New Cross Street, Bradford

Background:-
A road over rail bridge in Bradford, West Yorkshire, failed stringent assessment tests calling into question as to whether it could be certified fit for purpose without major work. HBPW was asked to review third-party assessments and recommend a strategy going forward.

Challenge
The Network Rail bridge in question at New Cross Street in West Bowling, failed to reach the required 40 Tonne capacity. Whilst it was concluded that some elements of the structure would require conventional strengthening, it was also determined that the element requiring of the most strengthening, namely the edge girders, would also benefit from the use of further sophisticated analysis. Analysis codes for certain forms of construction, especially half-through girders, often used on rail bridges, are known to be inherently conservative.

Solution
By utilising Non-linear Finite Element Buckling Analysis HBPW was able to remove those conservatisms, providing for full utilisation of the plastic capacity of the bridge’s girders.

In the case of New Cross Street, the edge girders were failing in shear, so engineers needed to use a Non-linear Finite Element Buckling Analysis to realise their full capacity. However, in addition to the under-capacity on the edge girders, the inner girders also failed the assessment, although engineers concluded that a buckling analysis would not yield the same benefits and was, therefore, of less value.

It was eventually proposed that a new concrete slab over the centre of the bridge be installed to improve load distribution and to remove the need for reliance on the deck plates which had also failed assessment. Consequently, deck plates could be ignored, and the girders only needed some simple strengthening following a less complex grillage analysis.

Outcome
The combined use of sophisticated analysis and simple strengthening significantly reduced the overall cost of getting the bridge to the required 40 Tonne capacity.