P/S Bridge Girders in CONSPAN
P/S Bridge Girders in CONSPAN
(OP)
I am analyzing a 2-Girder 90 foot span with train loading. The worst-case beam seems to work as I increase the tendons everywhere except for allowable stresses in the bottom flange from about 0.7L to Midspan. If I allow CONSPAN LA to "Auto Debond" the stress is decreased, but not enough. Any suggestion to manually input debonding lengths (maybe a good methodology) so that the span may work with only 2 girders with a reasonable amount of tendons.
Thanks, Any input is greatly appreciated - even if it is on p/s beam design with CONSPAN - am new at it.
ASaldana
Thanks, Any input is greatly appreciated - even if it is on p/s beam design with CONSPAN - am new at it.
ASaldana





RE: P/S Bridge Girders in CONSPAN
You didn't specify what kind of railroad loading you are using. Please indicate what kind of "train" loading you are designing for.
Purdue86
RE: P/S Bridge Girders in CONSPAN
RE: P/S Bridge Girders in CONSPAN
Is this LFD or LRFD? If LFD, are the stresses you're talking about at Final 1, 2, 3, or at release? What type of beam section? I think we need more specifics to offer meaningful suggestions.
RE: P/S Bridge Girders in CONSPAN
ASaldana
RE: P/S Bridge Girders in CONSPAN
As you are the "Design Engineer" on this, you should not be relying on software to design it in lieu of your lack of understanding of the design methodology. Software should be used to augment you design ability, not mke up for a lack of undersyanding of it.
Learn how to do the calculations by hand before using software and then you will be able to see what the problem is and the solution. You are being paid to be the "engineer" on this, the software is not. Software is a tool to help experienced engineers do the calculations quickly, not to "create" experienced engineers.
RE: P/S Bridge Girders in CONSPAN
ASaldana
RE: P/S Bridge Girders in CONSPAN
If its a derailment that controls, I would consider puting that load in the extreme event category if you haven't already. This would allows you to increase your allowable stresses. Anyone else have thoughts on this? Have you checked AREMA for guidance?
I do agree with Rapt, at final 1 if your beam is failing I doubt debonding will help. Sounds like you need more PS steel in the bottom.
The PCI bridge design guide has some very good design examples to follow. You need to be careful with Conspan, I've found the input can be a little tricky sometimes. As they say garbage in, garbage out...
RE: P/S Bridge Girders in CONSPAN
Debonding is only useful in relieving transfer problems at the ends of beams.
If debonding is reducing the stress at midspan in a determinate member, throw the software away because either it is wrong or you are using it wrongly. debonding will only affect the results at the cross-sections where the strand is debonded and you can only debond at the end of the strands.
As I said, do the calculations for yourself so that you can learn the different effects of changes you make (such as debonding) so you know how it should be solved. Your program obviously does not know and you need to know to be able to realise this and to use any software properly!
RE: P/S Bridge Girders in CONSPAN
RE: P/S Bridge Girders in CONSPAN
ASaldana
RE: P/S Bridge Girders in CONSPAN
Debonding can be done in the middle too. Not necessarily at the beam ends. Also, CONSPAN does allow debonding both the at ends as well as in the middle of the girders.
PCI manual is of a great help.
-Rao.
RE: P/S Bridge Girders in CONSPAN
Debonding is mnormally done on the ends of the bottom strands to allievate transfer stress problems at points where the P.e is high but the self weight moment is low. This is simply done by sleving or greasing the end of the strand so that it does not bond to the concrete. The strand effectively starts at the inner end of the debonding as far as the beam is concerned. The debonded part is simply there because the strand cannot be cut shorter in a pretensioned member due to the stressing requirements.
Can you describe how the debonding is done in the middle of a beam?