Irish Railway Record Society
Journal 171
River
Shannon Bridge, Sligo Line
AIDAN McADAM, Specialist Engineer; Structural Section, IÉ
OLIVER DOYLE, Operations Schemes Development Manager, IÉ
When
the Grand Canal reached the River Shannon in 1804, the small village of Drumsna,
Co. Leitrim, became the limit of navigation northward and a distribution point
for goods to the surrounding area. The opening of the Shannon Navigation through
the Jamestown Cut and the Albert Lock in 1848 diminished Drumsna’s importance
as vessels could then access Carrick-on-Shannon and Leitrim village. This was
soon followed by the opening of the railway from Longford to Sligo on 3 December
1862. The bridge across the River Shannon was just 2 miles south of the village
and a station was provided about 11/2
miles from the village on the opposite side of the Shannon.
The
Midland Great Western Railway was the main provider of rail services in the
province of Connaught with its main line from Dublin (Broadstone) to Galway and
two other important routes, Westport & Achill, and Sligo. The Galway route
was double track except for two sections, Ballinasloe-Attymon and
Athenry-Oranmore. On the Mayo line the double track was constructed as far as
Roscommon. When opened to Longford on 8 November 1855, the Sligo line was double
track and some passive provision was made for double track onward to
Ballysodare. The railway between Ballysodare (MP 1293/4)
and Sligo (MP 1341/4)
was double track from the opening and this was extended a mile southward to
Carrignagat Junction (MP 1283/4)
with the opening of the Sligo Leitrim & Northern Counties Railway on 1
September 1881. On the Longford-Sligo section provision was made for a second
line of rails on the bridge over the River Shannon by constructing double-track
abutments and piers – Underbridge (UB) No. 500, MP 92, about a mile east of
the station at Drumsna.
ORIGINAL
BRIDGE
The
original bridge was supplied by Fox, Henderson & Co., Derby. The company was
co-founded by Sir Charles Fox who drove the locomotive Novelty
at the Rainhill
trials on the Liverpool & Manchester Railway in 1830. Fox Henderson supplied
the roofs of London Paddington, Bradford Exchange and Birmingham New Street
stations but their best known structure was the Crystal Palace for the Great
Exhibition of 1851. In Ireland, they also constructed the MGWR bridge at Athlone
and the Chetwynd Viaduct on the Cork & Bandon Railway.
The
bridge was shipped in through Limerick and taken up the River Shannon to the
site. With an overall length of 94.4m, the bridge consisted of six spans – two
9.2m spans at each end and two 23m spans in the centre. Spans 1 & 2 form an
interesting opening section, spans 3 & 4 are single spans each using lattice
girders whereas spans 5 & 6 are a single lattice girder with Pier 5 acting
as a central support. With a height of 1.98m and square ended, this span differs
from the two central spans which are 2.45m high and have the top ends curved.
The bridge was maliciously damaged during the Civil War by an explosive device
on 9 October 1922. The damage is said to have been mainly burning of timbers and
the line was quickly re-opened. In the 1950s, spans 5 & 6 were replaced by a
single long bridge section recovered from a disused line, though which line
could not be established.
Locally
the eastern end of the bridge is known as the Leitrim end and the western end
the Roscommon end, but for clarity in this paper Dublin and Sligo ends are used
respectively.
The
railway across the bridge was supported throughout on way-beams which, with
modern standards, limited the speed to 25mph. However, due to the age of the
bridge, the speed was reduced to 10mph on 12 December 2004, with cascading
restrictions of 35mph for 3/8-mile
approaching the bridge and a restriction of 50mph for 3/4-mile
before the 35mph restrictions.
On
span No. 1, lattice iron girders support the railway using conventional
cross-members with the rails on way-beams. However, the railway on span No. 1
was supported on two lattice girders resting on recesses in both the Dublin side
abutment and Pier No. 1, with cross members
on the girders to carry the track. The cross members at the Dublin end
were attached to the short fixed side girders extending about 1/3
of the way across the span.
The
arrangement for the opening span, No. 2, was unusual as it spanned the then
navigation channel and was a single-leaf bascule structure pivoted over the
water on the Dublin side of Pier No. 1. A continuation of the No. 2 beams extend
about 2/3rd
way across span No. 1 where there is a counter-balance weight. On the Dublin
side of the counter-balance the steel girder was rather crudely cut suggesting
that originally it may have had a clearance problem.
