THE MOBILE BRIDGE GANTRY SYSTEM: AN INNOVATIVE … · mobile bridge gantry system which allowed us to replace bridge spans quickly, ... that it could be used to replace any size of

THE MOBILE BRIDGE GANTRY SYSTEM:AN INNOVATIVE APPROACH FOR BRIDGE SPAN REPLACEMENT

David A. Cook – Canadian National Railway Company8050 Cavendish Blvd, Montreal (Quebec), H4B 2G4Phone: 514-734-2278 E-mail: [email protected]

No. words: 1960

ABSTRACT

In 2011, CN decided to increase the capacity of the bridge at mile 164.70 Mont-Joli subdivision to 286k. Typically, bridge span replacement is done by installing a large crane as close to the bridge as possible in order to be able to lift the old span out and put the new span in. However, bringing a crane of suitable size close enough to the bridge would have required the building of a very large crane pad in the middle of a tidalriver with a sensitive habitat on the riverbed. Working in that kind of environment is time consuming (length of permitting process) and expensive (engineering & construction),and potentially quite damaging to the environment. After assessing several different engineering options, CN decided to partner up with anengineering contracting firm specializing in heavy lifting (Western Mechanical Ltd) to devise a solution. Knowing that similar work would be required in the future we focused on finding a method that could be easily used at other locations, keep the project out ofthe water and minimize workblock requirements. Together we designed and built a mobile bridge gantry system which allowed us to replace bridge spans quickly, reliably and safely. In addition to meeting all the technical challenges, we also realized some significant economical gains: using this method has resulted in over $1M in savings per span and provided a four-fold increase in workblock productivity. These savings can be repeated every time we have to replace a bridge in difficult to access locations.

INTRODUCTION

In February 2011 CN’s special marketing department, in response to customer demands, decided to push ahead with an initiative to increase capacity to 286k on the Mont-Joli subdivision. Of all the upgrades required to complete the project, one in particular posed an interesting challenge: the replacement of three 115 foot long, 107 year old deck truss spans at mile 164.70. This bridge spans over the Trois-Pistoles River near the town of the same name, in the Province of Quebec. The spans to be replaced were #2-3-4 of a five span bridge, span #1 is over a roadway, all the others over the river itself.

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Picture 1 – View of Trois-Pistoles River Bridge before upgrade.

During the pre-project phase the concept was to build a large crane pad off the east bank and extending into the river up to pier 3. The river is fairly shallow there and deepens considerably between piers 3 and 4. This approach would have allowed us to setup a large conventional crane near the centre of the bridge with enough capacity to reach all three deck truss spans. A similar approach had just been used at another location the year before, and it seemed simple enough to use the experience acquired there and port it to this new project. Although it was possible to use a much larger crane directly from the shore, the cost of terrain preparation and mobilization for such a crane was deemed far too prohibitive.

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Picture 2 – Example of a crane pad being constructed on a shallow riverbed.

However soon after starting the permitting process, the project suffered an unfortunate setback. The bridge is located right over the outlet of the Trois-Pistoles River, where it meets up with the Gulf of St-Lawrence. At this location the riverbed had developed into an ideal habitat for several species of molluscs and shrimps. This signified that any disturbance of the sensitive riverbed habitat would require that the environmental impact assessment process be quite a bit more involved than initially anticipated. In fact, the regulating authorities required a period of at least one year in order to properly study the situation and process the application. This sort of delay was deemed unacceptable, and so another solution had to be devised.

BRAINSTORMING

It was at this point that we decided to tackle the problem from another direction. Instead of trying to build an access in order to bring in the required heavy lift equipment, could we not build a heavy lift machine that could use the existing access (e.g. the right-of-way)?

Like most railroads, the CN bridge plant includes several steel structures that are over 100 years old, and many will require replacement in the near future. Rather than devising a project specific solution, it would make sense to find a solution that could be

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easily re-used. The search for an engineering partner on the project started out with the following requirements:

1- Must stay out of the water.2- Must use the right of way for access.3- Must be easily portable to future projects / other locations.4- Must minimize railway shutdown time (short workblock requirement).5- Must be economical.

After discussions with several engineering firms and contractors, CN partnered with Western Mechanical Limited, a specialized heavy lift and hydraulics contractor headquartered in Barrie, Ontario. This firm was chosen not only for their competitive pricing, but also because they had successfully completed challenging railway projects in recent years. Western Mechanical has a reputation for tackling projects in a professional manner, with ingenuity and optimism; making them an ideal partner for this endeavour.

