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Alternative to Mitek Wood Truss Software 2
- Thread starter Jim508
- Start date
msquared48
Structural
RISA 2D and 3D work well for trusses. Don't know about the compatibility with MiTek though.
Mike McCann
MMC Engineering
Mike McCann
MMC Engineering
EngineeringEric
Structural
msquared, how do you deal with plates/connections with RISA 3d? I can analyze and design members to no tommorrow but have a diffclt time being comfortable with pressed metal truss plates... I typically am doing repairs so use plywood gussets and that i can analyze...
This is the reason I share the same question of software options.
This is the reason I share the same question of software options.
- Thread starter
- #4
Thanks for input Mike. I need a dedicated wood truss software though, something that is specifically made to analyze and design sawn lumber wood trusses with light gauge steel connection plates(just like MiTek)
I was told that MiTek doesn't really sell it's software. So I'm trying to determine where I can get software to aid me in truss repairs.
Best Regards,
Jim, P.E.
I was told that MiTek doesn't really sell it's software. So I'm trying to determine where I can get software to aid me in truss repairs.
Best Regards,
Jim, P.E.
msquared48
Structural
RISA will analyze the forces, stresses, and deflections, but the design of the connections is up to you.
Mike McCann
MMC Engineering
Mike McCann
MMC Engineering
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1
- #6
JoshPlumSE
Structural
My guess is that you need the plate connections to be modeled as having some connection rigidity rather than as idealized pinned or as idealized fixed connections. Am I right?
There are ways to do this in RISA, but it is not very common. What I usually tell people (when they want to do this type of thing in RISA) is to model a small link beam for the connection. This link beams would have fully fixed end releases on both ends. You can then adjust the rigidity of the connection in any direction by changing the properties of this link beam. If the link beam has properties identical to the member which it is replacing then it will behave as a fully fixed connection. Reduce the properties and you will get closer and closer to an idealized pinned connection.
Honestly, it's not really all that difficult. The only tough part is knowing how rigid or non-rigid you want to make the connection. That's where I would assume the proprietary wood truss companies (MiTek) has a lot of internal rules for setting this connection rigidity.
There are ways to do this in RISA, but it is not very common. What I usually tell people (when they want to do this type of thing in RISA) is to model a small link beam for the connection. This link beams would have fully fixed end releases on both ends. You can then adjust the rigidity of the connection in any direction by changing the properties of this link beam. If the link beam has properties identical to the member which it is replacing then it will behave as a fully fixed connection. Reduce the properties and you will get closer and closer to an idealized pinned connection.
Honestly, it's not really all that difficult. The only tough part is knowing how rigid or non-rigid you want to make the connection. That's where I would assume the proprietary wood truss companies (MiTek) has a lot of internal rules for setting this connection rigidity.
msquared48
Structural
Didn't know that Josh. Thanks.
Mike McCann
MMC Engineering
Mike McCann
MMC Engineering
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1
- #8
Jim:
Those types of programs are proprietary to the plate manufacturers like MiTek, and their own testing of their products. They’ll let you (your truss design dept.) use them if you are going to manufacture trusses and use truck loads of their plates each year. If you could show them enough business, I suspect they might be more cooperative. Otherwise, I suspect they keep the actual coding (internal operations and methods) pretty well locked up in their little black boxes. As has been suggested, any good program will analyze the truss members, but maybe not as efficiently as their proprietary program does, and theirs spits out cutting dimensions and angles to boot. Then, to the actual joint design, they probably have an algorithm which goes something like this: given the size and geometry of the members coming into a joint and the loads on the members from the truss analysis; they mask out edge and end distances on each of the members which are not allowed to count, even though they may be partially effective; compression members will act in end bearing on adjacent members to transmit part of their loads; now how big a plate, from our stock, do I need to pick up the loads from each member? Plate buckling vs. plate gage will come into play, and the teeth have one allowable load, as a function of the wood density, when the load is perpendicular to the tooth face and another when the load is in the plane of the tooth; and Hankinson’s formula might even be applied to the wooden members to determine the controlling tooth value. I would guess that most of this would be revealed by a close look at the TPI literature and at the plate manufacturers literature and their ICC ES reports. The plate people also have tons of testing on which to base adjustment factors, etc.
I did some of these types of calcs. years ago, when the world was a simpler place, and would have to do some serious review to come up to speed with the current codes and methods. Maybe the simplest repair solution for you and me is just a perforated plate, in several different gages, and many sizes. Now, tooth orientation is out of the picture. We know what the shear value for a 16d x 1.5" or 1.25" nail in that plate is in a tight hole, and can make some generalizations about buckling loads, etc. Then, for the most part, it is just how many nails do I need, parallel to the grain, for that member’s load; keeping end and edge dist. in mind, of course. I drew the joint full scale, and had a plastic overlay with the punched hole layout on it; then I could start to size the plates I needed, by shifting this plastic sheet around for a best fit. But, I’m dating myself here, sometimes my slide rule or drafting pencil got in the way while shifting the plastic sheet around.
Those types of programs are proprietary to the plate manufacturers like MiTek, and their own testing of their products. They’ll let you (your truss design dept.) use them if you are going to manufacture trusses and use truck loads of their plates each year. If you could show them enough business, I suspect they might be more cooperative. Otherwise, I suspect they keep the actual coding (internal operations and methods) pretty well locked up in their little black boxes. As has been suggested, any good program will analyze the truss members, but maybe not as efficiently as their proprietary program does, and theirs spits out cutting dimensions and angles to boot. Then, to the actual joint design, they probably have an algorithm which goes something like this: given the size and geometry of the members coming into a joint and the loads on the members from the truss analysis; they mask out edge and end distances on each of the members which are not allowed to count, even though they may be partially effective; compression members will act in end bearing on adjacent members to transmit part of their loads; now how big a plate, from our stock, do I need to pick up the loads from each member? Plate buckling vs. plate gage will come into play, and the teeth have one allowable load, as a function of the wood density, when the load is perpendicular to the tooth face and another when the load is in the plane of the tooth; and Hankinson’s formula might even be applied to the wooden members to determine the controlling tooth value. I would guess that most of this would be revealed by a close look at the TPI literature and at the plate manufacturers literature and their ICC ES reports. The plate people also have tons of testing on which to base adjustment factors, etc.
I did some of these types of calcs. years ago, when the world was a simpler place, and would have to do some serious review to come up to speed with the current codes and methods. Maybe the simplest repair solution for you and me is just a perforated plate, in several different gages, and many sizes. Now, tooth orientation is out of the picture. We know what the shear value for a 16d x 1.5" or 1.25" nail in that plate is in a tight hole, and can make some generalizations about buckling loads, etc. Then, for the most part, it is just how many nails do I need, parallel to the grain, for that member’s load; keeping end and edge dist. in mind, of course. I drew the joint full scale, and had a plastic overlay with the punched hole layout on it; then I could start to size the plates I needed, by shifting this plastic sheet around for a best fit. But, I’m dating myself here, sometimes my slide rule or drafting pencil got in the way while shifting the plastic sheet around.
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