SIGNALLING
The
MGWR signalling diagram dated June 1897 shows a signal cabin on the down side at
the Dublin end of the bridge. It had 5 levers:
1
Up
Distant
2
Up
Stop
3
Bridge
Bolt Locks and Dis-engagers
4
Down
Stop
5
Down
Distant
A
masonry dome topped mooring dolphin was provided up river from the bridge close
to the Dublin bank of the river for boats to moor awaiting the bridge to open.
On
26 March 1934, the signal cabin and associated signals were removed and replaced
by a one-lever ground frame with an Annett’s lock located on the down side at
the Dublin end of the bridge and released by the Drumsna-Dromod Electric Train
Staff. According to the 1935 GSR Appendix to the Working Timetable, the
Stationmaster at Drumsna had to advise the Permanent Way Ganger when it is
required to open the bridge so that his men could attend and disconnect the
rails and assist with the opening and closing. When the Stationmaster
was satisfied that the PW Dept were in attendance, he obtained a Drumsna-Dromod staff
from the signalman at Drumsna
and then proceed with the staff
to the bridge and unlocked the one-lever ground frame. This freed the Bridge
Lock Lever, allowing the bridge to be unlocked. The Stationmaster was also
required to telephone his counterpart in Dromod before the bridge was opened and
after it was closed. The bridge was not opened in many decades and its last
suggested opening was in the early 1950s to allow a residential barge, which had
spent many years moored in the nearby Jamestown Cut, to pass through.
WINDING
MECHANISM
The
bridge was hand wound using a basic crank-handle (1) rotating a small pinion
which, in turn, rotated a much larger gear wheel (2) with a ratio of
approximately 5:1. This large gear wheel was fixed to a shaft which had a brake
drum (3) and a small 3-toothed pinion (4). The brake drum used a hand-operated
iron band to control the bridge speed where necessary. The 3-toothed pinion was
710mm (2’ 4”) in circumference and engaged a long chain (5) to rotate a much
larger toothed wheel (6) of 4,260mm (14’ 21/2”)
circumference with 5 teeth which gave a ratio of 6:1. The chain was alternating
between a single and double link. The drive shaft, on which the large toothed
wheel was mounted, extended to both sides of the bridge, where each side has a
small pinion affixed. At each side of the bridge the small pinions engaged with
a quadrant (7) affixed to the bridge pivot with a ratio of 4:1 – the small
pinion had 10 teeth while the quadrant had 44 teeth. However, the 44th
tooth was blocked by a limiting nut to prevent overthrow and disengaging.
Mathematically it would have taken approximately 120 turns of the handle to move
the quadrant 90° and open the bridge fully. Apart from two lengths of chain
between two iron posts (8), there was little to safeguard the bridge operator.
The winding mechanism was attached to the pier on the Sligo side by two rods (9)
each side of the bridge, anchoring it about three-quarter way down the pier. Two
Barlow rails braced it to anchor points about three quarters way down the pier
on both sides on the Dublin side.
OVERALL
RENEWAL PLAN
In
the early 2000s, the bridge was being considered for renewal but the cost was
high. Eventually in 2008, it was decided funding had to be allocated to the
bridge’s renewal. The cost, €5.5m,
was funded by the Government’s Railway Safety Investment program. The planned
new structure was to be of four spans, increase the vertical clearance for river
craft by a metre, and have a ballasted deck for the railway, thereby allowing
trains to cross at the full line speed of 75mph.
The
plan was that the new spans would be fabricated by a specialist contractor and
taken to a riverside site where the concrete deck would be poured together with
the ballast containment side walls. One of the world’s largest cranes would be
hired to lift out the old spans, lift in the new bed stones, and follow with the
new spans. New track would then be laid across the bridge and connected to the
existing track. The track approaching the bridge would have to be raised by up
to a metre at each side. The program was carefully planned to fit within a total
line closure of eleven days.
SPANS
The
bridge was designed by IÉ’s
Structural Design Section at Inchicore Works. Taking all factors into account,
it was decided to use four Half Through Girder Warren
Truss spans, two of 25m length for the centre spans and two 22.2m units for the
end spans. These weighed 129t and 122t respectively. The Warren Truss provides
optimum efficiency and was in keeping with the design of the original bridge.
