Author Topic: Ground Snow Loads  (Read 21570 times)

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Offline Medeek

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Snow Load Calculator
« Reply #25 on: June 02, 2014, 09:45:05 PM »
The snow load calculator has now been upgraded with a PDF report output, which is really nice for printing out hard copies.

http://design.medeek.com/resources/snow/snow_calculator.pl

It was a real pain to format this document from HTML to PDF.  I will probably do the same PDF report format for the wind, seismic and ground snow load maps as I get time.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline MountainDon

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Re: Ground Snow Loads
« Reply #26 on: June 03, 2014, 03:53:08 AM »
 [cool]
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline rick91351

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Re: Ground Snow Loads
« Reply #27 on: June 03, 2014, 05:31:54 AM »
Yikes!!   There are some mighty significant snow loads in ID!

Yep told you so!   ;) 

Part of the reason for that is refereed to as the Hawaiian Express.  The warm moist Pacific Storms the jet stream pulls them along and if things are right we get dumped on.  Has not happened as usual for some time now.  We blame the Salt Lake Ski Areas magnetically pulling our rightful storm away from us.   :D 

No really the Hawaiian Express pulls those storms in to us.  Idaho of course are on the west edge of the those mountain ranges that make up the northern part of the continental divide.  It is actually are very sheltered most the time from the bitter cold of Montana and Wyoming because of a balance there.  Yet that cold ridge stands high above.  Those moist pacific storms hit the wall of mountain ranges and cold air and snow occurs.   ;)   Some times a lot of snow then to complicate things a little more.  Then the moist warm storms start to break down the ridge of cold air and things start turning to very wet snow and rain.  From what I understand that is why the serous snow loads in certain locations. 
Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

Offline Medeek

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Re: Ground Snow Loads
« Reply #28 on: June 03, 2014, 10:43:14 PM »
I've added the PDF report option to the ASCE Ground Snow Load Map, give it a shot and tell me what you think.  I think the output is more complete than the interactive map since I'm also doing a reverse geocode on the lat/long however the downside is the KML layer can't be overlaid on the static maps shown in the PDF document.

http://design.medeek.com/resources/snow/groundsnowloads.html
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline rick91351

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Re: Ground Snow Loads
« Reply #29 on: June 04, 2014, 02:57:00 AM »
Idaho Ground Snow Loads Map is now in Beta testing:

http://design.medeek.com/resources/snow/idahogroundsnowloads.html

This map is quite complex compared too all of the previous ones and requires a much more complicated alogrithm to interpolate between NGSL isolines.  Additionally, there are some specific locations on the map that do not conform to the isolines and those are in the process of being added into the final calculations.

This one was definitely a challenge but that is what makes it fun.  The detailed report is also a work in progress but it should provide some insight into how the interpolation is achieved and what limitations, if any, exist.

The Idaho map is not coming up......
Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

Offline Medeek

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Wind Speed Map and Idaho Ground Snow Loads
« Reply #30 on: June 04, 2014, 10:00:31 AM »
I've now updated the wind speed map with a PDF report as well, much more useful now with the ability to print out a legible hard copy:

http://design.medeek.com/resources/wind/basicwindspeeds.html

I apologize that I forgot to mention that I moved the Idaho ground snow load map due to copyright restrictions and also due to further testing.

I'm happy to announce that the copyright issue with using the original snow load study data was resolved and the Dept. Chair at the University of Idaho (Civ. Eng.) was able to give me the green light on the project.

I've temporarily posted the Idaho map here for testing purposes:

http://design.medeek.com/resources/snow/idahogroundsnowloads_BETA.html

Please be advised that the data presented is still in question.  More specifically I have the following questions that I am trying to resolve (the document referenced is the Idaho Snow Load Study by Dr. Ronald L. Sack and A. Shekh-Taheri in 1986):

1.  On page 9 it states that if a circular contour is encountered one should assume that the increasing values would make this is a peak.  Obviously the next contour interval is not shown so the peak does not rise to the next contour interval however what assumption should be made as to the maximum value for the NGSL at the center of the region or peak?  My best guess at this would be to assume that the peak max. value is midway between the next possible isoline.  So for example  if the circular contour is .020 and the values are rising the peak value in the center of this contour would be .0225 and not .025.

