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To the History of Construction With the introduction of the railways and steam machinery, trans­portation and manufacturing costs were considerably reduced and concrete came to be more widely used, but it was still very much a neglected material. Therefore, good concrete was scarce and a great deal of poor concrete was used. The big break-through was the discovery of Portland cement by Joseph Aspdin in 1824, a worker in an English town. When he was working an idea came to him as to how to make his work better. He started his experiments. After some time he obtained a powder. When it was mixed with water and allowed to stand it "sets" forming a hard substance. This substance was so much like the building stone from Portland that the powder was named Port­land cement. As years passed different materials were found in many countries from which Portland cement could be made. Portland cement was first used on a large scale in the construction of the Thames tunnel in 1828. As early as 1830 the first idea of reinforced concrete was men­tioned in a publication, which suggested that a lattice of iron rods be embeded in concrete to from a roof. Patents were taken out for all sorts of systems in all countries. The development of reinforced concrete really got under way in the 1850's and 60's. Lambort, a French contractor, built a concrete boat for the Paris International Exhibition of 1855, with 2 inches sides reinforced with a skeleton of iron rods. W. Wilkinson, who patented a method of constructing a concrete floor in 1854, is considered by many to be the inventor of reinforced concrete as well. -But many people say that a Frenchman, J. Monier, who took out a patent in 1867 for the construction of plant tubs, tanks, etc., made of concrete reinforced with a mesh of rods or wires, should be credit­ed with the invention. Certainly Monier did a great deal to develop the use of reinforced concrete and his name came to be so closely linked with reinforced concrete that reinforced concrete was known as the Monier System. Wilkinson, however, certainly appears to have been the first. His patent covered for concrete floor slabs reinforced with a network of flat iron rods placed on edge. One of his main claims was the good fire resistance of the floor. He appears to have understood the princi­ples of reinforced concrete, for he stated that the reinforcement was to be placed in the concrete to take the tension. A number of buildings were erected, using Wilkinson's system. He also described method for the construction of pipes, reservoirs, and walls of concrete reinforced with metal sheets, bars and chains. Freyssinet is known for his work in prestressed concrete for which he had his first ideas before First World War. With the improved materials and the new knowledge available, Freyssinet realised the advantage to be obtained from prestressing, and he used his system in prestressed works. From now on structures became bigger, better and more excit­ing, and concrete steadily strengthened its position as a building material. Reinforced concrete was recognized as the best material for all types of structures. The post-war era has given the biggest boost to concrete, both reinforced and prestressed. After the war steel was short in Europe and many architects had to use either reinforced or prestressed con­crete in their structures in order to economize in steel. Architects were perhaps a little surprised to discover that in many cases reinforced concrete structures, apart from using the minimum of steel, were also cheaper than other forms of construction, and could be erected as quickly. They also discovered that they had more freedom for planning than they had ever before, and a larger number of different solutions to each structural problem were available. Beams could be eliminated, floor spans could be increased, and shells were available for roofing large areas. Another big factor, which encouraged the use of concrete, was the introduction of fire regulations, which recognized the superiority of concrete over other structural materials in its fire resistance properties.

Лошара12летемае 06 нояб. 2013 г., 21:45:32 (10 лет назад)

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