Long hours, language barriers and pushing the limits of a massive falsework system could all have played their part in the Almuñécar falsework collapse.
BRIDGE WORKERS on the new motorway from Malaga to Almaria in southern Spain were nearing the end of their 11 hour shift on 7 November when tragedy struck.
They were relocating a major piece of movable falsework used to support deck casting operations for the 68m high viaduct when the temporary structure suddenly collapsed, killing six (News last week).
Giant twin trusses supporting the travelling shutter high above the valley floor had just been rolled along supporting saddles into position for the next pour.
This operation would have been complicated by the horizontal curve on the viaduct, but this curve is not thought to have been a factor in the collapse.
Immediately after the trusses had been moved, workers had to run for their lives as tonnes of steel came hurtling down on top of them. For the workers harnessed to the trusses there was nowhere to run.
NCE has examined the wreckage and photographs taken before, during and after the collapse. With the aid of British bridge experts it has produced its own assessment of how the collapse occurred.
This indicates that the travelling formwork had reached a critical point in its progress along the bridge. Just before the collapse, contractors had finished the first half of the longest section - the 130m span central arch.
To build the second half, contractor Puentas y Calzadas had to slide parallel support trusses from saddles mounted on the pier to the west of the arch and on the arch crown to span the gap between the arch crown and eastern pier. This involved positioning the travelling formwork above the arch crown to minimise loads carried by the tapered truss ends.
Failure to centrally position the travelling shutter before moving the trusses caused them to pivot round the arch crown saddle and then slip off, bringing the falsework crashing to the ground.
Design of the 500m bridge suggests that the falsework was being pushed towards its design limit on the arch section where spans between crown and pier were 65m. Spans between the approach piers were much shorter at around 55m.
Redesign of the viaduct to ensure shorter spans would also have proved expensive.
Using the arch crown to take the shutter while the trusses were slid forward would have added very little cost but considerable risk, as the accident showed.
How the shutters came to be in the wrong position during the move, or how the move was allowed to take place with the shutters in the wrong position, could prove key to unearthing the true causes of the collapse.
It appears that working practices on site could have contributed. Labour for the deck construction came from Portuguese company Douro, as is common on many Spanish projects. This is because Portuguese labour is relatively cheap, although it creates a potential language barrier.
Interviews with the Portuguese workers by Spanish newspapers reveal they had been away from their families for three weeks when the accident happened. Language barriers and tiredness from long shifts could also have affected work on site. In the end these could have had as much to do with the tragedy as the technical shortcomings which finally caused the falsework to fall.