The ability to form complex shapes in concrete allows material efficient structural elements to be constructed. There have been a number of projects looking specifically at structural form: for beams, columns and concrete shells.
An extended programme of research involving doctoral and masters students has led to the development of a form-active structurally efficient beam. The beam consumes approximately 35% less embodied energy that a comparable rectangular beam. The web of the beam is shaped to follow the bending moment diagram for a uniformly distributed load.
The bending moment at the of a simple beam is zero and therefore the section diminishes towards the support. there has been a number of studies into such beams and, not surprisingly they fail by shear at the supports. The geometry of the beams was developed incrementally to improve the shear resistance,whilst maintaining the form active web. The thickness of the flange of the beam increases from the mid point to the support and the web reduces in depth but widens to meet the flange. Thus the flange follows the shape of the corresponding shear force diagram. With this final configuration the beams failed in flexure at mid-span by the primary steel yielding. Shear failure was avoided with out the use of shear reinforcement .
Along with the improvements in form there was an increase in load carrying capacity.
The final beam forms demonstrated considerable ductility.
The image below shows a typical beam after failure, note the distribution of cracks and the absence of shear failure.
The study shows that fully effective form-active beams can be designed and constructed using fabric formwork, The beam designed did not require shear reinforcement. Furthermore the method of construction required less effort than a corresponding conventionally formed beam.
Lee S H, 2010, Study of Construction Methodology and Structural Behaviour of Fabric-formed Form-efficient Reinforced Concrete Beam, Phd Thesis, University of Edinburgh