The Australian city of Wagga Wagga boasts a population of 57,000 people, and lies 450 kilometres southwest of Australia’s largest city, Sydney. One of the largest inland cities in Australia, Wagga Wagga boasts retail, government and agriculture as its largest employers. It is an unlikely setting for two of the largest cranes in Australia to be brought together on a single project, particularly one within the boundaries of the city itself.
The city lies on the Murrumbidgee River, and road and rail bridges straddle the river—some of them quite old. The rail bridge on the main north-south rail line was a wrought iron truss bridge built in 1881 (the components were shipped from Scotland) and it was operational until the end of 2006.
As would be expected of a structure built for trains far smaller than those that used it in its latter years, the bridge had been modified and strengthened many times, but it operated under a 20km/h speed restriction that had a significant effect on trip times on the route. Caissons were beyond economic repair, and a decision was made to replace the bridge.
The rail line is on the main north-south route on Australia’s populous east coast, and could not be closed for long during construction. Conventional wisdom suggested that a new bridge be built beside the old one, and the rail line be realigned to suit.
However principal contractor Arenco (NSW) Pty Limited submitted an innovative tender whereby the existing bridge would be dismantled and replaced with a 208m (680ft) long precast concrete structure within a four-day shutdown over the Christmas and New Year period, when disruption to normal rail traffic could be minimised. This option avoided costly track alterations on the embankments while imposing very tight time constraints, and was accepted by track owner the Australian Rail Track Corporation Ltd (ARTC).
The key to Arenco’s proposal was the use of large cranes, allowing the existing bridge to be removed in large sections without the need to double-handle those sections.
Further demolition of those sections could take place outside the shutdown time window. The craneage requirements were worked out in conjunction with heavy lift specialist Wheelers Cranes Pty Ltd (Wheelers), whose principal Fred Wheeler has a good working knowledge of the cranes available in Australia, and their capabilities.
Wheelers has considerable experience in large, challenging, lifting projects and has a team of people from around Australia that it brings together for such projects. In this instance the cranes were brought in from other firms, as Wheelers’ own Liebherr LTM 1300 was deployed on another project and its Liebherr LG 1750 was not expected in Australia until after the lift.
Other works were scheduled outside the track shutdown period where possible. The most critical was the construction of the concrete piers and headstocks of the new bridge, which finished below the deck of the original bridge. Deep precast concrete planks brought the new bridge up to the height of the original bridge. The tops of the existing piers had to be demolished to make room for these planks to be placed.
With the bridge having longer approaches on the northern embankment than on the southern embankment, a 600t capacity Demag CC 2800 crawler crane was stationed on the northern embankment, on three lifting pads. The crane moved progressively from the pad at the approaches to the pad at the river bank, from which it could reach the centre spans.
A 550t capacity Liebherr LG 1550 mobile lattice boom crane would work from a fixed location on the southern embankment from which it could reach both the centre and the approach spans. The lift pad for the LG 1550 and the pad closest to the river for the CC 2800 were concrete, and founded on deep piles.
A 300t capacity Liebherr LTM 1300 hydraulic all terrain crane would follow behind the Demag on the northern embankment, erecting the precast bridge while the Demag continued to remove the wrought iron bridge spans progressively as it relocated towards the river bank. The comparative speed of the all terrain crane meant that the new bridge could go up almost as quickly as the old bridge came down, allowing the more time-critical ballast placement and track laying to commence as early as possible.
With the age of the bridge and the number of modifications made over the years, the weight of the bridge was not known with any certainty, and a major engineering exercise was undertaken to estimate the weight of each section that would be lifted. The engineering exercise also addressed the stability of those components for lifting, and any reinforcing that would be required for the lift (the weight of such temporary strengthening was taken into account in determining weights).
Samples of material from the truss were examined, and the bridge was surveyed, to arrive at close approximations of the weight of the bridge. Cuts of the truss were to be made over the headstocks of the piers of the new bridge, and the bridge was propped from the headstock, on either side of the cut, using SYS 30 props and lateral and diagonal steel EA bracing.
Cutting lines, lifting points and bracing positioning were planned for each piece of truss. The set-down positions were determined in advance to ensure that there was space for each piece. Cuts were angled for easier separation of the cut section.
Each truss section was stabilised with vertical SYS 30 props, horizontal push-pull props and diagonal chains and dogs. Of the 13 spans, all except the mid-stream and end spans were lifted out complete. End spans 1 and 13 were lifted in two pieces as they combined around 6m of viaduct with a 10m truss section. To reduce weight, the transoms for the centre sections 7-10 were cut and lifted out separately. Spans 7 and 10 were lifted out in two halves, while spans 8 and 9 were lifted out in three sections cut longitudinally (two side trusses and the centre deck section). The deck section required additional bracing, and 460 UB 74 beams were attached lengthways. These were fixed at every second cross girder and braced at every fourth cross girder.
The heaviest of the whole sections was span 4 (82.5t), and it was picked up at 14.9m radius and placed at 19.7m radius. The spans removed whole were in the 65-80t range, and the longest radius for one of these lifts was 23.3m. The most demanding lift of the centre sections was a 29.1t section picked up at 55m. The time spent in calculating weights was vindicated with all actual lift weights being below their estimate, but within a tonne.
The Demag CC 2800 was rigged with a 54m boom and 160t of counterweight while the Liebherr LG 1550 was rigged with a 63m boom and 200t of counterweight. Rigging was not changed on either crane during the main lift programme.
Lift rigging comprised 16m slings with 32mm chains of 50t breaking strength attached around the bridge sections at the corners. Riggers worked from elevating work platforms beneath the bridge to attach the loads. For the river spans, the work platform was mounted on a barge.
While equipment was on standby to cover downtime on smaller equipment it was not feasible to do this for the main lifting machines. The cranes were thoroughly checked before arriving on site, and a fitter was on hand to cover any breakdown. Although a seal burst on the Demag, the fitter rectified this in less than the cycle time between lifts, so there was no interruption to the lifting programme.
To get an early start on track laying, the Liebherr LTM 1300 worked behind the Demag to place the precast planks of the new bridge as quickly as possible. There were eight planks per span. Each plank was 16m long and weighing between 27.1t and 27.5t. The stockpiling of the planks close to the lift area kept most lifts below 30m radius. Congestion on site meant that the LTM 1300 could only place five spans, and the Demag placed the remaining three spans installed from the northern embankment. The Liebherr LG 1550 installed the planks for the remaining five spans from the southern abutment.
To speed track installation, sleepers and rail were fabricated on site into 18m long panels weighing 14.5t each prior to the shutdown, and these were installed by crane.
The result of the detailed planning and meticulous attention to detail was that, despite two storm interruptions, all major construction work (including placing and bolting the 104 planks) was completed within 50 hours, leaving the remaining time to complete track installation. The bridge was ready for traffic 3 days, 10 hours after Arenco took possession of the track.
The LG 1550 lifts a full bridge span from the southern bank Liebherr LG 1550 The CC 2800 lifts a full bridge span from the northern bank Demag CC 2800 The LTM 1300 quickly installed new bridge planks to allow rail work to commence, while the lattice boom cranes continued to dismantle the old bridge LTM 1300 To increase the margin of safety while dismantling the centre spans, portions of rail and sleeper were removed, and the transoms and side trusses were lifted separately Parts
