Terminology

[Polecat]

Being from the old school, I was curious as to why the engineering standard reference for "moment", which has been termed "foot-kips" for over 200 years, somehow morphed into the nonsensical term "kip-feet." Who started this and why?

http://www.spiraleng.com

 

[hokie66]

Maybe it is just a first step toward adopting an international standard? Most of the world uses kNm (kilonewton metre). So the force first, then the distance.

 

[Lomarandil]

It's easier to fix if I'm rushing through a calc and realize I've written a moment demand in kips?

Saves a letter (you know us engineers and efficiency)?

Rolls off the tongue better?

I don't know (although I suspect the latter has something to do with it).

 

[jayrod12]

Think of how the moment formulae look typically,

M=wl^2/8
M=PL/4
M=Pab/L

I would be inclined to think it has more to do with that.

 

[DETstru]

I don't recall what I learned in school but I've always written "k-ft"

Never though about writing it the other way until reading your post.

 

[TLHS]

How is kip-feet any more nonsensical than foot-kips?

 

[Polecat]

Thanks for the enlightenment, fellows.
When I considered the formulas that Jayrod mentioned, the force-distance nomenclature makes sense.
Hokie66's mention of an international standard (kNm) format is also reasonable.
However, my favorite answer is from Lomarandil --- it rolls off the tongue better (as long as you are speaking English, that is).

http://www.spiraleng.com

 

[andriver]

I use kip*ft but when referring to an internal combustion engine it's foot-pounds.

 

[Polecat]

To TLHS:
kip-feet becomes nonsensical only to one who originally learned and has used foot-kips all of his life! Like I said, I'm "old school."

http://www.spiraleng.com

 

[MacGruber22]

I always thought that the order of units switched depending on if you were talking about units of energy and not mechanical torsion/moment.

length-force <--> energy
force-length <--> mechanical torque



"It is imperative Cunth doesn't get his hands on those codes."

 

[SlideRuleEra]

As a historical check, what came to mind is AISC's labeling of the graphs for "Allowable Moments In Beams", as shown in the various editions of the "Manual of Steel Construction". Here is what turned up in the copies I have:

AISC 9th Edition (1989) Kip Ft. (Page 2-149)

AISC 6th Edition (1963) Kip Ft. (Page 2-48)

AISC 5th Edition (1946) Kip Feet (Page 203) Notice it is spelled this time, not abbreviated.

Maybe "Kip Feet" has been hiding out longer than we realized.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[JAE]

I also have the 5th, 7th and 8th Editions of AISC's manual - all refer to Kip-Feet. However I tend to say Foot-kips.



Check out Eng-Tips Forum's Policies here:
faq731-376

 

[Lomarandil]

Good point, if I'm talking about fastener torque, that's still ft-lbs or in-lbs. It's only structural moment/torsion where I switch it to kip-ft.

Though pounds is a softer sound, so maybe that still fits in my theory about rolling off the tongue.

 

[TLHS]

AISC 1941 uses ft-kip for beams but kip-in for pins

 

[SlideRuleEra]

Checked some of oldest books I have... interesting result. No mention of either kip-feet or feet-kips at all.

1934 Carnegie Pocket Companion
1917 Cambria Steel Handbook
1892 Pencoyd Wrought Iron & Steel In Construction

All three use either foot-pounds or inch-pounds. This is even when the magnitude of the numbers is large, say >> 100,000 inch-pounds.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Ron]

Torque was almost always referred to as "ft-lbs"....whether talking about buildings or autos. Torque is moment, or is it "moment is torque".....I'm usually confused anyway!

 

[XR250]

I still use ft-lb or ft-kip for everything

 

[Polecat]

Slide Rule Era, you really started me on a roll.

I dug up a Concrete Engineer's Handbook that my father had that was dated 1918, and it referred only to inch-lbs.
ACI's 1955 Reinforced Concrete Design Handbook uses ft-kips only.
My old Strength of Materials book dated 1951 uses ft-lbs only.
My textbook on Statically Indeterminate Structures dated 1951 refers to ft-kips throughout.
My textbook on Timber Engineering dated 1949 uses inch-lbs.
My PCI Design Handbook dated 1992 uses ft-kips throughout.
I have a Standard Handbook for Civil Engineers dated 1996 in which the chapter on concrete design refers to in-kips, the chapter on wood design shows in-lbs and the chapter on steel design uses kip-inches.
My 2001 design manual for Engineered Wood Construction uses in-lbs.

Hence, my conclusion from this interesting exercise and the input that all of you have made is that the term kip-ft seems to have appeared much earlier in steel handbooks and texts, and that how one refers to bending moment seems to be related to which discipline you are working in. Wood and concrete still seem to use the Distance-Load units while steel seems to have changed to a Load-Distance terminology.

Since I've mostly worked with concrete, I guess that's why I am hung up on the ft-kip reference. So, it looks like everyone is correct --- its just your own preference that counts.

Thanks to you all for your participation in this thread.

http://www.spiraleng.com

 

[Hokie93]

I was taught in undergraduate mechanics courses that the unit of moment is kip-feet (force-distance) whereas for torque it is foot-pounds (distance-force). Expressing moment in units of kip-feet also agrees with the classical definition of moment, M=Fd (force x distance), as jayrod12 indicated. My statics and mechanics of materials textbooks all use kip-feet (or kN-m) for moments.

 

[TLHS]

SRE,

I'm wondering if the lack of kips in the earliest documents you were looking at is more related to the fact that 'kilo' hadn't moved into common english usage yet. I'm going to see what the oldest engineering sources I have at home are, if I remember to, and see what they use. I'm pretty sure I have some stuff circa 1910.

I don't think metric started moving out of France and heavily French influenced regions prior to the mid-19th century, so it wouldn't surprise me that kilo wasn't common in the late 19th century in areas that weren't familiar with the system. I'm not really sure though.