Hello. In this video, I am going to talk to you about steel shear walls. In the previous lecture about superimposed shear walls, you have been led to see how we could design a structural system constituted of concrete walls, of wall-beams, of shear walls which are superimposed on top of one another. That is a solution which is very efficient as I have shown you, but it is also possible to make this same system using a steel structure. That is what I am going to show you in this video with a very nice example of a very beautiful structure. That is the school of Leutschenbach in Zurich, also designed by the architect Christian Kerez and the engineer Joseph Schwarz. We can see the principle of this structure on the right, that is a model of this structure to the scale 1/10 which has been made and exposed within the framework of a contemporary art museum. So we have here a system. This system, we can also see it on the right, is clearly composed of shear walls since it has several floors. We have a first large truss which takes support - by the way, that is worth mentioning it here - which takes support on a system of six tripods and these tripods comply with the needs which I have brought to your attention in the previous lecture, to be able to also resist seismic effects. So these tripods are not only able to carry vertical loads, but also horizontal loads. On top of this structure, we have a second truss which is only one story deep, which is arranged in such a way that it leans on the initial red truss. Thus there is also a truss over the width, I should maybe have signaled it here because that is very important, at the level of the red truss, there is obviously a truss which goes in the other direction, which leans on all these small tripods about which I will talk to you later. And then, a large depth truss takes support on this blue truss. Actually, it is only one story deep because the upper floor is a gymnastic hall, so we need a large depth but that is only one story. And that is a large outlying truss which goes around the structure, obviously without any intermediate support because it is a gymnastic hall. So we can notice, if we want to get a closer look on them, that there is here the support of the green truss on the blue truss and then, there is here the support of the blue truss on the red truss. And then, these red trusses take themselves support on the six tripods of which I talked to you about before. That is the principle of this structure; let's see how it has been built. On the left, you can see another model where we can clearly see the tripods in the lower part. And then, on the right, you can see the beginning of the building process of this structure. We have already made a large part of the ground floor slab and then we can see these large trusses which are developing. We can see here, that is the red truss and then here, perpendicularly, we have the blue truss which is being assembled. Here, the construction process is more advanced. We have been able to remove the formwork of the first floor. You can notice how free this structure is. There are only the six supports of which I talked to you about. Otherwise, we have the impression that it floats above the ground, that is wonderful. And then here, we can see the progress of the structure with the truss which I called the green truss before, which is the gymnastic hall at the top of the building. It is interesting to also note that great care has been given to the details in this structure. We have here the tripods about which I talked to you, they are the supports and then the truss system of the first floor, so I had drawn it in red before. Here the red color is not refering to the internal forces but to the level of the trusses. And we can notice that the slab is very technological, with a particular shape which enables it, of course, to resist the internal forces, but also to contain all the conveyances of water, of fluids, of electricity, of light, and so on, in such a way that we have a structure which is free of installations under the slab. The shape which you can see is the definitive shape which we can see in the building. In this video, I have shown you that it is possible to create superimposed shearwalls with a steel structure. That is a very technological structure which implies large depth trusses but the principle of superimposed shear walls is also valid. What is interesting in this structure, is to also see that there is a logic to correspond to the various functions of the different stories of the building.