The chapter presents a review on earthquake design and assessment of masonry structures, together with applications of different methodologies. Masonry is a heterogeneous material that consists of units and joints. The mechanical behaviour of the different types of masonry has generally a common feature: low tensile strength. This property is so important that it has determined the shape of ancient and modern masonry constructions. In the case of seismic loading, it is certain that non-linear behaviour is triggered at early stages of loading and linear elastic analysis seems not to be an option. Therefore, the traditional design and assessment method of modal superposition, possibly with a three-degree-of-freedom system per floor, is not applicable. The alternative options seem to be push-over methods, as recommended in most codes for earthquake safety assessment, or a non-linear time integration method, which is a complex and time consuming tool hardly available for practitioners.

Another very relevant property in the case of seismic loading is the presence of floors that provide diaphragmatic action and the so-called "box-behaviour". This possible feature holds for ancient and modern unreinforced masonry buildings, requiring different models of analysis.

Modern masonry buildings usually adopt solutions for the slabs that provide considerable in-plane stiffness. This is done by using monolithic solutions for the floors, in concrete and steel, and also by establishing an effective connection between slabs and walls. Moreover, many existing buildings originally constructed with timber floors are capable of providing diaphragmatic actions or have been rehabilitated by stiffening the floors and by providing adequate connections. Methods based on macro-elements have been developed, particularly in Italy [1,2,3], and validated [4,5]. Their performance is good and the knowledge is sound, with some corrections needed in the recent European regulations (Eurocode 8).

When box behaviour cannot be guaranteed, the analysis of masonry structures becomes rather complex [6]. The use of macro-models and limit analysis seems the current trend but difficulties arise in the practical use, namely with respect to validation of the hypothesis of the user and the risk of selecting inadequate failure mechanisms. The non-linear static analysis could be a good and easily understood approach, because it is based on the simple evaluation of the requested deformation with respect to the displacement capacity of the building. This approach is in agreement with the modern provisions for structural assessment. Still, two case studies have been discussed, and the results obtained from the non-linear static and dynamic analyses indicate quite different responses of the structures to earthquakes [7,8]. It is therefore concluded that non-linear pushover analysis does not simulate correctly the failure mode of masonry structures without box behaviour, even if higher modes are considered via modal pushover analysis.

[1]

L. Gambarotta, S. Lagomarsino, "On the dynamic response of masonry walls", Proc. National Congress "La Meccanica delle Murature tra Teoria e Progetto", Messina, 1996 (in Italian).

[2]

G. Magenes, A. Della Fontana, "Simplified non-linear seismic analysis of masonry buildings", Proc. of the British Masonry Society, 8, 190-195, 1998.

[3]

N. Augenti, "Seismic design of masonry buildings", UTET Libreria, 2004 (in Italian).

[4]

G. Magenes, "Masonry building design in seismic areas: Recent experiences and prospects from a European standpoint", First European Conference on Earthquake Engineering and Seismology, Geneva, keynote K9, 2006.

[5]

P.B. Lourenço, "Computations on historic masonry structures", Prog. Struct. Engng Mater., 4(3), 301-319, 2002. doi:10.1002/pse.120

[6]

F. Peña, P.B. Lourenço, P.B., N. Mendes, D.V. Oliveira, "Numerical models for the seismic assessment of an old masonry tower", Engineering Structures, 2009 (submitted for possible publication).

[7]

N. Mendes, P.B. Lourenço, "Seismic assessment of masonry "Gaioleiros" buildings in Lisbon, Portugal", Journal of Earthquake Engineering, 2009 (accepted for publication).

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