Concrete Hyperbolic Paraboloid Shell Roofs ~ these can be
constructed in reinforced concrete (characteristic strength 25 or
30 N/mm^2 ) with a minimum shell thickness of 50 mm with diagonal
spans up to 35„000. These shells are cast over a timber form in
the shape of the required hyperbolic paraboloid format. In practice
therefore two roofs are constructed and it is one of the reasons
for the popularity of timber versions of this form of shell roof.
Timber Hyperbolic Paraboloid Shell Roofs ~ these are usually
constructed using laminated edge beams and layers of t & g
boarding to form the shell membrane. For roofs with a plan size of
up to 6„000 ¾ 6„000 only 2 layers of boards are required and
these are laid parallel to the diagonals with both layers running in
opposite directions. Roofs with a plan size of over 6„000 ¾
6„000 require 3 layers of board as shown below. The weather
protective cover can be of any suitable flexible material such as
built-up roofing felt, copper and lead. During construction the
relatively lightweight roof is tied down to a framework of
scaffolding until the anchorages and wall infilling have been
completed. This is to overcome any negative and positive wind
pressures due to the open sides.
Typical Details ~
Shell Roof Construction