Truss Type Selection & Configuration 1

[mohammed43]

Hello,

This might be a basic question but can anyone tell if there are any guidelines/thumbrules or basic concepts involved in the selection of truss type.
I mean to ask the orientation of inclined members, spacing & type of truss.
For Example if I had a Cantilever space 2 level truss, is there any guideline related to the orientation of inclined members & spacing.
In my case the depth is fixed.

Iam looking for some information or theoretical concept..

Thanks

 

[hokie66]

It is generally more economical to have longer webs in tension, with shorter webs in compression. Thus the Pratt truss is a popular form. Not sure what you mean by "cantilever space 2 level truss".

 

[mohammed43]

I meant truss which is fixed at one end & free at the other end. & has three longitudinal chord memebrs.

Iam assuming that in the above case the right half (free end) diagonal members to be inclined towards centre(right to left orientation) and left half (fixed end side) diagonal members incline towards centre (left to right orientation).
Do I need to mirror image for the second level.
Hope Iam using the right terminology..

Thanks

 

[BAretired]

If your truss is a cantilever, there is no need to reverse the direction of the diagonals for gravity loads. If you decide to make all diagonals tension members, then they will all slope downward to the right (assuming fixed end left).

The middle chord doesn't contribute very much to the strength of the truss.

BA