1
00:00:01,649 --> 00:00:06,650
In this case we are going to talk about structures.

2
00:00:06,650 --> 00:00:20,649
Well, each object also always have at least a structure and is the shape.

3
00:00:20,649 --> 00:00:30,649
And the shape, you can get the shape joining different elements, different structural elements.

4
00:00:30,649 --> 00:00:39,670
So we can define a structure as a set of elements arranged in an optimal way to support a body or an object.

5
00:00:40,229 --> 00:00:48,990
It gives the object its shape, although it can be under different loads, different forces.

6
00:00:51,270 --> 00:00:54,829
So we can have different types of structures.

7
00:00:54,829 --> 00:01:05,469
we can have carcasses that just only protect part of the machines but they are never under any load

8
00:01:06,909 --> 00:01:16,989
but in other case we have mass structures without any hole, truss structures composed by bars

9
00:01:16,989 --> 00:01:28,150
which can form triangles, frame structures which are formed for columns and beams that

10
00:01:28,150 --> 00:01:35,650
support different elements such as buildings for example, or suspended structures that are

11
00:01:35,650 --> 00:01:47,709
holding by different types of cables. Indeed, you have three main important things. One is

12
00:01:47,709 --> 00:01:55,709
is the materials in which you build the different parts of the structures.

13
00:01:55,709 --> 00:02:06,709
Structures are usually composed by a set of elements, so each element is built in a specific material

14
00:02:06,709 --> 00:02:14,710
that in conclusion is supporting the forces.

15
00:02:14,710 --> 00:02:30,569
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.

16
00:02:30,569 --> 00:02:48,569
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.

17
00:02:48,569 --> 00:03:00,689
So, this is a force and forces are something that we are going to explain better later.

18
00:03:02,919 --> 00:03:06,819
Forces are under the dynamic law.

19
00:03:06,819 --> 00:03:25,379
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.

20
00:03:25,379 --> 00:03:28,699
The other two is in this slide.

21
00:03:29,439 --> 00:03:41,520
Force can be mass and acceleration, and the forces usually works in pairs.

22
00:03:42,699 --> 00:03:53,479
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.

23
00:03:53,479 --> 00:04:09,860
Apart from this, in a structure is also important how the different elements join, what we usually call ligatures.

24
00:04:09,860 --> 00:04:23,860
We can have some ligatures that can move, but in other times we need some ligatures such as guides

25
00:04:23,860 --> 00:04:37,860
guides, such as others, that can rotate, for example, joints can rotate or have different types of movement.

26
00:04:37,860 --> 00:04:53,000
So, from the material's point of view, if one material is under loads, is under forces, they can have different behaviors.

27
00:04:53,000 --> 00:05:22,240
In this sledge the better or the best, for example is for materials, you always have a zone in which if you stop applying the force, the material can recover its shape, its length.

28
00:05:23,000 --> 00:05:36,000
If you apply a force, obviously, it tends to change its length, which is usually called deformation.

29
00:05:36,000 --> 00:05:51,000
Some materials, if you continue increasing the force, you can change the shape of the materials in a permanent way.

30
00:05:51,000 --> 00:06:04,000
but without breaking, but others break if you try to change its shape.

31
00:06:04,000 --> 00:06:17,000
So, when you are building different structures, you always have to build in the elastic zone,

32
00:06:17,000 --> 00:06:27,899
in the zone in which the materials can recover its length so not only so is important

33
00:06:30,060 --> 00:06:37,180
the quantity of the of the stress but it's also important how you do this stress you you can have

34
00:06:39,019 --> 00:06:46,620
five elements five elements stresses that are compression if you tend to

35
00:06:46,620 --> 00:06:59,560
to do the elements shortened, tension if you increase its length, shear if you try to cut

36
00:06:59,560 --> 00:07:12,060
in something, bending when you flexure or bend, or torsion if you torsion something.

