Bar Reinforcements - Products
Soil Bar Reinforcement Info
Standards and specifications for the manufacture and processing of reinforcing steel are well established, although they have gone through a series of changes over recent years. The specifications which cover design of concrete structures are also well established, including those parts which refer to the manufacture and use of reinforcing steel and associated processed reinforcement. The following three grades of reinforcing steel are specified by
• BS44419;2OO5
• BS414149;2OO5 Grade BBOOA
• BS441419:2OO5 Grade B5OOB
• BS4l4119;2OO5 Grade BBOOC
These designations describe steel with a yield strength of 500MPa. Within this description of grade, the capital letter B preceding the yield strength denotes reinforcing steel.
The capital letters A, B and C following the yield strength denote the ductility class, with A being the lowest.
With the exception of BS4449 Grade B5OOA in sizes below 8mm diameter, these conform to the three ductility classes of BS EN 19924-1 :2004, Annex C.
Use of the correct grade of ductility is important, as greater ductility assists in ensuring structure robustness. lt has been concluded that a minimum ductility class of B is needed if more than 20% moment re-distribution has been used in design to BS EN 1992-1-1.
For common building structures, i.e. those designed to 558110, use of steel bars of ductility class A in sizes 12mm and below is not of concern, as it is unlikely that in flexure the members concerned will be structurally significant.
In bridges however, steel of ductility class B is required to ensure that the usual assumptions made regarding adequacy of elastic global analysis can be made. As a result, reinforcing steel with a minimum of ductility class B should be used in bridges and in any other structure where moment redistribution of greater than 20% has been assumed in design. Key concrete construction specifications such as the
National Structural Concrete Specification and the Specification for Highway works are clear in their approach to the use of steel with a particular ductility. The National Structural Concrete Specification requires reinforcement to ductility class B, and that care should be taken to avoid inappropriate use of material to ductility class A. The Specification for Highway Works requires ductility classB or C for structural applications.
Whilst BS4449 GradeB5OOA reinforcement is excluded in structural applications under the Specification for Highway works, Grade BBOOA fabric reinforcement is permitted, provided that this is not taken into account in ultimate limit state verifications.
Further information is provided in the Highways Agency’s Interim Advice
Note: lAN 70/06.
Despite what might therefore seem an orderly situation in design terms, there has been concern expressed that reinforcing steel of the required level of ductility is not being received by the contractor at site.
The construction specification specifies strength and ductility levels by reference to BS4449. Reinforcement fabricators invariably produce cut and cut and bent shapes, not directly from specifications however, but from cutting and bending schedules.
The cutting and bending schedule is therefore the vehicle by which the requirements of the construction specification are transmitted from the designer, via the reinforcement detailer, to the reinforcement fabricator. lt does this by using BS8666: 2005, the specification for reinforcement scheduling, dimensioning, bending and cutting of steel reinforcement. Table 1 of BSSGGG specifies the grade of steel to be used via a system of steel notation.
Unfortunately it seems that the requirements of the specification, via this notation, are often not transferred accurately on to the cutting and bending schedules.
The steel notation which receives almost universal use is that of H. This allows the reinforcement fabricator to use either Grades BEOOA, B or C.
Whilst the most commonly stocked steel grades in the Ul< are that of Grade
BEOOB and also Grade BBOOC, there is a significant amount of Grade BBOOA
stocked, mainly in the sizes 8mm through to l2mm in diameter, although sizes up to 16mm diameter can be found. It is in these larger bar sizes, particularly in loose straight bars, that the supply of Grade BBOOA steel is creating most concern to designers.
ln sizes 12mm diameter and below, particularly when used by the reinforcement fabricator in coil form for use on his automatic link bending machines, Grade BBOOA is a popular product, This is because that, despite being the least ductile of the grades included in BS4449, the process commonly used in its manufacture tends to lead to a bar which is easier to "work". As a result, greater accuracy of bending can be achieved, enabling tighter tolerances. The use of Grade BEOOA reinforcing steel in the manufacture of links therefore minimises the risk of an oversize product which may reduce the concrete cover. This may in turn decrease reject rates or supplied reinforcement at the customer. Pre-cast concrete
producers eften apprecrate this.
Taking account of the use ot BSBGGG in the relationship between the design specification and the steel supplied, BSSGGG has recently been amended with the intention of reducing the risk of steel with inappropriate ductility being delivered to the construction site.
Table l of BS8666, Notation of Steel Reinforcement, has been amended with the result that, for steels of diameters up to and including 12mm when using the notation H, Grades BBOOA, B or C may be supplied at the discretion of the reinforcement fabricator. For bar diameters above 12mm, the notation H will require
that Grades BBOOB or C be supplied.
BS8666 allows other specific ductility classes to be specified.
Grade BBOOC is likely to be needed in particular circumstances or for design to resist seismic forces.
To corordrnate current NSCS specifications vvith this change, until the next edition resolves the discrepancy, the following standard change to the NSCS should be
incorporated in section P1.5i:
Schedule.doc
