Last week I talked about how pricing will be different in the future. This week I’ll make the same claim about the loading of trusses. One day, not so very far in the future, the trusses you will be building will be using loads developed within the model (the 3-D layout) itself. And although you might think this would only be of interest to engineers and truss designers – it may mean a whole lot more than that. This brave new world of loading adds a potential new product line to our business – information. Time will tell if these ‘information products’ will generate additional revenue, or simply become an expected part of what the “truss guy” provides at “no charge.” Now is the time to be thinking about it. More about these new products later. First, let’s review where we’re at.
Loading of trusses from the Beginning of Time to the present
Trusses are designed in basically the same way as they were 25 years ago. Key elements of this ‘old world’ are:
1. Basic loads are applied to the truss (expressed in a few values) and applied uniformly
2. Each truss is analyzed and approved in isolation from all the other trusses
Thirty years ago it was a major feat of computer engineering to model a truss, evaluate the forces and stresses and specify at least an initial solution. Layout software did not exist. Engineering software needed everything about the truss typed in on every truss. Each truss was examined in isolation because, in part, that’s all the software could do. This legacy is deeply ingrained. Consider the evidence:
1. We seal one truss at a time. How enthusiastic is your engineer to review and seal the entire roof system?
2. How easy is it for a truss designer to line up the webs throughout the entire roof or floor system?
3. Say your first 10 trusses after the gable are all “T1” trusses. The first “T1” is in the wind “End Zone.” The others are in the wind “Interior Zone.” Can you analyze the T1 for both conditions? If all the trusses are carried by a girder, is the girder loaded accurately, or with the “worst case?” Isn’t the girder highly overdesigned (think uplift) if you do that?
4. Does your labor estimation formula take into account how similar (i.e. same pieces) the different trusses in a particular table production group are?
None of these four things is “easy” because the software, still looking at each truss in isolation, does not easily lend itself to these situations.
What’s wrong with this picture
Good ol’ simplified loading works. It would be nice if we could continue to live in that world, but we can’t. Beginning more than 20 years ago, the introduction of wind loading began the march towards where we are today. Picture a banner held high that reads, THE MARCH TOWARDS EVER MORE ACCURATE LOADING OF YOUR TRUSSES being carried by the building code specifiers of our world. To accurately design your trusses today you have to (for each truss, mind you) specify (manually) the Height Above Ground, Wind (answer about four questions), Snow (answer about 5), bearing material, bracing material, building code, AC loads, light storage loads, drag loads, sprinkler loads, unbalanced loads, and so on. The Jeffersonian in me particularly likes the codes that require that open sections of panels be designed for storage loads, even if no homeowner in their right mind would crawl deep into a hip system to store their blankets and old cook books.
The engineering people would have us load our trusses accurately. Well, we’ve reached the limit of what we can do looking at each truss in isolation. The newer building codes, specifically as they apply to wind and snow, make it impossible to accurately load the truss without taking into account where the truss actually is within the structure. We have arrived at a place where we need to model the structure, and have the model inform the truss design engine all the pertinent information so we don’t have to. There’s just too much of it to do it accurately.
It’s Coming
This model-driven loading is coming. By this time next year (if not sooner) it will be available within the MiTek software suite. Other software suppliers either already claim to have it, or will, shortly. I’m convinced it really will be a better world, once the kinks are worked out. Each individual component will have the correct loads applied and load paths will be traced throughout the structure. I expect that once in use and established, that building codes will begin specifying that that each component must be designed for its exact condition of use (where it is within the structure), rather than simply as “20-10-10 with 90mph wind and 80 lbs. Ground Snow.”
What’s the Benefit?
First, it should be said that this doesn’t have to have a benefit – it’s coming regardless. It is more accurate, and the last 15-20 years have shown a relentless march to more accurately loaded trusses.
But there will be benefits, and I want to list the ones I can think of here. You will likely be able to think of many others.
Benefits for designers
· No longer have to hand calc
o Floors carrying wall and roof above
o Wall girders
o Girders carrying both roof and floor loads
· The information common to all components (building code, structural materials, wind and snow rules will reside in the structure.) Change the data in one place and have it promulgate through the components in the structure.
Benefits for the Business (“Information Products”)
· Ability to easily calculate the loads for:
o Headers
o Beams
o Columns
o Foundations
· Other information useful to the builder
o Square footage of roof and floor decking
o Rough opening takeoff
o Drywall square footage
o Lineal footage for trim, fascia, gutters
OK, I’ll admit these last ones have nothing to do with loading, but the point is that once we have created the model, one of the returns on that investment is ready access to lots of information about the stuff in the model – both structural and cosmetic. Be thinking now about what information is in the model that is valuable to someone you know. Can you get that information now? If not, why not ask that it be provided? That’s what the software is there for.