topic Re: Warren Truss (height flex problem) in Revit Structure Forum

Warren Truss (height flex problem)

Avaris. — Sun, 16 Sep 2018 13:24:34 GMT

I tried to make a truss with a warren configuration, it is made as a 'structural truss family'.
The diagonals are always spanning 3 meters, I made one array for the diagonal going up, one for the diagonal going down. The flexing in width is without a problem (if you keep the parameter for the array above 1).

Flexing in height is a different story, as soon as you put a diagonal in an array it loses its connection with the bottom chord. However, Revit has a 'Howe flat truss' which does exactly that, flexing in width ánd flexing in height although it is an array. Does anyone know how they built that family, I can't see any constraints within the array?

Re: Warren Truss (height flex problem)

ToanDN — Sun, 16 Sep 2018 17:55:31 GMT

Share you progress family.

Re: Warren Truss (height flex problem)

Avaris. — Sun, 16 Sep 2018 18:24:23 GMT

I did only one side of the Warren type, but I think you get the picture. I also included the Howe type, because that one flexes within the array.

Re: Warren Truss (height flex problem)

barthbradley — Sun, 16 Sep 2018 18:34:34 GMT

Open the Howe Truss and turn on the Annotation Categories (under View VG Overrides). You then see how it's built and constrained.

Re: Warren Truss (height flex problem)

Avaris. — Sun, 16 Sep 2018 18:46:38 GMT

It seems like there is a dimension within the array, but when I try to include the dimension in my array it gives an error:

"The elements you have selected for grouping contain dimensions or tags whose references are not all included in the selection being grouped and are not all included in a common model group. As a result, some of the selected elements have not been included in the new group."

Re: Warren Truss (height flex problem)

barthbradley — Sun, 16 Sep 2018 19:21:32 GMT

All elements that the dimensions reference must be included in the Group.

...this is Howe Truss Panel Group. The horizontal dimension is pulled between the TIP of the diagonal web to the vertical web. The TIP is a snap point that you can tab-select.

...actually, both vertical and horizontal dimensions are pulled from tips. No Ref. Planes in Group.

Re: Warren Truss (height flex problem)

Avaris. — Sun, 16 Sep 2018 19:43:57 GMT

Even though I exactly select the tip, it says constraints can not be met within array. Without array, it works fine.

Is there also a specific order in which to draw these lines and constraints?

Re: Warren Truss (height flex problem)

barthbradley — Sun, 16 Sep 2018 20:02:04 GMT

Post what you've have so far.

...I think I figured out your problem with your first file. The Array number parameter is zeroing out. An Array can have less than 2.

Re: Warren Truss (height flex problem)

Avaris. — Mon, 17 Sep 2018 06:40:30 GMT

No that is not the problem, I do know that error. In this case it gives an constraint error: "Constraints are not satisfied"

Re: Warren Truss (height flex problem)

ToanDN — Tue, 18 Sep 2018 00:01:20 GMT

Try this family.

Re: Warren Truss (height flex problem)

Avaris. — Tue, 18 Sep 2018 18:20:41 GMT

It definetly works, but what is the reason your family works and mine does not. Even when I include the web at the bottom, my second item of the array fails... Is there a secret in the sequence of dimensioning and drawing?!

Re: Warren Truss (height flex problem)

ToanDN — Tue, 18 Sep 2018 18:26:53 GMT

I had to draw the web triangle outside of the chords so that I can dimension it independently from the chords. Array it and move the array groups to place, then constrain.