Tensile/Bearing stress in a cantilever member.

  • #1
Two steel straps are use to hold member BCD level. The size of each strap is 12 mm thick and 50 mm wide. A 16 mm diameter bolt is used to connect thesteel straps to the 89 x 89 mm post at A. A 25 kN is applied at the free end of the cantilever at point D. Determine:
the tensile stress developed in the straps, and;
the bearing stress between the bolt and timber post at A.

diagram: http://s11.postimg.org/vqnu3bo8j/Untitled.png

I know the bearing stress will be the projected area of the bolt through the horizontal member as the denominator to (I think?) the 25 kN force plus the vertical component of the tensile stress in the metal straps. But I have no idea how to find that.

Are the only relevant measurements those which define the support triangle on the right?

Relevant Formulas:

Stress:
upload_2015-9-19_17-58-23.png


Bearing Load:
upload_2015-9-19_17-58-54.png


Trig functions.
 
Last edited:

Answers and Replies

  • #2
SteamKing
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Two steel straps are use to hold member BCD level. The size of each strap is 12 mm thick and 50 mm wide. A 16 mm diameter bolt is used to connect thesteel straps to the 89 x 89 mm post at A. A 25 kN is applied at the free end of the cantilever at point D. Determine:
the tensile stress developed in the straps, and;
the bearing stress between the bolt and timber post at A.

diagram: http://s11.postimg.org/vqnu3bo8j/Untitled.png

I know the bearing stress will be the projected area of the bolt through the horizontal member as the denominator to (I think?) the 25 kN force plus the vertical component of the tensile stress in the metal straps. But I have no idea how to find that.

Are the only relevant measurements those which define the support triangle on the right?

Relevant Formulas:

Stress: View attachment 88920

Bearing Load: View attachment 88921

Trig functions.
The first order of business is to create a free body diagram of the cross bar BCD and figure out all the loads acting on it in order to keep it in static equilibrium.
 
  • #3
The first order of business is to create a free body diagram of the cross bar BCD and figure out all the loads acting on it in order to keep it in static equilibrium.


Ok so some background: This is the first physics class I've had in just over a year. This is on an assignment and we've done no questions so far that involve distances (I only vaguely remember how they factor in as in lecture he always skips the summation of forces bit and gets right down to the formulas aforementioned).

There's going to be a downward force on the right end (represents the X-component of the tension acting through the metal straps) equal to 25kN? And 50kN going upwards at the bolt? Or am I completely off base?
 
  • #4
SteamKing
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Ok so some background: This is the first physics class I've had in just over a year. This is on an assignment and we've done no questions so far that involve distances (I only vaguely remember how they factor in as in lecture he always skips the summation of forces bit and gets right down to the formulas aforementioned).

There's going to be a downward force on the right end (represents the X-component of the tension acting through the metal straps) equal to 25kN? And 50kN going upwards at the bolt? Or am I completely off base?

It's not clear why "distances" should be such a problem.

If you haven't studied physics in over a year, perhaps some review work is needed. In particular, I would review the equations of static equilibrium. You are not going to solve this problem unless and until you figure out the forces acting on the bar BCD.
 
  • #5
It's not clear why "distances" should be such a problem.

If you haven't studied physics in over a year, perhaps some review work is needed. In particular, I would review the equations of static equilibrium. You are not going to solve this problem unless and until you figure out the forces acting on the bar BCD.


Maybe I'm very wrong but I don't think the point of a homework help forum is to ignore the questions I've posed and tell me to seek help elsewhere. I'm aware I need to balance the forces (I tagged this at statics for one) but am unsure how to go about doing so. If you aren't actually going to give me some guidance on how to do that why waste our time?

Part of why I mentioned that we have done nothing with distances in class is to illustrate my skepticism that I need more than the ones that make up the triangle. We have used no formulas involving distance and (obviously) seen no examples that use it either.
 
  • #6
SteamKing
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Maybe I'm very wrong but I don't think the point of a homework help forum is to ignore the questions I've posed and tell me to seek help elsewhere. I'm aware I need to balance the forces (I tagged this at statics for one) but am unsure how to go about doing so. If you aren't actually going to give me some guidance on how to do that why waste our time?

Exactly. The rules at PF allow HW helpers to make suggestions, but they do not allow us to do the student's work for them.

I have suggested that you write the equations of static equilibrium for the cross bar after drawing a free body diagram of it, but I have yet to see any evidence that you have done this.

Part of why I mentioned that we have done nothing with distances in class is to illustrate my skepticism that I need more than the ones that make up the triangle. We have used no formulas involving distance and (obviously) seen no examples that use it either.

Then this is something you'll have to take up with your instructor for this course. I haven't been in your class, and I don't know what you have been taught or what you are expected to know.

You have come here asking for help on how to solve this problem. I have given you the requisite starting point for solving this problem. The formulas you have quoted can be used to obtain a solution, but these formulas are not sufficient by themselves to find a solution.
 

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