A significant milestone has been reached in the upgrade of Bank Station in London as a massive temporary truss is installed to allow the construction of its new eight-level deep station entrance.
Robert Bird Group (RBG) said the new truss was an innovative alternative approach to support the slabs which would eliminate the health and safety risks associated with using a plunge column technique within the low level 20m deep shaft.
“The use of a traditional plunge column in this position would have compromised the construction of the lower level slabs within the sprayed concrete lining shaft at the bottom of the station box with reduced working space,” said RBG managing director Simon Nicholas.
“Also, the presence of the existing DLR [Docklands Light Railway] structures beneath the box restricts the capacity of plunge piles. The team overcame these issues by designing an innovative temporary truss to hang the station slabs, enabling the top down construction.”
The new truss supports four levels of basement slab within the 18.5m deep piled basement structure and will now enable the entrance of the station to be constructed.
The 100t steel truss has a jacking system which is used to counteract the “complex” response from incremental load of the slabs as they are progressively constructed and the progressive excavation below during the staged top down construction sequence. The truss had been designed to resist 1,800t at ultimate limit state (ULS).
At present one of the four slabs has been constructed, with the remaining three constructed in the coming months.
The truss had been conceived in collaboration with Dragados, and fabricated and installed by Byrne Bros as part of its overall concrete station box package. RBG is also responsible for the trusses on-going monitoring and jacking.
The monitoring regime will ensure its design assumptions are validated, reducing project risk and ensuring slabs remain parallel and end in the correct final position.
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