Flexural behaviour of multi-celled GFRP composite beams with concrete infill: Experiment and theoretical analysis

This research introduces multi-celled glass fibre reinforced polymer (GFRP) beam sections partially filled with concrete. Hollow pultruded GFRP square tubes (125 mm × 125 mm × 6.5 mm) were bonded together using epoxy adhesives to form the beams using 2-4 cells. Concrete with 15 and 32 MPa compressive strengths was used to fill the top cell of the multi-cell beams. These beams were then tested under static four-point bending and their behaviour was compared with hollow beams. The results showed that up to 27% increase in strength was achieved by using multi-cell beams compared to a single cell beam. Filling in the top cell of the beams with concrete enhanced the capacity as well as the stiffness of the beams. The multi-celled GFRP beams filled with concrete at the top cell failed at 38-80% higher load and exhibited 10-22% higher stiffness than their hollow counterparts. The increase in the compressive strength of the concrete infill from 15 MPa to 32 MPa resulted in up to 14% increase in the failure load but did not enhance the flexural stiffness. Finally, the proposed prediction equation which account for the combined effect of shear and flexural stresses showed a good agreement with the experimental results for hollow cells and up to 3 cells of concrete filled beams. The bearing stress equation gave a better estimation for 4-cell filled section.