Spanner truss not acting how i think it should...

[Jayme McColgan]

hey everyone,

 

this is kinda hard for me to explain over text so I'm going to try my best... I'm having an issue where using a spanner truss is returning weight loads that I wouldn't expect it to.

 

here is the configuration... the truss running from the top to the bottom is my spanner truss. in the show, these will be butted up against each other and connected with cheeseboroughs or a spanset.

 

the image below shows if I remove the spanner and put in a "fake motor" (the red box is where the spanner was) it says that the motor is picking up  ~656 lbs. When I replace that back with a spanner why in the image above would it push the 2 points just outside of the spanner close to 1000lbs? 

 

the image below shows that if I bump the spanner up a few inches to disconnect it from the truss and "insert a drop" I get closer weights to what I expected but the weights on the spanner truss motors seem low...

 

I'm not really sure whats going wrong here but it's hurting my brain... lol any advice would be appreciated. thanks everyone

[jcogdell]

The first thing I notice when looking at you original image is that you have the trusscross connection between the spanner truss set to flexible, not fixed. This will affect how the the calculation is done, flexible is for connection like a spanset or steel rope and fixed is something like a scaff clamp (like you are using)

 

13 hours ago, Jayme McColgan said:

the image below shows if I remove the spanner and put in a "fake motor" (the red box is where the spanner was) it says that the motor is picking up  ~656 lbs. When I replace that back with a spanner why in the image above would it push the 2 points just outside of the spanner close to 1000lbs? 

What safety factor are you using in the Braceworks calculation?

 

13 hours ago, Jayme McColgan said:

the image below shows that if I bump the spanner up a few inches to disconnect it from the truss and "insert a drop" I get closer weights to what I expected but the weights on the spanner truss motors seem low..

Without seeing the file I can't say for certain what is happening.

Part of the issue will likely be the lack of Braceworks data for the truss type you are testing with, Tomcat have so far declined to share any of this with us for Braceworks.
If you can DM me the file I can take a look and see what is happening.

 

 

[Jayme McColgan]

I DM'ed you the file. 

[jcogdell]

I had a look at your file

 

On 9/21/2023 at 8:01 PM, Jayme McColgan said:

the image below shows if I remove the spanner and put in a "fake motor" (the red box is where the spanner was) it says that the motor is picking up  ~656 lbs. When I replace that back with a spanner why in the image above would it push the 2 points just outside of the spanner close to 1000lbs?

 

If you calculate the truss line without the spanner truss or fake hoist supporting it, the 2 hoists have around 1000lbs motor load each (975lbs M18 and 1088lbs M19).
With the spanner truss M18 has 819lb and M19 941lbs, so the spanner truss is taking part of the load but because this 'pick up' is not connected directly to the ceiling it spreads the load differently than if a single hoist hung directly from ceiling is used, since its going to multiple points, has to account for the spanner truss's own load and any other loads acting on it that would affect the calculation.

 

 

 

[Jayme McColgan]

hmm, interesting. That's not how I've been taught that spanners should work. I guess I have to revisit that. 

 

if I wanted to send the spanner 10' above the truss and connect them with a motor or dead hang what's the proper way to do that? 

[stayathomedad]

Hey @Jayme McColgan !

 

You would want to use the Insert Connection Tool with the tool set to Insert Drop. Then select either the hoist you want to use or the Dead Hang hoist symbols in the VW library. Note that some of those Dead Hang symbols have weirdly classed objects and settings and they need a little attention to have correct visibilities.

[Jayme McColgan]

Thanks, Harry! didn't know you hung out in the forums.