Little Cheverell

Little Cheverell is a single span bridge, at a 45 degree skew, carrying Cheverell Road over two tracks of the Stert and Westbury Line (SWY) between Stert and Westbury. The superstructure consists of early steel main girders and transverse troughing in half-through formation. The substructure comprises engineering brickwork abutments flanked by engineering brickwork wingwalls at each corner.

The original structure was built in circa 1899 and raised to its current level at date unknown, presumably to increase the headroom and/or accommodate track lifts.  

Scope of services

Nuttall Bowser undertook repair scoping survey to establish repairs required to meet a 25-year major maintenance free period, achieve a condition rating BCMI score of above 60 and strengthen the bridge above the current 7.5T weight limit.  

Nuttall Bowser subsequently undertook detailed design for repair, strengthening and remedial works to various defects including main girder bottom flanges, main girder webs, repairs to padstones and the addition of edge protection to the wingwalls.  Nuttall Bowser provided construction site support to accommodate alternative web repair construction methodology.

Challenges

The webs of the main girders are partially hidden due to the haunching to half height to the internal faces and presence of the trough deck supported at bottom flange level.

There are previous repairs present with bolted connections adjacent to locations requiring further repairs/strengthening. The presence of the trough decking presented access limitations for the installation of new flange plating.

There were numerous repairs with interacting elements namely the flange repairs, flange angle repairs and web repairs to the main girders.

Value added

Nuttall Bowser presented our clients with alternative web repair connection concepts to alleviate access constraints and provide options to the fabricator ahead of the undertaking the main works to aid access planning. 

Nuttall Bowser held constructability reviews with the principal contractor and fabricator to establish a construction methodology and ensure a clear understanding of permitted loading during repair works and works sequencing. 

In order to ensure strengthening requirements were achieved Nuttall Bowser undertook structural assessment of key bridge elements to ensure repairs/strengthening met required strength requirements and that additional repair weight did not adversely affect assessed capacity ratings of non-strengthened parts.

The detailed drawings provided clear sequence of works per repair with specific focus on interacting repairs and the requirement for temporary connectors. Nuttall Bowser detailed design drawings provided clear requirements for overall sequence, whether live load was permitted and the requirements for completion of prior work stages.

For locations of adjacent previous bolted repairs Nuttall Bowser employed over sized holes and top hat sleeve solution (enabling conversion to regular sized holes to enable repair/strengthening plates to be offered up the bridge without the removal of bolted connections in mass - thus enabling a safe bolt replacement methodology on a one out one in basis as per standard best practice.