Old lady fit again
How long can the building work needed to modernize the entire Tower Bridge control system take? "No longer than 39 days!", Bosch Rexroth Limited, the overhaul project's general contractor in Britain, was told.

60 staff members working in two shifts around the clock successfully ensured that the old bridge's joints were set right in record time.

The modernization focused on checking, maintenance and replacement of electro-hydraulic components such as hydraulic valves and pumps, hydraulic cylinders and aggregates.

Modernization was necessary because the vibrations from ever-increasing traffic loads had already led to wear in the bridge mechanics.

The project was completed precisely on schedule on February 15, 2002, when the bascule bridge resumed operation. It is opened up to 1,000 times a year. The normal opening operation takes about one minute.

Even safer to open
Tower Bridge now opens up to 1,000 times a year. The normal opening operation takes about one minute. During the modernization, Bosch Rexroth improved all features designed to increase the reliability and safety of the bridge mechanics.

Bosch Rexroth significantly improved the technical dispersion of the bridge load. Previously the bridge load could be wrongly dispersed into the construction through the main trunnion bearing. Today, it is distributed evenly along the purpose-built support blocks. They are controlled electronically and monitored permanently to ensure that maximum loads are not exceeded.

Gates to stop pedestrians and vehicles are controlled by two stored program control systems (SPC) and doubly secured. All processes are monitored by video cameras around the clock.

Tower Bridge fascination
Tower Bridge took eight years to build until it was completed in 1894. The edifice has been admired worldwide ever since, though the contemporary London press also described it as "absurd architectural charlatanism." The two 69-yard Neo-gothic towers that form Tower Bridge are connected by two high walkways. The road below is 67 yards long and consists of two bridge flaps that can be hoisted to an angle of 86°. The normal opening process only uses an angle of 45°, however.

The built-in counter-weights for lifting the flaps consist of 29 tons of lead and 60 tons of iron. This is equal to the weight of about 15 adult elephants.

Rexroth already participated in replacing the bridge's original steam-hydraulic drive with a modern electro-hydraulic system in 1975. At the time, the original controls were an absolute sensation in the field. The former engine room can now be viewed in the Tower Bridge Museum.