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Thread: determined metal thickness needed

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    determined metal thickness needed

    Hello everyone. I've been welding for a few years now and always had the thickness of materials always told to me or i just really made it way over kill. How do you go about doing the calculations on determining the actual thickness needed. Like if i wanted to build trailing arms for my truck for example. I know i can cut them out on a plasma table out of some 1/4 but i feel like thatis way overkill. Thanks for the input.

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    Re: determined metal thickness needed

    Experience,study engineering or copy a proven design or all of the above. If you copy a proven design be sure to discover and copy the same alloys and heat treatment. Sometimes the shorter, quicker and cheaper solution is what you've already described....overbuild until you have enough of the first one, experience. Observe lots of failures and try to understand causality. Some failures are not under built, just overly abused. Mostly have fun and learn from you failures and sucesses.
    ---Meltedmetal

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    Re: determined metal thickness needed

    Quote Originally Posted by Meltedmetal View Post
    Experience,study engineering or copy a proven design or all of the above. If you copy a proven design be sure to discover and copy the same alloys and heat treatment. Sometimes the shorter, quicker and cheaper solution is what you've already described....overbuild until you have enough of the first one, experience. Observe lots of failures and try to understand causality. Some failures are not under built, just overly abused. Mostly have fun and learn from you failures and sucesses.
    Thank you.

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    Re: determined metal thickness needed

    Quote Originally Posted by Meltedmetal View Post
    Observe lots of failures and try to understand causality. Some failures are not under built, just overly abused.
    For examples of this, please head over to the trailer fail thread. Very interesting under/over builds.

    Sent from my SM-G960U using Tapatalk

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    Re: determined metal thickness needed

    Quote Originally Posted by welndnfab View Post
    Hello everyone. I've been welding for a few years now and always had the thickness of materials always told to me or i just really made it way over kill. How do you go about doing the calculations on determining the actual thickness needed. Like if i wanted to build trailing arms for my truck for example. I know i can cut them out on a plasma table out of some 1/4 but i feel like thatis way overkill. Thanks for the input.
    While there are many methods to "determine" the metal thickness required, as meltedmetal mentioned, if you want to be able to apply and work out the proper equations to work out numerical calculations for stress/deflection, then that is exactly what needs to be done via engineering. I hope you have a strong background in physics/analytical mechanics (IOW you need to know calculus, as a lot of stress/deflection models require integrating).

    Area Moment of Inertia or Moment of Inertia for an Area - also known as Second Moment of Area - I, is a property of shape that is used to predict deflection, bending and stress in beams. - Engineeringtoolbox.com

    Obviously there is FEA analysis that can do all the stress/deflection analysis you need, and it surely has just a steep a learning curve.
    1st on WeldingWeb to have a scrolling sig!



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    Re: determined metal thickness needed

    Educated guess (and experience) a lot of the time. Sometimes you want thicker material for rigidity more than for strength. Looking at commercially made items similar to what you're building and/or wanting yours the same strength or stronger.

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    Re: determined metal thickness needed

    There two basic ways
    Find trailer you like and is right size and just copy the metal size.
    The other way is to calculate the metal need for trailer

    Dave

    Quote Originally Posted by welndnfab View Post
    Hello everyone. I've been welding for a few years now and always had the thickness of materials always told to me or i just really made it way over kill. How do you go about doing the calculations on determining the actual thickness needed. Like if i wanted to build trailing arms for my truck for example. I know i can cut them out on a plasma table out of some 1/4 but i feel like thatis way overkill. Thanks for the input.

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    Re: determined metal thickness needed

    Quote Originally Posted by Oscar View Post
    While there are many methods to "determine" the metal thickness required, as meltedmetal mentioned, if you want to be able to apply and work out the proper equations to work out numerical calculations for stress/deflection, then that is exactly what needs to be done via engineering. I hope you have a strong background in physics/analytical mechanics (IOW you need to know calculus, as a lot of stress/deflection models require integrating).

