Dr.Jayalath manoratne

 

                                Eiffel Tower

The Eiffel Tower is a wrought iron lattice tower on the champ de mars in paris,   France. It is named after the engineer Gustave Eiffel, whose company designed and built the tower.

Locally nicknamed "La dame de fer" (French for "Iron Lady"), it was constructed from 1887 to 1889 as the centerpiece of the 1889 world's fair  and was initially criticized by some of France's leading artists and intellectuals for its design, but it has become a global culrural icon  of France and one of the most recognizable structures in the world. The Eiffel Tower is the most visited monument with an entrance fee in the world; 6.91 million people ascended it in 2015. The Tower was made a Monument historique in 1964 and named part of UNESCO World Heritage Site ("Paris, Banks of the Seins") in 1991. 

The tower is 324 metres (1,063 ft) tall, about the same height as an 81-storey building, and the tallest structure in paris. Its base is square, measuring 125 metres (410 ft) on each side. During its construction, the Eiffel Tower surpassed the Washington Monument  to become the tallest man made steucture   in the world, a title it held for 41 years until the chrtsler buiding  in New York City was finished in 1930. It was the first structure in the world to surpass both the 200-metre and 300-metre mark in height. Due to the addition of a broadcasting aerial  at the top of the tower in 1957, it is now taller than the Chrysler Building by 5.2 metres (17 ft). Excluding transmitters, the Eiffel Tower is the second tallest free standing structure in france after the millau viaduct. 

The tower has three levels for visitors, with restaurants on the first and second levels. The top level's upper platform is 276 m (906 ft) above the ground – the highest observation deck  accessible to the public in the European union.  Tickets can be purchased to ascend by stairs or lift  to the first and second levels. The climb from ground level to the first level is over 300 steps, as is the climb from the first level to the second. Although there is a staircase to the top level, it is usually accessible only by lift.

Origin

The design of the Eiffel Tower is attributed to Maurice koechlin  and Emile Nouguier, two senior engineers working for the compagnie des etablissements eiffel.   It was envisioned after discussion about a suitable centerpiece for the proposed 1889 exposirion universelle,   a world's fair  to celebrate the centennial of the french rwvolution. Eiffel openly acknowledged that inspiration for a tower came from the Latting observatory  built in New York City in 1853. In May 1884, working at home, Koechlin made a sketch of their idea, described by him as "a great pylon, consisting of four lattice girders standing apart at the base and coming together at the top, joined together by metal trusses  at regular intervals". Eiffel initially showed little enthusiasm, but he did approve further study, and the two engineers then asked stephen sauvestre,  the head of the company's architectural department, to contribute to the design. Sauvestre added decorative arches to the base of the tower, a glass pavilion to the first level, and other embellishments.

The new version gained Eiffel's support: he bought the rights to the patent on the design which Koechlin, Nougier, and Sauvestre had taken out, and the design was put on display at the Exhibition of Decorative Arts in the autumn of 1884 under the company name. On 30 March 1885, Eiffel presented his plans to the Société des Ingénieurs Civils; after discussing the technical problems and emphasising the practical uses of the tower, he finished his talk by saying the tower would symbolise

[n]ot only the art of the modern engineer, but also the century of Industry and Science in which we are living, and for which the way was prepared by the great scientific movement of the eighteenth century and by the Revolution of 1789, to which this monument will be built as an expression of France's gratitude.   

First drawing of the Eiffel Tower by Maurice Koechlin including size comparison with other Parisian landmarks such as Notre Dame de paris, the statue of  liberty and the vendome column. 

Little progress was made until 1886, when Jules Grevy   was re-elected as president of France and Edouard lockroy  was appointed as minister for trade. A budget for the exposition was passed and, on 1 May, Lockroy announced an alteration to the terms of the open competition being held for a centrepiece to the exposition, which effectively made the selection of Eiffel's design a foregone conclusion, as entries had to include a study for a 300 m (980 ft) four-sided metal tower on the Champ de Mars. (A 300-metre tower was then considered a herculean engineering effort). On 12 May, a commission was set up to examine Eiffel's scheme and its rivals, which, a month later, decided that all the proposals except Eiffel's were either impractical or lacking in details.

After some debate about the exact location of the tower, a contract was signed on 8 January 1887. Eiffel signed it acting in his own capacity rather than as the representative of his company, the contract granting him 1.5 million francs toward the construction costs: less than a quarter of the estimated 6.5 million francs. Eiffel was to receive all income from the commercial exploitation of the tower during the exhibition and for the next 20 years. He later established a separate company to manage the tower, putting up half the necessary capital himself.

Construction

                                                         Foudations of the Eiffel Tower    

Work on the foundations started on 28 January 1887. Those for the east and south legs were straightforward, with each leg resting on four 2 m (6.6 ft) concrete slabs, one for each of the principal girders of each leg. The west and north legs, being closer to the river seine, were more complicated: each slab needed two piles  installed by using compressed-air caissons 15 m (49 ft) long and 6 m (20 ft) in diameter driven to a depth of 22 m (72 ft) to support the concrete slabs, which were 6 m (20 ft) thick. Each of these slabs supported a block of  limestone  with an inclined top to bear a supporting shoe for the ironwork.

Each shoe was anchored to the stonework by a pair of bolts 10 cm (4 in) in diameter and 7.5 m (25 ft) long. The foundations were completed on 30 June, and the erection of the ironwork began. The visible work on-site was complemented by the enormous amount of exacting preparatory work that took place behind the scenes: the drawing office produced 1,700 general drawings and 3,629 detailed drawings of the 18,038 different parts needed. The task of drawing the components was complicated by the complex angles involved in the design and the degree of precision required: the position of rivet holes was specified to within 1 mm (0.04 in) and angles worked out to one second of arc.  The finished components, some already riveted together into sub-assemblies, arrived on horse-drawn carts from a factory in the nearby Parisian suburb of Levellois perret   and were first bolted together, with the bolts being replaced with rivets as construction progressed. No drilling or shaping was done on site: if any part did not fit, it was sent back to the factory for alteration. In all, 18,038 pieces were joined together using 2.5 million rivets.

At first, the legs were constructed as cantilevers,  but about halfway to the first level construction was paused to create a substantial timber scaffold. This renewed concerns about the structural integrity of the tower, and sensational headlines such as "Eiffel Suicide!" and "Gustave Eiffel Has Gone Mad: He Has Been Confined in an Asylum" appeared in the tabloid press. At this stage, a small "creeper" crane   designed to move up the tower was installed in each leg. They made use of the guides for the lifts which were to be fitted in the four legs. The critical stage of joining the legs at the first level was completed by the end of March 1888. Although the metalwork had been prepared with the utmost attention to detail, provision had been made to carry out small adjustments to precisely align the legs;  hydraulic jacks  were fitted to the shoes at the base of each leg, capable of exerting a force of 800 tonnes, and the legs were intentionally constructed at a slightly steeper angle than necessary, being supported by sandboxes  on the scaffold. Although construction involved 300 on-site employees, due to Eiffel's safety precautions and the use of movable gangways, guardrails and screens, only one person died.