Jacking 26 girders at one time
Jacking 26 girders at one time
(OP)
We are about to design a elastomeric bearing pad replacement project. It will require the lifting of 26 concrete girders at one time. The girders are about 100 feet long. Do you think this is possible or have you ever done this? Also, this is an extremely well traveled bridge so one of the constraints is that they would like to limit the work time to lift, change the bearings and lower the bridge to 5 hours. Do you think this is enough time? I think it is but it will be costly.
RE: Jacking 26 girders at one time
As for jacking the girders, make sure you dont crush them at your jack point.
RE: Jacking 26 girders at one time
With 26 girders, that means 52 bearings, so you have less than 6 minutes, on average! May wish to consider jacking and bearing replacment at one end in the first 5 hours, then the other end in a another shift - if the bridge structural system will permit such staging.
You have not stated if the girders are steel or concrete, so i am not sure what type of weight is required to be lifted. Also, you have not stated where you are located - in some locations there are a lot of expertise in bridge bearing replacement, so i would encourage you to speak to a specialised contractor in your area.
It would be prudent to have a "trial lift" before you elect to go for replacing 26 (or 52) bearings in one shift. Presumably you are going to specify hydrailic jacks for this purpose. I would state that the contractor to place and synchonize the jacks, and do a "trial lift" to see the duration it takes, and sort out some "bugs". Then upon success, in following shifts, replace the bearings.
FYI - the Kingston Bridge in Scotland in 1999 was lifted 15mm off its piers - the superstrcuture weighs 52,000 tonne!!! The lift was maintained for a duration of 9 months whilst major repairs were undertaken.
HTH
RE: Jacking 26 girders at one time
In that case your project becomes closer to:
1. Assemble all lifting jacks in position(s)
(possibly several days involved)
2. Shut down traffic (begin your timer)
3. Lift girders (all personnel in safe positions)
perhaps a half hour to a full hour - your contractor will be able to give a good idea.
4. Personnel into position to change (all) bearings.
perhaps another 1/2 hour
5. Bearings changed. Allow a generous time span for possible set-backs. An hour? Two? You would know best on this. Talk to the specific personnel that would perform the work.
6. Personnel moved back to safe positions - another 1/2 hour.
7. Girders lowered. Perhaps a 1/2 hour. One hour?
(Timer stops)
8. Release traffic again.
9. Remove jacks. a few days.
Obviously, this is an over-simplified time-chart - but it should give you a good idea of the feasibility. It certainly seems like you should be able to accomplish it, if you have sufficient personnel. Obviously, the ease of change-over will be a big factor also - - if they can be 'slapped in' by one man in 5 minutes, you may only need a crew of a half-dozen or so. If there is any reason to suspect it might take a three man crew two hours to replace a single bearing...well, then things will change, won't they?
Just some 'common sense' stuff from a project-engineer's viewpoint.
Curmudgeon
RE: Jacking 26 girders at one time
In general, the superstructure is lifted only a limited amount and the old bearing are extremely heavy. This will require quite a man-effort. The effort is intensified by significant height (piers vs. abutments). Additionally space is limited because the temporary jacking towers are usually close required by design.
Time must be taken to ensure that the bearings are set properly as well.
I would, if you haven't already, request to see some type of plan in writing or drawn up which details all aspects of the operation.
RE: Jacking 26 girders at one time
Alright, things sometimes go as planned. How 'bout this - things RARELY go as planned.
5 hours sounds tight to me. Let us kow what happens.
RE: Jacking 26 girders at one time
All work performed by union Ironworkers from Los Angeles.
Some problems with welding and heat treating the T-1 steel resulted in some degree of panic from time to time, a broken tap in one of the hold downs was another, but by and large it went smoothly well within the required time limit.
I realize this does nothing toward answering your question or solving your problem. I do hope, however, it will give you a little insight as to the difficulty I perceive in your project.
Rod
RE: Jacking 26 girders at one time
RE: Jacking 26 girders at one time
I would suggest oversizing the hydraulics as my experience with synchronized jacks is that the sum of the parts doesn't usually seem to equal the whole!
RE: Jacking 26 girders at one time
Some additional information is that we will be changing only 26 bearing pads at one time. The other side will be left for changing at another time. We think that we will jack the bridge five separate times at five different locations to change out all of the pads. In my limited experiance, it took us four hours to change out 10 pads on another project. For your info the task that took the longest to do is removing the old pad and cleaning the surface. Primarilly the contact cement used to hold the pad in place. Why do they use that anyway? The forces exceed the strength of the glue and it just makes it more dificult to remove later. However, the way I look at this is, albeit a simplistic view, is that if it took us 4 hours to remove 10 pads 26 can be remove within the same time frame providing the number of crews are increased proportionally. While it is true that removal of the pads math wise will only allow about five minutes per pad but 26 crews will allow 5 hours. I think the solution is providing the number of crews somewhere between 1 and 26 and like someone stated have proper planning. I know the time frame is extremely tight, hence my question to this forum. Again, thanks to all.
RE: Jacking 26 girders at one time
I have never tried to coordinate 26 separate crews but I did run a job with 5 crews, about 50 men, in a refinery. It was an all consuming effort and not at all easy. If it can go wrong, it WILL go wrong (Murphy # 1 law of probability).
The more people you get in a confined work area, the less work accomplished, overall. BUT---IF YOU THROW ENOUGH MONEY AT IT---(Ronald Reagan # 1 law of economics).
I do truly wish you the best of luck.
Rod
RE: Jacking 26 girders at one time
As words of advice - - do a dry-run walk-through or two with the actual crewmen you intend to use. If they will be working in teams (as it sounds) - try to have at least one experienced man on each team, and at least one experienced 'floater' to come to the aid of that one team that always seems to have unexpected problems.
Also, sitting down with the crew-leaders and writing up a step-by-step flow-chart can be quite revealing for all parties. This was a life-saver for myself and my crew when we had a major project loom up in another state, where we had limited or poor help from the on-site locals. Myself, my draftsman, and the three main crew-leaders sat down for two different two-hour sessions and flow-charted and brain-stormed a project, that we all originally thought would be three weeks, into a long week for the main crew, plus one more week for the electricians and 'hook-up' crew. Every single person at the table managed to save the crews at least 2 man-days by their suggestions.
My draftsman and I heard from just about every person on the crews that went, and from a half-dozen of the locals from the site, that they had never seen a project of that size go so quickly, and with so few snafus. ummm.... not that there were NO snafus, you understand. But there was actually spare time available to address them when they popped up.
Just like they teach you in school - - Prior Planning Prevents Poor Performance.
Curmudgeon
RE: Jacking 26 girders at one time