    Area Moment of Inertia or Moment of Inertia for an Area - also known as Second Moment of Area - I, is a property of shape that is used to predict deflection, bending and stress in beams. - Engineeringtoolbox.com

    Obviously there is FEA analysis that can do all the stress/deflection analysis you need, and it surely has just a steep a learning curve.
    Most of the failures today come from modern "math". They rarely use math to make something better they use it to cut into the ten-fold safety margin that has existed in buildings and cranes for over a hundred years. As far as software analysis it is a gamble as well. Experience is the only solution. Looking at modern builds is a bit dangerous, they are often built only to perform in a perfect world not in the actual world under the actual conditions it will face. Once you see a few devices or structures fail from the slightest deviation of "normal stress" you realize that the people who designed it are either on drugs or live in an isolated bubble away from the rest of the world or both. Experience is the best.

    Sincerely,

    William McCormick
    If I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.

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    Re: determined metal thickness needed

    "Design of Welded Structures" by Omer W. Blodgett is a book that is (or was) very commonly used by structural engineers. It's a heavy book for its size and for its math.
    https://www.amazon.com/Design-Welded.../dp/9998474922

    https://www.jflf.org/SearchResults.asp?Cat=81

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    Re: determined metal thickness needed

    one lower iq method people left out is load to failure (destructive) testing, and it's less truthful cousin load testing.

    The final test for cranes and load bearing equipment is usually a "proof" test. Overload to the intended safety factor and pray to the sweet metal gods up above, or down below (can't figure out which side metal work is on yet!).

    BE READY FOR PROOF TEST TO FAIL, be as overly safe as possible with live things first and equipment second.

    Of course it's not always possible to do with every project etc [inset not so common sense disclaimers here].

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    Re: determined metal thickness needed

    If the math is done right and use the right table it will not fail.
    I did metal work engineering for 30 years and everything is still standing today. Even in tornado world.

    Dave

    Quote Originally Posted by William McCormick View Post
    Most of the failures today come from modern "math". They rarely use math to make something better they use it to cut into the ten-fold safety margin that has existed in buildings and cranes for over a hundred years. As far as software analysis it is a gamble as well. Experience is the only solution. Looking at modern builds is a bit dangerous, they are often built only to perform in a perfect world not in the actual world under the actual conditions it will face. Once you see a few devices or structures fail from the slightest deviation of "normal stress" you realize that the people who designed it are either on drugs or live in an isolated bubble away from the rest of the world or both. Experience is the best.

    Sincerely,

    William McCormick

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    Re: determined metal thickness needed

    Quote Originally Posted by smithdoor View Post
    If the math is done right and use the right table it will not fail.
    I did metal work engineering for 30 years and everything is still standing today. Even in tornado world.

    Dave
    There is no way that math could be working when it is being done on structures that are engineeringly unsound or the math is done on methods that should not be allowed. There should not be welding on buildings but they do some math and it is all good to weld. You may have added in some common sense and used some formulas to determine what you believe to be the right calculation but I can assure you the math being taught today will not create safe structures. We have seen it here and on other forums, someone with the current method of calculating something comes along and claims that a certain formula is what you should use. But when you use the old school method that is infallible it proves beyond a shadow of a doubt that the new math was made to allow poor buildings to go up. But those that believe what they are taught rather than look for the truth or question what they are taught support what is obviously wrong. It has been this way for thousands of years, that is what America was supposed to be about individual spiritual freedom.

    It is like an outside support wall in a building, it supports half the weight of the floor it supports. If you cantilever the floor over the wall, it suddenly supports the whole weight of the floor it supports. I had supposedly intelligent individuals tell me that is not so. It got to a point they were basically making me explain why someone would teach them that if it was not true, even though they knew from the demonstrations I did, the graphics I presented, and the explanations I offered that what I was saying was accurate. They just could not live with reality, they now knew how far from reality they were and they just didn't want it to be true.

