Changes in dynamic characteristics of Lorca RC buildings from pre- and post-earthquake ambient vibration data

This paper estimates fundamental translational period and damping ratio parameters and examines the changes in dynamic characteristics of a set of low-to-medium rise buildings in Lorca town (SE of Spain) affected by the May 11th, 2011 earthquake. These building parameters have been calculated analysing structural dynamic response from ambient vibration measurements recorded at top RC buildings pre- and post earthquake, using the Fast Fourier Transform and the Randomdec technique. The empirical expression relating period $$(T)$$(T) and number of floor $$(N)$$(N) here obtained analysing ambient noise recorded on 59 healthy buildings before the earthquake is $$T= (0.054\pm 0.002)\, N$$T=(0.054±0.002)N, very similar to others empirical period–height relationships obtained for RC structures in the European built environment but quite different from code provisions. Measurements performed in 34 damaged buildings show a period elongation after the quake according to $$T^{*} =(0.075\pm 0.002)\,N$$T∗=(0.075±0.002)N expression. Moreover, we found a rise of the fundamental period with the EMS’s grade of damage of buildings. In contrast to natural frequency, damping ratio $$(\xi )$$(ξ) do not shows a significant variation with earthquake damage degree and the product $$\xi \, T$$ξT remains near constant.