How to calculate the normal stress of a Howe reinforcement?

[Tapias5000]

Homework Statement

I am asked to calculate the forces of the bars specifying if it is in compression or tension, then I am asked to calculate the normal stress in all the bars.

Relevant Equations

Σfx=0 and Σfy=0

This is the structure

I already made the calculation of all the bars T = tension and C = compression, these are the results.

now I am asked to calculate the normal stress in all the bars but I don't understand where to start, could you tell me how? here is the diagram of the first node but I really don't know where to start.

 

[haruspex]

calculate the normal stress

Don't you need to know the cross-sectional area of the bars for that?

 

[Tapias5000]

Don't you need to know the cross-sectional area of the bars for that?

It seems that way, I looked for a lot of information and most of the exercises had the data of the normal effort, or the area or some other, here I have nothing that.

I don't know if because they are "triangles" I should calculate their area through centroids.

I also have to choose the material of this structure, some type of beam, I don't know if by choosing it I will obtain any data to calculate it, but if I follow the order, they first ask me to calculate the normal stress and then choose a beam for the structure.

I also found information on a method called normal bending stress, where none of this data is available, but I did not find any example that did it with a structure like this or similar.

I'm really very confused ...

 

[haruspex]

It seems that way, I looked for a lot of information and most of the exercises had the data of the normal effort, or the area or some other, here I have nothing that.

I don't know if because they are "triangles" I should calculate their area through centroids.

I also have to choose the material of this structure, some type of beam, I don't know if by choosing it I will obtain any data to calculate it, but if I follow the order, they first ask me to calculate the normal stress and then choose a beam for the structure.

I also found information on a method called normal bending stress, where none of this data is available, but I did not find any example that did it with a structure like this or similar.

I'm really very confused ...

Sounds like an error in the question. Is there a list of beams to choose from? If so, does it specify only the material, or material and section?

 

[Tapias5000]

Sounds like an error in the question. Is there a list of beams to choose from? If so, does it specify only the material, or material and section?

no, I'm supposed to look for and choose the beam too

 

[haruspex]

no, I'm supposed to look for and choose the beam too

Then all you need is the forces you calculated.
My guess is the part asking for normal stress is left over from an earlier version of the question.

 

[Tapias5000]

Then all you need is the forces you calculated.
My guess is the part asking for normal stress is left over from an earlier version of the question.

Ok, so there is no other method to calculate the normal stress without having at least one data? I just follow the order of the points and first is to calculate the normal stress and then choose a beam.

First I would have to look for information about a beam and then calculate the normal stress then?

 

[haruspex]

Ok, so there is no other method to calculate the normal stress without having at least one data? I just follow the order of the points and first is to calculate the normal stress and then choose a beam.

First I would have to look for information about a beam and then calculate the normal stress then?

Each material will have a safe normal stress limit, and from that and the force you can calculate the required cross-section.

 

[Lnewqban]

I don't understand the meaning of "the normal stress in all the bars".
Could you show us the whole text of the problem?

 

[Chestermiller]

Ok, so there is no other method to calculate the normal stress without having at least one data? I just follow the order of the points and first is to calculate the normal stress and then choose a beam.

First I would have to look for information about a beam and then calculate the normal stress then?

These are not beams. This is a pin-connected truss made up of struts that can only support tension or compression. There are no bending stresses. The main principal stress of each strut is oriented along the strut, and the other two principal stresses are zero. To get the stress in each strut, you need to know its cross sectional area.

 

[haruspex]

I don't understand the meaning of "the normal stress in all the bars".
Could you show us the whole text of the problem?

"Normal stress" is the force along the bar divided by its cross sectional area, i.e. stress normal to the cross section.