Value of shock transmission units for Mumbai Bridge

The Second Bassein Creek Bridge at Mumbai (formerly known as Bombay) is the first highway bridge in India to have shock transmission units (STUs) installed. The original bridge, which carries the existing two-lane highway adjacent to the second bridge, had faced many problems with caisson foundations during the construction in 1963–1970. During the design of the Second Bassein Creek Bridge the design and proof check consultants realised that, as the site conditions were rather difficult, it was prudent to limit the size of the caisson foundations to a maximum of 12·5 m o.d. These, however, would be unable to take full seismic and other short-term horizontal loads. They resolved this problem effectively by using STUs to distribute seismic loading on various substructure elements of the bridge, thereby limiting the foundation size. This paper describes the difficult site conditions for the construction of caisson foundations and evaluates the usefulness and cost-effectiveness of STUs for the bridge.