Bridge Jacking 4

[kkelley]

I'm currently working on a bridge rehab project requiring a complete abutement replacement. This of course requires constructing a temporary bent and jacking the superstructure up off the existing abutment. Does anybody have any helpful tips or "lessons learned" with this type of project?

 

[Ingy]

are you asking as a design engineer or as the contractor?

 

[kkelley]

sorry.....I'm the design engineer.

 

[SlideRuleEra]

I have been on both sides (Contractor & Engineer) of this type situation (at different times, of course). This is what I have learned:

From a Contractor's viewpoint, leave the "means and methods" to the Contractor. If the design engineer specifies the details he is not only taking on the responsibility for success, but also may drive the bid price higher - not all Contractors will have the materials and equipment it takes to meet the Engineer's requirements. Contractors may have suitable substitutes, but will most likely place a bid based on renting or purchasing items that the Engineer required. If the Contractor gets the job, then he will try to talk you into allowing him to use his substitutes. This may be totally acceptable, but the Contractor will "pocket" most or all of the cost savings.

From an Engineer's viewpoint, while leaving the "means and methods" to the Contractor, require that he submit plans for your review and acceptance. These plans to signed and sealed by an Engineer of the Contractor's choosing, at the Contractor's expense. You avoid the liability, yet have control of what is done.

http://www.SlideRuleEra.net

 

[broekie]

Make sure all of the girders are jacked at the same rate. If not, you will get cracks everywhere in the existing deck.

 

[bridgebuster]

I've done this before and I'm currently working on a similar project. I agree with SlideRuleEra and broekie; leave the M/M to the contractor and jack at the same rate.

However, your plans should have a workable concept as well as any precautions the contractor must observe. The contractor doesn't have to follow your concept but it shows bidders that the jacking scheme has been thought out.

That's how it is typically done on NYSDOT projects. The contractor submits a design that's been prepared by a PE.

 

[DRC1]

We have done this to replace bearings, not to replace an abutment. Some notes on the jacking: Despite what a lot of people tell you jacking can & does occur under live traffic, however we will stop traffic durring the actual raising of the jacks for certian conditions. Use hydraulic jacks with locking collars. Never run jacks to full stroke or more than 80% of capacity. I like to set jacks at all jacking locations and jack each girder individually. Check capcity of end diaphragm. Generally you can go 1/16 with out a problem. Lift each location succesively then work back until the bridge is raised approx. a 1/4 inch. Generally depending on bridge design, jacking is done under the beam or along side the beam under the end diaphragm. Generally the deck is poured down to the end diaphragm top flange. Check for stiffers at the jacking location. Check the stability of the jack for overturning due to lateral loads if under traffic.

Relocating the support to the abutment raises several questions: Can the load be transfered to that point structurally? What will the temporary bearings be? How much deflection will there be at the ends of the beams?
Will the new support be able to take lateral loads from the demolition such as unintentinal equipment strikes?
What code will the temporary supports be designed to?

 

[LittleWheels]

DRC1 has covered most of it.

If you have big service bays on a smallish bridge, you may require different jacking forces at the external beams, compared with the internal beams.

In Britain, temporary supports for highway bridges need to be protected from or designed to withstand vehicle impact loading.

 

[Dinosaur]

I once worked on a bridge jacking problem. I recommend you use an extremely stiff beam running transverse under the bridge beams and jack that beam at several locations along its length to create a mechanism that lifts the bridge uniformly. The beam under the jacks will have to be very stiff also. In RR work, I believe they require the jacks to have 150% capacity of the lift. Probably not a bad idea. You can get some guidance about required minimum horizontal loads from the AASHTO Guide Specificaitons for Bridge Temporary Works. The minimum horizontal load in there, as well as the Division II - Construction portion of the AASHTO Standard Specifications is 2% of the vertical load. I would also use some magnitude of wind and breaking (LF) force. Oh, your bridge is straight, right?

 

[kkelley]

Yes, It's a straight bridge on a slight skew (about 8^) and about a -1% grade. 87' simple span, 76' gutter to gutter.