Explain the principles of structural analysis and their application in civil engineering design. Elaborate on the various methods used for analyzing structures, including but not limited to classical methods like force method and displacement method, as well as modern computational techniques such as finite element analysis $($FEA$).$ Discuss the fundamental assumptions underlying each method and how they influence the accuracy and efficiency of structural analysis. Additionally, delve into the importance of considering factors like material properties, loading conditions, and boundary conditions in structural analysis, highlighting their role in ensuring the safety, stability, and functionality of civil engineering structures. Evaluate the advantages and limitations of different analysis methods in addressing various engineering challenges, and explore emerging trends in structural analysis research aimed at advancing the field's capabilities and addressing complex engineering problems.