MAPPING AS-BUILT DETAILS OF A BRIDGE APPROACH STRUCTURE

OBJECTIVES

TRACE was instructed to undertake a non-intrusive structural investigation of a cantilever span box beam within a bridge approach structure. The investigation was required to resolve discrepancies in existing records by determining the as-built configuration of the box beam, with particular focus on the presence and location, of post-tensioning tendons and anchorages.

SOLUTIONS

TRACE developed a bespoke NIA investigation strategy combining complementary non-intrusive techniques: GPR and eddy current system. A nominated section of the cantilever span was investigated with scanning undertaken from the soffit and side elevations only due to access constraints, with access to the structure achieved via MEWP.

Intrusive coring was planned to supplement the investigation. However, this was suspended on site due to the potential presence of asbestos-containing material. The non-intrusive findings were therefore used to guide future the investigation strategy.

KEY FINDINGS

The investigation successfully established the as-built construction details of the nominated box beam section, including:

• Confirmation of the presence and alignment of post-tensioning tendons

• Identification of anchorage locations using consistent, repeatable non-intrusive indicators

• Improved understanding of the internal configuration and condition of the box beam cell

The findings were delivered with a high level of confidence, providing engineers with reliable structural evidence to support decision-making.

BENEFITS

TRACE’s bespoke investigation enabled the client to confirm critical as-built information without the need for intrusive intervention, significantly reducing risk to both the structure and site operatives. This was particularly important given the potential presence of asbestos. The works were delivered efficiently despite constrained access and night-time working conditions, minimising disruption while maintaining programme certainty. TRACE also provided clear recommendations for next steps, identifying where further targeted investigation would deliver additional insight into specific areas of the structure.