[LandXML] Re: LandXml question spiral types 'cubic' and 'cubic Parabola' and 'rev'

  • From: "John Keays" <john@xxxxxxxxxxxx>
  • To: "Eric Hall" <Eric@xxxxxxxxxx>
  • Date: Tue, 22 Jul 2008 16:11:57 +1000 (EST)

To Eric,

Thanks for your comments.  Many of the Road Authorities and Railways
insist on spirals.  They are a required design option. The different
varieties produce different results so the survey setout programs must use
the same spiral formulas as in the design phase.  I have put all the
variations in my software just to conform to the various standards.  In
the pre computer days the spirals were developed by the earthworks
operators and they worked fine.

The Euler curve corresponds to moving the steering wheel in a constant
fashion as you go from the straight to the circular curve.  The exit is
the reverse.

Super elevation tries to get a balance between Coriolis force of the
circular arc and the cross slope of the road so that the weight of the
wheels acts perpendicular to the road surface at the design speed. 
Typically the banked slopes at Indianapolis race track are set to keep the
cars from slipping at racing speeds.  When the car slows down the car
falls to the inside of the track.

In some TV shows on the race track they put a camera on the kerb line and
watch the cars go by. I get awe struck on how accurately the drivers hit
the mark on the race track.  But that's not how I drive.  I am Mr Magoo. 
I need the extra space...  I would like to find somebody who has actual
driving stats on the freeboard issue in driving in a traffic lane.

Please add some more comments....


John Keays

John said > Eric Hall
>>> Hi John,
>>> You made a couple of statements in your email that are not exactly
>>> I understand to be the case.
>>> In many cases, you can live without spirals in your roads. However,
there are many places, like British Columbia and other mountainous
>>> where the extra widening room used on flat-land roads is not available
and spiral curves are a must. Typically, clothoid (Euler, Cornu)
>>> are used for road building... at least in the US and Canada. So,
>>> are very necessary in some road building applications.
>>> Sena's death was very sad. The bumps probably played a roll, but the
intense downforce created by the ground effects and the car possibly
bottoming out and the resultant loss of the ground effects all
>>> to send him off track. That is a pretty extreme situation though. It
isn't something that normal road designs have to account for.
>>> I don't know if race tracks use spirals, but the designs I have seen
typically don't. The driver will describe a spiral when turning into a
corner because there is no other way to turn a car (assuming tire slip
angles within the normal region). When you turn the steering wheel,
>>> resultant ground track is a spiral until the point where you stop
turning the wheel and hold it steady; then you are in an arc. This is
also true of normal driving of course. Some roads are designed with a
widened road width to allow for the driver to create their own spiral
entry when there is enough room to do so. Otherwise, a spiral curve
>>> to be designed in.
>>> Also, the spiral entry does not reduce the loads to 0 g. They may
>>> initial loads allowing them to build more slowly, but the final g load
is a function of the radius achieved and the speed of the vehicle.
>>> are fun on the track :) )
>>> Sorry, I am not trying to be nit picky. The main point was that
>>> are very necessary in some road building environments so you really
can't live without them (well, you and I can personally, but roads do
need them). They are avoided when possible because of the added
complexity, but with modern CAD and field data collectors, a lot of
>>> complexity is removed and makes the spiral somewhat easier to use so
>>> see them more often now.
>>> Regards,
>>> Eric
>>> -----Original Message-----
>>> From: landxml-bounce@xxxxxxxxxxxxx
>>> On Behalf Of John Keays
>>> Sent: Monday, July 21, 2008 4:32 PM
>>> To: Alfonso.Ruiz@xxxxxxxxxxxxxxxxxxxx
>>> Subject: [LandXML] Re: LandXml question spiral types 'cubic' and
>>> Parabola' and 'rev'
>>> To Alfonso,
>>> As a developer of software I have to include spiral details into my
software.  My attitude to spirals is that for road design you can live
without them.  Maybe for railways a spiral is needed for low speed
>>> work.  If you put a spiral in the system you will need a surveyor on site
>>> for checking.  It generally adds to the cost of construction specially if
>>> the project includes bridges.  If you look at formula One racing the
tracks are flat and the race line is probably a spiral but the track
>>> done with circular curves.  Arton Senna died when there was a bump on the
>>> track that lifted the car off the ground.  Construction toleerances
>>> important.  Generally the race cars pull several G's around a curve.
Spirals are usually introduced so that there is approximately zero G
forces around the curve.
>>> I went to Tasmania last week and travelled on a rail track designed
>>> built around 1880-1900.  It was done with old railway curves and
>>> rods.  I don't think any curve was properly calculated for spirals. They
>>> just used a deflection per rail length with a length of transition
>>> curve to straight.  Checking curve deflections per length is pretty close
>>> to the Euler spiral.  it might be bumpy now but it is okay and they built
>>> the rail line in two years from start to finish in terrible terrain.
Each country will have an academic that prefers a method.  The
>>> cubic parabola is a formula that could be calculated on a hand held
calculator or done long hand as the additional terms of the Euler
>>> are only required for the longer spirals. With computer software it
doesn't matter how many terms are used.  I found that 4 or 5 is enough
>>> normal curves.  I found millimeter differences between the cubic parabola
>>> (2 terms) and the MOSS Euler (5 terms) at a 40 or 50 metre length.
>>> ride ability is the same.  I used three different curves for 20 years. I
>>> added Nathan's curves in after I got hold of his paper.
>>> To set out the curve in hte filed we just create an XYZ table of
>>> at
>>> an agreed interval and set out either as an EDM with a surveyor or as
>>> chainage and offset if there is only a foremen present.
>>> In writing the software I use the Newton Rapson technique to solve for
>>> line spiral intersection and it works the same for the different curve
formulas.  I only need say 6 or 7 functions for the different spirals
>>> give a length, delta x and delta y off the tangent and the angle of
>>> tangent relative to the TP point along the X Axis.  Only an additional
twenty or so lines of code for each spiral type. That way I don't have
>>> suggested which formula is appropriate.  Let the user decide. I worked
through each of the funny formulas that Nathan Crews found from his
travels.  The Bloss the cosine seem to come from the German train
technology as it gives a better pull on the train around the curve at
>>> velocity.  My guess is that technology was passed to the Japanese
>>> World War 2 just like Siemans and Fujitsu with communications
>>> technology.
>>> The Japanese like to write their own software so its fitting they have
their own spirals.
>>> I really enjoyed looking at Nathans paper on the curves.  We all have our
>>> own way of doing things.
>>> Cheers
>>> John Keays
>>> John said > Alfonso.Ruiz@xxxxxxxxxxxxxxxxxxxx
>>>>>> Dear colleagues,
>>>>>> having a look to the different Spiral types there are several
>>> types
>>>>>> available:
>>>>>> - what is the difference between  'cubic' and a 'cubicParabola' ? -
>>> when should I use the 'rev...' types (e.g 'revBloss' or 'revCosine'
instead of 'Bloss' or 'Cosine' ?
>>>>>> Thanks in advance for your efforts and explanations.
>>>>>> best regards
>>> --
>>> John Keays,Keays Software PO Box 80, Toowong, Q 4066
>>> 9/621 Coronation Drive, Toowong, Qld 4066, Australia
>>> Phone +61-7-3870-1711 fax +61-7-3870-1784
>>> Web home page: www.keays.com.au

John Keays,Keays Software PO Box 80, Toowong, Q 4066
9/621 Coronation Drive, Toowong, Qld 4066, Australia
Phone +61-7-3870-1711 fax +61-7-3870-1784
Web home page: www.keays.com.au

Other related posts: