Date of Award
Doctor of Philosophy in Civil Engineering - (Ph.D.)
Jay N. Meegoda
Bruno M. Goncalves da Silva
Bruce G. Bukiet
Thomas Michael Juliano
Infrastructure is the backbone of national security, economic growth, public safety and other aspects of the society. Nationwide, the condition of America’s infrastructure was graded as “D+” by the American Society of Civil Engineers (ASCE) in 2013.
Owners and responsible agencies have employed various cost-effective maintenance and repair methods as well as analytical tools to repair and extend the service life of the infrastructure. However, without a long-term plan, maintenance work can be delayed by lack of funds. Maintenance delay may cause significant reduction in condition state leading to premature failure of the infrastructure. Consequently, a long-term rehabilitation plan is needed to find the best time and the amount of investment needed to avoid catastrophic failures.
In this research, three methods are proposed to compute the long-term annual investments for a culvert network. They are modified worst first method, network optimization approach and estimation by the maximum deterioration rate. The performance of a 15-culvert system was evaluated using the above methods. The method based on maximum deterioration rate is very simplistic and can only be used to estimate the lower bound value of the investment. In the modified worst first method, a fixed yearly budget is allocated and the project level corrective actions are suggested for each culvert for each year. Then the budget allocation is changed and the analysis is repeated. One could imagine this procedure as current practice of fixed budget allocation projected into the future. To do the network optimization approach, the computer program LINGO was used for the budget optimization. Developed constraints and one objective function were used based on financial requirements. Based on the simulation results, the modified worst first method is computationally intensive but provides the optimum budget. The method using maximum deterioration rate provides the lower bound value and should be used as the absolute lowest value that should be allocated. The optimization method uses computer programming and provides an upper bound value for small networks. It is anticipated that for large culvert networks the network optimization approach can be used to provide reasonable long-term annual budgets.
A long-term maintenance plan for culvert networks can be accomplished only if correct condition states of all culverts are known by inspection. However, the culvert material influences the inspection method. Concrete, metal and plastic are the most common culvert materials. In the USA, 78% of culverts are made of concrete because concrete culverts are strong, durable, and economically preferable.
In the research, several common concrete inspection methods were reviewed. By comparing all these methods, ultrasound was found to be the most reliable, fastest, and most widely used NDT method. Ultrasound wave velocity is related to the elastic properties of the material. Thus, a finite element analysis was used to simulate concrete with voids. Concrete blocks with different void sizes and distributions under dry and fully saturated conditions were simulated. Using back-calculated Young’s modulus values, ultrasound wave velocity was computed and compared with experimental results from the literature. A good comparison provided a theoretical basis for the relationship between ultrasound velocity and material porosity.
Ultrasound velocity and ultrasound diffusion method to characterize concrete were reviewed in this research. However, these methods are unable to account for the influence of the fluid in voids. Therefore, a new hypothesis of shock wave transmission in voids was studied. When high frequency and high energy ultrasound are applied to concrete, a shock wave will be generated at the edge of the voids and propagate through the voids. An ideal 1-D model was used to simulate shock wave velocity propagation. The high sound pressure of the solid will move like a piston to generate shock wave in voids. First, shock speed was studied by solving the Riemann Problem. After the piston stops, rarefaction will be generated and its speed is much faster than the shock. The interaction of rarefaction waves with shock waves was studied. The results show that when the rarefaction hits the shock, the shock wave velocity is reduced. Furthermore, the energy lost was also studied during the rarefaction interaction with the shock. The total energy is the same but due to the reaction the energy is spread during the propagation. Consequently, bigger voids will allow more of the rarefaction to interact with the shock and the velocity of the shock will decrease. In addition, the energy will spread to a longer volume and the total energy density will decrease, causing a reduction of wave amplitude.
Zou, Zhenting, "Long-term management and condition assessment of concrete culvert" (2017). Dissertations. 43.