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UNIT OF CALCULATION

  • 1.  UNIT OF CALCULATION

    Posted 04-18-2018 02:45 PM
    Edited by Tirza Austin 04-18-2018 02:44 PM
    I can´t understand why in these times of computers and calculation tools, civil engineers that have been taught to do all kind of calculations, have problems with measurements units. 
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    Alvaro Villamizar-C P.E., M.ASCE
    Port Coquitlam BC
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  • 2.  RE: UNIT OF CALCULATION
    Best Answer

    Posted 04-19-2018 10:31 AM
    Edited by Alvaro Villamizar-C 04-20-2018 12:39 PM
    Alvaro,
    I believe that you have stated, exactly oppositely, of why there is a problem with units.
    When an engineer is dependent on a computer and cannot visualize whether the result is reasonable or not, there are going to be problems.

    One problem with the SI system is that the units are not humane.  The mm is too small, the meter too large for many uses, and the cm is not an official unit of the system.  This is but one example of the difficulty in using this system of units.

    I have worked (in Europe and the US) using both the metric and in-lb unit systems.  It took about a month of daily use to get used to visualizing in the metric system (not the SI system thankfully, this was ages ago) and then it was quite convenient to use. It then took a couple of weeks to get back into the in-lb system when I returned to the states.  It is not easy going back and forth, and the average person does not want to spend the effort to make the jump the first time.

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    Gregory Thomas M.ASCE
    Laboratory Director
    Terrasense, LLC
    Totowa NJ
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  • 3.  RE: UNIT OF CALCULATION

    Posted 04-20-2018 11:14 AM
    The centimetre is an official unit of the SI system and is used for dimensioning all over Europe. The problem is not units it is the people who use them. A much bigger problem is the use of the comma as a decimal point in Europe or the decimal point to separate hundreds from thousands etc. Thus 1.000,001 is one thousand and one thousandth, namely 1,000.001.

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    Tim Clark, FRAS, R.A., M.ASCE,
    President Emeritus RIBA-USA,
    Deutsche Bahn Engineering,
    Bavaria, Germany.
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  • 4.  RE: UNIT OF CALCULATION

    Posted 04-20-2018 05:24 PM
    I stand corrected on the cm being an official unit, thank you for pointing this out.  When I was originally exposed to it on one project all units were prefixed according to powers of 3 ("m' for.001,"" for 1,"k" for 1000, etc.) but this may have been a project specific requirement.

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    Gregory Thomas M.ASCE
    Laboratory Director
    Terrasense, LLC
    Totowa NJ
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  • 5.  RE: UNIT OF CALCULATION

    Posted 04-20-2018 11:57 AM
    Edited by Tirza Austin 04-20-2018 11:56 AM

    I don't view it as a calculation problem or an engineering problem, per se.  This community is made of mostly highly competent engineers who would have little problem working in either system, as project needs dictate.  In fact, many aspects of civil design use a sort of hybridized unit (e.g., decimal feet vs. fractional inches).  However, unless there is a broad sweeping change across the AEC industry, there is little point to deviate from standard convention.

    I mean, you could calculate your stormwater flow in cms, size your pipe, and determine you needed 600mm, for example.  But go to a major pipe US manufacturer's website, and you may be hard pressed to find that size within their catalog (although I'm sure they have it available overseas).






  • 6.  RE: UNIT OF CALCULATION

    Posted 04-20-2018 01:26 PM
    Edited by Tirza Austin 04-20-2018 01:25 PM
    Gregory.
    The use of any kind of units depends on the job that you usually are performing. In every activity the most important is visualize the units that you use. For example, during my work as Hydraulic and Irrigation designer in many Latin American countries, I have had to use all kind of unit systems. For example for soil infiltration and rainfall, I use mm/hr or in/min, for discharge, I use m3/s and g.p.m. (pumps), m3/hr and g.p.m(sprinkler design), for distances and lengths I use m, km, feet, etc. A good idea is use metric system when you are in a Latin Country and English units if they are used in that country. In every case, I use the main unit followed by the other between brackets.

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    Alvaro Villamizar-C P.E., M.ASCE
    Port Coquitlam BC
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  • 7.  RE: UNIT OF CALCULATION

    Posted 04-22-2018 09:54 AM
    Alvaro:
    Sure we need to use the units of measurements in what ever country we operate, especially as it final results are in the units of the land.

    I see the problem, which it is not, in the USA, not in the calculation arena, but in putting into effect  the final designs into construction information that the worker have grown up with. Of my 64 years in engineering and construction I spent 8 of them in the fabrication and detailing of Rebar (in USA units)  while I went to engineering school at night. During that hands on experience I bent thousands of tons of bar and detailed hundreds of significant rebar projects, all put to use without construction difficulties... A very valuable experience in visualizing the spacial aspects of the work involved in terms of carrying it over to the development construction plans for all types of projects and in effective modular dimensioning.

