The vulnerability analysis is a quick solution for the identification of buildings that, because of the materials characteristics or construction quality or structural scheme, are in critical conditions with respect to their seismic vulnerability, such that either damage or collapse may occur in case of earthquake. The analysis results, carried out on concrete and masonry buildings through the filing of I and II level records /1/ /2/, are based on weighted sums of 11 (12 for concrete) parameters to which the data collectors assign a quality class, taking into account the observed situations during an inspection, the similarities with comparable buildings (with relation to the construction period and the used technology) and the geometrical features, such as the average floor area and the resistant areas. In case of vulnerable buildings, more detailed analysis will be further necessary to define the collapse mechanism and to assess, in case, the necessary rehabilitation works
Edifici in muratura
How code-based linear static analysis for the seismic design of masonry buildings may fail to be conservative
Linear static analysis is the easiest method for the seismic design of unreinforced masonry buildings. What makes this method particularly convenient to apply is that the fundamental vibration period of the structure may be obtained conventionally from a formula given by the codes of practice, rather than being calculated rigorously. Usually, the code-based formula overestimates – sometimes significantly – the rigorous value of the fundamental period of vibration of masonry structures. By referring to a series of unreinforced masonry buildings, the paper shows that the conventional period may be even 4-9 times greater than the rigorous one. However, overestimating the fundamental period may lead to a reduction of the design loads to be applied in the static method. This occurs, in particular, when the design response spectrum decreases in the short-period range, where natural periods of masonry buildings typically fall. Some codes do not allow design spectra to be negatively sloped in the short-period range. While others, such as the Italian code of practice, do allow it, and in so doing, they make the linear static method non-conservative (in the given examples the shear at the base of masonry buildings may be underestimated by even as much as 35% when compared to the values obtained from the more precise linear dynamic method). The paper gives some hints towards making the code-based static method for seismic design of masonry buildings safe.
Seismic performance of a mixed rc-masonry building strengthened with fiber composites
In this paper the performance-based assessment of a masonry building strengthened with fibre re- inforced polymers to improve seismic resistance is carried out. At first, a specific procedure was used to calibrate the finite element model according to the experimental dynamic properties. Then, pushover analysis was carried out with an adaptive load pattern which allows for the redistribution of load as an effect of non-uniform yielding. A homogenous and isotropic smeared cracked model was used for non linear modelling of masonry. An incremental non-iterative procedure, that is an adaptive extension of the capacity spectrum and the inelastic demand response spectra method, was used for the displacement-based seismic assessment of the building. The proposed procedure was validated by comparison with the results from seismic response testing on a scale model. The final objective of the paper is the assessment of the effectiveness of retrofit as far as the safety not only at collapse but also at the other limit states.
For this paper is available an extended abstract after the text in Italian
Analisi statica non lineare di edifici in muratura esistenti mediante modelli strut and tie
A strut and tie model for not reinforced and not confined masonry panel is defined. This model permits to estimate the behaviour of the wall both in the linear elastic field and after the peak load, that is in the cracked non linear field up to the mechanism state. This model constitutes the base of non-linear static analysis method for existing masonry buildings that can be utilized into the practice.
This paper is available in Italian only.
Analisi sismica di edifici esistenti in muratura con metodo dinamico: applicazione a Villa Faule (SI)
In this paper a general method is given to evaluate the collapse seismic load of existing masonry buildings. The method is based on numerical analyses in which both linear and nonlinear models are used to evaluate the seismic response of the masonry assemblage. The structure is first idealized by a F.E. model to investigate the stress patterns produced by the static loads, then a simplified nonlinear dynamic model is used to predict the collapse seismic load. In addition, the F.E. model is useful to identify some mechanical parameters of the masonry and to establish the accuracy of the simplified approach. To this aim the first two modal shapes of the building are used. To exemplify the general methodology here discussed an application is presented for Villa Faule, to be found in the Tuscany countryside in the neighborhood of Colle di Val d’Elsa (Siena). The Villa Faule was built at the end of XVIII century and is representative of many similar country houses located in the same geographic zone. Considering the dilapidated state of the walls, of the timber floor slabs and of other architectural elements, in recent times a design was approved to strengthen and to rehabilitate the building. The subject of this study is the strengthened building because the large-scale numerical models are more reliable for such types of structures. The results showed that both the procedures were useful to investigate the structural problem. The F.E. model furnished a good prediction of the masonry stresses under vertical loads and predicted the modal shapes of the structure; at the same time it revealed that the simplified model was accurate. The nonlinear simplified method gave a prediction of the seismic ground acceleration intensity to be applied to achieve the building collapse. To this purpose the structure was subjected to the N-S acceleration record of El-Centro (Imperial Valley’s earthquake, 1940). The results showed that the value of the collapse peak ground acceleration was equal or more than 2.75 m/s2.
This paper is available in Italian only.