A recent project in London utilised internal climbing cranes that used chocking frames to provide horizontal restraint to limit sway and deflection of two internal climbing tower cranes for the construction of a 35 storey structure in Central London.
What Is A Chocking Frame?
A chocking frame is a structural component used in crane operations, designed to provide horizontal restraint by tying the crane into the building’s structure.
Chocking frames are used when cranes are required to run through structures, and there is a requirement for horizontal restraint, either to limit the sway and deflection of the crane, or to limit the moment on the crane or the foundation to allow for the structure to be built taller.
Chocking frames operate similarly to traditional crane ties but are internal to the structure, tying into floor plates, steel beams, or directly back to the core.
Chocking Frame Case Study – Leadenhall One
One Leadenhall is a 35-storey structure adjacent to Leadenhall Market in Central London.
The project was to design and sequence two internal climbing crane choking frames to be used during the construction of the structure.
The design that was developed was for a series of compression frames that climb with the crane. These frames transmitted all the horizontal loads from the cranes, both the in-service and torque loads from the crane operating and the out of service loads due to high winds. These frames act as a force couple and resist the imposed moments on the crane.
Corner skids were designed to run up the corner walls to transmit the loads. Jacking positions were incorporated that allowed for the tolerance of the core during construction.
Single frames can also be used where the crane remains attached to the anchors, and the choking frame is designed to limit sway or the imposed forces in the crane mast.
Resources –
Further guidance on Chocking Frames can be found
Cirria C761 – Guide to tower crane foundation and tie design
Leadenhall Internal Climbing Tower Crane Case Study- Full overview of the project.
One Leadenhall Webinar – Review of the engineering to design of the chocking frames and tower crane grillages for the construction of a 35-storey structure adjacent to Leadenhall Market.
