With the MiTek software being so powerful these days, one thing truss designers often overlook is the proper application of analog on an “M-Block” end condition. This condition is also referred to as the “Leg-Up” as well. For those that might not know, analog is what determines the critical factors in the truss design and determines load direction through the members (chords/webs/plates).
How does this affect our designs? Why does this matter? These two questions are the purpose of this article.
Here at Gould Design, Inc., we strive to provide the right product for every customer, every time. In order to do that, we provide necessary training to our component design professionals. This ensures that our customers receive a product that is correct and ready to be fabricated.
The design shown below is an example of properly designed analog over an M-Block condition at the bearing.
One item often overlooked and the application of the top chord bearing truss design is that the end of vertical of an M-Block condition is actually a chord. When this member is added as a web (rather than a block), it distorts the analog and therefore the plate size required to handle the proper load resistance.
As you will see below, by not using the proper analog and the design, it significantly changes the direction of the forces and also the plate “tooth grip factor” required to sustain them.
In order to properly apply the correct application in this design, MiTek has what’s called the “Top Chord Bearing” tool. Now, you can do this manually in VersaTruss if you want to, but it will take multiple clicks costing you precious time. By using this tool in the engineering software, it reduces this to a mere minimum of mouse clicks.
What you will notice is that when the member is entered as a web rather than a chord, it does not properly distribute the load to the bearing, but rather it transfers down through the truss. In essence, what you were doing is giving the software the wrong information.
As shown above, this causes the following complications:
- Affects the size of the plate
- Can affect the reaction (especially on girders)
- Affects the “leg” analysis
- Affects lumber grades
- Could potentially cause an issue on the job site
So, take a minute, right now, and learn how to apply this condition properly in the MiTek software. It may save your company a headache down the road. Additionally, take a minute to educate your peers sitting next to you in the office.
By not providing this type of for the proper application you may find yourself getting some TDM’s back from your MiTek engineer. And no one likes those, especially your manager!
If you’re like most designers in the industry, you probably design without having your analog shown. However, you can turn this feature on under your settings as to what you view if you so choose.
This is one of those things that often gets overlooked and usually never comes up until it’s a problem and usually a back-charge. By then we have lost revenue somewhere and we have an unhappy manager, salesman and customer. Take a proactive stance and prevent that problem from ever happening by educating your “Apprentice” or “Junior” designers.
Your MiTek engineer will thank you for it!
NOTE: This same mindset also applies to Tail-Bearing trusses (more on that in a future article)