Steel Bridge Launching through Incremental Method

[struct4me]

Hello..

I need some expertise views in Bridge Launching aspect, we are building a aqueduct (steel bridge Pratt type) for carrying water under pressure through steel pipes over the bridge. The pipe starts from an Underground tunnel and after crossing the bridge ends in the tunnel on the other bank. Since, the tunnel is accessed from one end, so launching of bridge can be done from the left tunnel only. so the method proposed as incremental pushing the bridge from one abutment with the balancing nose in advancing portion.
However, the bottle neck is that the abutments on the other bank is not getting accessed from hill roads (due to steep climb or the tunneling from the other side).
One idea may be to bring nose near to the far end abutment so that man and material can be transported to the other side, Bring back the nose to the erection point (the near end abutment). After, the abutment prepared and excavation of the tunnel done (manually) for the length required for advancement of the nose & removal there off, the bridge will once again pushed to finally install to both the abutment.
Is it possible, I heard incremental launching can push a bridge, but can it be customized to pull from the same end.
Span is 46.8m and bridge is above a narrow stream of height 70m.
Any one's help will be highly appreciated.
Sketch attached (all dimension in meter). Please ask for any clarity.
Thanks..

 

[dhengr]

Struct4me:
1. You might want to talk with a few contractors who would likely do this work for you, and get their input. Their methods, experience with such construction, available equipment, etc., will dictate some of what can best be done, and what you will have to do the structural and foundation design around.
2. I take it that you have two 4m dia. (13’ dia.) steel pipes making this crossing. The clear span is about 47m (155’), and the two pipes fit, side by side, within a 9m (28’ or 29’) wide tunnel. The pipe over this span may have a thicker wall than the pipe which can be supported regularly on foundation points on the ground. While I’ve not run any numbers at this point, that pipe section will span some considerable distance under its own strength. And, the pipes may be easier to launch in a cantilever fashion than the whole truss bridge. You can just add some back span pipe, which will become part of the final pipe line, but also act as the back span counter weight. Furthermore, void of water, they could provide for a small track and railcar system for transport of equip and materials to the other side. They may need to be supported with additional structure at several locations over the whole span for the construction loads. Or, they may be the nose support needed to launch the through truss around them.
3. It might be interesting to consider a suspension cable support system for the pipes, much like a suspended highway bridge. The major foundation and structural work would be much further up the hill sides where access from above would be easier. And, once this suspension system was far enough along, it might act as the cross-river material transport system, with a suspended trolly system, prior to the pipe installation. Parts of that trolly system will exist for the pulling of the main cables and for hanging the suspending rods or cables.

 

[struct4me]

yes, I like the launching of pipe by counter weight method from one side and after I transport man, material through empty pipe (penstock) to other side & prepare the abutment that side, then we can take away the pipe, install the bridge and then supported one pipe on the bridge on concrete pedestal. Here, bridge is planned to take the hit of rockfall if any from two side. Can you please add a hand sketch for this suspension pipe system launching (point 3)...Thanks anyway.

 

[HTURKAK]

Pls correct me if i understood wrong and confirm my assumptions ;

-The flow is from left tunnel ( say upstream ) to right tunnel ( downstream side), the pipe sloped also from left to right.
- The tunnels with dimension 9m W X 6.20 H except the bridge zone,
- The penstock is steel pipe with welded joints,
- The left tunnel+ bridge + right tunnel are on the alignment,
- The tunnel excavation will be with NATM method in the rocky zone,
- The project is design and build , the contractor is free to choose some alternatives




If these assumptions correct , here is a short method statement with a different approach , could be helpful , more economic and constructable..
- Construct the left tunnel with conventional NATM method with dimensions 6 m W X 6.20m H ,
- Construct a service bridge having width 6m and capable for loading of EMPTY pipe and service loading .. This bridge would be in the range of 25 tons and could be erected with a mobile crane,
- Construct the right side tunnel with access from left tunnel and service bridge,
- Interior Concrete lining of the tunnels ( may be not necessary),
- Construct the RC sleepers to support the penstock,
- Construct a steel launching ramp at the beginning of left tunnel,
- Welding and incremental launching of PL. from the beginning. ( If tunnels are curved , this method will not work ),
- The tunnels will not be concrete filled after completing of the PL erection.
- If the tunnels curved on plan, install monorail to the top of tunnel for pipe transport. In this case, the PL erection will begin from the far end of right tunnel.

I hope my respond will be helpful and initiate a different approach.

