2.4 Special inspections

Special inspections may be needed if a structure is at risk, or if there is a problem requiring further investigation. The frequency will therefore vary, and the person undertaking the inspection will vary according to the circumstances. For instance a qualified bridge engineer will be needed to investigate a serious structural defect, but inspection of a flood damaged bridge might be undertaken on a daily basis by an engineer.

The inspection may comprise a close examination of a particular area or defect causing concern. This may be extended to the whole of the structure depending on the condition or level of deterioration.

In some cases access equipment may not be needed. On other occasions it may be necessary to employ specialist inspection firms and equipment.

Examples of times when a Special Inspection shall be carried out are:

• When further detailed examination is needed to investigate a special problem, either found during inspection or already discovered on other similar structures.
• For structures which have weight or other restrictions to reduce traffic loading. These inspections shall be at intervals not exceeding six months.
• When a structure has to carry an abnormal heavy load. The inspection takes place before, during and after the passage of the load if either an assessment has indicated that the margin of safety is below the current design stansard, or, similar loads are not known to have been carried by the bridge.
• In locations where ground movement is suspected or is taking place. Steps need to be taken to monitor the rate of movement and to assess the urgency of remedial measures.
• If settlement is observed greater than that allowed for in the design. The cause will need to be identified and steps taken to monitor the rate of settlement and to assess the urgency of remedial measures.
• To river bridge foundations and embankments after flooding. Where probing indicates the possibility of scour, further underwater inspection shall be carried out.
• After a major accident, chemical or fuel spillage or fire adjacent to a structure, to investigate possible damage to the structure.
• After a significant earthquake to investigate possible damage to the structure.
• For special bridges, such as Karnali for special circumstances.
• On hoists and winches that are used for access - prior to use and at prescribed intervals - in accordance with HED and inspection manual requirements.

Reporting will vary with the composition and cause of the special inspection. For a simple check after a flood the Superficial Inspection Report Form may be used. For more comprehensive investigations all or part of the Principal Inspection forms may be used augmented where necessary with additional detail and/or specialist reports. Specialist access or equipment inspection may be called for.

2.6 Summary

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

*Initially more frequent for a new structure