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A fixed expression

Concrete Middle East

Against the odds, British engineers are battling to design essential repairs to Iraqi bridges.

Alan Sparks reports from the nerve centre in Dubai.

Conflict in Iraq saw key pieces of infrastructure bombed and blown up as coalition forces sought to hinder the movement of Saddam's retreating forces and Iraqi fighters threw obstacles in the path of advancing US and British troops.

Now the task facing engineers is speedy restoration of vital bridge links to assist postconflict trade, coalition military movements and reconstruction.

Bridges being patched up stand between Baghdad and Jordan, Baghdad and Mosul, and Mosul and Irbil (see map). At least three others will also be repaired as part of British consultant Halcrow's contract with US contractor Bechtel, which holds the US$665M overarching reconstruction contract from the US Agency for International Development. Halcrow's role is to produce initial damage extent plans and bills of quantities from photographs before detailing the replacement and repair of any significant damage.

The firm is working from the safety of Dubai, the hub of its Middle East operation.

Most of the structures being tackled are of prestressed concrete beam and composite slab construction.

'This composite action was lost as a result of much of the damage assessed so far, and it has been possible to see beams deflect significantly under light vehicular loading with no lateral restraint, ' explains Halcrow's Iraqi-born bridges manager Ayad Habboush, who is heading the design team. Transverse diaphragms have been lost and detailing replacements will form a large part of the work.

Highly restricted site access has been a major factor of the project as any personnel on site present a target for terrorist groups - the threat of sniper fire, grenade attacks and land mines is ever present. 'We have had to rely on second hand information and to scale dimensions from photographs, ' says Habboush.

Without accurate information, assessing what work is needed, and in particular the dimensions of replacement components, has called on intuitive design and detective-like deduction. Using early pictures Habboush's team has made educated guesses about how the structures they are repairing really work - where lateral restraint comes from, how the deck slabs are oriented and how these elements relate to each other.

'By dissecting photos of the damage and rubble we're able to make some assumptions.

But we often need subsequent information from site to prove these assumptions are correct, ' explains Habboush.

Halcrow regional director for Iraq, Rab Brown, holds up the 745m, 19 span Tikrit Bridge between Baghdad and Mosul by way of example. The structure - a favourite fishing spot of Saddam Hussein's - is by far the most complicated of those currently being tackled.

Two of its approach spans had been lost and the bridge had suffered some column damage.

There was also damage to several of its steel rocker bearings.

Initial inspections and photo detective work on this unusual structure were carried out by tiptoeing around landmines but failed to yield sufficient information. One of Halcrow's Iraqi employees was therefore tasked to take a closer look. The data he gathered has proved invaluable. 'But there was no way we could send him back if we wanted a little more detail - he only had one shot at this, ' says Habboush. And while he had been able to take photographs, taking measurements would have been impossibly risky.

So when it came to working on its custom-made bearings, nobody knew their dimensions.

'Fortunately his picture of the bearings included his shoes, ' tells, Brown. He had been forced to lie feet-first in the cramped space under the bridge to get the shot. 'Ayad recognised the shoes and knew that the colleague who owns them is about the same height as him, ' Brown continues.

'Assuming his shoes were the same size as mine, we scaled the size of the rocker bearings from my size seven-and-a-halves. It was the only reference available, ' Habboush concludes.

Remarkably, when local contractors later went to site to gather measurements for detailed design, they revealed the assumptions made for the early calculations were just 15mm over the actual 435mm depth.

The one-off bearings were supplied originally from Yugoslavia and to match their dimensions a German fabricator is being contracted to cast replacements from Halcrow's drawings. Engineers were initially shocked to see there was no lateral support for the rocker bearings. 'When the bridge expands or contracts longitudinally there is nothing to stop the bearings toppling like dominoes, ' marvels Habboush.

'But when we looked closer we could see that between every third longitudinal deck section there were vertical rocker bearings resisting some of the horizontal movement that acted as a form of expansion joint. These were connected by tension wire running straight through them, so effectively acting like a pin. Although this system is far from ideal, we felt it was best to maintain the existing articulation and not upset the behaviour of the structure, which has survived this long.'