The weight of the structure to be replaced was estimated at 240,000 lbs for the steel structure with bearings, plus another 60,000 lbs for the ties, rail and track hardware. Subsequent test lifts with hydraulic jacks confirmed the total weight to be 293,000 lbs. In past projects, with cranes for example, the span replacement is done in six operations: first remove the rail, then remove the ties, then remove the span, then repeat the process in reverse. Our goal was to simplify the process down to two operations, meaning to lift the entire span with all the ties and rail still on it, then install the new span with new ties and rail. All that would then be needed during the workblock before the lift would be to unbolt the rail joints, and afterwards bolt the new joints back together and the bridge is ready for traffic. This type of operation would allow us to shave a lot of time off the workblock.

THE DESIGN

The machine was engineered to meet all the above specifications and also designed so that it could be used to replace any size of single track deck-plate girder span (although the existing spans in this project were deck-trusses, they would be replaced with deck-plate girders; according to CN specification the maximum allowable span length for deck-plate girder spans is 120 ft).

The machine, labeled “mobile bridge gantry system”, was also designed with mobility in mind. Not only can it easily be brought from the staging area to the bridge site, it can also lift itself onto the platform of two rail cars and fold up for easy shipment by rail to any location across the CN system.

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Picture 3 – The gantry ready for shipment by rail.

The gantry is powered by two diesel generators and the primary lifting action wasprovided by the 150-ton hydraulic cylinders located at each corner. The cylinders are 130 ft apart longitudinally and 14 ft apart laterally, allowing for any sized deck-plate girder span to fit easily underneath. The lateral spacing allows for CN standard 13 foot wood ties to pass through, however longer ties (such as the ones supporting walkways) must be cut or removed prior to the span replacement. These gantry legs, i.e. the four hydraulic cylinders, are affixed to specially designed support beams resting atop the ends of each adjacent span.

On top of the gantry are two hydraulic powered dollies on Hillman rollers. These buggies carry a beam to which the slings that actually lift the spans are attached. This allows for the longitudinal movement of the spans under the gantry during the change-out process.

THE PROCESS

The entire replacement process goes as follows:1- Bring gantry to bridge from staging area.2- Set up gantry over span to be replaced.3- Lift old span up, until the bearings clear the top of the adjacent span.4- Move old span longitudinally to one side, place onto rail carts.

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5- From other side, bring new span to gantry.6- Attach gantry to new span, move new span over “hole”.7- Lower new span into place.8- Detach gantry from new span, bring it back to staging area.

This can best be explained through a series of diagrams:

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Figure 1 – Gantry is set up over span to be replaced.

Figure 2 – Gantry lifts old span.

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Figure 3 – Old span is shoved eastwards by power dollies to rest on buggy #1.

Figure 4 – Old span is shoved fully eastwards, resting on buggies #1 and #2.

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Figure 5 – Gantry receives new span from the west.

Figure 6 – New span is carried under gantry by power dollies.

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Figure 7 – Gantry begins to lower new span into place.

Figure 8 – New span is in place, gantry can be detached and removed from bridge.

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Picture 4 – Replacement of span #4 with the Mobile Gantry System

CONCLUSION

Advantages gained by developing and using the Mobile Bridge Gantry System at this location:

1. Great increase in workblock productivity: In 2010, using a large crane installed at the foot of the bridge (i.e. traditional bridge span replacement method), CN replaced two spans at mile 111.06 Montmagny sub. Each span required a 10-hour block and 34 CN employees. In 2012, at the same bridge, the bridge gantry system was used to replace 4 spans. The first two spans took 9 hours of block time for both, the next two required only 7 hours of block time for both. Each operation required only 16 CN employees. In terms of man hours this represented afour-fold improvement in productivity.

