helfreco
Structural
- Feb 15, 2011
- 21
Hello All,
I am designing a braced frame and doing the modeling in STAAD. I am using a single angle for my diagonal bracing, and we draw the brace 1/8" to ensure that it is erected taught. Do I need to consider the draw as a pretension in my model? I am thinking that I do. The member is already designated as a tension only member.
Will the pretension effect more the deflection of the frame or the stress in the brace? When I try to model it, I am getting some screwy results. I use PL/AE to figure out the pretension load of the brace for a 1/8" draw. When I apply that load to the brace and add just the dead load of the frame, I see that the overall tension in the brace is the sum of the pretension plus the dead loading, and the frame deflections are greater than if I had no pretension at all. This seems counter intuitive to me, I would think that as the brace tries to resist the pretension it would contract the frame and my deflections would be smaller.
I can't imagine why my deflections increase when I add pretension. Is my logic wrong on this, is it incorrect to add draw in a brace as a pretension load, or am I missing something else? thread507-192634 touches on this, but does not really get to the root of my question. Any help would be appreciated.
Thank you!
I am designing a braced frame and doing the modeling in STAAD. I am using a single angle for my diagonal bracing, and we draw the brace 1/8" to ensure that it is erected taught. Do I need to consider the draw as a pretension in my model? I am thinking that I do. The member is already designated as a tension only member.
Will the pretension effect more the deflection of the frame or the stress in the brace? When I try to model it, I am getting some screwy results. I use PL/AE to figure out the pretension load of the brace for a 1/8" draw. When I apply that load to the brace and add just the dead load of the frame, I see that the overall tension in the brace is the sum of the pretension plus the dead loading, and the frame deflections are greater than if I had no pretension at all. This seems counter intuitive to me, I would think that as the brace tries to resist the pretension it would contract the frame and my deflections would be smaller.
I can't imagine why my deflections increase when I add pretension. Is my logic wrong on this, is it incorrect to add draw in a brace as a pretension load, or am I missing something else? thread507-192634 touches on this, but does not really get to the root of my question. Any help would be appreciated.
Thank you!
