In the case of a structure composed by a regular distribution of masonry square blocks, it can be modeled by assuming that the material does not have the capacity to transmit any tensile stress along the joints' direction, but that a low and significant tensile resistance can arise by means of a suitable relative stagger between the blocks. So the panel can be associated with an homogeneous bi-dimensional continuum by considering a very low tensile resistance due to the combined action of the friction and of the stagger of the bricks, in the absence of the breaking of the single block.

In order to study a masonry having an irregular texture, the no-tension (NT) model can be assumed as reliable, exhibiting a simple linear elastic behavior under compression stress states and no resistance in tension, and, thus, resulting in an overall fragile non-linear behavior. If the loading capacity of NT structures can be investigated by means of the tools based on limit analysis (LA) theory, on the other hand, the study of the intermediate crack situation can not be performed by LA techniques, whilst the elastic analysis of the masonry tissue under the assumptions of perfect integrity of the structure and of purely compressive stresses [1,2,3] can lead to significant results. Moreover, optimization procedures, deriving from the implementation of the basic variational methods extended to NT models, can, then, be developed. Since the inner constraint is mainly concerned with the stress or the fracture strain components (according to the used method), a discretization with constant stress/constant strain elements is adopted.

In the paper in order to study the behavior of a masonry wall, the NT model is assumed. Then a computational procedure for two-dimensional equilibrium problems, which are representative of the behavior of masonry walls loaded by in-plane forces, is reported. An optimization procedure according to the conjugate gradient method interpolated with relaxation intermediate steps is used to search for the solution. The procedure is tested from the point of view of accuracy and convergence, with reference to a masonry wall with openings, stringcourses and architraves, subject to horizontal loading. In the second part of the paper data from laboratory experiments on masonry panels under lateral loads are reported and compared with the results relevant to a finite element NT model of the specimen, which are obtained by numerically implementing the described theoretical approach. The same experience is also repeated in the case of some fibre-reinforced polymer reinforcement, providing comparison with theoretical data also in this case.

In both cases, experimental and analytical results appear in excellent agreement thus validating the general theoretical approach, even in the reinforcement modeling and in its coupling with the masonry model.

1

A. Baratta, "Statics and reliability of masonry structures", in F. Casciati, J.B. Roberts, (Editors), "Reliability Problems: General Principles and Applications in Mechanics of Solids and Structures", CISM, Udine, Italy, 1991.

2

A. Baratta, "Structural Analysis of Masonry Buildings", in A. Baratta, T. Colletta, (Editors), "Seismic Risk of Historic Centers. A Preliminary Approach to the Naples Case", La Città del Sole B.C., Napoli, 76-122, 1996.

3

A. Baratta, G. Voiello, "Analisi di pareti murarie con tessitura a blocchi", Proc. of 9th National Conference AIMETA, Bari, Italy, 1988, (in Italian).

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