Bridge Bearing Jacking Structure

[MohawkNE]

I am jacking a bridge to replace some bearings. I'm erecting temporary columns on each side of the pier column and placing jacks at the tops to lift the structure under full dead and live load.
At the bottom of the columns I am bearing on the old pier footing. My temporary columns are made up of four ibeams with bearing plates. AASHTO bearing pressure loads are just within limits, but I am analysing the footing for the excentric loads of the temp jacking columns.
The existing footing is on piles with the pier pedestal in the center and is six feet thick. It looks like it's designed correctly. My temporary jacking structures are located outboard of the pier column and extend to the edge of the footing. I am looking at a possible failure mechanism where the edge of the footing breaks off at a 45 degree angle from the face of the existing pier col. to the outside face of the footing (nothing in AASHTO manual seems to address this condition).
Is this something I will need to drill and add steel bars for? Somehow it feels like I am creating a problem out of nothing. The 45 degree shear face has some Vc, but not enough (Vc=.95(4000psi)*1/2. It is appearing like I have to add almost 15 1.5" 150 ksi dywidag bars vertically into the footing to add resistance.If I do this on all six piers under all bearings I will have to drill 180 holes.
The footing is unreinforced except for a couple horizontal bars just above the piles. the footing is 14.5 x 14.5 feet, 6 feet thick with a 7x7 foot pier column (at base). My temporary columns are 7 x 3.75 feet in outline and extend to the edge of the footing between the pier and the footing edge (both sides of column) and support 1,700 kips (DL and LL with 50% markup).
Does anyone have any comments or experience with this sort of thing?

 

[dhengr]

Mohawk:
Why don’t you show us a plan with the beam center lines, sizes, etc. the pier cap and the columns or pier and footings. Show an elevation and side view of the piers. A few sketches with all of the important design info. and dimensions for this problem will be worth more than a thousand words. And, you’ve already used most of those up without conveying your problem in a meaningful way.

I’ll bet you want to hang your jacking beams off the two edges of the pier cap, and then use smaller temp. columns just to take the eccentric jacking loads out of these beams. The columns can be shimmed up under the beams and bolted to the beams.

 

[MohawkNE]

The pier caps have very limited room to hang any structure from them. The existing anchor bolts must be retained and the new bearings lifted and assembled in pieces to allow them to fit into the limited space. Seems like completely seperate jacking towers are necessary.

I have attached a pdf showing most of the information relating to the arrangment. Additional information is available as requested.

Thanks for your interest. I have uploaded the file to the forum storage area and the link provided is part of this reply.

 

[chicopee]

Is his the same Mohawk Steel in Ct. where foreman Danny Shay worked during the early 2000?

 

[chicopee]

If something is to go wrong, it will. I would study the installation of reinforcement along the entire perimeter of the top of each pile cap with "I" beams so as to minimize the chance of edge cracking, just as you would have with sheet pile cofferdams except these "I" beams would be inside to resist water pressure.

 

[ImminentCollapse]

Couple higher level questions you've probably explored, but worth asking:

Why are you doing this under full LL? No detours or short duration closures possible?

How old is this bridge? It could have been designed to be jacked without temporary shoring from the existing bridge seats.

Finally, when shoring towers are impractical, I've seen above deck options with reaction beams and drilling bars through the deck, but those are not cheap or easy either and if you can't close the bridge, obviously impossible.

IC

 

[bridgebuster]

Using 150% of Service Load seems like overkill.

I wonder if the designer looked into the footing issue when he came up with his concept. Typically, we don't design shoring but put a workable concept in the plans. If the shear is a problem, you could put a grillage under your columns that runs the width of the footing to distribute the load uniformly. If the footing is failing at 150% of SL I would check the footing for service load at the face of the column for service load only, as a sanity check. The bridge is still standing.

