Info

Figure2. Wall injection procedure: (a) sealing of transversal sides with polyurethane foam; (b) injection equipment and (c) injection works.

without adding extra stiffness to walls and (f) preparation of the grout and injection under a low pressure of around 0.1 N/mm2.

3.3 Test procedure and test setup

All walls were tested under monotonic compressive loading, using a 2 MN closed-loop servo-controlled testing machine. The tests were performed under displacement control at a displacement increment rate of

3 |xm/s. In order to prevent the total collapse of the walls, tests were stopped during the softening branch when specimens were about to fail. Whenever possible, walls were dismantled in order to check the efficiency of the strengthening procedure.

For the measurements of the displacements, an internal setup and an external setup were used. The internal setup was composed by LVDTs connected directly to specimens and measuring vertical, horizontal and transversal displacements (see Oliveira et al. 2006 for further details). The external setup was constituted by the control LVDT that measured the displacement between the machine plates. This last setup was used to control the test and to obtain the plot of the post-peak force-displacement curve.

4 WALL TEST RESULTS 4.1 Plain walls

Table 2 summarizes the test results for the four unstrengthened walls (associated with the three series) in terms of compressive strength (fc), peak axial strain (eap), initial Young's modulus (E0) computed between 0% and 20% of the wall's compressive strength and Young's modulus computed between 30% and 60% of the wall's compressive strength (E[30-60y). The computation of the Young's modulus was performed according to two different criteria in order to assess its degradation with increasing stress levels.

The considerable scattering computed mainly for the deformability parameters is essentially due to the

Figure 3. Axial stress - axial strain curves of the unstrength-ened walls.

influence of workmanship and the variability of natural and handmade materials.

Figure 3 represents the axial stress - axial strain curves of the unstrengthened walls. Two distinct stiffness degradation zones can be observed, which seem to be associated to the detachment of external leaves. However, this behaviour was not observed in wall 1W2 (see Figure 3 and Table 2), probably due to an unexpected improved connection between leaves, originated during the construction of the wall.

The observed failure modes of the unstrengthened walls showed that the collapse mechanism of these walls is governed by the out-of-plane rotation of the external leaves. In order to evaluate this feature, the adimensional parameter k is now introduced. Here, k is given by the average value of the four rotation angle tangents of the external leaves. This parameter can be seen as a damage measurement of the out-of-plane behaviour. The relationship between the k parameter and the axial compressive stress is given in Figure 4 for the unstrengthened walls. This figure allows to identify the beginning of leaves separation and to better recognize the atypical behaviour of wall 1W2.

Experiments showed also that the out-of-plane rotation of the external leaves was caused by the development of three hinges along bed joints close both

Figure 4. Unstrengthened walls: evolution of the k param- Figure 6. Axial stress - axial strain curves relative to the eter with regard to the axial stress. transversal tied walls.

Figure 5. Crack pattern of the unstrengthened wall 3W1 (The top and bottom hinges are not represented).

Table 3. Summary of results of the walls strengthened with transversal tying.

Figure 5. Crack pattern of the unstrengthened wall 3W1 (The top and bottom hinges are not represented).

Table 3. Summary of results of the walls strengthened with transversal tying.

fc Ea,p Eo

Figure 7. Walls strengthened with the transversal tying technique: evolution of the k parameter with regard to the axial fc Ea,p Eo

Was this article helpful?

0 0
Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

Get My Free Ebook


Post a comment