Identifying the foundation stiffness of a partially embedded post from vibration measurements

Foundations of posts such as lighting columns can suffer damage or deteriorate over time, rendering the post unsafe. Quick, inexpensive and non-intrusive measurement procedures are required to monitor periodically their structural integrity. This paper investigates the behaviour of beam-like structures with a view to identifying a suitable monitoring technique for post foundations. In this initial study a lighting column is modelled as a uniform rigid beam that is constrained by collocated equivalent translational and rotational springs. Expressions are derived for the equivalent spring constants as functions of foundation profile and depth. and static responses are presented as functions of foundation properties. The inverse problem of identifying the foundation stiffnesses from response measurements is discussed. A simple method is proposed based on quasi-static stiffness measurements obtained from impact tests. The method is validated using measurements of a laboratory scale structure.