Key Terms

Tier 1 bridge assessments are performed using the reference vehicle technique, comparing the worst load effects of an application vehicle on a given structure compared to a reference vehicle which would be considered suitable to travel over the structure. Key inputs to the assessment are:

• Span Length
• Span Continuity
• Design Vehicle or known Acceptable Loading Configuration
• Level 2 Structure Condition (includes design drawings fully defining all geometry and reinforcing, any material specifications used that define required material performance and as-built records – whether as-built drawings if available).

A Tier 2 bridge assessment focuses on using structural engineering principles to identify the theoretical maximum load effects the structure can withstand as governed by the material and configuration (capacity assessment). Two-dimensional analysis techniques such as a grillage analysis or a line model analysis using girder distribution factors are typically used to determine the theoretical loads from the application vehicle load case. The results of the loading analysis are then compared to a theoretical estimate of the structural capacity of each member of the bridge.

Key inputs to the assessment are:

• As-Built Drawings (if available),
• Component Geometries and Material Properties to construct analytical models,
• Site Measurements (if necessary),
• Assessment Vehicles, and Level 2 Structure Condition.

Where assets do not have the capacity to support the desired heavy vehicle movements on the network an Asset Improvement Report will outline the actions required to improve the asset capacity; repair or renewal.