 

[dhengr]

Mohawk:
It’s really tough to see the clearances, spaces and sizes you have up at the top of the pier. The top of the pier looks to be 5' or 6' sq., with 2.5' to 3' to the underside of the plate girders. You’re going to work from either side of the girders, on the rocker bearings, in about a 6' space btwn. the jacking systems above the pier cap. I take it that the 1700k is per beam, at each bearing, or 1700k per side of the pier, and that the pier is able to take something akin to a total of 3400k to ground. Those are some pretty nasty loads, you might be well off fabricating most of this from plate, so you can put the welds and plate thickness where you need it, not where some WF member doesn’t have it. At the moment, your three layers of perpendicular beams, with web stiffeners looks very complicated and difficult. At each flg. to flg. layer (faying surface) you are taking about 1700k/6 web over web intersections, in bearing. That’s 283k on about a 2 or 3 sq. inch bearing area, maybe not impossible, but a very difficult load path. And, all of those web stiffeners have to be fitted t&b to make it work, a nasty task.

My sizes, thicknesses, etc. (concept too) need considerable design work, but are intended to express concept. You have about 1' below EL. 58.83, over the top of the conc. beam btwn. the two piers, for structure which spans in the same direction as the plate girders (the bridge span). This acts mostly in tension to hold the two jacking beams together, but is also a work platform on each side of the pl. girders. They are maybe 8' wide (perpendicular to the pl. girders) by 18-20' long, with the bottom of their top pl. resting on the top of the pier, at EL. 58.83. The two jacking beams, 5' wide x 4-5' deep are fabed. box beams, and on their upper/inner corner, their top flg. pl. projects 8" onto the top of the pier (pl. bot. el. at 58.83). Maybe this edge detail is an 8x8x1 angle with the horiz. leg on the pier top. I want to get half the jacking load reaction onto the to of the pier. From the jacking beam, down 10 or 15' is a 3 or 4 legged kicker frame, sloping back into the face of the pier. At about EL. 40 the columns on this kicker frame are spliced, can be shimmed, and are carried down to the found./pile cap, right along the face of the pier. This cuts the column loads about in half and gets them away from the edge of the pile cap.

Maybe there is some food for thought for you above. I need to think about it some more, and would have to see a lot more existing detail to go much further.

 

[MohawkNE]

The load from the pier spreads out through the footing thickness directly to the piles. Assumed 45 degree angle.
This temporary supporting structure stands on the section of the footing that is not really part of the load distribution of the pier, other than towards the bottom of the footing. The shear surface I am interested in starts at the pier face and goes outward at a 45 to the edge of the footing, approx 5.3 feet long. This is the possible failure surface I am interested in. As a possible solution and avoiding the cost of drilling 15+ 1.5 inch holes with reinforcing added to supplement the Vc value, is to connect the two temp. support structures across the pier column with a steel member to keep them from moving if the footing decides to crack along the possible shear line. If the support members are secured with anchor bolts and connecting member, the whole thing will remain stable (and possibly not crack the footing if nothing can move). Less costly. My concern is whether or not this failure mode is a valid concern. This solution would be similar to the response from "chicopee" but less expensive.
"immenent collapse" Lane closures not an option. Good idea, but not possible.
"bridge buster" The 150% load increase has been addressed by using working stress where there is a 67% safety factor already imbedded in the equations. Straight service loads are used. Good point. Temporary Shoring via
AASHTO also requires a 2.5 FS in the Fa calc.s for the columns of the support structure as well. Please see above for failure surface description regarding the stability of the existing pier and how it is not an issue.

 

[MohawkNE]

"dhengr"
This is the lowest and lowest loaded pier. The temp support structure is going to be modular to address piers 75 feet high and loads much greater. There is very little space at the tops and the jacking structure cap and the bearings will have to be lifted in pieces and assembled at the top. You have a good appreciation of the challenges.
As the piers get higher, the footings get thicker and wider. My support structure will have the same footprint, but the failure surface in the footing will still exist in all the piers.
It's a good challenge that is stretching my conceptual awaness of the possible limitations of the concrete bearing surface made up of the existing concrete footing. It looks like a possible failure plane and I have learned as "chicopee" expressed that if something can go wrong, it will. If I identify a possible challenge, then it is worth chasing it all the way down.
What do you think about my idea to connect the two temp support structures across the existing pier to keep them from moving outward if indeed a crack occurs?

 

[chicopee]

The steel ring that I was proposing would be under tension, compresse the concrete pile cap at the top to contain it from cracking, and relatively easy to install. If one row of that steel ring is not enough, space another one some distance below from the top one.