 

[dhengr]

Struct4me:
Some additional thoughts on your pipeline span problem…

Make the left tunnel portal large enough to be able erect the truss bridge during the construction on the right side of the river. Once I had the pipe across the ravine, I would not pull it back. I would use it as part of a scaffolding system to erect the truss bridge around and under it. Push the pipe across and temporarily set it high enough so that the truss bridge can be built around and under the pipe within the left tunnel portal. The temporary pipe supports at the left end will actually need to be two supports some distance (in length) apart, so that each time a horiz. floor member on the bridge truss moves longitudinally (is encountered), these supports can be removed and/or be replaced by each other temporarily to allow the bride longitudinal movement.

You will have to put a strong sloped roof (a gable roof) on top of the truss to deflect and absorb any rock falls. If a single large rock hits a top chord truss member (without a roof) the truss could easily fail, be brought down. You will probably need a protective roof over an exposed (naked) pipe also.

Any suspension bridge type support system will be highly dependent on the soils and foundation conditions on the mountain sides. You need to get your GeoTech guys involved in this analysis and determination. There will be large tieback foundation blocks, far uphill, and suspension cables; maybe towers on each side of the river, over which the cables are strung; maybe just the cables hanging directly from some tie-off structures at the tieback foundation blocks. Look up suspension bridges or construction cableways in any civil or structural engineering handbook for starters. Without knowing much more above the actual situation, I don’t really know what to say in more detail. A construction cableway could actually be used to move construction materials during found. work and to launch the pipe and/or truss bridge across the ravine.

You might shorten the truss bridge or pipe span by looking at some additional foundation locations, on the pipe center line, but below and down hill from the current invert elev. by 6 or 8m. Then provide vert. struts and inclined struts, say 20° or 30° from vert., reaching out and up over the ravine another 6 or 8m, from these lower foundations, thus making the main span only about 30m. These lower foundations might be set into the hillside at about the elev. of your (CC of bearing, 46.800) dimension line on your sketch.

 

[struct4me]

Thank HTURKAK

Your assumptions are right, plan was to build a pratt type truss as I attached in my first post, the bridge to be launched through incremental method, however the problem was not anticipated was the approach to the right abutment which is not accessible, so how to prepare the right abutment before start of pushing the permanent truss from left excavated (accessible) tunnel.
You mention service bridge, but how to erect without a proper right abutment, may be we can kept as cantilever for few month, in that period, the right abutment for support of permanent bridge and few meters extra tunneling on that side is completed, for incremental method with nose attachment, you have to give some space beyond right abutment.
Can the service bridge to be launched through rollers and counter support from the left side, i want to bring this close to right bank and transport the minimum required man materials. When everything is ready, take away the service bridge and launce the permanemt bridge through IL method. Pl suggest.
Thanks for your advice.

 

[struct4me]

Thanks dhengr !!

For your reply, the pipe is one number 4 m dia, will be taken over the Pratt type steel truss with concrete pedestal. Actually water coming from the tunnel is taken through the pipe to cross the stream below. Scaffolding seems difficult from the bottom river which is 70 m below.
Appreciated for your reply, I am attaching a plan and section of the scheme in the next reply.
Regards
Raj

 

[struct4me]

Attachments!!

 

[struct4me]

Plan...

 

[struct4me]

L-section.. access is from left side..

 

[HTURKAK]

The service bridge need not to be launched . I do not know the geotechnics. IMO, the service bridge can be constructed as cantilever cable stay bridge. The last 10 m can be cantilever. From left the first 40 m can be constructed with cable stayed method. If geotechnics is not suitable, You may construct a tower at left having h=20m and integral with balancing concrete anchor slab L= 20 m . the sloped cables would be anchored to the anchor slab.

IMO, the permanent Pratt type bridge no more needed . I suspect that, the 4m penstock will support the bridge rather then supported..

P.S. The last three sketches that you have posted not readable..

 

[dhengr]

Struct4me:
Whatever you do with the pipe in the way of its strength and support to allow it to serve the right side foundation construction, men and materials movement, etc., should make it strong enough to hang some work scaffolding system off of, to help in the construction and launching of the through truss bridge. The truss bridge might be started in the left tunnel, around and under the extended pipe and then pushed across around the pipe, with the pipe acting as part of the truss nose support during the push process.

What thickness is the typical 4m dia. pipe? How thick can we make that 60 or 70m length of pipe (46.8m plus back span, etc.) to make it work as a spanning member for its launching and then use as a material transport member?

Note that a construction cable way would allow work on the right embankment without the need for launching the pipe or the truss bridge. And, it would also facilitate the launch of the pipe and the launch of the truss bridge, or its building over the ravine and around the pipe.

