 

Client: NS Department of Transportation and Infrastructure Renewal

Value: $16 M (Approximate)

Year: 2009-on-going

Role: Lead Engineer