Reinforcing steel

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Reinforcing bar BSt500 - on the left two bars with rolled-in ribs on both sides
Reinforcing bars in a foundation
Reinforcing steel for bored piles

Reinforcing steel , concrete reinforcing bars or reinforcing bars , formerly reinforcing steel , serves as a reinforcement (reinforcement) of reinforced concrete elements and after installation in the formwork with the concrete poured.

Shape and property

Today is in Germany exclusively reinforcing steel with a characteristic flow or yield strength of 500 N / mm² are used. The required properties are regulated , for example, in DIN 488 (formerly DIN 1045-1) or in the European standard EN 10080. The reinforcing steel is produced in various forms. The following are available in Germany:

  • Reinforcing bars B500B (according to DIN 488) (formerly "BSt 500 S (B)"), as hot-rolled and ribbed bars with diameters of 6, 8, 10, 12, 14, 16, 20, 25, 28, 32 and 40 mm and Delivery lengths up to 18 m (as special rolling up to 24 m). In Switzerland the diameters 6, 8, 10, 12, 14, 16, 18, 20, 22, 26, 30, 34 and 40 mm are available.
  • Reinforcing wire mesh B500A and B500B (according to DIN 488) (formerly "BSt 500 M (A) and (B)"), in different versions, as ready-welded mats made of ribbed and profiled as well as cold-formed steel bars (ductility class A) or hot-rolled reinforcing steel (ductility class B ) with diameters of 6 mm to 14 mm (14 mm only in highly ductile design, 6 to 12 mm in normal ductile or highly ductile design, welded wire mesh in ductility class B (highly ductile) are only produced on request, no storage),
  • Reinforcing steel in rings B500B (according to DIN 488) (formerly "BSt 500 S (B)") hot-rolled, in the diameter range from 6 to 16 mm and or B500A (according to DIN 488) (formerly "BSt 500 S (A)") cold ribbed , in the diameter range from 6 to 12 mm for further processing on straightening, cutting or stirrup bending machines.
  • Reinforcement wire B500A + G smooth or B500A + P with flat profile (according to DIN 488) in the diameter range from 4 to 12 mm for the reinforcement of e.g. B. reinforced concrete pipes or aerated concrete (formerly aerated concrete) or manhole components.
  • Lattice girders as rigid reinforcement for semi-finished ceilings and walls

In terms of their deformation properties, modern reinforcing steels are characterized by a modulus of elasticity of 200,000 to 210,000 N / mm² and the division into ductility classes. In Germany there is the normal ductile class A for cold-formed steels with a ratio between tensile strength and yield point of at least 1.05 and a steel elongation under maximum load of at least 2.5% and the highly ductile class B for hot-formed steels with at least 1.08 or 5%. In addition, the highly ductile earthquake steel class C with a ratio between tensile strength and yield point of at least 1.15 and a steel elongation under maximum load of at least 8%, which is used in parts of Europe and has a reduced yield point of 450 N / mm².

The average coefficient of thermal expansion for steel is the same as for concrete [1 / K], whereas the thermal conductivity of 50 [W / (m · K)] differs from concrete. Today's reinforcing steels are all suitable for welding .

Reinforcing steel set in concrete

An important property of reinforcing steel is its bond with the surrounding concrete. To improve the bond, ribs are rolled up or rolled on. The ribs have a maximum height of 4.5% and a spacing of 60% of the rod diameter. The ribs create a local interlocking between the concrete and the steel, which enables optimal power transmission over a short bond length.

Corrosion protection

Parking garage ceiling with hot-dip galvanized reinforcing steel

Possible causes for the corrosion of the reinforcing steel are flaws in the concrete due to cracks, gravel pockets or insufficient concrete cover, which allow the effect of chlorides from de-icing salt or the marine atmosphere. The cement stone contained in the concrete protects the reinforcing steel against corrosion due to its alkaline environment with a pH value of 12-14. With a value <10, this protection, the so-called passivation, is no longer ensured. As the concrete carbonates from the outside inwards over time (reaction of the alkaline hydrated lime contained in the concrete with air carbon dioxide to form limestone (Ca (OH) 2 + CO 2 → CaCO 3 + H 2 O)) and its pH value sinks, the reinforcing steel must be completely enclosed with a sufficient concrete cover. Tying the individual reinforcement elements together using wire ( tying ) and installing spacers (e.g. clamped-on plastic wheels or blocks made of concrete) between the formwork and reinforcement ensures that the reinforcement steel is in the planned position in the component with sufficient concrete cover.

Hot-dip galvanized reinforcing steel with Ü mark for general building inspectorate approval .

Reinforcing steel can be hot-dip galvanized or coated with epoxy for improved corrosion protection or as protection against rust runs in thin-walled exposed concrete components. Stainless steel is another option. The fiberglass reinforcement is relatively new . For smaller cross-sections, textile reinforcements, especially made of fiberglass fabrics, are also used.

To protect the reinforcing steel from corrosion as a result of carbonation or chloride penetration, cathodic corrosion protection with an impressed current anode, which is controlled by rectifiers with a protective current (actually only one polarization), can be used. This can be used, for example, in bridge construction .

All variants are subject to building supervision in Germany . This means that supporting structures that deviate from the standard require a building authority approval for the components used or approval in individual cases for the special building project by the state building authority. The German Institute for Structural Engineering keeps a list of reinforced elements approved by the building authorities .

Surface protection systems , such as the impregnation of the concrete surfaces with a water repellent or the application of coatings, also serve to improve the corrosion protection of the reinforcing steel, especially if the concrete is already carbonated to the depth of the steel (e.g. in the course of repairs).


