Forth Road Bridge engineers show true grit

Engineers on the Forth Road Bridge have been using gritters to carry out a controlled test to check out structural behaviour on the bridge, which was closed on Friday because of a crack in a steel support beam member.

The 2cm-wide fracture in the load-bearing truss end link appeared at the north tower but engineers are also concerned about the seven other similar sites.

They used gritters for the controlled testing because "they are most convenient and we know their weight".

FRB engineers tweeted: "This allowed us to measure the rotation of the pin in the joint and will inform detailed design of the repair."

The device they used to measure (called a Moire Tell-tale) can detect rotation down to 0.1 of a millimetre.

Engineers intend to carry out an interim repair to weld on strengthening plates to get bridge open in January.