2.  On the same note what about depressions such as Grangeville or even Nampa/Boise?  Comparing with the tabulated values it appears that the NGSL value used for Nampa and Boise is .005 and not a linear interpolated value which would be considerably lower.

3.  With local exceptions what would be a reasonable distance to apply them at, or do they vary by location?  For instance if my building site was 2 miles outside of Salmon would I use the .005 local exception as the NGSL or would I use .010 which is the closest circular isoline (values decreasing), or would I interpolate between the bottom of the depression (assume NGSL = .0075 at its center) and the .010 isoline.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Arizona Ground Snow Load Map
« Reply #31 on: September 26, 2014, 09:59:17 PM »
Here is my first draft of the (Online) Arizona Ground Snow Load Map:

http://design.medeek.com/resources/snow/arizonagroundsnowloads.html

The interpolation routine may be too simplistic.  The data seems to have a lot of sporadic zero snow loads that may make generating isolines somewhat tricky in my opinion.
I am currently only using the three closest stations to interpolate from for a given point of interest, perhaps using more points might be a better method (or worse).  I am currently waiting on a response back
from the creators of the Montana Snow Load map to get some guidance and  feedback on their method of choice in this regard.

Another interpolation method that may be more accurate is the Kriging method but I am researching that further, for now I have implemented IDW (inverse distance weighting) which seems like a fairly rational approach.

 I think it would be useful to take current map I have created and script a program that queries the map on a grid at approximately every 2 miles, from that (30,000 data points) a surface plot of the NGSL data can be constructed and then reviewed for any anomalies.  Then if feasible a hard copy map can then be generated with NGSL isolines similar to the Idaho Ground Snow Load map.

There are currently no local exceptions and the weighting and interpolation routine used for each climate zone (entire map) is the same however all of this can easily be customized by zone, elevation, or any other parameter that comes into play.  In other words an entirely different interpolation routine could be used for each zone, county, even city or elevation depending on what trends are observed.  The IDW interpolation itself can also be adjusted with the "P" factor to give more influence to data points that are closer or farther away to the point of interest.  In a nutshell what I have created is simply a rough draft, there is a significant amount of fine tuning and tweaking that can be done and will probably need to be done to make this a usable product.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Ground Snow Loads
« Reply #32 on: September 29, 2014, 06:17:49 AM »
Here are some surface plots of the Normalized Ground Snow Loads using the 3 and 4 point interpolation algorithm of the online map:





The top image is the entire state of Arizona, with interpolated data points every 0.05 degrees (approximately 3.5 miles). The script actually chugged through it even though there were 14,400 data points to calculate. I'm currently using Chartdirector as my surface plotting software. Does anyone have any suggestions on an alternate plotting software. I need something that can handle lots of data points and has a lot of controls for tweaking the cubic spline of the surface plot.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline Medeek

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Re: Ground Snow Loads
« Reply #33 on: October 01, 2014, 01:16:06 AM »
Updated map using the new algorithm with clickable imagemap:

http://design.medeek.com/resources/snow/arizonagroundsnowloadmap.html

This map was generated using the interpolation routine described above.
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

Offline rick91351

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Re: Ground Snow Loads
« Reply #34 on: October 01, 2014, 02:44:13 AM »
Updated map using the new algorithm with clickable imagemap:

http://design.medeek.com/resources/snow/arizonagroundsnowloadmap.html

This map was generated using the interpolation routine described above.

What a great tool - me being an armchair untrained geologist / earth science buff.  I played around with your map and I really love it. Looking at the different marked areas and how they climb or descend.  Speaks volumes of Arizona's  topography.  Might not be what it was intended for but I really like it.  I give it a  [cool] plus four!!!!
Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

Offline Medeek

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Re: Ground Snow Loads
« Reply #35 on: October 01, 2014, 04:09:47 PM »
Its that crazy topography that makes mapping snow loads difficult and sometime nearly impossible.  The scatter in some of the data caused by drastic elevation changes and hence microclimates is hard to reconcile into a smooth contour plot.  Interpolations of the data at certain spots tend to break down.

