Design Charts for Reinforced and Prestressed Fibre Concrete Elements

Foundations of buildings near trees Dr. Ian Richardson, a biologist with a particular interest in tree/building investigations, has been stimulated, by the contribution of Gordon Rose on this topic in our column for 21 November, to offer his own comments: An engineer friend has shown me correspondence in The Structural Engineer regarding foundations of buildings near trees. As one concerned with many hundreds of subsidence cases involving tree roots each year, particularly when I identify the source of the offending roots, and as coauthor of the book Tree roots and buildings, I would like to comment on a problem underlying Mr Rose’s thoughts. Verulam

Full-scale testing of 200mm-deep floor slabs has shown that the shear transfer capacity between units depends on the development of shear friction by aggregate interlock, and on dowel action of the reinforcement in in situ concrete end beams. Interface shear stresses are in excess of working load by a factor of at least 2.15. Cyclic loading causes a degradation in shear stiffness Ks, and an increase in residual permanent deformation in the slab and in the reinforcement. Friction factors, which are in excess of design values, were the result of clamping forces generated by the axial restraint stiffness Kn, of the reinforcement. Ultimate failure was due to horizontal splitting of the in situ concrete end beams. G. Davies, K.S. Elliott and W. Omar