    Most people do not know but they did away with the actual scientific method after World War Two. They took out step two, "demonstrate the hypothesis you wish to prove with your experiment to your peers." Since that was removed we no longer have science or engineering. They dropped the bomb on Hiroshima and claimed it was an experiment. They went on to claim that the experiment had proven the tremendous force of cohesion that when broken liberated that great force. They also stated in the same breath that we should not fear because they were going to keep the secret of the atom and atom bomb from the citizens of earth. This leaves me wondering if they are not citizens who are they. George Washington claimed that although we take on the role of the soldier we do not give up the citizen. So that act seems pretty unamerican. My point is that science, math, history, chemistry, English, and physics, have been tainted on purpose by the government that openly claimed it was for our own good and safety. A stupid citizen is a safe citizen was their motto. We must be the safest lot of idiots on earth. My point is that if you end an apparent force of cohesion there would be no energy liberated the objects would just no longer be held together it would be a rather lackluster event. But people do not ask them to demonstrate a force of attraction, even though there are no forces of attraction in our universe, only apparent forces of attraction that can only be explained by pushing forces. Universal Scientists did ask Chaswick and his crew to demonstrate their hypothesis, and they could not so instead they took out that step from the scientific method, and now it proves nothing.

    Sincerely,

    William McCormick
    If I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.

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    Re: determined metal thickness needed

    Quote Originally Posted by William McCormick View Post
    There is no way that math could be working when it is being done on structures that are engineeringly unsound or the math is done on methods that should not be allowed.
    I think I will take my engineering theory from the likes of Galileo, Bernoulli and Euler, and not McCormick.


    Quote Originally Posted by William McCormick View Post
    It is like an outside support wall in a building, it supports half the weight of the floor it supports. If you cantilever the floor over the wall, it suddenly supports the whole weight of the floor it supports. I had supposedly intelligent individuals tell me that is not so.
    Being a somewhat 'intelligent individual', I will state that is depends on the span (length) of the cantilever to the main span - and also on the floor framing type (eg steel beams, 2-way slabs etc). There is a 'sweet spot' where a cantilever will provide such a distribution, but commonly it does NOT.
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    Re: determined metal thickness needed

    Quote Originally Posted by Ingenuity View Post
    I think I will take my engineering theory from the likes of Galileo, Bernoulli and Euler, and not McCormick.




    Being a somewhat 'intelligent individual', I will state that is depends on the span (length) of the cantilever to the main span - and also on the floor framing type (eg steel beams, 2-way slabs etc). There is a 'sweet spot' where a cantilever will provide such a distribution, but commonly it does NOT.
    As soon as you create a cantilever, you double the weight on the wall supporting it. That is just the plain and simple truth of a lever. The fulcrum has twice the weight on it than it had before you cantilevered it. Often because things were engineered better years ago you do not see it fail. However as "math" is employed to get buildings to go up the slightest movement and suddenly walls are cracking and windows are shattering. This is not something I am dreaming up this is modern "math" at work in the real world.

    Of course, in both cases, the weight of the I-beam is also upon the H-beam as well as the payload. As you build a wall past the H-beam, it doubles the weight of the wall and whatever it is supporting above. This can cause the wall to not only support the wall above but the entire weight of the floor it is supporting. As soon as you cantilever you double the weight of whatever it is supporting before cantilevering it.

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    This is another one that is totally misunderstood because they don't want to see the reality and the crap they have built.

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    Sincerely,

    William McCormick
    If I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.

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    Re: determined metal thickness needed

    Quote Originally Posted by William McCormick View Post
    As soon as you create a cantilever, you double the weight on the wall supporting it. That is just the plain and simple truth of a lever.
    William:

    That is incorrect. You only 'double the weight' if the cantilever span equals the backspan. For any other ratio of backspan/cantilever the distribution of support reaction is as follows:


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    This is first-year engineering statics - for some folks it was high school math/physics.


    Quote Originally Posted by William McCormick View Post
    This is another one that is totally misunderstood because they don't want to see the reality and the crap they have built.
    Evidently, it appears to be misunderstood by you. The scale is NOT calibrated to read half the load placed upon it. The scale reads the tension in the cable - and assuming frictionless pulleys - is equal to the load at one end. If the load at each end was NOT equal the loading system (in this example) would move (displace) until it was in equilibrium.

