Hello. In this video, I am going to talk to you about superimposed shear walls, we could also say about the superimposed wall-beams. The principle is to put a shear wall or a wall-beam, on top of another and as you will see, that enables us to have a great flexibility in the creation of rather modern buildings which have a free layout. The structure I am showing you here is a very simple structure, it schematizes modern buildings, I will show you by the way some examples thereafter which are very dispossessed and which have of a great freedom in the layout of the storeys thanks to the use of superimposed wall-beams. We only have four posts at the ground level which can only carry a vertical internal force, to be honest, that is clear that in a structure nowadays, there should also be elements to carry horizontal internal forces, for example the ones induced by earthquakes or wind, in this example here, that is not considered but obviously, it would be necessary to add these elements. That would be some additional horizontal load-bearing elements. Here, I add a first level which is constituted of four beams which cross in twos. I put the intersections of the beams on the columns and you can see that I can very easily place my load of 10 Newtons on this structure which is however only constituted of cardboard elements. I now place the cardboard which represents the slab under this story to have a complete structure. I then add two walls in cross on the previous structure, so the slab remains between both, and again I can add my load of 10 Newtons on this structure, still only constituted of cardboard which resist very well and which does not deform. The last story finally, is composed of an outlying wall, which is a bit inside the building, enabling for example a corridor or a balcony and then, which leans on what we have built so far and here again, I still can place my 10 Newtons, so I have a structure which is very stable despite its large dimensions. Let's see how it works: we have here four columns at the level of the ground floor, I add the shear walls which we have seen for the first story, so these are two shear walls in each direction which cross above the columns What is interesting in this configuration is that at the level of the ground floor there are only the four columns so there is a wide range of possibilities to organize this ground floor, even, for example if it is a school, to have a part which is outside- a playground covered by the building. I then add on these four red shear walls two blue shear walls, which have the particularity that they do not really touch the red shear walls except in four points, on which they can take support. We have to remember that these shear walls are beams whith a small slenderness ratio and a large depth so they are able to carry loads, we are going to come back to this in a short time, they will be able to carry loads over relatively short distances and then the system is really stable. The third story is constituted of a green outlying wall, this wall only takes support on four points on the blue walls of the lower story which, I remind you, only take themselves support on four points on the red walls, which themselves lean on the four columns. So we have a system which is absolutely stable, a structure which works, obviously the internal forces must be quite significant, that is important that these pink and green nodes are correctly dimensioned. Well, let's see in principle how we are going to be able to dimension this shear wall on the ground floor, so we are going to look at the internal force in this shear wall of the ground floor, here on the right. That is the internal force which comes from the blue story through the shear wall and it is constituted in particular of the internal forces which are carried by the green outlying walls. I only look at the red walls in this configuration, so I have a very large load, but this very large load is going to be easily carried by a structure, we can call that a truss or an arch-cable. I am going to have a large compression in the concrete of these walls, and I am going to place a significant amount of reinforcement at the level of the slab. Here I have a lot of space to place it, so I will be able to easily resist tension. The question we asked ourselves before was: where could we create openings? Very clearly, in this configuration, if I want to place a door I can absolutely place it here, obviously on the other side, but, if I have enough depth, we can even imagine placing an opening here. So despite the fact that we have concrete walls, we can place a certain number of openings, we could also place windows, which enables to have a relatively flexible structure. Of course, if these concrete elements had to become much wider, we would maybe start having a problem because we would start encroaching upon the planned size of the door. So of course, we could place it somewhere else or else the other solution would be to increase the thickness of the wall to respect the internal force which must be carried. As I said in the previous video, we do not directly perceive what the thickness of the wall is so it is not necessarily problematic to have a slightly thicker wall. Of course, it is going to cost money. What is interesting with this configuration is that, you see, I can switch the two last stories and I also get a solution which still remains stable and enables to carry loads. So if we come back here now, to this configuration, we can see, here we had the points on which - there is probably one just behind here - here, the second story leans on the first story and on the top, we have these points where the third story takes support on the second story, there are obviously four all around. When we switched both structures, the points on which the stories lean on changed, but the principle still remained the same, that is to say that it is always possible to make the loads go down so we have a big flexibility; if we decide to have a large free space with nothing inside at this level here, we can absolutely have it, or else, if we prefer to have four large rooms, well, we can quite freely choose where we want to have these system changings. Of course, we could also have the same system over several stories. Here I have an example: the Kerez house which has been created by the architect Christian Kerez and the engineer Joseph Schwarz, in Zurich. We can notice before going any further, that the thicknesses both of the slabs and of the walls, are quite significant. That is something which belongs to architecture but we will see, that is also something which is necessary for this structure to work. Aside from this, we can also notice a big transparency since we have glass to make the balustrades and we have large bay windows in this house. On the right, you can see the model which has been made by the architect of the structure, we can recognize on the left, here, and in the middle, the entrance tunnel for the underground car park. We want to look at how this house has really been designed starting from the bottom, so here we have the car park, we have this entrance tunnel which I have just indicated to you and then an ideal car park in which there are no columns, no load-bearing elements, so a large degree of freedom to place the vehicles without risking to hit something. So we have load-bearing walls all around and here some particular walls. On the ground floor, we have these blue walls and we can notice that these walls do not correspond at all to what we had downstairs, that is normal, we are not in a car park anymore. Some of these walls clearly take support on the pink walls of the lower story. Others, however, do not lean on these walls since they are located at a certain distance. It is however necessary to take into account the fact that we have here slabs which are thick so thanks to the thickness of the slab, we are going to be able to transmit an internal force from the end of the blue wall to the pink wall, through the thickness of the slab. So, this is an explanation of why these slabs are thick. On the first floor, we have these sky blue walls and we can notice that some of thems take support perpendicularly on the blue walls of the lower story, that is quite clear, others are laterally staggered, probably that this lateral gap is acceptable thanks to the large thickness of the slab. So here, there are clearly again supports of the sky blue wall on the wall of the lower story. If we move to the second floor, these green walls take support in a certain number of cases, on the blue walls. That is quite clear. However, in some other cases, we can notice that for example here, these walls are really staggered, they are really far away from each other and the only way in which this wall here... that corresponds to - I am going to draw it in yellow for us to see it well, that is this wall here, this wall is too much staggered compared to the lower wall and the only way in which we are going to be able to carry it, is holding it from the top thanks to what is possible on the upper floor. We even have walls which are hung up. This is the last floor, we precisely have these orange walls, we can find this orange wall which clearly hangs up the green wall, there is no problem, we can see that here this other green wall is also hung up on the yellow wall of the upper floor. I do not pretend to explain you all the functioning of this house, I hope you are not going to start too quickly to design such a complex structure, but however, that gives you and idea about the very large flexibility that this system prof superimposed shear walls can give us in combination with appropriate thicknesses. In this video about superimposed shear walls, I have shown you how, by placing them in crossed configurations we can get a very large degree of freedom to change the spatial organisation from one floor to another. This enables variations from one story to another, that provides a large degree of freedom. I have also shown you in the example of the Kerez house in Zurich, that we can even go slightly further in this freedom using a gap between some walls taking advantage of the thickness of the slabs or even hanging up certain walls on the walls of the upper floor.