The Warren Truss is a parallel chord truss with diagonals in alternating
directions creating a “W” pattern. SIAC Butlers Steel, Portarlington, were
awarded the contract for the fabrication of the units using S355J2+N steel. The
spans are first fabricated and then grit blasted followed by a thermally applied
metal spray. Two intermediate modified epoxy aluminium coats were then applied
and the bridge then finished off in a green polyurethane paint. On completion in
February 2009 they were transported by road in April to IÉ
Bridge Gang depot in Mullingar for storage until the reception area at the
bridge site was ready.
RIVERSIDE
SITE
The
bridge has always been remote from any road and before a construction site could
be established adjacent to the bridge, a road 900m long had to be built from the
nearest public road, at OB 498, to the proposed site. There were three elements
required at the river; offices as well as equipment and material storage, space
for the bridge spans, and a strong concrete pad for the crane. First, a 7m road
7m wide was constructed 800m to the site. There an
office compound was established and on the riverside of this four pairs of
concrete pads were cast in situ, with a temporary steel bearing on each side to
receive the spans in preparation for concreting.
Given
that the crane, when moving the furthest span into position, would have an
all-up weight close to 2,500t a substantial concrete pad was required. First,
sheet piles were driven in along the riverside perimeter of the site and then
back filled to a depth of 11/2-2m
with boulder clay excavated from the access road site. Then 239 piles of 323mm
diameter were driven into the area allocated to the base and a blinding layer of
concrete applied. Steel plates, 450mm2, were welded to the top of the
piles and then the reinforcing steel H25 (25mm) was fitted and 900m3
of 50kN
concrete was poured to give a finished slab thickness of 750mm.
TRANSPORTING
THE SPANS TO SITE
The
road network between the main Dublin-Sligo N4 road at Aghamore and the riverside
site was quite unsuitable for transporting the spans because of their size. It
was decided to take them to a roadside site, which proved very suitable, between
two over-bridges (OB 489A & 490) near MP883/4
and crane them onto railway bogies. The road at the site was part of an earlier
upgrade to the N4 but had been recently bypassed by a further upgrade and
getting a road closure would not cause any significant inconvenience to local
residents.
To
transport the spans to the site, IÉ
purchased two air-braked 4-wheel bogies from Unilokomotive Ltd. (Unilok), Tuam,
Co. Galway. Each bogie has self-levelling cross members controlled by an
inclinometer, which gives an electric signal to a process controller. This in
turn controls the hydraulic lifting and lowering system to maintain the load
level at all times the cross-members are fitted with special pads at each
end to receive a bridge span. The pads are adjustable to receive different width
spans. The cross-member can be adjusted ±50mm.
The bogies have 900mm diameter wheels at 3m centres. When travelling light they
are coupled by a drawbar and when loaded they are attached to the underside of
the end of the span or beams they are conveying. The bogies, which proved
extremely useful for the Shannon Bridge renewal, are a long term investment for
bridge renewals and between tasks they are stored at the IÉ
Bridge Gang’s depot at Mullingar.
To
haul the bogies a Unilok locomotive was hired from the manufacturers. This was
an 0-4-0
Model E125-s Tracktronic with a 190hp Deutz 6-cylinder water-cooled engine. The
four wheels are all independent and not axle mounted, allowing simple adjustment
of the gauge. For this project they were, of course, set to 1,602mm (5’ 3”)
as they had been for a NIR contract. The locomotive involved had also worked on
1,435mm (4’ 81/2”)
gauge in the UK and USA. The rail wheels, which are 760mm diameter with UIC
profile and are at 3,100mm centres, have a hydrostatic drive. The unit is a
road-rail type with four road wheels in addition to the rail wheels. The front
road wheels are retractable on a swivel-pinion suspension axle and the rear
tyres are retractable independent trailing arm units. An important feature of
the locomotive is its underside mounted, retractable, turntable making it a
highly versatile machine.
For
the UB 500 job, the locomotive and bogies were parked at over-bridge No. 498 at
MP 911/2
on a specially prepared site. Each of the four nights that the spans were being
moved, the trolleys were lifted onto the track by a HIAB (a company specialising
in load handling solutions) telescopic jib of a lorry, but the locomotive drove
on using its road wheels, dropped its turntable and rotated about 90°, raised
its road wheels and when the turntable was retracted the locomotive became rail
mounted. It then coupled to the bogies and propelled them to the loading site.