What is interesting is this map is the normalized ground snow load (effect of elevation theoretically removed).  If I now plot the actual snow load data (NGSL x elevation) it will probably be even more dramatic and reveal the true topography of the state.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Ground Snow Loads
« Reply #36 on: October 01, 2014, 05:22:46 PM »
The NGSL map and the Pg map are fairly similar as can be seen from a block of the map below:



What this tells me is that the relationship between snow load and elevation is not linear and a truly normalized snow load would probably need to involve a power function of the elevation.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Ground Snow Loads
« Reply #37 on: October 01, 2014, 11:17:57 PM »
The image below shows the Ground Snow Load (Pg) overlayed onto Humphries Peak just north of Flagstaff.

The contour map is shown below:







The snow load is pretty much as expected however the small mountains at the north border of Flagstaff do not seem to as high as a snow load as I would expect. What this tells me is that where there is high elevation and no monitoring station the Normalized ground snow load will probably be underestimated. What it really boils down to is that without a lot of data points this method of interpolating (IDW) is not granular enough to account for mountainous terrain especially when the NGSL is obviously being influenced by elevation.

At this point my thinking is that the interpolated data from the snow stations is good but that should also be compared or averaged with a snow load value based purely on elevation and maybe some other general climatic criteria. I've been looking at the Utah snow load equation for exactly that reason. Even though the data from Freestone's study does have a lot of scatter there is still a discernible relationship between elevation and snow load. This will require further thought and investigation.

http://www.seaoa.org/Resources/Documents/A%20Review%20of%20Ground%20Snow%20Loads%20in%20AZ.pdf
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Ground Snow Loads
« Reply #38 on: October 01, 2014, 11:24:52 PM »
Another interesting thing I noticed when looking at the overlay is that the Station on the west side of the peak is listed as Pg = 272 psf, about the same as the eastern snow station.  You'll notice that the isolines show its location at about 239 psf.  At first the discrepancy had me boggled but then I looked at the station data and compared it with the actual elevation data from google earth.  The lat and long that places this station into the map is not granular enough, only to the second decimal place, hence it actually is placed slightly down the slope from where it actually should be.  The really cool thing is that the interpolation routine automatically deals with this and the isolines are not terribly affected.

However it does make me question the lat and long values for each station and even the elevation data, all of which will now need to be checked.
Nathaniel P. Wilkerson, P.E.
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Offline rick91351

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Re: Ground Snow Loads
« Reply #39 on: October 02, 2014, 03:08:00 AM »
I look at what they are going in that state makes a lot of sense yet is very hard for a contractor to even give a ballpark figure to a potential client - DIYer to budget until all the data is run...... or even going shopping for a lot or acreage to build.  Or you just bite off the toughest snow / wind load on the hill and go with that. 

I now understand some of the comments made about building with in Az snow zones.   
Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

Offline Medeek

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Re: Ground Snow Loads
« Reply #40 on: October 09, 2014, 05:58:31 PM »
Here is a graph of the NGSL vs. elevation for each non-zero station.  There is a lot of scatter in the data however I think I see a general trend which I have tried to capture.



I've inserted and additional piece of logic into the interpolation routine which checks the distance to the nearest station, if it is above some threshold (20 miles) then the interpolated NGSL is averaged (IDW) with an NGSL that is based off of the power function given above.  It would probably be more accurate to use a regression curve specific to each climate zone however the number of data points is not sufficient in my opinion to achieve this.  Furthermore when the NGSL or Pg values are plotted against elevation for each climate zone the scatter in the data does not significantly approve.

I'm not entirely sure what to set the max distance at but 20 miles seemed a good place to start as any.  Most points within the state fall within 30 miles of a station so 20 miles is about as high of a max distance that will still influence the final determination of the snow load.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Ground Snow Loads
« Reply #41 on: October 11, 2014, 06:04:09 PM »
Updated the map with the PDF output option for generating reports.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Massachusetts Ground Snow Loads
« Reply #42 on: January 21, 2015, 07:59:22 PM »
Massachusetts Ground Snow Loads Map is now up:

http://design.medeek.com/resources/snow/massachusettsgroundsnowloads.html

I still need to add the pdf output feature.  Notice how the general trend of the snow loads approximates the ASCE 7-10 national map.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Ground Snow Loads
« Reply #43 on: February 13, 2015, 07:33:54 AM »
The medeek API now also includes IBC 2012 seismic data.  I am currently working on integrating some of my state snow load maps into it as well so it can retrieve the national level data as well as the state or jurisdiction level data.
Nathaniel P. Wilkerson, P.E.
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State Snow Loads and the Medeek API
« Reply #44 on: February 17, 2015, 07:37:23 AM »
I am currently testing some new features with the Medeek API.