37
00:07:12,060 --> 00:07:24,569
you have more than one type of this, an addition of more than one, well and so

38
00:07:24,569 --> 00:07:38,540
you have a different forces, stresses and moments. One thing important is moments and

39
00:07:38,540 --> 00:07:48,449
stresses, moments and loads are vectors. What does this mean? Well, in vectors you

40
00:07:48,449 --> 00:07:58,009
need to give more information than just only its value. You need to study

41
00:07:58,009 --> 00:08:06,009
them as vectors with a point of application, direction, sense and also

42
00:08:06,009 --> 00:08:23,569
So, if you want to do the sum of two vectors, it's not just only to sum its values.

43
00:08:23,569 --> 00:08:30,949
You can do this if the vectors have the same direction, but if the direction is different,

44
00:08:30,949 --> 00:08:42,809
You must do the polygon to know the value of the force or the value of the addition.

45
00:08:42,809 --> 00:08:52,789
So sometimes it can be important and if you want to have a structure in a static equilibrium

46
00:08:52,789 --> 00:08:59,830
is obviously important that all the forces and all the movements can be compensated

47
00:09:01,429 --> 00:09:10,470
that is means that the sum is O but this sum are vectorial sum you must do the sum

48
00:09:10,470 --> 00:09:21,690
in a vectorial way apart from this you have some typical elements of a structure such as arches

49
00:09:21,690 --> 00:09:32,309
pillars, straps, beams, that are always, for example, arches are always under bending,

50
00:09:32,309 --> 00:09:42,450
pillars are always under compression, straps under tension, beams under bending also. So if

51
00:09:42,450 --> 00:09:48,570
you can know the different elements in a structure, you can also know the type of

52
00:09:48,570 --> 00:10:02,779
stress that they are a to to have a better structure without so many ways

53
00:10:02,779 --> 00:10:12,919
without increasing it ways you can use a what we usually call triangle triangular

54
00:10:12,919 --> 00:10:29,210
triangular structures in this case if you do the triangle is the

55
00:10:29,210 --> 00:10:43,490
polygon will have just only three bars in this case or three sticks so they

56
00:10:43,490 --> 00:10:55,389
can change its shape and this can make the structure more standard, more

57
00:10:55,389 --> 00:11:07,980
stringy. If you have to study different structures you must

58
00:11:07,980 --> 00:11:13,519
take into consideration the equilibrium of forces and also the

59
00:11:13,519 --> 00:11:26,480
of movements and in each part of this structure you can know its value using the polygonal addition

60
00:11:26,480 --> 00:11:37,399
and scale. If you do a scale the polygonal addition you can know the value of the forces

61
00:11:37,399 --> 00:11:51,409
in each bar, and obviously the type of stress that they are supporting.

62
00:11:51,409 --> 00:11:59,129
You also have another type of method to resolve or solve different types of structures, as

63
00:11:59,129 --> 00:12:08,009
you can see here, if the structure, for example, is asymmetric, you can use Cremona method

64
00:12:08,009 --> 00:12:17,929
return that is more or less what I have already explained but in this case for more complicated

65
00:12:17,929 --> 00:12:29,519
structure. To do a good analyze of the structure we usually use some types of diagrams.

66
00:12:29,519 --> 00:12:49,519
For example, here we know the diagram of the shear force, and to understand this, you can know it is traction, compression, cutting, and types of movements.

67
00:12:49,519 --> 00:13:05,279
And here you have, for example, for forces, you can use the stress and surface, and for movement you can use this other thing in which you have other parameters.

68
00:13:05,279 --> 00:13:20,059
In each part is also important the shape of the bar, because the distance to neutral free bar is also different.

69
00:13:20,059 --> 00:13:31,059
So it can be different the dimensions in a bar depending on the profiles.

70
00:13:31,059 --> 00:13:43,759
And finally, the structure as a whole must be studied because it must be obviously stable.

71
00:13:43,759 --> 00:13:58,679
And to study the stability of a structure, we need to know the point, the action of gravity,

72
00:13:58,679 --> 00:14:06,080
we need to know the point of application of the weight of the structure.

73
00:14:06,080 --> 00:14:16,279
to do this we use this point and must must have to if I want a very stable

74
00:14:16,279 --> 00:14:30,440
structure this point must be in the low zone and between the legs or the super

75
00:14:30,440 --> 00:14:38,759
versus supports. This is all about the structures. I hope you can understand it better.