| Three bridge sites in Alabama are investigated for potential seismic-foundation retrofit. A new seismic foundation method that uses Fiber Reinforcement Polymer (FRP) to strengthen the head of pile (FSHP) is proposed. Two FRP specifically, Carbon-Fiber Reinforced Hybrid-Polymer- Matrix Composite (CHMC) and Carbon Fiber Reinforced Polymer (CFRP), are used in this new seismic retrofit method. Finite Element Seismic simulation (FEM) is used to examine the seismic retrofit performance of bridge foundation. Both CHMC and CFRP FSHP retrofitted piles are shown to survive the design-earthquake, but it is shown that CHMC, which is a wrap / epoxy / spray-on material, provides markedly better energy absorption than CFRP wrap / epoxy material. Additionally, the environmental durability of CHMC and CFRP is studied using an environmental accelerated aging test, and the influence of environmental aging is assessed by tensile and compression testing in accordance to various types of environmental immersion conditions: moisture, acid, alkane and salt exposures. Results show that although CFRP coupons have higher moisture resistance (per unit weight), their acidic, alkane and salt resistances are less than those of CHMC coupons because of: spray-on polyurea top-coat, which provides added environmental durability, and also interface engendered by reaction of migrating species of curing epoxy and (pre-polymerized) polyurea functional groups. Specifically, epoxy curing time (tc) controls certain environmental and mechanical properties (affiliated to tension and compression strength) that are linked to this new hybridized interface, forming a chemically bonded layer (≤ 50 mum wide). The results indicate that mechanical capacity and total energy absorption are a cogent function of tc. A function of retention strength related to acidity is fit to CHMC data using least square method, where results of coupon-scale specimens under a tensile load for various acidic exposures, are analyzed. |
