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Last Updated: Thursday, 9 August 2007, 20:29 GMT 21:29 UK
US bridge 'design issue' detected
A US Navy personnel inspect the debris
The search for bodies amid the debris is proving long and arduous
US investigators have found a possible "design issue" in the bridge that gave way over the Mississippi river.

The parts causing concern are the steel plates that connect girders.

Federal officials have urged states to carefully consider the additional weight placed on bridges during construction or repair projects.

Crews were working on the bridge when it collapsed last week, killing seven people. Divers found two more bodies on Thursday and six people are missing.

The National Transportation Safety Board (NTSB), whose full investigation is set to take months, has not yet indicated any definitive cause for the collapse of the eight-lane I-35W highway bridge.

BBC graphic
Loads and stresses on the gusset plates are being investigated

But safety officials have found a "design issue" with what are known as gusset plates - the steel connectors that tie together the angled steel beams of the bridge's frame - at particular locations on the bridge.

Investigators are trying to verify the loads and stresses on the gusset plates and the material used to make them.

One possible stress may have been the weight of construction equipment and materials on the bridge at the time of the collapse, the NTSB reported on its website.

In response, federal authorities called on all states to take extra care with how much weight is placed on bridges of any design when construction crews are sent to work on them.

More than a week on from the collapse, divers are continuing to cut through the tangled debris of the bridge in the search for bodies.

Teams of Navy and FBI divers, who were brought in earlier this week, are trying to go deeper than local divers were able to.

Two more were found in searches on Thursday, police said.

I-35W BRIDGE 9340
Eight-lane, steel-arch bridge
Built in 1967
Used by 140,000 cars a day

But the search amid the huge chunks of concrete and mangled wreckage submerged in the Mississippi's swift and murky waters has proved difficult. Divers were carrying out "a very meticulous hand-over-hand search of the scene", their spokesman Dave Nagle said.

It will now be at least a week before cranes start regularly hauling out large pieces of debris, police officials have said.

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