Reinforced hybrid concrete beams with a U-shaped SHCC mould

Abstract

Hybrid concrete-SHCC beams are a new development in construction techniques. SHCC stands for Strain Hardening Cementitious Composite. In such beams, the tension zone could for example consist, next to the traditional reinforcement, of a material that shows strain hardening behaviour. That helps with controlling the crack width. In traditional (non-hybrid) beams, the steel reinforcement would have to control the crack width on its own. This means that there are situations that the steel reinforcement fulfills the strength requirements, but additional steel reinforcement is needed to limit the crack width. Therefore, a certain amount of steel reinforcement is needed for meeting the SLS (Serviceability Limit State) requirements, while it is not used for the ULS (Ultimate Limit State) requirements. The use of hybrid beams consisting of an SHCC layer applied in the tension zone in which the reinforcement is embedded, solves this problem. This was shown in previous MSc studies by Huang and Singh. In this study, the concept of the hybrid beam is extended. A design was made of a reinforced U-shaped SHCC mould, to be used for casting a hybrid beam. In that way, a reinforced hybrid concrete beam is created, in which the webs of the U-shape prevent the need of temporary moulds at the side of the beam, which reduces costs. A complete design is presented which is ready for further research. Next to that, it is investigated how the bending behaviour of beams, that are made using this concept, can be modelled. This was done by extending the multi-layer model, that was first proposed by Hordijk in 1991. Different from the previous built models, the model proposed in this thesis includes additional aspects, such as imposed deformations caused by drying shrinkage, and the possibility to model hybrid beams (with a U-shape). After this model was extended using VBA in Microsoft Excel, it was successfully verified by comparing its results with experimental and analytical results from previous research. Comparing the force-to-displacement curves showed that the end-resistance of the beams is predicted well by the extended multi-layer model, and that generally the same trend of the curve is followed by the model. The bending resistance of the proposed experimental setup of a hybrid beam containing a U-shape was also modelled. However, as this experiment has not been performed before, there were no experimental results to compare with. Therefore, the results for this setup are to be compared with the results that follow after experimenting with the presented design of the beam.