An innovative approach to the design of pile supported SFRC slabs: Fid-Bau Portal

An innovative approach to the design of pile supported SFRC slabs

Hedebratt, J. / Silfwerbrand, J.

Pile supported concrete slabs, have until recently, and in most cases, been made as heavily reinforced concrete slabs with increased shear and flexural capacity in a square around the pile. The shear reinforcement has primarily been stirrups or additional flexural reinforcement (bars or welded fabrics). The normal ways of calculating the need of reinforcement are to divide the slab into strips and obtain moment equilibration or to use yield line theory. Another way of constructing these suspended pile supported slabs is to exchange part of the main reinforcement with steel fibres. The latter reinforcement solution has now been used for floors in several major building projects totalling hundred thousands of square meters. To add extra economical advantage, the system may be designed as solely a steel fibre reinforced concrete (SFRC) slab. In fact, it is possible to design such floors using ordinary yield line theory. The SFRC slab will result in an attractive floor solution when the pile distance is moderate. A thicker floor is needed in cases where the loads or the pile distance increase. One way of reducing the slab thickness is to consider the arch action, a built-in resistance of the floor to carry loads through horizontal restraints. For most cases the pile distances are between 4 and 6 m. It has been shown that only small pile distances and loads could be used when making a traditional calculation with yield line theory for a piled slab with steel fibre only. However, the results indicate that a pile-supported slab could take loads even if large cracks have developed. Probably the slab will have large deflections but this may not be decisive in all cases. More research on the use of arch action, and its significance in serviceability limit states is needed.