    For the most part, engineers do not go to the field and build their design with the familiar units and the dimensioned products available in the land.  Until engineers work in the shoes for any length of time in any given land it will be appreciate what it means to work in the dimensional units practiced and available.  I believe there is too much ingrained/invested in the products and history of USA construction to ever see a change to the metric domain.

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    Allen Hulshizer P.E., F.ASCE
    Consulting Structural Engineer
    Chalfont PA
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  • 8.  RE: UNIT OF CALCULATION

    Posted 04-23-2018 10:39 AM
    I fully agree.
    The main issue arrising from the differences in units is that we loose the feeling of the results.
    I work mainly with SI but I usually read books in Imperial untis and I have this problem.

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    Nick Zygouris C.Eng, M.ASCE
    Structural Engineer
    Lithos Consulting Engineers
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  • 9.  RE: UNIT OF CALCULATION

    Posted 04-19-2018 10:32 AM
    Edited by Tirza Austin 04-19-2018 10:32 AM
    Alvaro: 
    It is not that engineers can't plug in and use any kind of numbers/units.  It is the use of these results in conveying information for construction application in the USA.  These construction units have been ingrained for so in the minds of the craftsman that they can readily envision what the dimensions represent. 

    One can measure things for approximation as an example, one inch for a thumb joint, nine inches for a hand span, step off distances in either foot or yards, etc.  While these are not that accurate for construction in USA they are helpful in keeping in mind what things represent before they are laid out. The closest thing that can be envisioned is a meter and we do that by comparing it to a yard for smaller lengths.

    Having been deeply involved in engineering and construction since 1954 (and still involved), I believe that the use of the fps units have been very successfully implemented for most, if not all USA major construction projects from housing, bridges, high rise to Nuclear Power Plants and that I have never come across a problem in construction that could be attributed to using the fps units to convey what is needed to build whatever.



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    Allen Hulshizer P.E., F.ASCE
    Consulting Structural Engineer
    Chalfont PA
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  • 10.  RE: UNIT OF CALCULATION

    Posted 04-19-2018 10:33 AM
    From a Civil perspective, ​I'll blame this on a lack of applicable field experience.  Until you've stood on the end of a 10,000 foot runway, you'll never recognize the scale of it, because on your desk, the entire facility fits on a 27" monitor.

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    Alan Palmer P.E., M.ASCE
    Principal Trans Engr
    Stanley Consultants Inc
    Muscatine IA
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  • 11.  RE: UNIT OF CALCULATION

    Posted 04-19-2018 10:33 AM
    ​I think tools like MathCAD may both hinder and help "unit awareness". Many people do a poor job of fashioning equations, usually opting to simply list and compute digits without considering the units. Unit-aware software helps maintain units and identify missing or misused factors.

    Half of my (literal) Engineering 101 class was on using dimensions in forming/deriving/filling equations. When this is done, it really does not matter what units, or mixture of units, is used. You can compute apples plus oranges, as long as you know the proportion of apple that is equivalent to an orange.

    Ironically, the people saying that we should force everyone to a single set of units are probably the ones who shortcut the most. People who understand units and math don't really have a problem switching between them. We also understand that numbers without units are meaningless.

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    John Turner CSP, P.E., M.ASCE
    Dallas, TX
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  • 12.  RE: UNIT OF CALCULATION

    Posted 04-19-2018 01:23 PM
    Edited by Chad Morrison 04-19-2018 03:20 PM
    Computers can handle units like champs.  The problem occurs when manuals written for use with hand calculations tend to omit units in formulas and constants.  The computer will immediately flag a conflict.  It is not that I entered the formula wrong... it was that the formula as it appears in the manual does not display the units!  This occurs in ASCE 7 and the Aluminum Design Manual among others.

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    Chad Morrison P.E., M.ASCE
    Professional Engineer
    Greenville RI
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  • 13.  RE: UNIT OF CALCULATION

