Snow Load Calculator 4

Very nice, medeek. Thank you!

Best to you,

Goober Dave

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For Utah ground snow loads I've added this map:

For the State of Montana I've added an interactive map that acquires its data from the Snow Load Finder from the University of Montana:

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

I've recently spent some time looking at the snow load requirements of the ASCE 7-10 and the various state modifications to the IBC and IRC. Obviously this is a gargantuan task, to summarize all this data and present it in a usable fashion. I have managed to chip away at a few states that have standardized snow load data or equations. The latest state I've tabulated is New York State:


My map of the ASCE 7-10 ground snow loads is still unfinished, not because I cannot finish it but because I am currently waiting on a response back from the ASCE licensing division about the reproduction of the data presented in Fig. 7-1 (ground snow load map). Reproducing or displaying a scanned version of the map seems to be less of a concern that creating an accurate electronic version of the map that is much more useful to the general public and engineering community.

I am summarizing each States snow load requirements on this page:


As you can see I've only just started. Some states such as Colorado let the local jurisdictions (City and County) set their own snow load requirements so creating a map for the entire state is more difficult but not necessarily impossible. Some states such as Oregon have developed much more sophisticated online systems, I applaud their efforts.

@medeek>>> Thanks for posting.

Oregon Snow Load map is up. This one, like the Montana Map, connects to the snow load database hosted by the SEAO. It also compares the retrieved value against the 20 psf snow load minimum as well as checks the modeled elevation against the actual site elevation and flags the user based on these checks.

The advantage to using this tool is that you don't need to know the lat. and long. off hand, just click on the map and it does the rest.


Also added in "tile" surface to the calculator per request from a southern California resident, not that they get much snow down there.

Just completed the Ground Snow Load Map tonight.


Digitizing it, so that it was accurate, took far longer than I had planned on but once I was underway I wasn't about to stop.

Note how most of the western US requires case studies, hence many of these states have their own snow load maps and research to back them up.

Interestingly I had a company that manufacturers and installs solar panels contact me regarding the ASCE ground snow load map. They were wondering if there was a way so that their website could send an http request to the map with a latitude and longitude and have it kick back the snow load. Since the map is already in digital format you would not think this would be hard to do. So I got thinking about how I could build a program that given a certain lat and long would automatically click on the map and then fire back the elevation, snow load, etc...

The only problem is google maps implementation of the KML layer does not allow this transmittal of information. So I basically banged my head against the wall for almost 2 weeks trying to do the impossible. However, I was not ready to throw in the towel just yet. Since the KML data is just plain text, (coordinates) I thought there must be some way to analyze this data and determine if a given location is within a certain polygon and if it is then be able to assign that polygon description (ASCE snow load details) to a variable which is then delivered to the client. Turns out this is called the point in the polygon problem and it is well documented:


So I was about to write an algorithm for ray casting which would have taken some time. Then I thought maybe someone else has done this before and sure enough I found a couple of good perl modules that handled this nicely and I narrowly avoided reinventing the wheel. Just a few lines of Perl later and I had managed to create a nice little API for the ASCE ground snow load data:

Added seismic and wind data to API

Wisconsin map is now up:

[URL unfurl="true"]http://design.medeek.com/resources/snow/wisconsinroofsnowloads.html[/url]

Note that this is not the ground snow load but the minimum roof design snow load. Wisconsin does things a little differently when it comes to residential design and has their own code (UDC) versus the more widely adopted IRC.

Michigan Ground Snow Loads map is now up.

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

This zone map is essentially an approximation of the ASCE snow load map with isolines fitted to county and township boundaries.

I'm not entirely satisfied with the appearance of this map since the county lines make the map appear too busy.

Vermont Ground Snow Loads Map is now complete:

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

This zone map defines ground snow loads by township and city boundaries and is derived from the zone map on page 48 of the 2012 Vermont Fire & Building Safety Code.

Vermont is a small state so the KML for this map was relatively easy to create.

I began working on the idaho snow load map based on the the snow load study by Dr. Ronald L. Sack done in 1986 and published by the University of Idaho. It has taken nearly three days to digitize the isolines to sufficient enough accuracy so that the normalized ground snow loads can be calculated. Other than the national snow load map this is probably my most ambitious project to date. I am now converting the KML polygons shown here:

Idaho Ground Snow Loads

into KML paths (isolines). The tricky part will be programming the algorithm that can interpolate between isolines. The basis for this algorithm is my previous study shown below.



The interpolation is further complicated with peaks, valleys, ridges and saddle points. In order to deal with these degenerate cases will require the addition of some virtual isolines to provide additional data points to the algorithm.

When I am finished the user should be able to click on the site location on the map and get an accurate NGSL which then automatically multiplied by the site elevation will give the ground snow load for that location.

(Except that your final formula needs a correction, as you acknowledged on 5th March in thread724-360891.)

The map is all there now, zone and isolines. Now I am trying to figure out the interpolation algorithms. For the linear interpolation between regular isolines the following equation holds:

V = (V₂h₂ + V₁h₂)/(h₁ + h₂)

For the interpolation at the peaks and valleys I've decided to use a non-linear method to better approximate what I would expect in reality. This equation I've derived as:

V = (6V₂h₂ + .5V₁h₂²)/(6h₁ + .5h₂²)

It would be nice if one could edit these post for typos. The first h2 in the numerator of both expressions should be h1.

The interpolation seems to be working. The detailed report is still under construction but give the app a try and tell me what you think:

Idaho Ground Snow Loads

The snow load calculator has now been upgraded with a PDF report output, which is really nice for printing out hard copies.


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

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.