Sensors to Monitor CFRP/Concrete Bond in Beams Using Electrochemical Impedance Spectroscopy

The use of inexpensive electrochemical impedance spectroscopy based sensor technology for nondestructive evaluation (NDE) of bond degradation between external carbon fiber-reinforced polymer (CFRP) reinforcement and concrete is examined. Copper tape on the surface of the CFRP sheet, stainless steel wire embedded in the concrete, and reinforcing bars were used as the sensing elements. Laboratory experiments were designed to test the capability of the sensors to detect the debonding of the CFRP from the concrete and to study the effect of short-term (humidity and temperature fluctuations) and long-term (freeze-thaw and wet-dry exposure and rebar corrosion) environmental conditions on the measurements. The CFRP sheet was debonded from the concrete, and impedance measurements were taken between various pairs of electrodes at various interfacial crack lengths. The dependence of the impedance spectra, and of the parameters obtained from equivalent circuit analysis, on the interfacial crack length was studied. Capacitance parameters in the equivalent circuit correlated strongly with the interfacial crack length and can be used to assess the global state of the bond between CFRP sheets and concrete. Impedance measurements taken between embedded wire sensors can be used to detect the location of debonded regions

FEM Simulation for INDOT Temporary Concrete Anchored Barrier

Portable Concrete Barriers (PCBs) are used to redirect errant vehicles to keep them passing to opposing lanes and to ensure safety of the people and any objects behind the barriers. In the state of Indiana, increments to the PCBs, such as L-Shape steel plates, have been applied to enhance the safety performance of these barriers. In this study, Finite Element (FE) analyses are performed to evaluate the safety performance of PCBs with and without the increments and get thorough information about the increments applied. A full-scale crash test (INDOT, 2001) was executed for an impact to the PCBs with a 2000 kg pickup truck at an angle of 25 degrees and an initial velocity of around 100 km/hr in accordance with National Cooperative Highway Research Program (NCHRP) Report 350 guidelines for Test Level 3 safety performance. Aforementioned full-scale crash test data are used to validate the FE model constructed. Roadside Safety Verification and Validation Program (RSVVP) was used to compare the crash test and FE model results quantitatively. Validating the results of the initial FE Model leaded the way in confidence to implement the increments in the following FE Models

Fundamental behavior and stability of CFT columns under fire loading

This dissertation presents: (a) experimental and analytical research of the fundamental behavior of concrete filled steel (CFT) members under elevated temperatures from fire loading, and (b) its use to investigate the stability of CFT columns under standard fire loading. The experimental investigations were conducted using an innovative experimental technique to determine the moment-curvature-temperature (M-&phis;-T) behavior of CFT beam-columns subjected to axial, flexural, and thermal loading. The testing technique involved the use of radiation-based heating units and digital imaging systems to measure deformations at elevated temperatures. Thirteen CFT beam-columns specimens were tested and the experimental results included the M-&phis;-T responses of the plastic hinges. 3D finite element models and fiber-based section models were developed and calibrated for predicting the M-&phis;-T behavior of the tested CFT beam-column specimens. These models provide significant insight and predict the behavior of the specimens with reasonable accuracy. The stability behavior of CFT columns under fire loading was investigated using a simple analytical approach, which was developed by modifying Newmark’s method for inelastic buckling analysis to include: (a) the effects of elevated temperatures and (b) section fiber models (of M-&phis;-T responses) at the station points. The analytical approach was used to predict the standard fire behavior and stability of several CFT columns tested by researchers around the world. The analytical predictions were verified by comparing them with: (a) experimental results and (b) analytical results predicted using 3D finite element models. The comparisons indicated that the simple analytical approach could predict the standard fire behavior of CFT columns with reasonable accuracy. The experimental approach for determining the fundamental behavior of structural members under fire loading is recommended for future research. The fiber-based section model for predicting the fundamental behavior of members under fire loading is also recommended for future development of modeling techniques. The simple analytical approach for predicting column stability under fire loading is recommended for future research focusing on the effects of various loading, restraint, and fire parameters on column inelastic behavior and stability under standard or realistic fire loading