steel cross frame stresses in a skewed bridge!
steel cross frame stresses in a skewed bridge!
(OP)
I need some intelligent advice for a bridge rehabilitation project.
The exisitng bridge has an skew of about 30 degrees.
It need to be raised up to get required vertical clearnace.
hence we r raising the existing beams up/providing a new deck above.
My question is.....will there be any stresses in cross frames if I raise the beams up by different amount at different supports?
If so ....how can I take care of that!
The exisitng bridge has an skew of about 30 degrees.
It need to be raised up to get required vertical clearnace.
hence we r raising the existing beams up/providing a new deck above.
My question is.....will there be any stresses in cross frames if I raise the beams up by different amount at different supports?
If so ....how can I take care of that!
RE: steel cross frame stresses in a skewed bridge!
RE: steel cross frame stresses in a skewed bridge!
I already checked that the main members (beams) got some stresses due to this .......upward settlement/raising but those are within the allowable limits.
Also I can check the cross frames for fatigue.
But.....my main concern is that .....
because the bridge structure has a high skew....although the main members are not stressed ....the cross frames may get high stresses due to differential settlement/raising.
...because ......in a particular direction parallel to a cross frames....different beams connected to it are raised by different amount.
The beams are arranged somewhat like this.....
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and cross frames are perpendicular to them.
I hope I am making my point clear.
So...How can I make sure that strsses in cross frames is within limits? Is there any way?
Also....can you please tell me where I can find that manual from AISC?
please help!
RE: steel cross frame stresses in a skewed bridge!
I recently completed the design of two steel bridges with non-parallel abutments and skew angles between 55 and 58 degrees. The individual girder lengths vary from 125' to 155'. One bridge has six girders and the other has eight.
We did a 3-D analysis using MDX and the maximum performance ratio in the X frames was 65%. The X frames consist of two angles 4" x4" x 5/8" Fy = 36 ksi.
To order the fatigue manual go to www.aisc.org
The manual is published by the National Steel Bridge Alliance group of AISC.
I hope this helps.
RE: steel cross frame stresses in a skewed bridge!
This shifts the loads from the x-frames to the abutment or pier cap -- so it will have to take the forces caused by the jacks lifting the structure. Also, traffic above will have to be re-routed or greatly slowed down. This will allow you to install a permanent shim or bearing assembly under the beam to raise it up.