Reinforced concrete is one of the greatest inventions of modern architecture. It continues to be one of the main materials that shape our world, thanks to totally new and unprecedented forms, bold cantilevers and many innovations that it brought.
From Concrete to Reinforced Concrete – Historical Development
Pozzolan concrete that Romans found has been developed in the historical process and contributed to the formation of modern concrete used in reinforced concrete systems today. The fact that concrete is only resistant to pressure when used alone and that it is impossible to produce high-rise, durable structures has been required new searches and techniques.
After John Smeaton discovered modern concrete, Louis Vicat produced cement by artificial means in 1812. In 1842, Joseph Aspdin found Portland Cement and formed the basis of today’s reinforced concrete material. All these new searches led to the most important unity in the history of building production: Concrete and Steel, also known as Reinforced Concrete…
- French farmer Joseph Lambot, who made a concrete canoe with a mixture of concrete and iron in 1848, exhibited this product at the Paris World’s Fair in 1855.
- French Engineers Coignet and Monier got the reinforced concrete patent in 1855.
- Engineer François Coignet produced walls and flooring with reinforced concrete materials in 1855 and used them in a structure.
- In 1867, Joseph Monier, the French gardener, designed a flowerpot for his flowers with the help of concrete and iron sticks and patented this new material.
- William E. Ward, whose houses were damaged by fire in the 1870s, designed a house for his family to protect them from fire danger. This building is known as the first house of America built with reinforced concrete.
- In 1892, François Hennebique took the use of reinforced concrete a step further in the building industry and discovered the T-beam. Also for the first time, He used the stirrup that allows the steel reinforcements to adhere better to concrete.
- Pont de Chatellerault, France’s first reinforced concrete bridge, was built in 1899 by Hennebique.
The use of concrete as a prevalent material in buildings took place in the early 20th century. One of the biggest reasons for this is the production of mixer vehicles that ensure the conserving of the concrete at the construction site, and the opportunity of bringing ready mixed concrete to the site.
These tools increase the use of ready mixed concrete in the world and facilitate the casting process of concrete. In addition, the production of concrete pumps, which significantly increase the construction speed, has facilitated the design of high-rise and large-scale structures.
Preparation of Reinforced Concrete
Reinforced concrete bearing systems can be produced in two ways: On-site production and prefabricated (pre) production.
1. On-site Production
Construction of reinforced concrete structures is a process that does not require skilled labor. Architects and engineers should make a good team work during the planning phase of the project in order for the construction management and production to run smoothly.
The reinforced concrete building project drawn by the architects is sent to the civil engineers. Engineers create the static project by making the necessary calculations for the strength of structure.
In this static project, concrete class (such as C25, C30, C35), amount of concrete, section calculations; In addition to them, the amount, class (S220, S420 etc.) and the diameter of the steel reinforcements are determined. Column and beam types, locations and numbers of them are also decisions that architects and engineers should consider in a coordinately. Because all these decisions are the main factors that determine the flooring, roof type, wall type and building materials to be used and affect the architectural design.
Things to do on the site:
- Firstly, the axes in the static project for the production of the reinforced concrete carrier system are marked on the field.
- Iron masters at the construction site cut steel reinforcements with required dimensions, then bend the stirrups at the measurements calculated by the engineer.
- Stirrups that allow the steels to stand together with the gaps calculated in the section are passed to the main reinforcement at certain intervals. At this stage, the concrete cover blocks (may be in the range of 2-3 cm, this range may vary depending on environmental conditions and coating materials) are used to protect the steel from external factors.
- Formwork masters prepare concrete molds that will wrap around the steel bundles. In order for these molds to be easily separated from the concrete, the inner surface is lubricated.
- Molders wrap this mesh steel reinforcement system with concrete molds (usually made with wood).
- It’s necessary that molds be supported with buttresses to remain standing after pouring of concrete.
- After the formwork system is prepared, concrete in the mixer is poured into the molds. The required air temperature for concrete pouring is between +5 and +35 degrees. If the weather conditions are unfavorable, concrete pouring is delayed or additives are used.
- Concrete must be distributed homogeneously throughout the formwork In order for the system to work properly. Tools such as vibrator are often used to ensure this even distribution. As a result of this vibration, the semi-fluid concrete spread more evenly in the mold.
- When the concrete reaches the required strength, the molds are disassembled. Although the mold removal time varies depending on the type of the building element, environmental conditions and the quality of the concrete, the average removal time is 7 days.
