Shear stress failure is parallel to applied force. Compression and tensile stress failure occurs perpendicular to appilied force. All compressive steel failures are plastic which is permanent. Elastic deformation is temporary. Once the applied force ceases the member will return to the original state. Tensile yeild strength is the point at which plastic deformation occurs. Compressive yeild strength is also ultimate.

 

We just need the force to begin we dont need the depth of the columns at the ground. The columns are 12ft apart and 15 ft tall. Right?

 

Well, we know the panels are 15 feet tall, but we have no idea of the depth of the columns. They could go 5 feet into the ground, or 12 feet. The depth of the columns would make a huge difference on how much slack the braces had to take up, when dealing with a constant force applied to the main wall.

 

Do the 17 pages of this thread indicate a lack of desire to accuse the creators of the wall of sheer stupidity, or is it because we can't figure out who is to blame?

 

All plastic deformation takes place in shear, in a process known as dislocation movement. For a unidirectional force, whether elastic or plastic, this movement will be at 45 degrees to the applied force.

A long column can start to buckle before the yield stress is reached in the outer fibers. This can be demonstrated with a ruler or a yardstick.

 

What you are describing is called deflection. The inner fibers are in compression and the outside fibers are in tension. That is why in a steel beam's inner fibers fail first. Tensile yield strength is greater than compressive yield strength. When you apply inward force, compression, to the yardstick , it bows which is deflection. Also elastic and plastic are descriptions of deformation not force. Elastic and plastic deformation occur due a type of force applied. Shear stress is a planar stress. Tension and compressive stress are axial. The 45 degree movement applies to columns. When you do a tensile stress test on steel, it fractures perpendicular to the force applied when it reaches ultimate yield strength. It has been pulled apart not sheared.

 

Sounds like you have never taken a course in material science or metallurgy. In a tensile test of a mild steel, the rod will thin down in a process called necking. This is because the dislocations are moving at a 45 degree angle to the axis. In a tensile test of a high-strength steel, new dislocations are prevented from moving by the grain boundaries, interstices, and existing dislocations. This is why the rod will fracture in a brittle manner along a plane that is perpendicular to the axis.

 

Degree in mechanical engineering. Graduated with honors. Required to take statics, strength of materials, structural analysis and dynamics.

 

Depth of isnt important when first starting, you find the resultant forces at the two columns. Then calculate the forces at ground and where the brace is attached. Then you could figure the depth by balancing the forces above and below.

 

Depth is important when figuring out how much of the force is being resisted by the braces.

 

Yes in the end not beginning. You have to have a starting point. This ia statics problem. The first thing you do in design is set parameters and go for. You have to know the reactions first from that you willl select what your components will be that meet your design criteria.

 

Well, the end is where we get our answer. That's what I'm saying. Without knowing the depth, we won't get an answer to how much resistance from walker pressure is being put on each brace.

 

ok, true we cant analysis the wall we have. Not enough info, but we can analysis what would be required for it to work We can find the depth required. Basically we would design our own wall based upon the configuration currently seen. Actually this is like a problem you would see on a test in structural design.

 

Sure, we could analyze a theoretical wall, I agree with that. Another thing that would make this difficult is that the 12 x 15 panels are not composed of one solid panel, but actually several smaller ones fastened together, and it appears secured together with steel beams. They could end up being the weak points of the system, which would change our entire answer. Trying to analyze the wall as it is, I think would be a pretty messy problem.

 

Then you should know that in a uniaxial tensile test of a mild steel, yielding will begin when the shear stress causes dislocations to move at a 45 degree angle to the direction of the load.

And since you are a mechanical engineer, not a civil engineer, you may not be aware of steel design codes that incorporate elastic buckling of columns and beam webs.

PS. That MatWeb site lists 22000 psi as the "allowable" compressive strength of mild steel. That also happens to be the "allowable" tensile strength of mild steel.

 

You have to know how much force you are resisting to detemine required depth. You have balance the forces. Required depth would be an unknown. Beam size would be unknown. The known factors would be height, distance between columns and amount of force you want the structure to resist. Amount of force would be a figure we would set ourselves.

 

Right, but we aren't trying to work backwards and determine what depth would be required for the braces to maintain resistance against a horde. If we do that, then we are putting the cart before the horse, and a priori assuming that the braces will hold the horde. What we are asking, is can they secure the horde? So we'd need to start with all the info, and work from there.

I think our best shot at finding these answers would be to give up on the idea of finding an absolute number for the stress put on the braces, and instead settle for a relative number [the resistance the braces would withstand being on the outside VS. the resistance they could withstand being on the inside]. Because in that case, the depth of the fence would be the same on both sides of the equation, so you could just factor it out, call it zero.

But this still has a lot of problems, because we don't know really how the braces are attached to the ground, and we don't know how they would be attached on the inside.

 

I dig engineer talk. Kind of geeky, but still pretty impressive. Does Jessie have a crush on Rick as well? Who cares! We're talking about tensile strength and steel design codes that incorporate elastic buckling of columns and beam webs.

 

http://www.matweb.com/search/datasheet.aspx?matguid=afc003f4fb40465fa3df05129f0e88e6&ckck=1
Allowable tensile yeild strength is 36 ksi

 

The ribs in the panels below are running horizontally (parallel with the ground). The "not sure of material" vertical beams placed inside structural ones. If I recall your post of the picture of the man carrying the section of fence under his arm, the ribs were again evidently cut into sections that would make the joint strong.

Hopefully image posts:

This would indeed brace the joined smaller sections very well. The problem however is that in pictures showing the larger portion of the fence, the ribs are running vertically (Similar to how my farm buildings are constructed and I have had to replace many many times!!!)!



Here are horizontal braces shown from the inside!