Structural Analysis can be initiated, when there has been a change in resistance. Such as structural deterioration due to time-depending processes (e.g. corrosion, fatigue) or structural damage by accidental actions. Also, when there will be a change in loading (e.g. increased traffic load) or an extension of the design working life.
In general, Structural Analysis is a process to determine, how reliable the existing structure is able to carry current and future loads and to fulfil its task for a given time period