Anchorage performance of BFRP anti-floating anchors: Field investigation and numerical simulation

Basalt Fiber Reinforced Polymer (BFRP) anchor bars offer several advantages including light weight, high tensile strength and good corrosion resistance, making them an ideal alternative to steel anchor bars in underground structures. This study through the pullout test of three 25 mm diameter fully threaded BFRP anchor bars and analysis using ABAQUS finite element software to investigate their anchorage performance and failure mechanisms. The experiment shows that the pullout capacity of BFRP anti-floating anchors exceed 400 kN, which meets the engineering design requirements for anti-floating. The axial stress of anchor bar is highest at the opening of hole and decreases rapidly with increasing depth. The depth of the axial stress transmission is approximately 2 L/3 (L is the anchorage length of the anchor bar). The shear stress initially increases rapidly along the anchorage depth, peaks near an anchorage depth of 0.75 m, and gradually decreases thereafter, with the peak shear stress increasing with higher load levels. The numerical simulation indicates that the bonding strength between the anchor bar and anchorage body multiple components during the pullout process, with the load transferring downwards from the opening-hole as the load increases, rather than being uniformly distributed throughout the entire anchorage length. Anchor bars with longer anchorage lengths exhibit a slower decay rate of axial stress and a deeper range of axial stress transfer, despite having the same diameter. The failure analysis has identified three failure mechanisms. The shear slip failure at the first interface is caused by a decrease in frictional force, mechanical bite force, and chemical adhesive force at the first interface under increasing load; the shear slip failure at the second interface is due to insufficient strength of the rock-soil mass. Anchor bar fracture failure originates from progressive fracture caused by localized stress concentration in the fiber bundles.