Marking of reinforcing bars BSt500

Reinforcing bars

Today's reinforcing bars have two rib surfaces. One of the surfaces characterizes the type of reinforcing steel through a special arrangement of the inclined ribs. The other area bears the identification of the manufacturing plant, which follow one another at least every running meter. These begin with two widened inclined ribs, followed by the land between the widened inclined ribs and then the relevant plant. The field for the work can be divided into tens and units.

country Mark
Germany 1
Belgium, Luxembourg,
Netherlands, Switzerland
France 3
Italy 4th
Great Britain, Ireland 5
Sweden, Norway,
Denmark, Finland
Spain, Portugal 7th
Greece, Latvia, Moldova, Austria,
Poland, Czech Republic, Turkey, Hungary
Bulgaria, China, Croatia, Moldova,
Poland, Romania, Turkey, Ukraine,

Notes: There are Polish, Turkish and Moldovan reinforcing bar manufacturers in both country groups 8 and 9.

Further reinforcement elements

Threaded steel is a reinforcing or prestressing steel with inclined ribs that are thread-like and manufactured by various companies. It was developed for reinforcement technology in order to enable a mechanical connection via screw sockets . Today the thread steel is also used in geotechnical engineering as a grouted pile and ground anchor .

There are double-headed anchors and dowel bars as a replacement for shear reinforcement.

Approved non-metallic GRP reinforcement can also be used in components with special requirements for corrosion , machining or electrical / magnetic properties .


Patent drawing 1878

Inventor of the iron reinforcement was the Frenchman Joseph Monier , according to him is called the reinforcement (Monierung) also Moniereisen (Under Construction jargon often as the verb "complain" pronounced). Monier was a gardener and was annoyed that the concrete planters for the portable orange trees in the manorial gardens he looked after broke too often. Other older, but still used names today are reinforcing steel (as opposed to structural steel ) or slack steel (as opposed to prestressing steel ).

Reinforcing steels cold-worked by torsion have an increased strength. They are known as TOR steel and for a long time were characterized by a twisted longitudinal rib from the roll protrusions, which has a favorable effect on the bond with the concrete. TOR steel was invented by the Austrian Rudolf Schmidt in 1936/1937. The name is still in use in Austria.

Rebar is now reaching the standard mechanical properties mostly on the developed in the 1970s Tempcore process hardened directly from the rolling heat or wire cold drawn . Strength is seldom achieved using alloys alone.

The reinforcement to be installed in reinforced concrete components is shown and dimensioned on drawings (installation plans) with regard to number, diameter, shape and position. Separate steel lists can also be created for ordering the reinforcement.

Development in Germany

Until the mid-1930s, no special reinforcing steel was used as reinforcement, but bars, flat iron and profiles with a smooth surface and a yield point of around or more than 250 N / mm². The activation of the load-bearing capacity of the smooth steel took place less through the bond between concrete and steel than primarily through the anchoring with hooks and loops. The Isteg steel, consisting of two wires made of smooth structural steel, which were stranded to form a 2-wire strand, was the first special German reinforcing steel with improved bonding properties from 1933. At the same time, the structural steel mesh, consisting of mats or rolls (up to 6 mm), was approved in Germany. From 1935 onwards, high-strength reinforcing steels were developed to save material by twisting round steel bars, initially without transverse ribs. In 1937 the reinforcing steel was divided into groups. Group I comprised the BSt 22/34 with a minimum yield strength of 220 N / mm², Group II the BSt 34/50 with a minimum yield strength of 340 N / mm², and Group III the BSt 42/50 with a minimum yield strength of 420 N / mm², and group IV corresponds to today's reinforcing steels. In the case of recalculations or the reinforcement of old structures, the strength of the old steel types must be taken into account in static calculations.

From 1959, the high-quality diagonally ribbed ribbed gate steel was approved by the building authorities as reinforcing steel IIIb. This was additionally cold-formed (in the factory) by twisting (twisting of torsion - hence the “gate” in the name) to increase strength. The current rib shape was finally developed from 1961 to improve the fatigue strength of reinforcing steel IV.

group designation Diameter
min. Yield point
[N / mm²]
Tensile strength
[N / mm²]
min. Elongation at break
I. BSt 22/34 - 220 340-500 18th
IIa BSt 34/50
( naturally hard)
≤ 18
IIb Special concrete steel BSt 34/50
(cold drawn)
≤ 18
≥ 500 14th
IIIa BSt 42/50 <18
> 18
≥ 500 18
IIIb Gate steel BSt 42/50 <18
> 18
≥ 500 18
IVa BSt 500A - 500 - 16
IVb BSt 500B welded wire
- 500 - 8th


  • Dieter Rußwurm: Reinforcing steels for reinforced concrete construction . 1993, ISBN 3-7625-3078-5 .
  • Peter Bindseil: Reinforcing steels - from the beginning of reinforced concrete construction to the present . ISBN 3-345-00803-3 .
  • Hansgerd Kampf: Reinforcement technology - basics-practice-examples-economy . Vieweg and Teubner, Wiesbaden 2010, ISBN 978-3-8348-0767-0 .

Web links

Commons : Reinforcing Steel  - Collection of pictures, videos and audio files
Wiktionary: Moniereisen  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1.  ( page no longer available , search in web archives )@1@ 2Template: Toter Link /
  2. Entry on reinforcing steel in the Austria Forum  (in the AEIOU Austria Lexicon )
  3. GCO Lohmeyer: Reinforcement of reinforced concrete components . In: Stahlbetonbau, Wiesbaden 1990, ISBN 978-3-663-11484-0 .