It
was originally planned to move a span each night from Monday 10 August to
Thursday 13 August but after a minor derailment on the first night, the plan was
reviewed and it was decided not to move a span on Tuesday night and extend the
program until Friday night.
On
the Monday night, a possession was taken between Dromod and Sligo, the principal
reason was to move the first span to the riverside site and also to allow the
local permanent way staff carry out other work in the possession. As the
possession could not be granted until the 19:05 Dublin-Sligo
train arrived in Sligo at 22:08, it, on reflection was deemed late, and on the
subsequent nights it was altered to the Dromod-Carrick on Shannon Loop section
to give a 21:20/25 possession start.
A
road closure of the older section of the N4 was arranged for each night and a
500-tonne lift capacity mobile road crane was erected nightly in time for the
rail possession. When the possession was granted, the Unilok locomotive and
trolleys were placed on the track and the trolleys were propelled to the loading
site and separated so that there was a trolley under each end of the span.
Earlier the lorry conveying the span had parked within reach of the crane, which
lifted the span over the side of the cutting, and slowly lowered it onto the
awaiting trolleys. The trolley at the Dromod end took the load first. The brakes
on the trolleys are ‘fail safe’ – brakes are normally applied unless air
pressure is applied to release them. The air brakes between trolleys were
connected by long air hoses running along the floor of the bridge span. A
generator on the span was used to supply electricity to power a light on each
side of each span so the staff, walking beside the span as it was slowly hauled
to the bridge site, could observe the wheels and call for the consist to be
stopped in the event of a possible derailment situation. The transport time
between the two sites at slow walking pace was three hours. On the final night,
14 August, the Central Traffic Control, Northern & Sligo lines signalman
granted the railway possession between Dromod and Carrick-on-Shannon Loop at
21:23 and at 23:07, the Unilok locomotive commenced the haul and the span soon
disappeared out of sight through the masonry arch of OB 490, the whole operation
taking just 1 hour 44 minutes.
On
the first night as the initial span was being towed at 5-7 km/h,
the up side wheel of the front axle of the rear bogie derailed near the 893/4MP
on a 1,818m radius curve where the cant was 95mm and proved difficult to re-rail
with a result the railway was closed until 14:32 the following day. Some
modification was
deemed necessary to the rear bogie to prevent a repeat and this
were carried out in time for the second move which was deferred to Wednesday 12
August and the speed was altered to 1-11/2km/h.
The modification was the addition of a centrally located pivot bearing located
on the self-levelling beam.
CRANE
Given
that the centre of the Sligo side span was 83m from the Dublin abutment, a crane
with considerable reach was required and it was decided to hire a 1,350 tonnes
maximum lift capacity crane from Mammoet, a worldwide hirer of heavy lift
cranes. The model selected was a LIEBHERR LR 11350 crawler type with a lift
capacity of 1,350t at 12m. The crane is powered by a Cummins 641Kw (872hp)
diesel engine with a hydraulic transmission and in full working order weights
2,500t.
Prior
to the IÉ
job, the crane was engaged at Heuston, Texas, and due to high winds there the
lifts could not be completed in time for the shipping deadline to Ireland.
Eventually the crane was loaded on the 8,448–tonne MV
EDMONDGRACHT, registered at Amsterdam, Netherlands. The vessel is equipped
with three derricks, each with a maximum lift capacity of 60t. The crane
sections were loaded onto and unloaded from the ship by the derricks as no piece
exceeded 50t. After first loading a part-cargo of rice in the Mississippi, the
vessel proceeded to Port Arthur, 90 miles east of Heuston, Texas, to load the
crane and from there it departed on 23 September, 12 days later than the
original schedule, with an estimated arrival in Killybegs of 4 October. The
crane sections were to depart immediately upon unloading for the bridge site and
it was estimated it would take 3-31/2
days to mobilise the crane and it would be ready for lifting on 8 or 9 October.
However, on 29 September the master of the vessel e-mailed
to advise that North Atlantic storms had further delayed the vessel, which was
then 3,238.4 nautical miles from Killybegs
and re-estimating arrival in Killybegs of 11:00 on
9 October. This was based on an average speed of 12.5 knots. After negotiations
with Mammoet, it was decided to defer the renewal of UB 500 until 10:05 Tuesday
27 October 2009 – the day after the Public Holiday weekend. The original
planned start date was planned for 5 October 2009.
