Security of performance

With the certification of steel being of growing importance in the UAE, Ben Bowsher, executive director, UK cares, discusses how manufacturers should go about providing the security of product performance.

COMMENT, Materials

The efficient use of reinforcing steel depends on the steel possessing, such as the correct mechanical properties, accurate cutting and bending and where applicable, technically sound prefabrication. The properties of the steel itself are determined principally by the steel manufacturer. This fact is important for steel bars and coils and consequently certification of the steel manufacturer has grown in importance to the degree that a large percentage of the UAE usage is now from CARES approved manufacturers. Unfortunately this is not so for those who fabricate and supply reinforcement to site.

The reinforcement fabricator is an important production link between the activity developing the mechanical properties and the construction site. Key responsibilities include maintenance of steel properties during cutting and bending; accuracy of cutting and bending; strict control of prefabrication; and traceability of steel.

A reinforcement fabricator must ensure that purchased material complies with specified requirements. CARES approved fabricators do this by buying only from CARES approved manufacturers, thereby negating the need for further inspection and testing at site. Contractors using reinforcement fabricators certificated by CARES may rely on this system. Failure to do so and instead to use suppliers not suitably certificated would put the onus of satisfaction on to the contractor.

The CARES scheme for reinforcement fabricators is based on an initial assessment and regular audits of each cutting and bending site against strict requirements.

The principal requirements of CARES in this key area are material sourcing and compliance; maintaining traceability; compliance with BS8666/BS4466; strict control of prefabrication, particularly when welding; quality plans for special non-standard requirements and documented complaints procedures of these activities, traceability and prefabrication merit further explanation.

Traceability

CARES require that cast identity of reinforcing steel be retained up to the point of delivery to site and that records permit the cut and bent bars, ready for fixing, to be traced back to the cast or casts from which they have been fabricated. This is achieved by recording the cast numbers against each bar schedule in the delivery and is retained in the fabricators internal documentation. In consequence, test certificates for this steel need not be passed on to the contractor but can be referred to when required. This procedure makes requests for copies of test certificates by contractors or engineers of limited value and could be usefully eliminated.

Prefabrication

Designers, engineers and contractors are increasingly seeing the benefits of specifying factory made pre-assembled welded fabrications to improve on-site productivity. Under controlled conditions, welding can provide efficient joining of reinforcement, robust enough to survive transportation, lifting and installation; when required, load bearing joints can be produced to specified strength levels; and pre-assembled welded fabrications can be manufactured into a range of shapes and sizes to suit applications such as pile reinforcement, beam and column cages and diaphragm walls.

Control of welding processes is vital, since the combination of heat input and rapid cooling rates has the potential to produce hard, brittle structures, susceptible to fracture. Improperly made welds also introduce defects into the material, such as cracks, pores and other stress raisers. These impair mechanical properties, and can act as initiation sites for failure.

All of the above effects can lead to degradation of material properties, whether the welds are locational (tack) welds, or structural welds. For this reason, all welding of reinforcing steel requires strict adherence to proven welding procedures and an acceptable level of welder competence. Welds must be fit for their intended purpose, whether they are load-bearing structural welds or non-load-bearing tack welds. Reinforcement fabricators need to demonstrate that welded assemblies meet the requirements of the reinforcing steel specifications, and are safe to transport, handle, lift and install. Improper welding can have severe effects on both the structural performance of the steel, and on the safety in use of welded assemblies.

Reinforcement fabrication

Reinforcement fabricators commonly claim not to need CARES approval because they use only steel from CARES-approved producers. All bar one of the reinforcement fabricators in the UAE remain outside this or any such product related certification scheme designed to provide the quality link in the supply chain from steel producer to site. As a result, CARES believe that contractors and clients are not receiving the security of product conformance that they should expect and sometimes believe they are getting.

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Construction Week in this column, please email angela.giuffrida@itp.com

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