Assessment and Optimisation of CFRP Reinforced Glulam Beams - A feasibility study in design stage reinforcement configurations for pedestrian bridge applications

Abstract

Abstract Timber has throughout history been a widely used construction material due to high availability and easy access. For civil engineering structures, the technical advancement and increased loads have made other materials, such as concrete and steel, more suitable. However, with a rising environmental concern, timber structures can serve as a more sustainable alternative. To address the growing demands, Carbon Fibre Reinforced Polymer (CFRP) laminas can be used to increase the flexural strength and stiffness in timber structural elements. By embedding the reinforcement in Glued Laminated Timber (Glulam) in the production stage, the structure can be designed with higher capacity or smaller dimensions. Further on, embedding the CFRP laminas gives a better protection towards moisture and UV-radiation, which otherwise might lead to chemical deterioration and loss of structural integrity. In this thesis, the concept of embedding CFRP in glulam beams was evaluated for pedestrian bridge applications. In design of timber pedestrian bridges, frequency and deflection demands are often governing, which usually results in structures with relatively large dimensions. Focus was therefore put on decreasing the structural height of the beams, making the concept applicable in cases where plain timber otherwise is not an option. In extension, the concept could also be used to decrease floor heights in timber high-rise buildings or create longer spans in warehouses, industrial halls and indoor arenas. Analytic calculations were performed to evaluate two beam configurations and to perform a preliminary sizing of a stress-laminated deck bridge. The concept was then evaluated with finite element analyses, where the purpose was to evaluate the shear stresses between timber and CFRP. To investigate the economic viability, an economic comparison with two pedestrian bridges in glulam and steel was performed. The analytic analysis showed that it was possible to reduce the height with at least 25% using a small amount of CFRP. Since CFRP is more expensive than timber, it is of interest to optimise this relation. It was shown that reinforcing the glulam beam with a small amount of CFRP is not significantly more expensive compared to an unreinforced beam, regarding material cost. The FE-analyses showed that the shear stresses between timber and CFRP would not cause a problem and that adding a pre-camber does not increase these stresses significantly. In conclusion, it was found that reinforcing the beam did reduce the height without compromising the structural capacity or economic feasibility. Further on, it was shown that it can compete within the same field as other lightweight structures.