I rather like HTURKAK’s cantilevered cable stay bridge approach. There appears to be reasonable space and terrain shape on the left embankment for this construction. If this approach was used, I would keep the pipe out of the way, out of the tunnel, until after the bridge was constructed, for ease of the other work. I would make the bridge deck and cable stay structure generally below the pipe invert elev., and then be able to use it to start the foundation and tunnel construction on the right embankment. The bridge could be used to feed pipe sections into the tunnel on the right embankment for later final connection. After the bridge was not needed for the right embankment construction any longer, the permanent pipe sections could finally be place on the deck of the bridge, and moving upstream to complete the left tunnel piping. Then, a rock-fall shelter can be built on top of the bridge and over the pipe. The bridge has to carry at least 10-12 kips/ft. just for the pipe and the water weights. This certainly may be the easiest and cleanest approach as compared to trying to launch the truss across the ravine.

I can’t read your sketches very well either. After I enlarge them to be able to read them, the notes and dimensions are just a blur of pixals.

 

[struct4me]

Apology, sending the PDF copy...Title block I have withdrawn due to property right issue. Thanks for yours feedback.

 

[LittleInch]

struct4me,

I'm still trying to work out your sequence of events and all the drawings and sketches are for the finished works.

It might help you and us if there is a series of sketches showing what is planned in chronological order.

It sounds to me like you're going to excavate the LH tunnel up and including the opening (not sure how stuff doesn't fall into the stream?) and then build or extend the bridge to the other side before you start on the RH tunnel??

Not sure why you can't build the two into the middle at the stream? Modern surveying systems should get you to mm accuracy on the line and level of the two tunnels so that they meet in the middle.

If you can explain better what your planned / required sequence is the better, but without some sort of interaction with the rock face or stream then it's difficult to see how you can cantilever out ~45m to get access to the other side?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[struct4me]

Hi..

The problem due to some clearance issue where you can not launch from the bottom and since when you say it will meet the two, I mean that you want assemble at the bottom stream level and then lift the bridge for 70m.Tunnel- bridge alignment is above 70m from the stream bed level. And, since the rock (hill) on two side are not even, it is difficult to launch from the bottom.
Our planning was straight forward, digging the tunnel from the left with enough size for bridge assembly to be done inside the tunnel, once we do the bearing ready, launch the truss by ILM. The problem came up that we can't access the other side, so we need a temproay arrangement to transport man, material to the other side.
When every thing is ready, I mean bearing and listing tunnel digging for nose advancement, we take away the temporary cantilever bridge and launch the permanent one as planned previously.
So, question is how cam I built a temporary steel walkway kind of arrangement which will go near to the right abetment, with winch, roller & counterweight. Length on the launching side would not be a problem. Its like a tower crane with a boom of 47m.
Thanks

 

[LittleInch]

What I meant was why don't you build both tunnels at the same time and meet at the gorge?

If not then you will need a long section inside the LH tunnel of probably 2 x the span as a counterweight.

At 45m you will have a certain droop so need to angle up the temporary bridge structure.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[struct4me]

Okay I got it, tunneling from the further end to the bridge location will take more than a year, so the plan is to build the permanent truss and excavated the tunnel downstream of the bridge from both side to reduce tunneling time. The permanent bridge would carry the tunneling equipment load initially as boomer, excavator, dumper will pass on it to access the other side of the tunnel. when it is done, the steel water pipe will be laid out and empty void in the tunnel to be filled in.
this is the construction methodology.
Thanks...

 

[LittleInch]

I think you're thinking of something like this??

https://www.youtube.com/watch?v=cKi8VWRDA_c

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[HTURKAK]

Er. struct4me (Civil/Environmental)(OP):

I am not sure that you got the necessary info and set-up for segmental/incremental bridge launching method..

I would like to remind that the subject method is economical for multi-span bridges ( box type ,steel or Prestressed bridges )and which the access from the ground is not feasible.

For your case , the bridge is single span PRATT type . With this method, you will need back span to act as counter weight + nose frame and skid , launching eq etc.. more improtant, you will need an expert company having tools and experience.

The following doc. gives some idea for this method and I have absolutely no involvement with the company ..

https://www.structuraltechnologies....s/2018/02/PT_Incremental_Launching_Method.pdf

 

[struct4me]

Thanks..LittleInch & HTURKAK

Regarding the video, we will not be taking all, as I told you I need a temporary cantilever arrangement to access the right abutment and if I can do that, I can erect the bridge from left with Incremental launching method, there is no dearth in space in left side inside the tunnel with enlarged section for bridge assembly.
For temporary cantilever arrangement, I think of tower crane top part with long boom or a cantilever portion of a suspended cantilever bridge, if those can be built and executed, a 46.8 m temporary arrangement can also be executed.
I will update, when we can froze the planning and design part.
What I feel, its a challenge, but doable.
Thanks mate for your valuable input....