2.3 Principal inspections

These are planned periodic inspections. They consist of a more detailed inspection of the structure generally from within touching distance, and often involving a certain amount of non-destructive testing. They will normally be undertaken by qualified bridge engineers, either from local consultants or from the DOR Bridge Unit. The frequency of these inspections will probably be between five and eight years. New bridges however should have a Principal Inspection as soon as practicable after completion and again four or five years later. This is to ensure that latent defects are recorded and appropriate action taken within the limitation period.

Comprehensive access equipment may be needed for some bridges, such as scaffolding and/or platforms suspended from the bridge deck.

Report forms for the Principal Inspection are given in Appendix C. The forms comprise fifteen master pages which detail the condition of each bridge component element including associated works, such as embankments and bridge protection works. Not all of the forms are used, this depends on the structure that is being inspected, however on occasion extra copies of some of the forms are to be completed, for example on large multi-span bridges. The Bridge Inspection Report Form - Bridge Identification and the Bridge Inspection Summary forms are also filled in.

The Principal Inspection is enhanced by a comprehensive report which will include site sketches, description of structure and inspection, maintenance history, photographs, notes, test results and interpretations of the results and other data.

The Department’s standard rating system for bridges is used for Principal Inspections.

Other more specialised equipment such as paint thickness gauge, a depth of cover meter for reinforcement and tell tales may be needed on occasions. Typical special inspection equipment is described in Appendix E, Testing, Methods of Testing, Special Testing Equipment

The Principal Inspection not only forms a basis to determine maintenance activities, but also forms an historical record of the bridge condition at a fixed time in the life of the structure. Analysis of the results help the designer to determine the time related performance of both structural configurations and associated component parts. It is important to rectify those repetitively weak design solutions that are the source of constant maintenance problems.

Analysis of the bridge ratings provide a deterministic means to verify that the unit value of the national bridge assets are being maintained. As such they can form an important guide as to future maintenance investment levels.

2.6 Summary

The different types of inspection described above are summarised in the following table.

*Initially more frequent for a new structure