Mechanical Behavior of Hybrid Concrete-Filled Fiber Reinforced Polymer Tube Columns

Much of America’s infrastructure is in a state of disrepair. Many bridges are approaching or have passed their designed service life. Engineers and bridge owners have an obligation to rebuild back better. This can be achieved, in part, through the utilization of novel high performance structural systems. One such technology, the concrete-filled fiber reinforced polymer (FRP) tube (CFFT) system has been extensively studied the past few decades as an alternative design for bridge columns. This column system greatly simplifies construction by eliminating the need for column formwork and associated scaffolding. It also contributes to the confinement of the concrete, improving performance. A CFFT system without the need of traditional rebar would even further simplify construction. This novel system, herein investigated, is achieved by embedding longitudinal steel fibers into the FRP tube of a CFFT. The goal of these steel fibers is to give the system the energy dissipation and ductility benefits CFFT’s gain from added rebar without the additional associated construction costs. Hybrid metal/non-metal fiber CFFT (HCFFT) and traditional all glass CFFTs were manufactured with varying glass fiber angles and number of layers. Specimens were tested under half-cyclic concentric and eccentric compressive loading. These tests are the first in a series to understand the behavior of CFFTs and HCFFTs under different loading and to construct column interaction diagrams. Later research on larger-scale specimens will include four-point bending and combined axial and lateral loading. The addition of longitudinal steel fibers into a traditional CFFT system may offer an improvement in energy dissipation capability before failure and slow damage progression. These steel fibers may lead to a reduction in ultimate strain capacity of the CFFT, depending on manufacturing method. Mechanical properties of the specimens are presented as well as data on energy dissipation, damage progression, and recentering capability