Habboush is impressed by how well preserved the bridge is, considering how crudely it was originally constructed. 'From my childhood I remember that the environment in the north is sweet - completely different to the harshness of other parts of the region.'

Proof came from pictures that show 30 year old unprotected steel stressing wires and exposed reinforcement, but still looking in very good condition. 'These wires were fitted in electricity ducts, are not spiralled together and do not even have grout protection.

Despite this, they remain in good nick and are doing their job well.'

Local contractors will produce and install prestressed concrete beams to repair the damaged side spans, Habboush says. 'Fortunately the three main span balanced cantilever concrete box girders escaped serious harm. Had replacements of the main spans been needed then local contractors may have struggled with the technical demands.'

As well as assessing repairs, Habboush's task has been to develop a practical design method for local consultants who have been left behind technically over the last 25 years. In terms of quality Habboush has no reservations: 'Calculations sent over from local firms were very good, but relied on out of date loading values and durability measures. Since we have been involved, the Iraqis have been very open and keen to learn modern concepts and methods.'

Time is tight

Sometimes extraordinary lengths are taken to glean precious fragments of information.

When Bechtel staff set out to conduct an inspection of the 13span 188m long Al Mat bridge on the main route between Baghdad and Jordan they were forced to undertake five days of travel for only four hours on site (see diagram).

The road from Baghdad is plagued by aggressive terrorist groups and even with a special forces escort, travellers are not safe. To get to site the engineers had to fly to Basra in southern Iraq, drive over the border to Kuwait, fly to Amman in Jordan and then be flown back towards the Iraqi capital in Apache helicopters under close protection of the special forces.

Access was restricted to a four hour slot. The area was cleared of rebel forces by the US army, but as light failed and the window of safety dissolved the team had to leave.

'Such was the danger and the pressure of the situation that Bechtel's engineers miscounted the number of spans, ' Brown says: 'It sounds amazing, but during the site visit they were under constant threat of sniper fire. Personally, I think they did remarkably just to be there to count them in the first place.'

Dedication situation Halcrow's bridges team is not working exclusively on the repair of the six bridges. This short notice work comes on top of all the other projects buzzing around the office, including design of integral abutment bridges. There are new highways planned for Dubai, Yemen and Sharjah also requiring major grade separated structures - not to mention proposals for the widest cable-stayed bridge in the world, which would carry 14 lanes of traffic.

But work on the Iraq bridges is dominating the lives of the Halcrow team of engineers and draughtsmen, and other work must be put on the back burner when the call comes from Bechtel.

'Bechtel demands swift response.

When we received the first photos in August a full damage assessment report was needed within three days, ' says Habboush.

The team are on 24 hour call - often dropping whatever else they are working on to focus on turning around the repair work as quickly as possible.

'We have received several calls as we are driving home for the evening. The whole team has had to come back in and has worked through nights and weekends. But because we feel part of something so special, to a man the team has risen to the challenge.'

The Tikrit bridge is on an accelerated reconstruction schedule as strengthening work must be complete before the rainy season hits in November.

Local talent

Between Mosul and Irbil stretches the four span, 120m long Khazir Bridge. This demands complete replacement of one span which traffic continues to use.

For the Al Mat bridge between Baghdad and Jordan, isolated replacement of longitudinal beams, deck slab and transverse members is needed. A Kuwaiti precaster was originally sourced to produce replacement beams. But as the project progressed it was felt local firms could benefit instead.

The original 20m long beams were 1,124mm deep prestressed I-sections. Suitable replacements that are buildable by local industry have been detailed to allow for the materials and methods used.

'These replacements are 100mm deeper than the originals, but by shaving the top of the beam over the bearing point and the plinth beneath the bearing, we were able to squeeze them in.'

Designers were able to play with the 150mm clearance between beam and column because flat jacks - not available at the time of original construction - mean less room is now needed for any maintenance jacking.

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