Seismic risk assessment of a 50 m high masonry chimney using advanced analysis techniques

• An old 50 m tall masonry chimney damaged by the 2012 Emilia earthquake was analyzed.
• A survey put in evidence diagonal cracks and mortar degradation in the upper part.
• Traditional pushover methods yielded unrealistic bending failure mechanisms.
• Modal pushover analysis (MPA) detected a shear failure mechanism of the upper part.
• Refined nonlinear dynamic analyses confirmed that the shear mechanism is crucial.

The analysis of a brickwork chimney damaged by the 2012 Emilia earthquake is presented. A survey campaign revealed evident diagonal cracks and a significant mortar deterioration in the upper part of the structure. Laboratory tests were carried out to estimate the masonry properties. Lateral force method and pushover analyses using traditional force profiles were shown to be unable to capture the seismic behavior of the chimney. In contrast, the modal pushover analysis (MPA) using force distributions based on six modes of vibration led to crack patterns consistent with the observed damages. The behavior factor to be used in modal response spectrum analyses, estimated from the MPA results, was shown to be slightly higher than unity, indicating a very low dissipative capacity of the structure. Finally, a number of nonlinear response history analyses were carried out using natural accelerograms. In particular, an accurate finite-element model was built using rigid triangular elements connected by means of nonlinear interfaces that incorporate suitable tension, compression, and shear constitutive laws. The results systematically emphasized a shear failure mechanism of the upper part of the chimney. The residual deformations obtained from the analyses were close to those measured after the earthquake.