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(article by François Dhôtel, architect)
| The Eiffel Tower, symbol of innovative
technique at the end of the 19th century, has maintained its universal
image. |
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Even if 6 million visitors climb the Tower each year,
the number of those who have set eyes on the Tower but never foot
coupled with those who know of the Tower but have never even caught
a glimpse of the monument are far more numerous.
Its simplified representation is but an inanimate object, an unchanging
reference point. Yet, differing from many other structures built
in the past, it is alive, ever changing and evolving.
The most spectacular transformations are also those
that are the most visible: it has changed color six times in its
lifetime and its lighting effects have been designed at different
moments to decorate the tower for a day or for longer periods of
time. Following many different lighting styles, the present day
system has been highlighting the internal structure of the Tower
for more than ten years now.
Less spectacular yet visible are the developments
that have been added to the different levels such as the various
pavilions and constructions on the first and second floors. Also
the roofing of the galleries and shelters providing refuge from
bad weather conditions including the landing stages, covered walkways,
etc., as well as the numerous technical and service quarters and
the spaces located directly over or under these levels.
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The elevator and staircases - construction or replacement of - and
the elevator platform could also fall into this same category of developments,
except in cases where they have become integrated parts of the structure.
Much less visible are the operations that have modified the original
Tower's structure.
Indeed, at different periods in time, even the skeleton structure
evolved, either little by little as the necessity arose or to reinforce
certain structural members that were damaged by various causes.
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| In the descriptive book "THE 300
METER TOWER" Gustave Eiffel gave precise indications concerning
his calculations, how many were used and detailed observation notes. |
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All of the documents dating back to 1889 and 1900,
including his numbered calculations are all taken from this original
work.
In fact, to obtain the 300 meters, the Tower is basically
composed of two elements :
- a base, which is a sort of bar stool, very sturdy, standing on
4 main pillars that are bonded and extended with a much lighter
batter at the smaller level that constitutes the second floor,
- a tower firmly attached atop.
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The value of the pillar base is directly related to the swaying caused
by wind forces.
The diagram of forces in Figure 2 shows the relational use of the
materials at the different levels in keeping with the simplified
calculations presented in Figure 3 and 4. We can observe the diminishing
wind forces and the ratio obtained at the base.
( To illustrate this construction
principle, read Gustave Eiffel's text. )
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That is what gave the theoretical form to the Tower,
but it had yet to be built.
The greatest difficulty in erecting it was the bonding
of the four main pillars at the first floor.
Indeed, considering the available equipment of the
period, it was necessary to implant as precisely as possible four
bases 80 meters apart from each other and then to raise the four
pillars at a slant and to prop them up employing millimeter precision
fifty meters above the ground.
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The erection of the pillars - auto-stable - above
the first floor was less difficult.
As for the tower, it was erected with even less difficult, apart
from working at heights ...
The principle behind the structure reveals two apparent sections
where it is in tension :
- the horizontal connections on the first floor (7-meter wide girders)
- the base of the tower top
These two points will be brought up farther on.
The structure was made of puddle iron and not steel.
The Tower was assembled using a limited number of fabricated parts,
evident in the list taken from Mr. Eiffel's book:
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Several other cast iron parts could be joined to this list of which
16 truss supports, connecting the masonry and the structure.
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The parts used to construct the Tower
All of the iron came from the
factories of Mr. Dupont and Mr. Fould, blacksmiths located in Pompey
(Meurthe-et-Moselle), who were represented in Paris by their director
Mr. A. Prègre and who kept us informed on iron grades. They
were delivered at the following prices:
| Equal angles from 40 to 100 |
.................................. |
13.25
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F per 100 kg |
| Standard sections, 1st and 2nd
grades |
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13.25
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F per 100 kg |
| Standard sections, 3rd and 4th
grades |
.................................. |
13.75
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F per 100 kg |
| Wide flat bars up to 500 |
.................................. |
15.00
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F per 100 kg |
| Ordinary sheet iron |
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15.50
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F per 100 kg |
| Checkered plate |
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16.50
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F per 100 kg |
| Special tee-sections (designated
in Eiffel's book) |
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16.00
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F per 100 kg |
| Open and closed angle sections,
at made to order angles |
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20.00
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F per 100 kg |
The rivets came from Mr. Letroyeur and Mr. Bouvard
in Paris. The quality was that of boiler or locomotive rivets.
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All rights reserved - © SETE - 2008
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