Innovative pre-stressing and cambering of timber-to-timber composite beams

The paper focuses on an innovative method to pre-stress and camber composite beams. The method relies on the compression force that can be generated by distributed screw fasteners inserted at an angle to the axes of the elements forming the composite structure (no external props or tendons are needed to pre-stress the structure). The method principles, which are applicable to different structural materials, are explained and then validated by referring to timber-to-timber composite (TTC) solutions. An analytical formulation to predict the final camber and the internal forces generated by the method is also provided. Additionally, a finite element numerical approach was developed and used to investigate the influence of the relevant parameters. To validate both the analytical formulation and the modelling approach, two full-scale TTC floor specimens, with a 6.4m span were assembled by adopting the method presented herein and then tested to failure. A remarkable agreement was observed between the predictions from the analytical, numerical models and the experimental evidence. From the research outcome, the proposed assembly method appears capable of producing significant levels of camber and pre-stress that can be accurately predicted and designed.