It has been awhile since we posted any development progress so I thought I’d drop by and give you guys an update. Rest assured this doesn’t mean we haven’t been working as hard as always it’s just a long process!
This is a sneak peek of StruCalc’s newest design module just integrated yesterday. The new Collar Tie Design Module is the newest form of user input in StruCalc 8.0. We put the controls on the diagrams so you know exactly what and where to enter the correct information to make your designs quick and accurate.
I shrank the screenshot down so you can also see StruCalc 8.0’s full new interface. All the familiar controls are in a left hand navigation bar allowing quicker and easier access to all the information for your current member. No more multiple forms here! It’s all in one place on one screen. Some video’s coming shortly will highlight the new navigation and design process that truly makes StruCalc 8.0 the next generation of engineering software.
As you can see the collar tie allows inputting of the rafter dimensions, a ridge point load, a roof live and dead load, roof pitch, bracing applied to the bottom of rafters, and a double eave live load. The properties of the rafters can be designed on the left hand bar and after choosing a placement for the tie StruCalc will calculate the size and type of collar tie the user needs for an adequate design. It also will give the information needed to correctly design the connection.
We hope everyone is as excited as we are about the new interface and design features. Our productivity has certainly increased since we started using the new program and we know your’s will to. Keep us posted with your great feedback we enjoy hearing from our users and look for some very exciting news in the next two weeks!
Adam Wilson
StruCalc Development Team
November 13th, 2008 at 8:49 am
I have been reviewing version 8.0.95 and I’m confused about the collar tie module. What are the bracing options refering to? What is the purpose of a collar tie, specifically - stiffness?, uplift?, holding rafters together? Is there assumed ceiling joists holding walls? Often collar ties are recommended for every other rafter - is this an option? How does this module relate to the Roof Rafter module? At this time I don’t have a help file available.
January 28th, 2009 at 10:47 am
Traditionally collar ties were used to distribute wind load from one side of roof to the other. Code requires one every 48″. They can can double as ceiling joists over a cathedral ceiling, in which case they also tie the rafters together, and would be spaced IAW CJ requirments. ref IRC 2006
January 28th, 2009 at 4:44 pm
It is usual that the roof of a wood frame house have a ridge board (as in contrast to a ridge beam). As I have known it as such in an over 50 years involvement in the architectural practice as both an architect and engineer that a collar tie has a different meaning than that as indicated in the StruCalc program. The roof rafters rest on the wall plate with the framing of the attic floor joists forming a simple truss. At the apex is the ridge board. The collar ties is a member located in the upper part of the attic space placed every second or third rafter for the purpose of holding the rafter/ridge board connection together (as from wind pressure). Nowhere have I found in the program the mention of a ridge board. I suggest that the program and manual give a better description of the collar tie methodology and purpose.
June 16th, 2009 at 6:45 am
We use StruCalc primarily for wood design. The collar tie function may be useful, but appears to need more input into the design allowances. Most all States require a minimum live load for attics. This may be for occupancy, as in a Cape Cod style home, or only a live load minimum required by the building code.
As I understand a collar tie, it is used to support a ceiling dead load, an attic live load, at the same time as tying the rafters together to solve the horizontal spread from the rafters. The collar tie is usually also the ceiling joist, for short span roof systems. For larger span roof systems, say a 24′ wide traditionally framed home, the function would need to incorporate a center support, such as a wall or beam, thus the ceiling joist would be spliced at the center support. In the wider configurations, the collar tie may also be repeated thus, you may have 2 collar ties. One at the ceiling level, and one some distance above that to help support the rafters from sagging. The function of any collar tie would be to support the ceiling load, the attic, or code imposed live load, and to support the rafters horizontally from spreading the building apart under the rafter load. We would like to see much more description as to the intended use of the collar tie function, along with very descriptive help area to tell what is being analyzed, and most importantly, how it is being done, so the program can be checked against manual calculations, (required by design professionals before it can be used). Is FEM being used, or is the system simply doing a static analysis of components? How are unbalanced roof load conditions handled? How are load cases of the building code handled; Wind, EQ, Snow balanced and unbalanced, live loads, and combinations thereof. These are code requirements that would need to be addressed before this module could be used efficiently by design professionals.
On the issue of the collar tie module of StruCalc, it is not clear in it’s current state, weather the collar tie section analyzes the roof rafter also, or does that have to be repeated in the rafter area of the program. it would be beneficial to have the rafter analyss, and the reporting be done from the same page as the collar tie. Hope this helps!
June 16th, 2009 at 6:57 pm
We are heading this off to our P.E. team. Thank you for the great input!
June 19th, 2009 at 10:07 pm
The collor ties main purpose has to do with the downward compression forces imposed by the roof loads. Typically we have ceiling joists located at the top of wall to deal with this to keep the walls from spreading due to this downward force. This is also why you take a bigger span reduction the higher the collor tie is placed. You must check the footnotes on the Rafter span tables in the building code for the reduction values.
As mentioned in the last comment the code does not allow the use of collor ties to prevent rafters from sagging. If your rafter is sagging it is overspanned and you will need a larger rafter or purlins to reduce your rafter span.