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Structures

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Subido el 22 de enero de 2020 por Isabel L.

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In this case we are going to talk about structures. 00:00:01
Well, each object also always have at least a structure and is the shape. 00:00:06
And the shape, you can get the shape joining different elements, different structural elements. 00:00:20
So we can define a structure as a set of elements arranged in an optimal way to support a body or an object. 00:00:30
It gives the object its shape, although it can be under different loads, different forces. 00:00:40
So we can have different types of structures. 00:00:51
we can have carcasses that just only protect part of the machines but they are never under any load 00:00:54
but in other case we have mass structures without any hole, truss structures composed by bars 00:01:06
which can form triangles, frame structures which are formed for columns and beams that 00:01:16
support different elements such as buildings for example, or suspended structures that are 00:01:28
holding by different types of cables. Indeed you have three main important things. One is 00:01:35
is the materials in which you build the different parts of the structures. 00:01:47
Structures are usually composed by a set of elements, so each element is built in a specific material 00:01:55
that in conclusion is supporting the forces. 00:02:06
And forces, what are forces? Well, it's complicated to, it's not easy to define force, but we can define force taking into consideration its effects. 00:02:14
What I'm trying to say is a force can change the movement state of the object or if the objects are unable to move, they change its form. 00:02:30
So, this is a force and forces are something that we are going to explain better later. 00:02:48
Forces are under the dynamic law. 00:03:02
We have three dynamic laws. First, tell us that what I have already said, that forces can change the movement state or they can change the shape of the element. 00:03:06
The other two is in this slide. Force can be mass and acceleration, and the forces usually works in pairs. If you have an action, you can also have a reaction force that usually is more or less the same, equal, and in different sense. 00:03:25
Apart from this, in a structure it is also important how the different elements join, 00:03:53
what we usually call ligatures. 00:04:06
We can have some ligatures that can move, but in other times we need some ligatures 00:04:11
such as guides or such as others that can rotate, for example joints can rotate or have 00:04:21
different types of movement. 00:04:35
So from the material's point of view, if one material is under loads, is under forces, 00:04:40
They can have different behaviors. 00:04:49
In this case the better or the best, for example, is for materials. 00:04:53
You always have a zone in which if you stop applying the force, the material can recover 00:05:03
its shape, its length. If you apply a force, obviously, it tends to change its length, 00:05:19
which is usually called deformation. Some materials, if you continue increasing the 00:05:32
force, you can change the shape of the materials in a permanent way, but without breaking. 00:05:42
But others break if you try to change the shape. 00:05:55
So when you are building different structures, you always have to build in the elastic zone, 00:06:05
in the zone in which the materials can recover its length. 00:06:17
So not only is important the quantity of the stress, but it's also important how you do 00:06:25
this stress. 00:06:35
can have five elements, five elements stresses that are compression if you tend to do the 00:06:36
elements shortened, tension if you do increase its length, shear if you try to cut in something, 00:06:48
bending when you flex your flexors or bend or torsion if you torsion something 00:07:01
usually you have a more than one type of this 00:07:11
an addition of most than one well and so you have a different forces stresses among 00:07:18
One thing important is moments and stresses, moments and loads are vectors. 00:07:29
What does this mean? Well, in vectors you need to give more information than just only its value. 00:07:41
you need to study them as vectors with a point of application direction sense and also value 00:07:53
so if you want to to do the the the sum of two vectors it's not it's not just only to sum its 00:08:08
values you can do this if the vectors have the same directions but if the direction is different 00:08:21
you must do the polygon to know the value of the of the force of the value of the of the addition 00:08:30
so sometimes it can be important and if you want to to have a structure in a key and a static 00:08:40
equilibrium is obviously important that all the forces and all the moments can be compensated 00:08:51
It means that the sum is O. But these sums are vectorial sums. You must do the sum in a vectorial way. 00:08:59
Apart from this, you have some typical elements of a structure, such as arches, pillars, straps, beams, 00:09:11
That are always, for example, arches are always under bending, pillars are always under compression, straps under tension, beams under bending also. 00:09:25
So if you can know the different elements in a structure, you can also know the type of stress that they are. 00:09:41
To have a better structure without so many weights, without increasing its weight, 00:09:52
You can use what we usually call triangular structures. 00:10:05
In this case, if you do the triangle is the polygon, we have just only three bars in this case, or three sticks, so they can't change its shape. 00:10:19
And this can make the structure more stringent, more stringent. 00:10:46
If you have to study different structures, you must take into consideration the equilibrium of forces and also the equilibrium of movements. 00:10:56
And in each part of this structure you can know its value using the polygonal addition and scale. 00:11:15
If you do a scale, the polygonal addition, you can know the value of the forces in each part and obviously the type of stress that they are supporting. 00:11:27
You also have another type of method to resolve or solve different types of structures, as you can see here, if the structure, for example, is asymmetric, you can use Cremona method or return, that is more or less what I have already explained, but in this case, for more complicated structures. 00:11:47
To do a good analysis of structure, we usually use some types of diagrams. 00:12:18
For example, here we know the diagram of the shear force. 00:12:29
And to understand this, you can know its structure, compression, cutting, and types of movements. 00:12:37
And here you have, for example, for forces you can use the stress and for movement you can use this other thing in which you have other parameters. 00:12:49
In each part is also important the shape of the bar, because the distance to neutral free bar is also different. 00:13:05
so it can be different the the dimensions in a bar is the depending of the profiles and finally 00:13:20
the structure as a whole must be a study because it must be obviously stable and to study this 00:13:35
the stability of a structure we need to know the point, the addiction, the action of gravity, 00:13:47
we need to know the point of application of the weight of the structure. And to do this 00:13:58
In this case, we use this point, and if I want a very stable structure, this point must 00:14:06
be in the low zone and between the legs or the superficial supports. 00:14:19
This is all about the structures. 00:14:33
I hope you can understand it better. 00:14:35
Idioma/s:
en
Autor/es:
Isabel Lafuente Reboredo
Subido por:
Isabel L.
Licencia:
Reconocimiento - No comercial
Visualizaciones:
190
Fecha:
22 de enero de 2020 - 23:12
Visibilidad:
Público
Centro:
IES JOSÉ GARCÍA NIETO
Duración:
14′ 39″
Relación de aspecto:
4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
Resolución:
1440x1080 píxeles
Tamaño:
118.70 MBytes

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