Inspection of works on site during construction is a high-risk activity which requires skill and experience. Inspections are of the utmost importance as they help to reduce the risk of defects being present within the structure of the building – although they can never guarantee it. They should only be performed by those who are familiar with the design of the works and the limitations of construction methods.
The construction phase of a project is the stage where its design is implemented. Unforeseen variables have an impact on the assumptions made and changes may occur to the original design. Workmanship is also important, as the structural model used in design assumes good practice will be followed on site. For materials for which the partial factors used in design vary depending on the level of workmanship/supervision, it is essential to confirm that design assumptions have not been jeopardised.
It is typically the responsibility of the main contractor, supported by the specialist contractors’ designers, to ensure that the works are delivered in accordance with the design documentation.
The principal way workmanship is assured is through supervision and oversight by the main contractor. Any inspection carried out by the client’s design team, including by the structural engineer, will be in addition to the contractor’s monitoring of progress of the works. Nonetheless, it is good practice for such supplemental inspections to occur.
Before attending site, it is important that the inspecting engineer understands the scope of the site inspection and its purpose; any review can only be based on a sampling of the works that are available at the time. Where intrusive works are required to achieve the objective of the inspection, the inspecting engineer must provide a detailed specification of what is to be done. Before attending site, they should confirm that the necessary opening-up works have been completed.
This Technical Guidance Note concerns the inspection of structural elements that are typically present within buildings during their construction and/or alteration. It describes the elements, aspects of the elements which consistently prove to be problematic and, to some extent, how to detect defects. The note assumes that the inspecting engineer has suitable levels of competency.
It should also be borne in mind that, no matter who is employing the engineer, they have a duty of care to the public to ensure a building is safe.
This note contains an error in Figure 2. The figure describes the indentation pattern on the surface of the concrete as ‘plastic settlement’, when in fact it is the far more common and benign effect of ‘reinforcement ripple’.
Further information on reinforcement ripple can be found in Concrete Advice Sheet No. 6 Reinforcement ripple, and further information on plastic settlement can be found in Technical Report 22 Non-structural cracks in concrete. Both texts are published by the Concrete Society.