# Static Analysis of Bolts on Multiple Surfaces

#### jsed

I am trying to analyze if the bolts in my design are sufficient to support the load on a shaft. Unfortunately, the bolts are not all located on one face, and though I know how to analyze each face by itself, but I would like to be able to combine them all into one problem. I have attached a rough sketch of the scenario for your reference, with each of the red dots representing a bolt location. Thanks in advance

#### Attachments

• 32.4 KB Views: 34
Related Mechanical Engineering News on Phys.org

#### AZFIREBALL

Can you provide us with some idea of the substructure the bolts are going through to hold the beam in place?

#### jsed

Can you provide us with some idea of the substructure the bolts are going through to hold the beam in place?
The bolts will be going through a fairly rigid structure of extruded aluminum framing, and the beam is also made of aluminum.

#### jsed

Yes, that is almost exactly right, except the bolts are only present on the side nearest us, the bottom of the beam, and the back face of the beam which butts up to the support plate. I tried to put arrows on your drawing to make it more clear

#### Attachments

• 167.6 KB Views: 26

#### AZFIREBALL

The bolts will be going through a fairly rigid structure of extruded aluminum framing, and the beam is also made of aluminum.
Like this?

#### BvU

Homework Helper
I know how to analyze each face by itself, but I would like to be able to combine them all into one problem
That invites the question: what did you do and what came out and why not just add up the three ?

Furthermore I am puzzled why post # 4 can be older than # 5 ?

Are the bolts all the way through -- as drawn in the side view it seems -- ? And they dont interfere with each other ??????

#### AZFIREBALL

So the top and side bolts do not go through? Is there an angle on the bottom of the beam attached to the plate?

#### jsed

That invites the question: what did you do and what came out and why not just add up the three ?
As far as what I am doing to analyze each "face" of bolts, I am basically using the concepts outlined in this web page: http://www.roymech.co.uk/Useful_Tables/Screws/Bolted_Joint.html

That invites the question: what did you do and what came out and why not just add up the three ?

Are the bolts all the way through -- as drawn in the side view it seems -- ? And they dont interfere with each other ??????
So the top and side bolts do not go through? Is there an angle on the bottom of the beam attached to the plate?
The bolts do not go through, they just screw into the beam itself, and they do not interfere with each other.

#### AZFIREBALL

So the top and side bolts do not go through? Is there an angle on the bottom of the beam attached to the plate
That invites the question: what did you do and what came out and why not just add up the three ?

Furthermore I am puzzled why post # 4 can be older than # 5 ?

Are the bolts all the way through -- as drawn in the side view it seems -- ? And they dont interfere with each other ??????
I withdrew my post to fix it...then re-posted.

BvU

#### jsed

To expand on my thought process: I could use the current analysis methods I am using to analyze each face, but the supports from the other bolts not on the face currently being evaluated would have an affect on the face in question. Originally, I was considering treating the centroid of each face of bolts as an individual support reaction and then splitting up those forces among the bolts on that face, but I am not too confident that will give me an accurate representation of both shear and bending stresses in each bolt.

#### AZFIREBALL

Yes, that is almost exactly right, except the bolts are only present on the side nearest us, the bottom of the beam, and the back face of the beam which butts up to the support plate. I tried to put arrows on your drawing to make it more clear
No bolts on the top?

#### AZFIREBALL

Correct, no bolts on top
Is there a reason for this? They would do a better job of resisting the load than bolts on the bottom.

#### jsed

Is there a reason for this? They would do a better job of resisting the load than bolts on the bottom.
The beam that we have been discussing is more of a representation of an assembly of a few components. Due to the function of the assembly, I am not able to design it such that the bolts are attached on the top face.

#### AZFIREBALL

OK. Now we need to draw force diagrams for each bolt. Number the bolts and show us a diagram of the forces on each bolt as you see it.

#### jsed

OK. Now we need to draw force diagrams for each bolt. Number the bolts and show us a diagram of the forces on each bolt as you see it.
This is what I'm thinking. Each bolt provides a force in the same plane as the applied load, and each bolt provides moments that counteract the rotation of the shaft.

#### Attachments

• 46.2 KB Views: 32

#### AZFIREBALL

This is what I'm thinking. Each bolt provides a force in the same plane as the applied load, and each bolt provides moments that counteract the rotation of the shaft.
Is the load off center of the beam as you show in the latest sketch?
Now we need to draw in-plane vector diagrams of each bolt's reaction to its load using the group centroids.
How are you handling vertical shear? (Should not be carried by bolts.)

#### jsed

Is the load off center of the beam as you show in the latest sketch?
Now we need to draw in-plane vector diagrams of each bolt's reaction to its load using the group centroids.
How are you handling vertical shear? (Should not be carried by bolts.)
Are you saying that I need to analyse the reactions of the centroid of each bolt group, and then analyze how each of the bolts contribute to that reaction?
As far as shear goes, the bolts will be handling the majority of the shear.

#### AZFIREBALL

Are you saying that I need to analyse the reactions of the centroid of each bolt group, and then analyze how each of the bolts contribute to that reaction?
As far as shear goes, the bolts will be handling the majority of the shear.
First question: Yes, that is right. Show directional vectors about the centroid and the resulting load directions carried by each fastener. Non-dimensional (Magnitude of load at each fastener location comes next)
Question 2: Is there an angle clip under the shaft at the attached end where 7 and 8 go through? That could carry the vertical shear load if the shaft sets on top of it.
Is the load off set, or centered on the shaft/beam?

#### jsed

First question: Yes, that is right. Show directional vectors about the centroid and the resulting load directions carried by each fastener. Non-dimensional (Magnitude of load at each fastener location comes next)
Question 2: Is there an angle clip under the shaft at the attached end where 7 and 8 go through? That could carry the vertical shear load if the shaft sets on top of it.
Is the load off set, or centered on the shaft/beam?
Thanks so much for your help.
To answer your question, there is an angled clip under the shaft to carry the vertical shear load. And the load is off set as well.

#### BvU

Homework Helper
The beam that we have been discussing is more of a representation of an assembly of a few components. Due to the function of the assembly, I am not able to design it such that the bolts are attached on the top face.
Changing the rules during the game ? Or just moving the goal posts ? What is it you want from PF ?

#### AZFIREBALL

Does this better represent the structure?

BvU

#### BvU

Homework Helper
Nice hand of drawing !
Bottom bolts seem pointless to me

Thanks.
They are.

#### AZFIREBALL

jsed:

Other considerations:
If possible, bolts in tension should have at least two times diameter thread engagement.
If the bolt diameter is 1/2, the thread engagement should be one inch.
Use thick washers under all bolts in tension to reduce ‘pull-through’.
Where applicable, check each bolt connection for bearing failure and edge distance tear-out in its primary and adjoining structures.
Torque all fasteners to spec for type and size.
Consider the use of a head locking device or thread lock material.
Consider increase margin of safety for oscillatory (variable) loading, vibratory environment, aging in harsh environment or dissimilar materials.

"Static Analysis of Bolts on Multiple Surfaces"

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving