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Reinforcing bar

Reassure

Celsa have a strong commitment to innovation and development. We are constantly striving to improve our processes, activities and technology in order to enhance the quality of our products. In line with the new ductility recommendations in Eurocode 2, we developed high ductility Grade 500C reinforcement.

The next stage of the innovation process is to develop a product with improved material quality and performance levels which performs above that specified by current standards. This product is called:

Reassure is a trademark for grade 500C reinforcement that has specific added value. Currently under development, Reassure material is subject to a significant amount of mechanical testing, across a range of diameters. Research has shown that Reassure material offers significantly better tensile, fatigue, bond and cyclic behaviour than the grade 500C material referred to in the standards. Ongoing mechanical testing aims to build a database of test data to back this up, giving designers the necessary confidence required to take advantage of these additional performance levels.

The quality and performance of the steel that carries the Reassure mark will exceed current British and European standards; therefore Reassure products will be guaranteed to comply with these standards. Products that are part of the Reassure brand will be easily identifiable by the RE✓ mark that is rolled at regular intervals on the surface of the bar or coil.

This improvement will be invaluable to engineers in applications where the inherent robustness of reinforced concrete is an invaluable asset: for example, in overload conditions, when last-minute design changes are made, when additional fatigue requirements are necessary, and where cyclic performance is important.

How have the standards changed to include ductility?

The introduction of Eurocode 2 for the design of concrete structures as the UK design standard, recognised the importance of ductility in reinforcing steel. New parameters for the specification of steel ductility have been introduced, in both Eurocode 2 and in material standards. Eurocode 2 recognises three different reinforcing steel classes (A, B and C) based on ductitlity. Design rules now recognise the importance of steel ductility and provide designers with the means of using the additional ductility provided by high ductility steels.

The British Standard for reinforcing steels (BS 4449) has been revised to reflect the ductility parameters of Eurocode 2. As well as increasing the characteristic yield strength from 460MPa to 500MPa, BS 4449: 2005 introduced Grade 500C reinforcing steel.

What are the advantages of using Celsa Reassure Grade 500C?

1. It is the highest quality reinforcing product available for specification in the UK with the new Eurocodes and standards.
2. It is a minimum of 50% more ductile than standard Grade B material.
3. Due to the way in which we manufacture it, we charge no more for this product than we do for 500B.
4. It is the only grade used in Spain and Portugal and can already be produced by many mills in Europe.
5. As Grade 500C achieves (and exceeds) all of the requirements for Grades 500A and 500B, and as there is never a reason as to why having more ductility is worse (only better), it is the only grade of reinforcement that we produce.
6. It performs in exactly the same way as standard reinforcement until significantly past its yield point – therefore makes no difference in terms of elastic design.
7. Its excessive plastic deformation can help designers in terms of increased moment redistribution or plastic design.
8. Its ability to deform has its most obvious benefits in terms of resisting overload conditions and robustness. Incidents such as explosions that may remove key structural elements, flooding, accidental damage, etc will all have reduced impact if Grade 500C reinforcement is used.

The advantages of using 500C over other reinforcing grades has been demonstrated in a number of laboratory load tests carried out by Cardiff University. Three concrete beams of dimensions 100 x 250 x 2500 mm were cast using the same concrete mix proportions giving a 28 day strength of 40 N/mm2. Each concrete beam contained two 8mm reinforcing bars in the top and bottom of the beam, as well as standard steel confinement. The only difference between each beam was that the main reinforcement in each beam was grade: 500A, 500B and 500C. Each beam was subjected to two point loading at the same rate.

The animation below represents a speeded up version of the test:

As can be seen from the results, the deflection at failure of the beam containing Grade 500C reinforcement was over 5 times greater than the beam containing Grade 500A reinforcement, and more than twice that of the beam containing Grade 500B reinforcement. In other words, ductility = safety!

Since each beam behaves the same until the steel yields in all cases, it is the behaviour after this point which is important. The additional ductility inherent in the Grade 500C steel ensures that reinforced concrete made with this steel will enable load to be carried much longer after yield.

How do you identify Grade 500C reinforcement?

In order to allow Grade 500C material to be easily identifiable from Grade 500A and B material, a new rib pattern has been introduced which has been specified in BS 4449:2005. The distinctive double-angled pattern is different from the herring bone pattern of Grades 500A and B, as shown below:

Grade B500A and B500B Reinforcement

Grade B500C Reinforcement

Further Information

We have a selection of technical and non-technical documents containing information on Celsa Reassure Grade 500C reinforcement. These can be downloaded from our downloads section.