which is a problem since, one more time, it can
scare someone who crosses a
footbridge, that is the example which we can see, here.
That is very funny to do that as sporting activity,
but it is less enjoyable to do that if we are
coming back to home
with shopping or a school bag, it becomes dangerous.
Likewise, if there are distributed loads which,
would maybe be more characteristic of groups
of persons, or of big trucks.
In this video, we first see the cable under its self-weight,
which has a certain shape, the shape of the catenary which we know well.
If we add a weight to this cable, it takes
a triangular shape with
very significant displacements.
In the second part of this video,
we have the same shape, but for
this shape, we have already added a series
of rectangular red weights which symbolize the weight of a
structure, since structures always have a self-weight.
This structures, let's say that it is made
of concrete, it is quite heavy.
If now, we add to it one, then two loads, we can
notice that yes, it always moves in the zone of the
loads, but in a much less pronounced way.
So, we have a way to decrease the deformations, if we start with a
significant weight. The first solution of stiffening is
thus a stiffening by a significant weight.
If we first look at the case of the roof
of the airport of Dulles, on the left, which we have already seen.
Well, when we send a few people on the
roof to do sealing works, for example,
we do not wish that these people be
in danger, respectively, that there are too much vibrations.
So, this structure has to be stiff enough.
Another case which often occurs, it is the presence of snow on the roof.
And if there is wind,
the snow will only pile up on one part of the roof.
For example, on the right, as I have shown.
The solution used for this roof to avoid
the problems, is that it is quite heavy, in concrete.
Thus, the weight of the persons is relatively
small compared to the weight of the roof.
Likewise, the snow load is relatively small.
The structure on the right, built by Le Corbusier, in France,
in Firminy-Vert, uses the same principle. We have a series of
load-bearing cables; here, we can
see them well; here, another pair.