PSI - Issue 29

A. Boostani et al. / Procedia Structural Integrity 29 (2020) 79–86 Boostani et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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similarly to C 0 . In the configuration C 2 , it is assumed that the layers of the perimeter wa lls have been consolidated by means of a reciproca l weaving or stitching, with the a im of inducing a unique overturning mechanism around a unique hinge. If, in addition to the stitching of the layers, it is assumed that an auxiliary buttress is built on the externa l part of the perimeter wa ll, configuration C 3 , represents the overturningaround a unique hinge at the foot of the wa ll, Figure 2.

(a)

(b)

(c)

(d)

Figure2. Scheme of each considered mechanism, (a) C0, (b) C1, (c) C2 and (d) C3.

Table 1. Synthesis of the results of the overturning mechanisms λ ci a 0 *

I S

C 0 C 1 C 2 C 3

0.103 0.068 0.260 0.349

0.882 0.554 2.10 2.88

0.240 0.151 0.572

0.785 Results of Table 1 show that in the current layered configuration, perimeter wa lls benefits from the presence of the debris layer, in fact the load multipl ier λ c1 is lower than λ c0 . Also, stitching together wa ll layers is an essentia l measure to avoid the future collapse of the wa lls, especia lly in view of the remova l of the debris layer. Second, the construction of an auxiliary buttress appears a furthermeasure and a remarkably va luable solution to guaranteeing a

tangible increase in the structural safetyof the monument. 3.2 Designing a compatiblestrengthening intervention

The eva luation of risk connected to seismic actions permitted us to define the requirements of the actions to be implemented in order to counteract the main two vulnerabilities of the building: the first depending on overturning actions, the second on the partia l decohesion of the materia l and on the activation of horizonta l bending mechanisms. In order to counter these threats, two different strategies had to be carried out . Present work tackles the first topic. The solution has to be based on the design of a stitching tool, composed of a series of bars crossing the different layers and able, thanks to the friction, to make them work as a single solid. As a preliminary test on site demonstra ted, wooden bars were rejected, and the focus was centred on types of solutions based on bars made of composite materia l. The advantage of this solution consists of the possibility of creating the bar in situ, by the combina tion of a reinforcement fibre and a matrix injected as grout into a hole implemented through the masonry leaves to be unified. With this solution it is possible to create a materia l with the mechanica l parameters most compatible with the origina l ones, (Misseri et a l., 2019a , 2019b) and, especia lly, to graduate its stiffness and strength, comparing different combinations. Following such principles, it seemed useful to choose a fiberglass net as reinforcement (not too stiff and easy to roll up) and a mixture of loca l earth and gypsum as components for the matrix. As regards the use of a matrix made by earth and gypsum, the choice depends on the building materia ls typica l of local culture andpart of the construction of themosque.