    If you removed the left 25 lb pail (for example), and replaced it with a fixed support - like a clevis to secure the left end of the scale cable - and only have the 25 lb on the right end, the scale will read 25 lb. Action, reaction and equilibrium.
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    Re: determined metal thickness needed

    Quote Originally Posted by Ingenuity View Post
    William:

    That is incorrect. You only 'double the weight' if the cantilever span equals the backspan. For any other ratio of backspan/cantilever the distribution of support reaction is as follows:


    Name:  CANTILEVER BEAM.jpg
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    Name:  CANTILEVER BEAM TABLE.png
Views: 146
Size:  42.4 KB

    This is first-year engineering statics - for some folks it was high school math/physics.




    Evidently, it appears to be misunderstood by you. The scale is NOT calibrated to read half the load placed upon it. The scale reads the tension in the cable - and assuming frictionless pulleys - is equal to the load at one end. If the load at each end was NOT equal the loading system (in this example) would move (displace) until it was in equilibrium.

    If you removed the left 25 lb pail (for example), and replaced it with a fixed support - like a clevis to secure the left end of the scale cable - and only have the 25 lb on the right end, the scale will read 25 lb. Action, reaction and equilibrium.
    You have shown that if someone with a degree tells you something or publishes something that it must be true. If they make a table and put an engineering firm's name on it then that is gospel. As soon as you hang something over a fulcrum point, it doubles the weight of the payload on the fulcrum. But you have a table that shows otherwise.

    Look at any lever scenario and realize that as you hang something, a payload over a fulcrum point the amount that it is hungover for example say three feet, requires the point three feet on the other side of the fulcrum to create 25 pounds of counterforce to support the payload like a balance requires equal weight on both sides to balance it. This is basic engineering stuff that should be understood before you pick up a hammer or pry something with a screwdriver. So as I stated as soon as you hang something over a fulcrum point a wall supporting a cantilever for example the weight on the wall from the payload doubles. But do some more math until I am wrong. Haha.


    Sincerely,

    William McCormick
    If I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.

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    Re: determined metal thickness needed

    Quote Originally Posted by Ingenuity View Post
    William:

    That is incorrect. You only 'double the weight' if the cantilever span equals the backspan. For any other ratio of backspan/cantilever the distribution of support reaction is as follows:


    Name:  CANTILEVER BEAM.jpg
Views: 149
Size:  19.9 KB

    Name:  CANTILEVER BEAM TABLE.png
Views: 146
Size:  42.4 KB

    This is first-year engineering statics - for some folks it was high school math/physics.




    Evidently, it appears to be misunderstood by you. The scale is NOT calibrated to read half the load placed upon it. The scale reads the tension in the cable - and assuming frictionless pulleys - is equal to the load at one end. If the load at each end was NOT equal the loading system (in this example) would move (displace) until it was in equilibrium.

    If you removed the left 25 lb pail (for example), and replaced it with a fixed support - like a clevis to secure the left end of the scale cable - and only have the 25 lb on the right end, the scale will read 25 lb. Action, reaction and equilibrium.
    Take a look at the reality.



    Sincerely,

    William McCormick
    If I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.

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    Re: determined metal thickness needed

    Quote Originally Posted by smithdoor View Post
    I did metal work engineering for 30 years and everything is still standing today. Even in tornado world.

    Dave
    oh, c'mon mr smith, we already listened how hot its been , and now we got tornadoes too ?

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    Re: determined metal thickness needed

    Quote Originally Posted by William McCormick View Post
    You have shown that if someone with a degree tells you something or publishes something that it must be true. If they make a table and put an engineering firm's name on it then that is gospel. As soon as you hang something over a fulcrum point, it doubles the weight of the payload on the fulcrum. But you have a table that shows otherwise.

