CH19 - abs. dis place m ont. top of the dome

CH19 - abs. dis place m ont. top of the dome

CH26 - diagonal wall deformation

CH20 and CH22 - abs .displacements

CH20 and CH22 - abs .displacements

Figure 7. Response during the test with intensity 1.5 g, phase 2.

Figure 7. Response during the test with intensity 1.5 g, phase 2.

The strengthening consisted of incorporation of horizontal belt courses for the purpose of increasing the integrity of the structure at those levels and providing as better as possible synchronous behaviour of the bearing walls:

• Incorporation of carbon rods in two longitudinal mortar joints around the four walls at two levels: the level above the openings and at the top of the bearing walls, immediately below the tambour. With the incorporation of these carbon rods, a horizontal belt

Figure 8. The strengthened model ready for testing, phase 3.

course was formed whereby the tensile resistance of the wall was improved and synchronous behaviour of the bearing walls was achieved.

• Formation of a horizontal belt course around the tambour by applying a CFRP wrap with a width of 10 cm.

• Formation of a horizontal belt course at the base of the dome by use of a CFRP wrap with a width of 50 cm.

The formation of these horizontal belt courses enabled better integrity of the tambour and the dome base and prevented "opening" of the dome which was the most common reason for occurrence and prolongation of cracks in the bearing walls.

The strengthened model is presented on Figure 8.

2.5 Phase 3 - Testing of strengthened mosque model

Before the seismic tests, the dominant frequencies of the model were checked.

The resonant frequency of 9.2 Hz was obtained and it was compared to the frequency of 8.6 Hz measured after the last test of testing in phase 2. This pointed out that strengthening had increased the resonant frequency of the model for about 8%, meaning that the stiffness of the model hadn't been recovered completely compared to the initial state.

During this phase, 24 tests were performed under input acceleration between 0.15 g to 1.5 g. The accelerogram of the Petrovac earthquake (N-S component) was scaled by 6 (compressed) in the first 15 tests. During the tests performed under input intensities between 0.15 g and 0.40 g. the model's behaviour was stable, without provocation of large cracks. In the next 6 tests carried out under input acceleration of 0.60-0.80 g, the dome experienced sliding at a visible horizontal crack at its base. To provoke more intensive response of the model, in the next tests, a time scaling

Figure 9. Damage of the model after phase 3 tests accomplishment.

factor of 3 was used, producing an input acceleration of 0.46-1.5 g. In this series of tests, many new cracks appeared in the walls as well as in the dome, decreasing the dominant frequency of the model to f = 4.4 Hz. This value was more than twice lower compared to the initially measured frequency of 9.2 Hz, thus indicating a pre-collapse state of the model.

The next two tests were performed by a scaling factor of 2, under an input acceleration 0.75-1.0 g. Progressive cracks appeared, but still without collapse.

The final test was performed by a scaling factor of 1, under an input acceleration of 0.35 g. Heavy damage occurred in many places on the dome and around the openings as well as big cracks and inclination of one corner of the model, including damage to the strengthening FRP belt at the lower level of one of the walls, after which the testing was stopped.

The damaged model is presented in Fig. 9. The characteristic response parameters during the seismic tests are given in Table 2. The representative time histories in the final tests are given in Fig. 10.

As a common conclusion after the performed experimental testing of the mosque model in phase 3, it might be said that the model's behaviour was evidently different in respect to that of the original model. Under tests of moderate intensity, the existing cracks were activated but during the subsequent more intensive tests, the failure mechanism was transferred to the lower zone of the bearing walls, in the direction of the excitation, where typical diagonal cracks occurred due to shear stress.

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