Elaborate on the theoretical framework underlying the design and analysis of prestressed concrete structures in civil engineering. Discuss how the principles of prestressing are applied to enhance the performance of concrete in both tension and compression. Include in your answer a detailed explanation of the concepts of pre$-$tensioning and post$-$tensioning, highlighting the differences in their application and the resulting stress distribution within the concrete. Additionally, explore the impact of various factors such as material properties, environmental conditions, and loading scenarios on the long$-$term behavior and durability of prestressed concrete members. Explain the significance of creep, shrinkage, and relaxation in the context of prestressed concrete and how these phenomena are accounted for in design calculations. Finally, assess the role of advanced numerical methods and computer simulations in predicting the performance of prestressed concrete structures, and discuss how these tools have improved the accuracy and efficiency of the design process.