    Look at any lever scenario and realize that as you hang something, a payload over a fulcrum point the amount that it is hungover for example say three feet, requires the point three feet on the other side of the fulcrum to create 25 pounds of counterforce to support the payload like a balance requires equal weight on both sides to balance it. This is basic engineering stuff that should be understood before you pick up a hammer or pry something with a screwdriver. So as I stated as soon as you hang something over a fulcrum point a wall supporting a cantilever for example the weight on the wall from the payload doubles. But do some more math until I am wrong. Haha.


    Sincerely,

    William McCormick
    I have a degree in structural engineering and have been in practice for over 30 years - if that disqualifies me in this discussion then so be it.

    But I shall minimize the math to avoid further confrontation.

    Let's use your fulcrum/lever example with say a crane beam with a 25 lb load on the LHS and a fulcrum such that the backspan:cantilever ratio is 3:1

    Name:  CRANE BEAM.png
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    To balance the 25 lb applied load on the LHS we need a counterweight of 3 times = 75 lb on the RHS. Now the system is in equilibrium.

    So the total load that the fulcrum must now support is 25 lb + 75 lb = 100 lb.

    If the backspan:cantilever ratio is 2:1 then for a 25 lb applied load we would need 50 lb counterweight, and the total load to the fulcrum will be 75 lb.

    By adding a cantilever does indeed add load to the supporting wall/column (fulcrum), but its magnitude is dependent on the ratio of the backspan:cantilever.
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    Re: determined metal thickness needed

    Quote Originally Posted by William McCormick View Post
    Take a look at the reality.



    Sincerely,

    William McCormick
    This Youtube video supports my position and the example I posted above.
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    Re: determined metal thickness needed

    Quote Originally Posted by Ingenuity View Post
    I have a degree in structural engineering and have been in practice for over 30 years - if that disqualifies me in this discussion then so be it.

    But I shall minimize the math to avoid further confrontation.

    Let's use your fulcrum/lever example with say a crane beam with a 25 lb load on the LHS and a fulcrum such that the backspan:cantilever ratio is 3:1

    Name:  CRANE BEAM.png
Views: 144
Size:  9.8 KB

    To balance the 25 lb applied load on the LHS we need a counterweight of 3 times = 75 lb on the RHS. Now the system is in equilibrium.

    So the total load that the fulcrum must now support is 25 lb + 75 lb = 100 lb.

    If the backspan:cantilever ratio is 2:1 then for a 25 lb applied load we would need 50 lb counterweight, and the total load to the fulcrum will be 75 lb.

    By adding a cantilever does indeed add load to the supporting wall/column (fulcrum), but its magnitude is dependent on the ratio of the backspan:cantilever.
    I would get my money back from the school you went to.

    What you are not compensating for is what the boom adds to the equation. As soon as you pass the fulcrum point with a payload, the boom now adds the extra weight to the fulcrum to at least double it. The payload now unnaturally has to try to lift the beam with an equal weight of the payload at an equal distance that it is extended over the fulcrum an equal distance away on the other side of the fulcrum. I figured this out while building boat davits and got my finger caught under a very light aluminum davit. I was stuck there for a long while I used the time to figure it out.

    Name:  CRANE BEAM Edited.jpg
Views: 141
Size:  87.5 KB



    Sincerely,

    William McCormick
    If I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.

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    Re: determined metal thickness needed

    Quote Originally Posted by William McCormick View Post
    I would get my money back from the school you went to.

    What you are not compensating for is what the boom adds to the equation. As soon as you pass the fulcrum point with a payload, the boom now adds the extra weight to the fulcrum to at least double it. The payload now unnaturally has to try to lift the beam with an equal weight of the payload at an equal distance that it is extended over the fulcrum an equal distance away on the other side of the fulcrum. I figured this out while building boat davits and got my finger caught under a very light aluminum davit. I was stuck there for a long while I used the time to figure it out.

    Name:  CRANE BEAM Edited.jpg
Views: 141
Size:  87.5 KB



    Sincerely,

    William McCormick
    Ok, so math is not your strong suit. I intentionally made the beam 'weightless' to reduce the math - for your sake.

