SEISMIC VULNERABILITY ASSESSMENT OF MASONRY TOWERS: FULL NON-LINEAR DYNAMICS VS PUSHOVER ANALYSES

The paper concerns the seismic vulnerability assessment of masonry bell towers in Italy, which is performed by comparing full non-linear dynamic analysis and non-linear static analysis. An idealized case study is considered, in order to assess some basic and common features of the seismic structural response and to appraise the performance of the proposed approach. The reference model is supposed to be structurally independent, i.e. with no adjacent interacting construction. The geometrical dimensions are chosen in order to represent an average north-Italian masonry bell tower, without the intent to cover all the possible situations. The seismic response of these structures involves a coupling between flexural and axial vibration modes, the presence of shear damage patterns, and high vibration modes causing the belfry collapse. The problem is simplified by using a plane 2D scheme. A specific Rigid Body and Spring Model is adopted to describe the in-plane dynamics. Constitutive laws were assigned following a simplified heuristic approach including the main meso–scale damage mechanisms: i) very low tensile strength; ii) significant post-elastic orthotropy plus texture effects; iii) different rules for post-elastic axial and shear damage; iv) different dependence of the shear strength on the vertical and horizontal axial stress component; v) hysteretic energy dissipation due to cyclic loading. Even using a quite coarse mesh, the model is capable to describe the higher vibration modes with a reasonable computational effort and using realistic accelerograms. Non linear static analysis was performed, by using the RBSM model, obtaining the capacity curve and assessing the seismic demand. A comparison between the two approaches is proposed, in order to appraise the difference in the results and to evaluate quality and significance of results in terms of operational drawbacks and reduction of computational times. Particular attention is devoted to the fact that static non-linear analyses tends to neglect the damage effects induced by higher vibration modes, as well as the influence of the shear response on the global damage