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Minimising geometric indicators can lead to struc-
tures that are at least three times lighter than
classic structures. To do this, one must limit the
compressed parts of structures by concentrating
the compression and by distributing the tension.
Philippe Samyn’s second patent
19
is a good example
of this: a lattice truss, fitted with a sufficiently large
number of radiant ties linking the upper gathering node
of each grid to a series of equidistant points at its base,
transfers a uniformly distributed load to the supports,
exclusively via stretched or compressed bars, and to
the exclusion of bent elements. The patent concerns
several variants of this principle, applied to beams and
bridges
(figure 25)
. A project for a 45-metre footbridge
over the River Leie in Kortrijk, designed in February
1998 and mentioned in the patent, was one of the first
applications of this concept
(01-366, figure 26)
. When
the optimum structural lightness has been achieved, the
engineer encounters new limits to the design that come
from stress variations over time and the correspond-
ing dynamic effects (vibrations) and fatigue effects
(large number of repetitions). This background means
that connecting elements are extremely important.
In general, welding is preferred to the use of bolts,
which is made possible by progress made in on-site
welding and anti-corrosion treatments. For example,
for the restaurant-bridge of the Orival service station
near Nivelles
(01-365, figures 27)
, Philippe Samyn
used full-penetration welds for the span. He is cur-
rently seeking to improve the sewing (linear) and the
sticking (surface), because this is the only way to bring
the weight of the stretched assembly close to zero. To
A new universe
of structures
increase the damping of vibrations under the effect of
dynamic actions, Samyn’s second patent includes a
damping arrangement that consists of two intercalated
viscoelastic joints on either side of the anchorage point
of a structure’s tie bar
(figure 28)
. Currently, he is also
studying the possibility of using absorbent and damping
polymer layers, placed between surfaces subject to rel-
ative movements (alternating slip), in order to disperse
shearing energy
(figure 29)
. When one accepts larger
displacements, this allows one to consider the use
of textile fabrics. In the case of a roof project for the
courtyard of Château d’Alden Biesen, Limburg
(01-425,
figures 30)
, Philippe Samyn used an ultra-light polya-
mide membrane, like the sails of boats, held in place by
polyamide boltropes, and no metal was used.
For wind turbine supports, optimum lightness means
that the quantity of material used can be cut by a factor
of four or five, as shown by the Eole design
(01-387,
figure 31)
, which was created for Fabricom-Suez and
Construction Soudée.
20
The lattice shape means that
the structure itself can be used to hoist the turbine.
This structure is the subject of Philippe Samyn’s third
patent.
21
It should be pointed out that Philippe Samyn
has set up a fund that receives 0.5 per cent of his
company’s net income, which offers one design per
year to a developing country (transportation costs and
accommodation not included). The first beneficiary has
been Moïse Katumbi Chapwe, Governor of Katanga,
for a design for a school of architecture in Lubumbashi
(01-537, figures 32)
. The structure of the classrooms
consists of corrugated metal sheeting held in place
by a metal truss consisting of a series of concrete
reinforcing bars. The structure is simple, but very care-
fully designed. It is the logical result of using materials
and skills available on site. In terms of ventilation, the
project uses a ‘termite-nest’ principle: the sun heats the
air inside the upper galleries; this heated air, which is
lighter than the outside air, rises and exits through the
top, creating a need for compensating air that enters
by other, lower galleries. Natural ventilation is accom-
plished via a very porous structure consisting of
25
Figure 31: Eole, a project for a light
support structure for a wind turbine
(01-387)
Figures 32: Project for a school of
architecture, Lubumbashi (01-537)
Figures 25: Philippe Samyn’s second
patent: a multi-tie rod truss