    Posted 04-20-2018 11:16 AM
    ​Shame on me if I am not fully grasping the heart of this conversation, but it strikes me that the arithmetic of converting from English to Metric units and vice-versa is easy. It's the growing up thinking in one versus the other and the size standards of the products that are manufactured and used in the built environment that are the challenge. You grow up developing a "feel" for inches, feet, yards, miles, pounds, horsepower, (pecks and bushels if you work on a farm) etc., and being called upon later in life to "translate" that "feel" into different units can be a challenge, although the math of doing so, and the myriad of tools available today that will quickly do it for you is easy. But if you couple that "feel" with the fact that builders in the U.S. think (and purchase products) in terms of 2 in X 4 in (which aren't) 4 ft X 8 ft sheets, 3/4 inch thick, 3/8 and 1/2 inch diameter, etc. and consider an entire society built upon structures constructed from pieces made to those units, then the notion of conversion becomes very daunting indeed. Anyone can quickly tell you that a 4 X 8 feet sheet of plywood or drywall is 1219.2 mm X 2438.4 mm, but what you'll see in metric countries is that off the shelf sizes are 1.25 m x 2.5 m, 2.8 m, 3.0 m & 3.2 m with some even saying that a 1200 mm X 2500 mm is a 4 ft X 8 ft equivalent, but does that readily and conveniently fill a 4 ft X 8 ft hole? Some industries in the U.S., autos and electronics for example, can fairly easily convert to metric (although don't get started on things like whether a 9 mm wrench works on a 3/8 in nut). But the built environment – the infrastructure and the living spaces – is a long way away from thinking and being in metric.

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    David Vanaman P.E., M.ASCE
    Assistant General Counsel
    WSP USA Inc
    Herndon VA
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  • 14.  RE: UNIT OF CALCULATION

    Posted 04-22-2018 09:59 AM
    At one time in the mid to late 1990s Caltrans was dead set on switching to metric units and some small projects  were designed and built using them. When the Alameda Corrridor project was being designed it was unclear as to whether this new convention would continue. In my case I spent most of my engineering career involved in right of way work coordinating between the engineers and the people who acquired the properties needed for projects. Since right of way work begins way out in front of design, we were unsure as to what units would be used in preparation for the legal descriptions for the property takes. Anyway I was able to convince the client to prepare two complete sets of right of way drawings one in SI and one in metric units so that we would be ready to go. The conversion factor used was really quite simple. For example a 100 ft. wide right or way was 100(12/39.37)=30.48 meters. This conversion (rounded to two decimal places) was considered adequate for surveying and property acquisition purposes. So the metric right of way plans were prepared using this ratio and we started to acquire properties using it as well. As you might imagine there was such a backlash from property owners, appraisers, and acquisition agents when they were asked to sell or dedicate a property using metric units. As far as I know Caltrans gave up on the idea after that.

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    Thomas Hanley P.E., M.ASCE
    Buena Park CA
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  • 15.  RE: UNIT OF CALCULATION

    Posted 04-22-2018 09:51 AM
    ​Like converting a written text from one language to another there is a caution in the cliché "lost in translation".  That caution must be emphasized and addressed by engineers, most especially Civil, in preparing documents for construction.  Already noted here in several other posts, the translation from one unit to another can be easily misread by construction tradesmen.  The design engineer needs to be aware of that fact and prepare documents that avoid the lost in translation error.

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    Stanley Bujalski P.E., M.ASCE
    Retired
    Campton NH
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  • 16.  RE: UNIT OF CALCULATION

    Posted 04-23-2018 10:43 AM
    Edited by Tirza Austin 04-23-2018 10:42 AM
    The US market is large enough to support staying with the existing "English" units for most trades. Those who need to use the metric system to integrate with international usage for some reason can readily do so on their own
    You hardly noticed when Detroit went metric, did you?

    One big problem when we had the big drive for everybody to go metric was that the people in charge of that program decided to outdo the Europeans and go really rigorously scientistic and came up with units I never heard of in Europe growing up. At least so in the highway business, and these units indeed did not make much practical sense and were difficult to use. No wonder this program met with widespread resistance and political opposition.


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    Hans Coucheron-Aamot P.E., M.ASCE
    Sr Civil Engr
    Albuquerque NM
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  • 17.  RE: UNIT OF CALCULATION

    Posted 04-24-2018 10:51 AM
    Edited by Tirza Austin 04-24-2018 10:50 AM
    This is a fun discussion.  Brings back lots of memories.  I've seen two efforts to make the switch.  The last in the 90's.  In my early experience as a surveyor in California I've had to work in spanish units of measure, that went to rods and chains and then to feet.  Never in inches except to measure the size of a witness tree. When bringing plans to the public we had to convert feet to feet and inches.  When doing projects in the 90's we found that most hardware was built to metric units and labeled in nominal inch dimensions for the American public.  100 mm pipe was 4 inch. When we attempted to comply with the State's requirement to use metric we did but the contractors attempted to convert our plans back to feet and inches in the field.  We gave them metric tape measures hoping to avoid errors.  That helped some but the resistance was there.  We can stay in our American measurement system or convert to what most everyone else uses.  Probably makes little difference.  But if we really want to convert we must do it and not waffle as we have ever since the  US adopted the metric system in 1975.

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    Wayne Peterson P.E.
    CE Retired
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  • 18.  RE: UNIT OF CALCULATION