Truss Design

[Capt Worley PE]

Looks impressive!

caveat:

 

[medeek]

Currently working on the plate calculations. Those will be rather lengthy but the upside is the summary is what most people will want or need, however I will show each lateral resistance, tension, shear, net section and moment check for each plated area of each joint. I'm doing one by hand first before I code it and I've already used 10 pages for the calculations and I still have to add the heel joint. I hope if nothing else people can use this app to at least better appreciate all of the checks that go into a simple truss.

 

[medeek]

26 pages of truss plate calculations for one simple fink truss.

It's no wonder we use computers for this sort of thing.

Now I just need to take it from this pseudo-code into Perl code with a bit of fancy logic and we've got her licked.

 

[medeek]

Took a break from coding in all of the plates calculations last night and started working on the wind load cases. In order to do this I had to crack open my brand new copy of the ASCE 7-10. I always knew about the multiple load cases using the ASD method however as I dug deeper and studied a few truss drawings produced by Mitek and other truss plate manufacturers it became clear that even for a simple truss they are running a number of load cases. Here are the load cases I need to run for a simple 4/12 pitch fink truss with a 24' span and 12" overhang, at least this is what I've come up with so far, please add to this list if you are familiar with trusses and see that I am missing something:

1. Balanced Snow Load (S) + TCDL + BCDL
2. Unbalanced Snow Load (S2) + TCDL + BCDL
3. Eave Loading (2Pf) + TCDL + BCDL
4. TCLL (20psf) + TCDL + BCDL
5 BCLL (10psf) + TCDL + BCDL

and the wind Load Cases which I'm still trying to figure out, ASCE 7-10 is a bit different in this dept. from ASCE 7-5.

 

[medeek]

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.

 

[medeek]

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.

 

[medeek]

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.

 

[medeek]

My plan is to expand my original truss calculator so that it can also handle plywood gussets for site built trusses.

https://www.kickstarter.com/projects/128644708/650483439?token=cb2534a2

 

[medeek]

I should have done this a year ago but better late than never:

http://design.medeek.com/calculator/changelog.html

The addition of the CSI and JSI limits makes it possible to further customized the engineering of the truss if a more conservative approach is required.

 

[medeek]

Updates:

Version 1.0.5 - 07.26.2014

- Added lumber species selection under advanced options.
- Tension perpendicular to grain check added for joint (6) and (7).
- Updated AutoCAD drawing generator so that it now draws the metal connector plates at the correct sizes.
- Limited heel joint plate selection algorithm so that the heel plate is single, symetric and does not exceed bottom chord depth in height.

 

[McEngr]

Have you included the 0.6D + W (ASCE 7-05) load combination? How are you determining your duration factor for when you have D+0.75(0.6W)+0.75(Lr or S) [ASCE 7-10]?

This should be a relatively easy question as compared to using the TPI and using offsets in your stiffness matrix. This is where I'd be throwing my hands up and cry uncle...

 

[medeek]

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:

 

[medeek]

Snow and Wind Load analysis added to the truss calculator as well as the estimated truss weight. See the changelog for details:

http://design.medeek.com/calculator/changelog.html

 

[medeek]

I haven't posted about the truss designer for a while, apologies for that.

Still trying to improve it as time allows. The list of upgrades and improvements was getting rather lengthy so I've started filling up the changlog page:

http://design.medeek.com/calculator/changelog.html

Unfortunately, I had to put a daily limit on its usage because the server was getting hammered but it is still free to use.

The biggest improvement is the ability to specify the lumber grade, size and species as well as utilize point loads. This should make this tool far more useful for those wanting to check their roof for solar panel installations.

I'm still thinking about generating a REVIT model for those wanting to import the truss directly into that software or even into Sketchup.

I appreciate all of the support I've received over the last couple of years on this project. Suggestions/feedback is always awesome.

 

[medeek]

Added SketchUp 3D (.rb) file output for the truss geometry. This file, when copied into the SketchUp plugins folder, will create a menu item within SketchUp allowing for unlimited creation of the given truss geometry within SketchUp. I think this feature will be particularly interesting to those DIYers who wants to draw up their own model and plans using SketchUp.

 

[medeek]

I've updated the code so that the plugin now allows for user input in order to specify number of trusses and spacing of the trusses. For example 4 trusses @ 24" o/c would give you:

The actual truss geometry cannot be altered within SketchUp it is hard coded into the plugin when it is created by the calculator. For different truss sizes and shapes it is simply a matter of creating and storing separate .rb files for them. Dropping these files into the SketchUp folder sets up the menu item. This method seems to be the easiest for interacting with the SketchUp API.

 

[medeek]

Version 1.1.6 - 11.26.2015
- Added Fan and Mod Queen common truss types.
- Structural outlookers (vert. & horz.) enabled under advanced roof options for Common (Fan & Mod Queen) truss types.

Four more common truss types still need to be added:

- Double Howe (6/6)
- Mod Fan (8/4)
- Triple Fink (8/7)
- Triple Howe (8/8)

For very large buildings one could also consider:

- Quad Fan (10/5)
- Quad Fink (10/9)
- Quad Howe (10/10)
- Quin Fan (12/6) ...

A quad fink truss (10/9) with a raised heel (slider):

 

[SE_FL]

We are looking for something similar to help speed up calcs for modified trusses. We have a lot of clients that want to modify standard trusses for tray ceilings and vaulted ceilings. Currently we use STAAD and it's workable, but the calculations take a while for each truss profile. It also seems to be a bit conservative once the bracing is compete. Does this program allow for unique bottom chord profiles?