Load Rating for Road Asset Manager

A road asset manager was undertaking a program of asset assessments to improve the accessibility of its bridges and culverts for heavy vehicles. To assist with this program, Sterling undertook Level 2 inspections and load rating assessments of 12 road bridges in Victoria and South Australia. The bridges included precast concrete super-Ts, steel I-girders with concrete decks and precast inverted-U decks.

The client required a comprehensive understanding of the bridges’ performance for a real set of vehicular loads and required an understanding of how defects impacted the performance.

Drawing upon our long and successful history of undertaking load rating assessments of many bridge forms for road and rail clients across Australia, Sterling completed physical site inspections, undertook desktop load rating assessments to AS5100.7 using 3D grillage models, and incorporated observed defects into the load rating assessment.

To reflect real loading scenarios, up to 20 design vehicles were analysed for each bridge, with each vehicle occupying up to four positions on the deck. These generated thousands of loading permutations which made standard design techniques inefficient.  The team developed a bespoke tool for efficiently post-processing the Spacegass data, reducing the time required to fully analyse a bridge by approximately 80%.

In addition, several of the bridges were built using a now-obsolete form: inverted-U deck units with unstressed transverse bars.  The behaviour of these structure – torsion and transverse load redistribution – is complex and difficult to quantify. To avoid undue conservatism, Sterling undertook a detailed analysis of the structures’ transverse behaviour to ‘tune’ the models and best represent the physical reality.

Sterling’s ultimate deliverable was a summary of all bridges’ load carrying performance under the full suite of loads and recommendations for remediation where load carrying capacity was deemed to be inadequate.