Is there an engineer in the house?
Moderator: Bill Edmundson
Is there an engineer in the house?
If so, please help me with a calculation of moment, simple bending stress:
Purpose: Spreader Bar (mild steel)
Design: Two 4" x 5.4(lb/ft) Cchannel facing opposite: ][
Gap: 1.5" (bolts regarded as shear property)
1" G5 bolts (3) located center and ends, housed in 1" i.d. pipe (spacers).
No cable/chains to be used above spreader... strictly moments to ends from center
Length between spreader ends: 8.0'
Area known on channel section: 1.59 sq.in.
Question: Given a safety factor of 5:1 (50,000psi base) @ 10Kpsi what can I expect for a working load on this spreader? I'd calculate the moment myself but I'm not skilled in working out the modulus and I'm finding the Machinery's Handbooks text to be a bit cumbersome. Not their fault, mine.
Any help with this MUCH appreciated!
 MJ
Purpose: Spreader Bar (mild steel)
Design: Two 4" x 5.4(lb/ft) Cchannel facing opposite: ][
Gap: 1.5" (bolts regarded as shear property)
1" G5 bolts (3) located center and ends, housed in 1" i.d. pipe (spacers).
No cable/chains to be used above spreader... strictly moments to ends from center
Length between spreader ends: 8.0'
Area known on channel section: 1.59 sq.in.
Question: Given a safety factor of 5:1 (50,000psi base) @ 10Kpsi what can I expect for a working load on this spreader? I'd calculate the moment myself but I'm not skilled in working out the modulus and I'm finding the Machinery's Handbooks text to be a bit cumbersome. Not their fault, mine.
Any help with this MUCH appreciated!
 MJ
Avoid Haste.
I am having trouble picturing what you are trying to do. If you are using this beam to hang a weight from, the load depends on how you are going to attach the ends of the beam
If the beam is going to be used in an application in which a compressive force is going to be used, there is a different animal to deal with altogether.
The needed information for calculating the section modulus is in a steel book, or from a vendor. I assume you have access to one or the other since you listed the cross sectional area.
If you could post a sketch of what you are trying to do I could help you with more details.
If the beam is going to be used in an application in which a compressive force is going to be used, there is a different animal to deal with altogether.
The needed information for calculating the section modulus is in a steel book, or from a vendor. I assume you have access to one or the other since you listed the cross sectional area.
If you could post a sketch of what you are trying to do I could help you with more details.
 Bill Edmundson
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 Joined: Wed Nov 23, 2005 6:45 am
 Location: Birmingham, AL, USA
 Contact:
The section modulus for C4x5.4 is 1.93 Back to back would be 3.86.
At 10 ksi x 3.86 =38.6 "k
Moment is PL/4 = 38.6 P= 4x38.6/96 = 1.6k or 1600#
Bill
At 10 ksi x 3.86 =38.6 "k
Moment is PL/4 = 38.6 P= 4x38.6/96 = 1.6k or 1600#
Bill
Mini Tug, KH Tahoe 19 & Bartender 24  There can be no miracle recoveries without first screwing up.
Tahoe 19 Build
Tahoe 19 Build
Bill, thanksBill Edmundson wrote:The section modulus for C4x5.4 is 1.93 Back to back would be 3.86.
At 10 ksi x 3.86 =38.6 "k
Moment is PL/4 = 38.6 P= 4x38.6/96 = 1.6k or 1600#
Bill
Questions...
PL/4? I don't understand the formula, had I known what to "plug" in I could have done it. I'm guessing distance x moment? When I mentioned modulus, I thought I had to perform a Young's modulus.
Also, section modulus? My charts in Machinery's Handbook gave area, how did you convert to section modulus?
Avoid Haste.
P is the load, L is the unsupported length, 4 is well you know
Stress = Moment / Section Modulus
Your allowable stress is 10 ksi, modulus is 3.86 in^3.
For your section at 8', the formula would be =>
(Yield strength of material / safety factor) * 3.86 * 4 * (1 / 96) * 1000
This would give you the working load in pounds
Section mod. is a property that depends only of the geometry/shape of the cross section of the beam.
One last thing, mild steel usually has a yield of 36 ksi (ship building mild steel), a safety factor of 5:1 would put you at an allowable stress of around 7.2 ksi with a working load of 1158#. 50  51 ksi is usually high strength material. You may want to double check the strength of your material before loading anything up.
Stress = Moment / Section Modulus
Your allowable stress is 10 ksi, modulus is 3.86 in^3.
For your section at 8', the formula would be =>
(Yield strength of material / safety factor) * 3.86 * 4 * (1 / 96) * 1000
This would give you the working load in pounds
Section mod. is a property that depends only of the geometry/shape of the cross section of the beam.
One last thing, mild steel usually has a yield of 36 ksi (ship building mild steel), a safety factor of 5:1 would put you at an allowable stress of around 7.2 ksi with a working load of 1158#. 50  51 ksi is usually high strength material. You may want to double check the strength of your material before loading anything up.
 Bill Edmundson
 Posts: 11576
 Joined: Wed Nov 23, 2005 6:45 am
 Location: Birmingham, AL, USA
 Contact:
P is you lifting force at the center. P/2 on each end. The distance from the end to the lift point is L/2. M= force x distance or P/2 x L/2 = PL/4
It's hard to believe that I made a living for almost 34 years on variations of one equation. Stress = P/A + MC/I.
Bill
It's hard to believe that I made a living for almost 34 years on variations of one equation. Stress = P/A + MC/I.
Bill
Mini Tug, KH Tahoe 19 & Bartender 24  There can be no miracle recoveries without first screwing up.
Tahoe 19 Build
Tahoe 19 Build
Thanks much for the responses.
I also was curious about the yield/ultimate strength because my manual (typical) gives the lowest carbon grade. It's A36, which used to be rated at 36K but is now rated @ 48K yield, 70K ultimate.
I'm not sure how that has happened, but several searches on google under "A36 steel yield strength" produced a number of testing results that reported the higher numbers.
I also was curious about the yield/ultimate strength because my manual (typical) gives the lowest carbon grade. It's A36, which used to be rated at 36K but is now rated @ 48K yield, 70K ultimate.
I'm not sure how that has happened, but several searches on google under "A36 steel yield strength" produced a number of testing results that reported the higher numbers.
Avoid Haste.
 Bill Edmundson
 Posts: 11576
 Joined: Wed Nov 23, 2005 6:45 am
 Location: Birmingham, AL, USA
 Contact:
Anyway, I think as more and more steel was recycled grade 50 steel got mixed with A36. The strength went up over time. It was sold for a while as "MultiCert". For all intents and purpose it is now 50 ksi steel.
But, if you want to be sure make sure you have Grade 50. I think it's A572 or A992.
Bill
Mini Tug, KH Tahoe 19 & Bartender 24  There can be no miracle recoveries without first screwing up.
Tahoe 19 Build
Tahoe 19 Build
Steve,leakcheck wrote:I have quite alot I could add, but I think I will let these guys kinda struggle along for a little while by themselves...it sorta builds character, then when they need my help they will come to me on their knees !!
Steve
I think they are doing pretty good on this one & don't really need our help!!

 Posts: 454
 Joined: Wed Nov 12, 2003 3:20 pm
 Location: Harlan, IN
These calculations are the type of thing that caused my daughter to switch majors from civil engineering to meteorology. I told her: "Smart choice, just think, you can be wrong half of the time, nobody is surprised, and you get to keep your job!"
MJ, congrats on the successful lift! Best wishes as you press on to launch.
MJ, congrats on the successful lift! Best wishes as you press on to launch.
Noah was a firsttime boatbuilder