- In order to minimize the shrinkage rate of the concrete, after the molds are removed, face of the concrete should be continuously wetted for 28 days.
- Thus, the reinforced concrete carrier system will produced in accordance with the project and it show its structural strength.
2 Prefabricated Reinforced Concrete Production
Reinforced concrete elements may sometimes be desired to be produced outside the construction site. While production can be done with standard sizes in factories, it can also be made in custom sizes optionally.
The prefabricated elements produced are transported to the construction site and assembled together with various connection apparatus such as anchors.
Compared with on-site production reinforced concrete:
- Pre-production of reinforced concrete panels is not affected by weather conditions.
- Since the process on the site is made up of joining the elements, the structure can be built in a much shorter time.
- It is not necessary to wait for the setting time or count the days for mold removal. As soon as the plans of the project are approved, reinforced concrete elements can be produced in the factory.
What kind of material is reinforced concrete structurally?
Reinforced concrete is a very strength and cheap material produced by using ductile structural steel and brittle concrete together. Inside, there is steel that is resistant to pulling and bending; Around the steel there is concrete that protects the steel from external influences and is resistant to pressure.
Concrete, which does not have enough strength to be used as a structural element, can be shaped as desired with the prepared molds. The most important feature of steel is that it is resistant to shrinkage and at the same time it makes ductile fracture. This contributes to the slow collapse of damaged structures. Thus, reinforced concrete, which makes it possible to cover the shortcomings of concrete with steel reinforcements, is one of the most preferred building materials.
Advantages of Reinforced Concrete
- It can be easily processed and shaped so that many building elements can be designed with reinforced concrete.
- There is little need for maintenance. It is less affected by environmental conditions than materials such as steel and wood. This in turn reduces the cost of repair and maintenance.
- Material content found in many parts of the world: aggregate, water, gravel
- It does not require detailed and qualified workmanship.
- It is quite resistant to pressure, suitable for high-rise building construction. Moreover, it is very resistant not only to pressure but also to fire.
- It is electric-proof and abrasion resistant.
- It is a material that can be built quickly.
- Materials such as sand, aggregate, water inside it are easily available in many parts of the world. By this means, reinforced concrete is an economical material.
- It remains durable for many years and even increases its strength for a length of time.
- Pests and insects can’t inhabit in reinforced concrete.
Disadvantages of Reinforced Concrete
- Molds should not be removed until the concrete reaches the required strength. This extend the building process.
- Reinforced concrete is a heavy material despite its strength. This, creates static problems in structures where wide opening is passed.
- Reinforced concrete constructions are affected by environmental conditions during construction. Construction activities are temporarily disrupted when there is no suitable weather conditions.
- Reinforced concrete is an unsustainable material that is quite difficult to recycle. It is both costly and difficult to pull down in contrast with steel.
- The margin of error is high in reinforced concrete. More materials are used since high safety coefficient should be taken in static calculations.
- It is a difficult material to strengthen and make adding. Therefore, while the project is in the planning phase, potential additions and possible load increases should be calculated.
The Most İmportant Reinforced Concrete Building Examples
1. Villa Savoye
Architect: Le Corbusier
Location: Paris, France
Construction Year: 1931
Villa Savoye is one of the most important works of Le Corbusier that 5 basic principles of him which can be clearly seen. In this modern structure of the architect, the reinforced concrete structure has been transformed into a life machine rising above the pilotis.
2. Unité d’Habitation
Architect: Le Corbusier
Location: Marseille, France
Construction Year: 1952
Another project of Corbusier, one of the most important modernist architects that comes to mind in the design of reinforced concrete structures, is Unité d’Habitation. Mass housing projects started to be produced in Europe, where the house shortage was experienced after the Second World War. Perhaps the most important of these is the work of Le Corbusier which was produced for the working class, with a capacity of over 1600. The building took its place in the history of architecture as one of the most valuable designs of the brutalism movement later.
3. Fallingwater House
Architect: Frank Lloyd Wright
Location: Pennsylvania, USA
Construction Year: 1937
If asked me what is the most known residential structure of modern architecture, my answer would definitely be the Fallingwater House. The house is one of the cult buildings of modern architecture, which has been inspiring architectural designs for nearly 100 years.
Reinforced concrete bearing systems have brought many innovations in the field of architectural design. The most important innovation brought by Wright in the building is reinforced concrete consoles, which are quite brave for that time. Another important feature of the building is that it was built on the waterfall, not opposite the view of the waterfall, and blazed a trail in architectural design in context.