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Determine the thickness of steel plate (based on S275 steel)

  1. Sep 2, 2009 #1

    I needed to design for a steel plate of S275 steel (275 N/mm2) that will resist a tensile force = 2 x 65 kN = 130 kN. The steel plate must not bend due to this tensile force = 130 kN. And I need to determine the minimum steel plate thickness that will resist the bending (due to the tensile force being applied by 2 anchor bolts) and fabricate the steel plate. Do I need to apply terms like Ixx & Iyy in these formulas?

    What formulas do I use to determine the min thickness of the steel plate. How is the material strength (275 N/mm2) used in the formulas? (I only know the material strength = S275 but I forgot how to apply this material strength)

    Is this material strength = 275 N/mm2 also known as the bearing strength? How do you define bearing strength?

    The setup of the test looks something as per attached document:
    (I scanned a pdf file which I have sketched all the details, how do I post on this forum)
    (Can't find the picture button which will allow me to upload the scanned pdf)

    Attached Files:

    Last edited: Sep 3, 2009
  2. jcsd
  3. Sep 3, 2009 #2


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    Go to the "Go Advanced" button and then select "Manage Attachments." A drawing would be very helpful.
  4. Sep 3, 2009 #3


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    The plate will bend, the only question is how much is allowable.
  5. Sep 3, 2009 #4


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    I work in USA units only, so i don't know what is meant by material strength. Usually for steel design, the yield strength is used with a factor of safety, or, alternatively, a load factor is applied to the design load, and bending stresses must not exceed the yield stress. Yield strength and bearing strength are not the same.
  6. Sep 4, 2009 #5
    Hi Fasten,
    This looks like a college excercise, in which case we would not want to overstep the line.

    In a sense you are asking how to design steel members which is a complete course of study.

    In your question you seem to be unclear about the differences between bending, tension and shear forces. With reference to your diagram, the plate is subject to both shear and bending and the threaded rod and anchor bolts are subject to tension. Going by the proportions of your sketch, I would guess that the weakest point in the system is the weld between the threaded rod and the plate or, if you change that fixing method, the tension in the threaded rod. It looks as though the rod will fail before the plate is subjected to significant strain of any type.
  7. Sep 4, 2009 #6


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    fasten: I will rename your "a" dimension t, and I will name the width of your plate b. To be conservative, you could design your plate as a simply-supported beam. Therefore, bending stress is sigma = M*c/Iyy = 1.5*P*L/(b*t^2), where P = 130 000 N, b = plate width (mm), t = plate thickness (mm), and L = distance between centre points of anchor bolts (mm). Ensure Ry = FSy*sigma/Sty ≤ 100 %, where Sty = material tensile yield strength = 275 MPa, and FSy = yield factor of safety, such as 1.70. But for a test fixture, you can use FSy = 2.0.

    You would also want to look at bending stress on the plate ends, at the anchor bolts, due to prying, which I didn't have time for; plus, we don't have all the dimensions of your parts. You would also want to analyze the threaded rod weldment, etc.

    Bearing yield strength can be approximated as Sbry = 1.5*Sty.
  8. Dec 18, 2009 #7
    Why is sigma = M*c/Iyy = 1.5 * P * L (b*t^2)?

    Also what is the "c" in this case? (from where to where)
    And b = width of plate (which is the shorter dimension when u look at the plan of the sketch?)

    I m quite confused now.

    This S275 steel material is the bending strength of the steel plate (Quote: BS 5950-1:2000, Table 16) But how does the bending strength & thickness relates to the tensile force being exerted in this exercise??

    Basically I just want to ensure the plate does not bend when the tensile force is applied upwards via the center threaded rod and that the plate does not fail in any other manner. (e.g. the holes that are made in the plate will weaken the plate but how do we calculate these checks?) And in doing so, I need to determine the minimum plate thickness and I think this is related to the material of the plate itself (so this 275 N/mm2 is related) but how to apply, I forgot already.

    I m a working adult engineer whom have gone through the whole steel design course but sad to say, I have returned most of it to my lecturers and I also have not been practicing steel design but needs to carry out this simple exercise for a testing I need to do. The formulas do look familiar and if someone can just explain to me what they stand for, I hope I will be able to recall back slowly what I have learnt last time.

    Will appreciate if someone can guide me step by step through it.
  9. Dec 19, 2009 #8


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    c = 0.5*t, and b is the shorter dimension of the plate. M*c/I is explained in your strength of materials text book; look up "bending stress" in the index. To compute sigma, just plug numbers into the right-hand side of the first equation given in post 6. After that, compute Ry, which is the second equation given in post 6. Go ahead and do this. Show your work; and someone might check your math.
  10. Dec 21, 2009 #9

    I have done up 2 calculations for
    1) bending strength check
    2) Deflection

    Kindly check if it is appropriate. I think my confusion on my calculation is on the "b" & "h" used in the section modulus & Ixx,Iyy.

    A) I read from my 10 year old strength of material textbook and it shows that section modulus = bh^2/6 for a rectangular section. But my confusion is which dimension is b&h if my plate dimension I m proposing = 0.2 m L x 0.1 m W x 0.015 m Thickness. I know the way the load is applied affects which is the "b" & "h".

    B) For deflection, I assumed the supports (in this case I interprete as the T bolts that is resisting the upward force as the supports; they don't look hinged to me;(i.e. they don't look simply supported) so I take it as they are fixed. I could be very wrong on this...
    Also is assuming it is simply supported the worst case scenario?

    Subsequently, I went to the internet, got the deflection formula for 2 fixed support with a central load, input the parameters inside (again to me the confusion is the "b" & "h") and got a deflection which is 50 mm. (which seems excessive to me for a small load = 18 kN with a 15mm thick plate)

    C) Is there any other checks I need to perform to determine that the plate is sufficiently strong?

    Feel free to email me. I welcome any feedback.

    Attached Files:

  11. Dec 21, 2009 #10
    Forgot to highlight that my main interest is the black plate currently as I have actually done single T bolt testing and the cast-in channel does not give way. So I just wish to check if thickness = 0.015 m or 15 mm is sufficient for the load = 18 kN (2 nos. x 2 x SWL) (4 x 4.5 kN)
  12. Apr 7, 2010 #11
    How do I determine the permissible bending stress in a plate base(in this case, for a slewing jib).i need this property to acquire the minimum required thickness of the base plate but from the infos i have, i only have the dimensions of the plate. anyone know where i can find the table for this steel property?
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