The Eiffel Tower was built in 1889 for the Universal Exposition celebrating the centenary of the French revolution. The Prince of Wales, later King Edward VII of England opened the tower, which had been chosen from 700 proposals submitted in a design competition. (1)
The contractor was Gustave Eiffel & Cie
The engineers Maurice Koechlin & Emile Nouguier
The architect Stephen Sauvestre
Studies began 1884
Construction took place between 1887 - 1889 (2 years, 2 months and 5 days)
50 engineers and designers produced 5,300 blueprints
100 ironworkers produced the 18,083 individual parts to be assembled, whilst 121 actually worked on the construction site. (2)
The workers began digging the foundations on January 26 1887. The first obstacle was to arise on receiving the initial bore samples, which raised questions about the stability of substrata. On one hand, the easterly and southern sample feet of the tower showed a typical mix of grey plastic clay resting on a solid foundation of chalk, whereas, the northern and westerly feet displayed compact sand resting on sloping gravel (due to the proximity of the River Seine). (3)
Using cylindrical pneumatic caissons with a diameter of seven feet, Eiffel dug to a depth of fifty-three feet to find the good grey clay of Paris. If he sank these foundations sixteen feet deeper than the East & Southern piers he would have solid footing. (Appendix 1)
Work began immediately, due to water seepage from the Seine, caissons were used - four per pier, sixteen in total. These caissons were fifty feet long, twenty feet wide and ten feet deep. The thirty four ton caissons were wedge shaped to form cutting edges with earth hoisted out of airlocks. 40,500 cubic yards of earth were removed from the four sites, it was only then, the foundations were actually laid.
Each pier would rest on cement and stone laid obliquely so that the curving columns that bore the weight of the tower would exert their thrust at right angles to the mast. In each excavator twenty foot deep quick setting cement was poured. Over the cement, blocks of limestone were laid and in turn, these were capped with two layers of ultra hard cut stone (as used for the Arc de Triomphe). Embedded in the centre of each mass were two great anchor bolts twenty six feet long and four inches in diameter, to which a cylindrical flanged iron shoe was attached. The column would be bolted to the shoe and locked into the stone mass, pressure from the columns was to be 10.2 pounds per square inch, whereas the stone could actually support 421 pounds per square inch.
These foundations were in place by June 30, five months after starting. These practices at this stage involved no new innovations, except that Eiffel placed a piston in the hollow of each shoe, which could be moved by water under pressure. These hydraulic jacks permitted him the ability to raise or lower each of the sixteen columns thus, ensuring the perfect horizontal place for the piers when the time came.
Each jack was capable of lifting 900 tonnes, Eiffel calculations indicated that pressure on the earth beneath the foundations would range from 58 - 64 pounds per square inch depending on wind force and which pier was being considered. Well within the limits of the substrata.
The Structural Frame
Built to celebrate the science and engineering achievements of the age, soaring 320.7m (including a mast), weighing 7000 tonnes, the structure consists of two visibly distinct parts.
A base composed of a platform resting on four separate supports (pylons or bents) joined into a rigid whole by horizontal bands, above, a slender tower, created as the bents taper upwards, rising above a second platform to merge in unified columns. (Appendix 2)
In the construction of the tower, the curve of the base pylons was precisely calculated so that the bending...