Behavior of GFRP tube confined hollow high-strength concrete short columns under axial compression

Aiming to improve the corrosion resistance of pile foundations in sea-crossing bridges and coastal projects, a new type of glass fiber reinforced plastic(GFRP) tube confined hollow high-strength concrete (GCHHC) structure is formed by placing Prestressed high strength concrete(PHC) pipe columns inside GFRP tubes and casting highstrength interlayer concrete between them. Existing research on GFRP tube hollow concrete structures is relatively small, and most of the concrete strength is less than 60 MPa. This paper presents the axial compression tests of 6 GCHHC short columns with 3 different GFRP tube thicknesses in the range of 4 mm similar to 8 mm, the effect of the configuration of ordinary reinforcement or not in the PHC tubes columns is also examined. In this paper, the main performance aspects evaluated were the test phenomena, damage patterns, load-displacement curves and load-strain curves of the specimens. The test results show that GCHHCs have high load carrying capacity and axial deformation capacity. The specimens showed two damage modes and were closely related to the GFRP tube thickness. Increasing the thickness of GFRP tubes can significantly improve the axial compressive load carrying capacity and axial deformation capacity of the combined column. The validated finite element model is used to analyze the parameters such as the thickness of GFRP tube, the diameter of common reinforcement, and the strength of sandwich concrete, and it is found that the thickness of GFRP tube is the main parameter affecting the axial compressive load carrying capacity of the combined column. Finally, the axial compressive load capacity calculation formula for the combined column is established based on the limit equilibrium method, and its applicability is examined.