gwynn
Structural
- Aug 26, 2007
- 233
Just looking for some thoughts on things that need to be taken into consideration and how to approach/analyze them at this point - I'm at the brainstorming/spitballing stage with this.
I have been doing a fair number of steel girder erection plans lately and I have one for a multi-span bridge with kinked girders coming up a couple of months from now. A total of five spans and eight kinks with each kink at a field splice (one kink in each of the end spans and two in each of the interior). Eight different girder sections in total, with the section changes and splices at approximately the same location on the interior and exterior girders (four girder lines and the section changes and splices look to line up radially on the curve of the bridge deck). The section changes include an increase in girder depth from ~5' to ~8'. The piers run square to the girders and are along the radius of control line curvature, but the abutments are skewed.
The bridge has diaphragms located either side of each kink. All of the diaphragms are detailed to fit under total dead load and the camber differential between girders is significant. I know this will cause problems for the erection.
At first thought I see a few erection options:
1. Erect the girder segments on shoring and twist/layover the girders enough to install the diaphragms. This will result in the flanges and webs of adjacent girder sections being out of plane when installing the splices and require jacking on the shoring or other means to twist the connected set of girders back to a near plumb condition before splicing.
2. Erect the girder segments on shoring with the minimal amount of bracing/diaphragms required for stability. Assemble the splices and then install the diaphragms. This will increase the forces required to orient the girders in the geometry required to install the diaphragms, as torsion on one girder segment would now be partially resisted by strong axis bending of the girders.
3. Similar to option one, but leave out the diaphragms nearest the splice locations. This would require a combination of the means that would be needed in options one and two, but may lower the demand required for each.
I would appreciate any thoughts on how to deal with this situation.
I have been doing a fair number of steel girder erection plans lately and I have one for a multi-span bridge with kinked girders coming up a couple of months from now. A total of five spans and eight kinks with each kink at a field splice (one kink in each of the end spans and two in each of the interior). Eight different girder sections in total, with the section changes and splices at approximately the same location on the interior and exterior girders (four girder lines and the section changes and splices look to line up radially on the curve of the bridge deck). The section changes include an increase in girder depth from ~5' to ~8'. The piers run square to the girders and are along the radius of control line curvature, but the abutments are skewed.
The bridge has diaphragms located either side of each kink. All of the diaphragms are detailed to fit under total dead load and the camber differential between girders is significant. I know this will cause problems for the erection.
At first thought I see a few erection options:
1. Erect the girder segments on shoring and twist/layover the girders enough to install the diaphragms. This will result in the flanges and webs of adjacent girder sections being out of plane when installing the splices and require jacking on the shoring or other means to twist the connected set of girders back to a near plumb condition before splicing.
2. Erect the girder segments on shoring with the minimal amount of bracing/diaphragms required for stability. Assemble the splices and then install the diaphragms. This will increase the forces required to orient the girders in the geometry required to install the diaphragms, as torsion on one girder segment would now be partially resisted by strong axis bending of the girders.
3. Similar to option one, but leave out the diaphragms nearest the splice locations. This would require a combination of the means that would be needed in options one and two, but may lower the demand required for each.
I would appreciate any thoughts on how to deal with this situation.
