Principal Investigator: Mohamed Elgawady
This report presents the behavior of hollow-core fiber reinforced polymer-concrete-steel columns (HC-FCS) under axial, combined axial-flexural, and vehicle collision loading. The HC-FCS column consists of a concrete wall sandwiched between an outer fiber reinforced polymer (FRP) tube and an inner steel tube. Four large-scale columns including a conventionally reinforced concrete (RC) column having a solid cross section and three HC-FCS columns were investigated during this study. Each column had an outer diameter of 24 inches and a column’s height-to-diameter ratio of 4.0. The steel tube was embedded into reinforced concrete footing with an embedded length of 1.6 times the steel tube diameter, while the FRP tube only confined the concrete wall thickness and truncated at the top of the footing level. The hollow steel tube was the only reinforcement for shear and flexure inside the HC-FCS column. The HC-FCS column exhibited high lateral drift reaching 15.2% and failed gradually due to concrete crushing, steel tube local buckling, followed by FRP rupture. The reference RC-column failed at drift of 10.9% due to rebar rupture. Finite element models using LS-DYNA software were developed and validated against the experimental results of the investigated large-scale columns and experimental results of small-scale columns available in the literature. The proposed model was able to predict the behaviors of the investigated columns with good accuracy. Finite element modeling of vehicle collision with RC and HC-FCS bridge columns was also presented in this report. Evaluation of the peak dynamic force (PDF) and the equivalent static force (ESF) through an extensive parametric study were conducted. The AASHTO-LRFD design force was found to be non-conservative when the column collided with heavy vehicles weighing more than 35 kips or with high-speed vehicles moving faster than 70 mph. A new equation for estimating the ESF based on the vehicle’s mass and velocity was developed. This approach will allow Departments of Transportation (DOTs) to design different bridge columns to different impact force demands depending on the anticipated truckloads and velocities. In general, the PDF values of the HC-FCS columns were lower than those of the RC column when they were subjected to vehicle collision.