Seismic Retrofit of Bridge Columns Using Fiber Reinforced Polymer Composite Shells and Shape Modification

Abstract eng:
Fiber Reinforced Polymer (FRP) composites can provide effective confinement to circular concrete columns for the purpose of seismic retrofit of bridges. However, the retrofit effectiveness of FRP confinement for square and rectangular columns is greatly reduced due to the flat sides and sharp corners. Shape modification is a possible approach for eliminating the effects of column corners and flat sides, thereby restoring the membrane effect and improving the compressive behavior of FRP-confined square and rectangular concrete columns. An effective method for performing shape modification with FRP composites is to use prefabricated (non-bonded) FRP composite shells with expansive cement concrete. A prefabricated elliptical/oval/circular FRP shell may be used as stay-in-place formwork for casting additional expansive cement concrete around the column with a square or rectangular cross-section to achieve shape modification. The restraint of the expansion caused by hydration of the component of expansive cement induces the active confinement pressure. Large-scale experimental results have shown that shape-modification using expansive cement concrete can achieve a higher axial compressive strength and ductility for modified square and rectangular columns compared to the original columns with the same number of FRP composite layers. An analytical model was developed to determine the stress-strain behavior of shape-modified columns with expansive cement concrete. In addition, a parametric study for the practical use of shape modification is carried out.

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