    Maybe you are a graphic person. Try this comparative graphic example:

    Name:  3 BEAMS.png
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    All three beams are in static equilibrium i.e. the sum of the forces in the vertical direction is zero, the some of the moments about any point along the beam is zero, and the sum of the forces in the horizontal direction is zero (which there are none in this example).

    If you cannot fathom this basic concept, then there is no hope.
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    Re: determined metal thickness needed

    What is a trailing arm?

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    Re: determined metal thickness needed

    Quote Originally Posted by Ingenuity View Post
    Ok, so math is not your strong suit. I intentionally made the beam 'weightless' to reduce the math - for your sake.

    Maybe you are a graphic person. Try this comparative graphic example:

    Name:  3 BEAMS.png
Views: 131
Size:  15.4 KB

    All three beams are in static equilibrium i.e. the sum of the forces in the vertical direction is zero, the some of the moments about any point along the beam is zero, and the sum of the forces in the horizontal direction is zero (which there are none in this example).

    If you cannot fathom this basic concept, then there is no hope.
    A fulcrum no matter the lengths of the lever or overhang require that the fulcrum point take at least twice the force of the greatest pressure upon either side of the lever, plus the weight of the lever.

    As soon as you create a cantilevered floor over a support wall, the length of the overhang of the floor cancels out the same length of floor on the other side of the supporting wall. You have created a one-to-one lever twice the length of the overhang. So the wall has to now support that combined length totally. Any weight you now add to the overhung floor must be countered with the same force and at the same distance on the other side of the support wall. You are correct, for a static load, as my video demonstrates, but as soon as a 120,000-pound truck goes by, as soon as the random load on the main floor is set in a certain location or jostled, the flooring structure starts to flex almost comically when vibrated or jostled. Well beyond what the weight of the overhanging payload or counterbalance would cause if supported at each end rather than at some midpoint. It has to do with start change and stop and the atoms in the material, that is why the overhang causes so much trouble as you add and take away even the smallest amount of weight from an overhang or the main portion of the boom. In a perfect world a static world, you are correct. In the real world doubling the boom diameter of a boom that would be sufficient in a static world might not be enough in the real world. If you look at older crane booms and older bridges they are designed with an arc shape, so they cannot flex. As soon as you cantilever something you have a wobbly overhang that always causes trouble with settling, compression of building materials, and strange bounce in flooring unless you overbuild it drastically.

    I was taught to stay away from building overhung floors, and or beef them up and the foundation below them substantially from people that built and designed the long-lasting things around us. I was taught to build huge gussets at the fulcrum point on the boom because of the fluctuating load that can bend a large diameter boom as if it was made of paper mache. I have seen the foundations settle only on the cantilevered side of the house or building. It causes momentary forces well beyond the static load and well beyond what the same load just supported directly will cause.




    Sincerely,

    William McCormick
    If I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.

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    Re: determined metal thickness needed

    Quote Originally Posted by Ingenuity View Post
    William:

    That is incorrect. You only 'double the weight' if the cantilever span equals the backspan. For any other ratio of backspan/cantilever the distribution of support reaction is as follows:


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    This is first-year engineering statics - for some folks it was high school math/physics.




    Evidently, it appears to be misunderstood by you. The scale is NOT calibrated to read half the load placed upon it. The scale reads the tension in the cable - and assuming frictionless pulleys - is equal to the load at one end. If the load at each end was NOT equal the loading system (in this example) would move (displace) until it was in equilibrium.

    If you removed the left 25 lb pail (for example), and replaced it with a fixed support - like a clevis to secure the left end of the scale cable - and only have the 25 lb on the right end, the scale will read 25 lb. Action, reaction and equilibrium.
    The scale in my graphic is showing that the scale is able to suspend 50 pounds against the force of gravity therefore it is under 50 pounds of force and registers half that force. Or I am missing something.

    Sincerely,

    William McCormick
    If I wasn't so.....crazy, I wouldn't try to act normal, and you would be afraid.

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