Reinforced concrete
reinforced concrete , an artificial building material, is a composite material from the two components concrete and reinforcing steel.
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components
concrete
see major item concrete
concrete is an artificial rock from cement, concrete addition (sand and gravel or split) and water. This building material is inexpensiveto manufacture, simply ductile and particularly suitably for massive construction units. Its mechanical characteristics are characterized by a relatively high pressure strength as well as a low tensile strength (approximate 10% of the pressure strength).
reinforcing steel
see major item reinforcing steel
reinforcing steel, also as reinforcing steels designation, is a special, nowadays serrated or formed round stole with a high tensile strength. This is built into the formwork of the construction unit and concreted afterwards. The reinforcing steels are completely wrapped by the concrete, whichthe group between both building materials causes.
carrying behavior
the group between the concrete and the reinforcing steels results from the adhesion of the bonding agent cement (detention group), by the friction between steel and concrete (friction group) and by thatdue to serrating the reinforcing steels produced form closure (Scherverbund). In ungerissenem reinforced concrete the stretches of the two building materials are equally large. This condition, without relative displacements between concrete and steel, is called also perfect group.
Unbewehrter concrete fails during tensile stress (z. B. Bending course) due to its brittleness without announcing cracking suddenly. This happens in the comparison to the compression stress already during small load, since the tensile strength is small. For this reason the course-stressed ranges of the concrete will provide with reinforcing steel, which is concrete-encased. Therethe concrete after course the large stretches of the steel not to follow can, tears it within the course range. In the range of a tear then only the reinforcing bars are effective. Course and/or. to bend-course-stress construction units can be measured and manufactured therefore in such a way that itselfthe construction unit failure by an intensive cracking and significant deformations in front-quits. With construction units, which are stressed on pressure, steel cores can increase the load-carrying capacity to pressure.
A condition for the application of the composite material reinforced concrete are in approximately equal to large Wärmeausdehnungskoeffizienten (10 -5according to the reinforced concrete standards) of steel and concrete, which entails with changes of temperature in approximately equal large thermal expansions of the two materials and thus reinforced concrete causes no considerable internal voltages in the composite material.
tears
Due to the carrying behavior tear is as a rule possible and permissible with the composite building material reinforced concrete. Only special construction components, like base plates of gas stations, must be tear-free, which by appropriate construction unit geometry and expansion joints or linking up is guaranteed. Otherwise the tears may, depending uponEnvironmental condition and use of the construction unit, computationally not more broadly than 0.1 to 0.4 mm its. A constructional measure against to large tear widths is inserting a sufficient armouring, which does not prevent the tears, but but ensures that instead of some less,according to broad tear more however narrow and thus harmless tears develop. Surface cracks are to be differentiated from these unavoidable constructional tears, which are in principle unwanted and frequently concrete-technological reasons have, like an unfavorable fresh concrete composition (with e.g. to high heat of hydration development), onenot normal concrete installation and a insufficient subsequent treatment of the fresh concrete surface.
building chemistry of the reinforced concrete
a further condition for the composite material is the hardened cement paste in the concrete and its alkaline environment with a pH value of 10-11, that the reinforcing steel before corrosionprotects. Thus a durable corrosion protection of the steel is guaranteed during sufficient concrete covering.
armouring cover
a sufficient armouring cover, in Germany usually as concrete covering designation, is necessary with reinforced concrete compound units, around the necessary group between concrete and armouring, a sufficient durabilityto guarantee the construction unit as well as an appropriate fire resistance. Due to the necessary group the armouring cover should correspond to the reinforcing steel diameter at least. From the environmental condition necessary concrete covering over the reinforcing steels results according to the DIN 1045-1 for the necessary durability. Smaller than 15mm may not be it, usually is 20 to 50 mm. Concrete covering is ensured by measuring rods and support supports and/or. - baskets. Support supports consist usually of according to curved reinforcing steels and particularly for the upper armouring situation by plates are used. Measuring rodagainst it for the Sicherstellung of the distance between armouring and formwork are used. This gives it in most diverse variations. Among other things small Klötzchen or queues from concrete can do and/or. Fiber-reinforced concrete its, besides also borders or rings from plastic are usual.
