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 x 125 mm x 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