A simplified method to assess the seismic vulnerability of school buildings

The Italian school building asset consists of over 40,000 units, 60% of which was built before the introduction of the national seismic design code. When dealing with existing buildings, a lot of structural information, such as dimensions of resisting elements, material properties, joint connection details, loading conditions, are not accessible. This might lead to uncertainties in structural analyses. In the last few decades, several structural health monitoring (SHM) techniques have been used to compensate such lack of data and perform more reliable analyses. However, SHM might result in costly and time-consuming surveys that can also be affected by uncertainties due to environmental effects, measurement noise, and signal processing errors. This paper proposes a simplified methodology to evaluate the seismic vulnerability of existing buildings by presenting a straightforward SHM procedure to collect the fundamental information required to build a finite element model (FEM). The methodology was applied to an existing school facility built in the 70s located in Melzo (Italy). Firstly, a series of non-destructive tests based on ambient vibrations and harmonic horizontal excitations induced by a vibrodyne was performed. Output-only and Input-Output techniques were utilized to obtain the dynamic properties of the structure, i.e. natural frequencies, vibration mode shapes and damping coefficients. Subsequently, the experimental results were used to create and calibrate the FE model. Nonlinear analyses were carried out to estimate the maximum capacity of the structure in terms of acceleration and base shear at different performance levels. Finally, the vulnerability index was computed following the guidelines provided by the current Italian seismic codes. The proposed methodology is advantageous for both damage detection and seismic retrofitting strategies.