One of these is to offer state snow loads in addition to the ASCE 7-10 national values for ground snow loads.

The testing API script is located at:

https://design.medeek.com/resources/medeekapi_TEST.pl

A sample test address is given below:

https://design.medeek.com/resources/medeekapi_TEST.pl?action=ascesnow&key=MEDEEK12721119&lat=41.6873&lng=-70.1054&localdata=1

Note the addition of the variable "localdata" which when set equal to "1" will trigger a local lookup of the snow load values. By default without setting the localdata variable the API will only give national level values (normal behavior) and the response from the API will remain the same as previous revisions of the API.

Also note that when a localdata lookup is triggered the API must perform a reverse geolocation of the latitude and longitude. You will probably notice the response time from the API increase by approximately one second.

Currently the states that have complete snow load data are:

New York
Massachusetts
Utah
Montana

Each State has different methods at arriving at their snow loads, so the addition of each State's data can be a time consuming process.

The plan is to add all of the States that have data that differs evenly slightly from the ASCE 7 ground snow load map.

Please feel free to test out this new feature. Additional output fields are still in flux, your suggestions and comments are highly valued in this regard.

Note:  Typically daily users of the service purchase a key however for the casual user the service is free of charge with the use of the test key above (daily limitations on usage apply, 500 requests per key per day).  The FAQ and documentation on how to use the API and what you can do with it is available at the page below:

http://design.medeek.com/resources/medeekapi.html

The new logo for the API is:

« Last Edit: February 17, 2015, 08:03:36 AM by Medeek »
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Ground Snow Loads
« Reply #45 on: February 18, 2015, 01:40:19 AM »
Nevada County, CA and the Town of Truckee ground snow loads are now part of the API, quite an interesting algorithm for the transition area between west and east zones, that was an interesting bit of programming.  The snow loads can be quite extreme at elevations in this region. 

Try this link:

https://design.medeek.com/resources/medeekapi_TEST.pl?action=ascesnow&key=MEDEEK12721119&lat=39.392925&lng=-120.12653&localdata=1

Once I get the other Nevada and California counties done I will present these as online maps so the data is much more accessible.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Re: Ground Snow Loads
« Reply #46 on: February 18, 2015, 11:41:01 AM »
Local ground snow load data is based on State, County and Municipal building codes and is often derived from snow load studies commissioned by the structural engineering associations within the state or jurisdiction. The specific source of the local snow load data is provided as part of the API output when the local data option is selected.
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Snow Load Calculator Update
« Reply #47 on: August 16, 2015, 02:14:39 AM »
I've added an attic truss option to the snow load calculator.  This one was quite tedious to program and may still have a few bugs with it due to the added complexity of two additional load cases but it does save me alot of time when checking reactions of attic trusses and sure beats doing this sort of thing manually.

http://design.medeek.com/resources/snow/snow_calculator.pl
Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Washington Ground Snow Loads
« Reply #48 on: September 02, 2015, 08:00:37 PM »
This state map is similar to the Arizona map in that I am looking at each weather station and interpolating with an inverse distance algorithm to estimate the ground snow loads.

http://design.medeek.com/resources/snow/washingtongroundsnowloads.html

The detailed report is worth looking at since it will allow one to compare the calculated snow load to the jurisdictions mandated ground or roof snow loads as well as compare with the 1995 Snow Load Study values established by the SEAW.  Typically the county or city snow load values are higher and thus more conservative.

Nathaniel P. Wilkerson, P.E.
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Offline Medeek

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Truckee
« Reply #49 on: September 06, 2015, 10:55:44 PM »
This area has always fascinated me with its crazy snow loads.  I worked out the algorithm for Nevada County and Truckee about 6 months ago and added it to the API but I finally got around to putting together a map for it this afternoon and evening:

http://design.medeek.com/resources/snow/nevadacountygroundsnowloads.html

The transition zone between the west and east sides of the town and county is probably what makes this one the most interesting out of any snow load zone I've looked at thus far.

« Last Edit: September 06, 2015, 11:10:00 PM by Medeek »
Nathaniel P. Wilkerson, P.E.
Designer, Programmer and Engineer

 

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