Optimal Selection of FRP Protection for Bridge Piers Against Continuous Ice-Floe Impact in Cold Regions: Numerical Simulation and Mechanical Response Analysis

During the ice-breakup period in cold regions, the impact of drifting ice floes on bridge piers readily induces extreme ice loads and structural damage, and because the ice is transported continuously by the flow, a pier is subjected to a sustained crushing process rather than a single free collision. Conventional protective techniques suffer from insufficient durability, whereas fiber-reinforced polymer (FRP) offers protective advantages owing to its light weight, high strength, and corrosion resistance. However, the differences in ice-impact protective performance among carbon (CFRP), glass (GFRP), basalt (BFRP), and aramid (AFRP) fiber composites remain unclear. In this study, ANSYS/LS-DYNA is employed to construct an explicit dynamic finite element model of continuous ice-floe impact on an FRP-strengthened bridge pier, in which the sustained driving action of the flow is represented by a constant-velocity boundary prescribed at the trailing edge of the ice. The elastic constants of ice are calibrated and the material parameters verified against published ice-concrete collision test data, reducing the relative error of the maximum impact stress from 22.5% to 7.89%; a purpose-designed scaled-model ice-pier impact flume test is further used for qualitative verification of the collision process. On this basis, 20 full-factorial parametric cases are designed to systematically examine the influences of ice-floe velocity, ice volume, and FRP type on the impact force, stress distribution, displacement response, and energy dissipation. Within the investigated parameter ranges and modeling assumptions, the results show that: (1) the peak impact force is governed mainly by the effective ice-pier contact area and the crushing strength of ice; for the unstrengthened pier, doubling the ice velocity raises the peak force by only 3.3–4.7%, and doubling the ice volume changes the peak force by only 1.5–2.7%; (2) the reduction in the peak impact force by FRP is strongly dependent on the ice condition, material differences appearing only under the small-volume, low-velocity condition (21.7–29.5%) and amounting to less than 0.1 percentage point under the other conditions; in terms of the mean impact force, CFRP is the only scheme that achieves a reduction under all ice conditions, with a mean reduction of 18.0% over the four conditions, superior to AFRP (12.3%), GFRP (9.5%) and BFRP (9.1%), although this ranking applies to the 5 mm equivalent shell and is thickness-dependent; (3) at the representative instant t = 0.2 s the peak von Mises stress of the pier decreases from 3.201 MPa to 1.111–1.693 MPa, a reduction of 47.1–65.3%, showing a far higher sensitivity to FRP type than the peak impact force; (4) the peak stress in the four FRP sheets amounts to only 0.21–0.36% of their fiber-direction tensile strength and their internal energy is close to zero, indicating that, within the present configuration (a 5 mm equivalent FRP shell held against the pier by a frictional, unbonded contact interface), the protective effect of FRP derives mainly from local stiffness enhancement and load diffusion rather than from tensile load carrying or energy absorption. The above mean impact forces and energy quantities are values truncated at t = 0.5 s. This study quantifies the differences in ice-impact protective performance among FRP types and provides a numerical reference for FRP selection and ice-resistant design of bridge piers in cold regions within the investigated parameter ranges. These findings, in particular the weak velocity sensitivity, are conditional on the adopted rate-independent ice model, which does not represent the strain-rate dependence of ice strength.