Double Pitched Joists

[dbaldacchino]

Hi all,

What are you guys doing for modelling double pitched joists? I don't believe there's a parameteric way to model these, since you cannot do calculations with the array number and thus change each array's depth, which is variable along the length of the joist. Do you resort to creating separate families for each length you need or do you just model the main chords and ignore the diagonals?

[rmcelvain.103137]

We've most typically seen these in Gymnasiums and have been modeling them for the specific length. They're pretty easy to whip out and don't change much during the project.

[dbaldacchino]

Thanks Rick, that's what I figured. I'm still playing around with trying to find some parameteric way of doing this but it's quite complicated. If one can live without the diagonals, you can make an easy parametric family, or start with this and create types, and then later add the diagonals and save them out as individual families. Anyway, I'll post back if I make any progress on this.

[shatcher]

Thanks Rick, that's what I figured. I'm still playing around with trying to find some parameteric way of doing this but it's quite complicated. If one can live without the diagonals, you can make an easy parametric family, or start with this and create types, and then later add the diagonals and save them out as individual families. Anyway, I'll post back if I make any progress on this.

Were you successful in creating a double pitched joist. We are trying to show k-series double pitched, but finding out it is not so easy.

[phoulx]

Were you successful in creating a double pitched joist. We are trying to show k-series double pitched, but finding out it is not so easy.

I found it easiest to modify the Howe Flat Truss.rfa and attach it to the roof to form the slopes. I constrained the bottom chord and the last web top chord panel point back from the left and right reference planes. In my model, I created a type with double angle top & bott chords, a 3/8" square plate for the webs and a height. Insert it an attach to roof.

No, it doesn't have joist seats and doesn't look or act exactly like the joist family but it's close. For me, the joist was not always the shape so I didn't want to create a family with forced slopes or lengths. My ridgeline remained straight but the bearing corridor walls jogged in and out. I'm not that concerned about exact web layouts since were not the joist supplier. This worked for us.

[dbaldacchino]

When I first started this thread, I was trying to create a parametric family that would change the webs as well. However the number of webs vary according to the length of the joist and they are not identical to each other like in the parallel version, so you cannot array the webs. That's where the difficulty lies. Other than that, it's easy to create one with either no webs or do the start and end webs and leave the remainder empty so when viewed in elevation, it's like you stopped drawing the rest of it (which is an acceptable hand-drafting technique). Maybe even show a partial web member. These non-arrayed elements can have their length and angle adjust parametrically just fine with the use of ref. lines or planes.