2. Huge cost saving opportunity: Cranes require extensive site preparation, a suitable crane pad must be built in order to support the very large loads induced into the ground by the crane. This crane pad must be engineered properly and the soils reinforced accordingly. At mile 111.06, the cost of the crane pad including all incidentals such as environmental review, rental of property, and subsequent removal of the pad; was over $300k. Site preparation for the gantry

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cost less than $10k. The cost of site preparation increases significantly when span replacement is required over a large body of water (as was the case at Trois-Pistoles). Building a crane pad, or a crane-capable bailey bridge, in a large body of water is very challenging and costly. For example, the temporary bridge built over the Chaudière River by the Ministère des Transports du Québec to allow a crane to work on the bridge reconstruction there cost $2M. In terms of capital dollars spent on machine rental and site preparation, using the gantry system represented a savings of at least $1.1M. We expect the cost saving to increase over time as this technology sees more use.

3. Increase in service: Since the time required to replace a single span is effectively halved, CN gained a huge amount of flexibility during the workblock planning process. This will have a large impact in busy single track territory, such as the Northern Ontario Zone, where long workblocks can be very disruptive to CN operations.

4. Reduced Impact on the Environment: Because the gantry operates solely from the bridge deck, there is no need to work in the water to construct a crane pad. Therefore there is no risk of contaminating thewatercourse with silt, and there is no potential for the harmful alteration or destruction of fish habitat. Additionally there is no lengthy permitting process, no environmental impact assessments, and no compensation plans.

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September 29 – October 2, 2013Indianapolis, IN

Mont-Joli 164.70

Task: Replace 3 bridge spans at mile 164.70 Mont-Joli sub near Trois-Pistoles, QC.

Time frame: Completion date before end of year 2011.Start date: February 2011.


ChallengeDue to time constraints we could not go and build a crane pad into the river. The riverbed is sensitive fish habitat (molluscs and shrimp).


ChallengeDue to time constraints we could not go and build a crane pad into the river. The riverbed is sensitive fish habitat (molluscs and shrimp).


Mobile Gantry System!

Advantages:1. Mobility (can be moved easily from site to site).2. Low cost (no costly site preparation).3. No environmental impact.

Disadvantages:1. New method, requires engineering, research and development.2. Risky: success is probable but not guaranteed.

Eureka!


Title

Text


Disaster!Broken axle on main line in the fifth hour of a 44-hour workblock.

Not good!!

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It gets worse!Second broken axle in hour no.15, we have no choice but to clear main line and cancel the work for today.


It gets much worse!

The day before our second attempt we recalculate our loading conditions and realize our safety factor is too low. For safety concerns, project is cancelled for 2011.

Now what?...


Refocus

Courage & Integrity

Teamwork & Engagement

Connecting the dots


Redesign

1. New, stronger buggies.


Redesign1. New, stronger buggies.2. Bigger, more powerful hydraulics

(more than double initial capacity).3. Improve structure of gantry (stronger, lighter).4. Many other significant improvements.


SUCCESS!

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SUCCESS!

First use (Aug. 14):One span replaced in 16 hours

Second use (Aug. 19):Two spans replaced in 11 hours

Third use (Sept. 16 – 111.06 Montmagny sub.)Two spans in 9 hours

Fourth use (Sept. 23 – 111.06 Montmagny sub.)Two spans in 7 hours


SUCCESS!Revolution in bridge renewal technology!

Advantages:1. Mobility (can be moved easily from site to site).2. Speed of installation (short workblock

requirements).3. Low cost (no costly site preparation).4. Increased productivity.5. No environmental impact.

By the numbers:• $1,000,000+ saved in site preparation per bridge.• 4 fold improvement in workblock productivity.• 50% reduction in workblock length.• Zero impact on the environment.


S t b 29 O t b 2 2013 September 29 – October 2, 2013Indianapolis, IN

SUCCESS!


With special thanks to:Steve Del Vecchio - Senior Manager, Bridges & StructuresDenis Fortier – Supervisor, Bridges & Structures Richard Gauthier – Supervisor, Bridges & Structures Yvon Roy – Supervisor, Bridges & Structures Pat Pucci - Engineering Officer, Bridges & StructuresBin Zhang – Engineer Bridge DesignGeorge Nowak – Senior Structural EngineerNigel Peters – Chief Engineer Structures & EngineeringNormand Taillon – Senior Manager EngineeringRick Haggart – Regional Engineering ChiefRob Doucet – Western Mechanical LtdDan Eisses - Western Mechanical Ltd

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THE MOBILE BRIDGE GANTRY SYSTEM: AN INNOVATIVE … · mobile bridge gantry system which allowed us to replace bridge spans quickly, ... that it could be used to replace any size of