On
the afternoon of Thursday 8 October the vessel entered the harbour at Killybegs,
swung around 180°
to position the derricks on the landward side of the vessel ready for unloading
on Friday and Saturday. This was the first trans-Atlantic vessel to dock at
Killybegs.
Killybegs
was an eminently suitable port for the importation as it was possible to store
all the crane sections on part of the large quayside. A 220t lift capacity crane
manufactured in Germany by Faun and supplied by Quinn Cranes Ltd., Derrylin, Co.
Fermanagh moved the various pieces from the shipside to the storage area. Two
40-tonne pieces were loaded directly onto seven-axle
heavy haulage trailers with the four rear axles
having steering facility. By Saturday evening the unloading was complete and the
vessel secured for sailing to Ipswich, England, with the rice cargo. Starting on
21 October, 77 lorry loads transported the crane sections to the construction
site. Using a 100t local crane, the giant Liebherr crane was assembled and ready
for use on 27 October. The 126m high red boom (measured from the pivot point
approximately four/five metres above ground) dominated the skyline and could be
seen for miles around. In contrast the Spire in Dublin’s O’Connell Street is
121.2m.
The
crane could accurately measure the weight of each lift and was fitted with an
anemometer on the top to measure the velocity of the wind. The crane was
restricted to operating where the wind speed was less than 36km/h
or Force 5 – Fresh Breeze - on the Beaufort scale.
On
completion of the work, the crane was disassembled between 1 & 6 November
and returned to Killybegs to await shipping. The 2,981t MV EENDRACHT was
chartered to convey the crane and, after the crane sections were loaded,
departed for Westdorpe in the Netherlands on 9 November, from where the crane
was taken to the next job in Belgium. OB Heavy Haulage, Mullingar, transported
the crane between Killybegs and Drumsna.
PREPARATORY
RIVERSIDE WORK
After
delivery, the basic bridge spans had to have a walkway for permanent way staff
attached to the spans on the down side. The walkway of galvanised steel, 1.2m
wide, was attached to the spans. Steel reinforcing was erected on the deck
which, with the shear pins formed a composite deck. The 200mm concrete floor was
poured on each span and when the floor was dry, shuttering was erected on each
side and a ballast containment concrete wall poured to give a finished wall
800mm high and 200mm thick. During the concreting process two of the bridge
sides were covered with shrink-wrap while the other two had corriboard applied
to prevent damage and concrete splashing on the painted bridge. Before
installation the concrete floor and walls had a water proof coating applied
using Sterling-Lloyd eliminator.
EXECUTING
THE PLAN
As
enabling work began, both close to and on the railway, the speed over the bridge
was reduced to 5mph on and from 28 September 2009. The guard rails were removed.
Spans Nos. 3 & 4 were a single bridge unit and as part of the preparatory
work riveted joining plates top and bottom were replaced by bolted places. The
piers and abutments were surrounded by scaffolding with walkways and debris
netting. A scaffold bridge was constructed across the river on the north side of
the bridge to give continuous access and had ladders dropping onto each pier.
Prior
to the railway closure, two traffic control boats with STOP/GO boards and
red/green traffic lights took up position at designated mooring positions north
and south of the bridge to control river traffic and create an exclusion zone
while the crane was operating over the river. At 10:07 on Tuesday 27 October
2009, the Central Traffic Control Signalman for the Northern & Sligo Lines
granted a possession of the railway between the down starting signals at Dromod
(SL806 & SL807) and Sligo buffer stop. The local permanent way staff and the
Bridge Gang from Mullingar began cutting the track at the span ends ready for
the lifts. Each span had brackets pre-fitted to the four corners and these were
used to jack the span up approximately 50mm before the crane lifts to ensure the
spans were free and ready to be lifted and not apply unnecessary strain on the
crane. However, just after midday the wind speed increased and remained too high
until 03:00 Wednesday so no lifts were possible. It was planned to remove the
spans from the Sligo end and to start with dropping in the new spans from the
same end. After the wind abated, the first three spans were removed before
daylight. Work started about 10:00 on the lift span but it proved difficult with
all its attachments. It was estimated that the span weighed 25t but ultimately
it was found to be 53t – possibly having lead in the counter balances or
additional iron plates having been added in earlier times. Care had to be taken
to ensure excessive lift was not applied by the crane, which could cause
whiplash and possibly buckle the crane boom. It was 17:00 before it was finally
lifted. Span 1
quickly followed.