special fittings
beside the reinforcing steels according to plan also different elements are concreted. These are called special fittings. They serve usually the attachment of elements at the reinforced concrete compound unit, like for example structural steelworks. In addition count among other things Anchor plates and anchor rails. Further special fittings,like peg borders or rope loops, replace a geometrically difficult and aufwändige reinforcing steel armouring by a developed “structural steelwork” special for the demand of the concrete.
meaning and application
reinforced concrete is the universal material 20. Century. Is thatConcrete also over 100 million cubic meters in the year the most important building material of Germany, during the portion of the reinforcing steels of the steel production in Germany approx. 12% and/or. approximately 6 million tons amounts to. The employment of reinforced concrete instead of the unbewehrten concrete is always then necessarily, if in the construction unit tensions can occur, those larger to be can than the tensile strength of the concrete. Compared with other building materials, like steel, wood or plastic, its application is meaningful whenever no filigranen and easyCarrying structures are necessary. As the employment shows with the building of shelters, reinforced concrete is suitable when sufficient dimensions also for extreme effects. In particular the non-combustibleness and the high fire resistance are favourable. Borders with the use of the building material result outthe high dead weight of the concrete, which increases and with slim constructions due to the cracking to large deformations leads the necessary reinforcing steel quantity as dead load. In these cases the employment of a composite structure is better or from prestressed concrete. The prestressed concrete differsof the reinforced concrete by a regular pre-loading (=Vordehnung) of the steel cores, the tendons in such a way specified. Thus an additional outside pressure longitudinal force is applied, whereby the tensions are overprinted and a cracking, the construction unit deformation, strongly are thus reduced.
history
basisthe development were the invention Romanzement in the year 1798 by the Englishman of the J. Parker and portland cement by the Englishman the J. Aspdin in the year 1824.
In the center 19. Century in France concrete construction units were strengthened for the first time by steel cores.1855 built J. L. Lambot a boat from iron-strengthened cement mortar, since 1861 placed the gardner Joseph criticize planting excavator buckets from cement mortar ago, which he strengthened with an iron network, so that they did not break so easily. it received on it a patent to 1867.To the today hot used round iron bars concrete reinforcing steel bars. Older names for reinforced concrete are Eisenbeton and Monierbeton. Already 1861 published F. Coignet of principles for the use of reinforced concrete and placed 1867 on the world exhibition in of Paris carriers and tubesfrom reinforced concrete. The property tenant Joseph Loius Lambot announced 1855 a patent for a new “timber construction material”, which called he “Ferciment”. The following can be taken from its patent specification:“My invention has a new product to the article, which serves for it, thatTo replace wood in the building of ships and everywhere, where it is humidity-endangered,…. I give a form, which in the optimum measure to the article is adapted to this net (from wire and staffs), which I want to manufacture and bed it afterwards inhydraulic Cement or like as bitumen, tar or their mixtures… “ this patent was then extended by Coignet. Parallel to French engineers the American attorney Thadeus Hyatt accomplished since 1855 attempts over the use of steel cores in concrete.In its basic patent of 1878 it wrote:" ... Hydraulics cements and of concretes of acres combined with metal bear and rods, so as tons of form slabs, beams and of arches. The tensible strength OF the metal is only utilized by the position,in which is placed in slabs, beams etc. it. … “. Hyatt had recognized the structural effect.
In Germany acquired 1885 G. Wayss and A. Freytag the Monierpatente. In the same year Wayss met the master of building of governments Matthias Koenen, that the linethe realm tag building then under construction was subject. After eliminating doubts because of the corrosion danger, adhesive strength and different temperature strains as well as due to attempts, Koenen decided to use the new system. Its realizations arranged to write it a brochure, the Wayss1887 under the title “the system criticize in its application to the entire building industry” gave change. Emil a little later brought a first scientifically justified representation of the impact of the Eisenbetons to rotten, how the reinforced concrete was called until 1920. This was published 1902.In addition Emil accomplished rotten as one of the first extensive test series. He was finally bridges and building of iron concrete at the technical university Stuttgart, curved from 1916 to 1948 a professor for statics of the solid wing units, and has there the calculation procedures for reinforced concretecrucially along.
See also: Overlapping joint prestressed concrete
literature
- K. Mountain master and J. - D. Wörner: Concrete calendar 2005. Ernst & Sohn 2004, ISBN 3-433-01670-4
- F. Leonhardt and E. Mönnig: Lectures on massive construction. Third part: Bases for reinforcing in the reinforced concrete construction.Springer publishing house Berlin, ISBN 3-540-08121-6
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