Preparations
were made to lift in span 4 and 3 starting at the Sligo end. The area for the
transition pieces at the Sligo abutment was prepared as was the top of pier No.
5, which was not being fitted with bearings as it would not be providing
support to the span. The bed stone for pier No. 4 was completed and the bearing
accurate positioned. The required accuracy for the bearing was ±2mm.
At 10:30 the crane collected span No. 4 from its pad but the wind velocity
increased and the unit had to be parked though the slings remained hooked up.
The Metrological Service was indicating that some drop in the wind speed was
possible but this did not happen. Overnight Wednesday/Thursday the wind
increased considerably and was accompanied by torrential rail. During Thursday
morning the forecasters were giving a considerable drop in wind speed and dry
weather to occur between 15:00 and 16:00. At 14:00 there was no indication it
would happen but at 15:05 the wind dropped dramatically and the rain stopped.
At
15:15 the decision was made to go with the installation of Span No. 4 and what
followed in the next 22 hours was a remarkable feat of engineering. All four
spans, three bed stones and four transition pieces were lifted into place,
completing the lifts, recovering the lost time, putting the program ahead of
schedule, and allowing the giant crane to be decommissioned.
First,
span No. 4 was lifted in and quickly followed by span No. 3. The next pieces to
be lifted in were the two transition pieces for the ballasted track at the Sligo
end. Meanwhile piers No. 2 & 1 were then prepared and the bed stones lifted.
It was decided to wait until daylight to lift in the last two spans. Between
09:00 and 13:00 the two spans were lifted in completing the lifts. All that now
remained was some tidying up and the installation of the ballast and track.
Where
the spans connected to each other, the final 1.5m of floor was not pre-poured so
the after installation a single pour could give a good connection between the
two spans. These were poured on Saturday 31 October and the following week the
waterproofing was applied. Where the spans abutted, the ballast containment
walls have sealed joints with steel plates on the ballast side to prevent the
ballast causing damage. Protection matting was fitted to the side walls and
floor to prevent the ballast damaging the waterproofing.
PERMANENT
WAY
With
the raising of the bridge by a metre,
it was necessary, of course, to raise the track either side. Ballast dumps were
provided either side of the bridge in advance and a total of 8,000 tonnes of
high speed specification type was delivered from Owen’s Concrete, Mullingar.
Immediately after the possession was granted the track was cut mainly into 9m
panels to comply with the standard for tandem lifting of track panels. On the
Dublin side the track was cut for 525m and on the Sligo side the distance was
360m. The panels were removed by two earth moving machines working in tandem.
Earth moving machines and dumpers then spread the ballast and by Wednesday night
the Dublin approach was ready for re-railing and early the following afternoon
the Sligo side was ready. Given that the new bridge was allowing an extra metre
clearance to river craft and the track was on a ballasted deck, the existing
track level had to be increased by up to 1,100-1,300mm to match the rail level
of the new structure.
On
Thursday 29 October the rail train from Portlaoise Depot approached the site on
the Dublin side and dropped new 144m long rails for the new bridge and where the
track had been cut into panels. The total length was 985m. Tamper No. 739 was
locked in the Sligo side once the old bridge was taken out. As well as preparing
and doing the ballast lift for the bridge, some essential maintenance was also
done.
At
10:54 on Friday 6 November the possession of the Dromod-Sligo section was handed
back to the Northern & Sligo Lines signalman and the 09:05 Dublin-Sligo
was the first train over the new bridge operating on schedule. A temporary speed
limit of 25mph was imposed for the reopening and this will be raised to 40mph
after some ballast retaining units are put in position on the up side on both
ends of the bridge. Later the speed will be increased to 60mph. The line speed
of 75mph will apply across the bridge as soon as the new track is consolidated.
CONCLUSION
|
The remainder of this article appears in IRRS Journal number 171, published February 2010. |
Copyright © 2010 by Irish
Railway Record Society Limited
Revised: January 04, 2016
.
