Experimental assessment of in-plane behaviour of three-leaf stone masonry walls

Construction and Building Materials 53 (2014) 149–161

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Experimental assessment of in-plane behaviour of three-leaf stone masonry walls Bruno Silva ⇑, Massimo Dalla Benetta 1, Francesca da Porto 1, Claudio Modena 2 Department of Civil, Environmental and Architectural Engineering, University of Padova, Via Marzolo, 9, 35131 Padova, Italy

h i g h l i g h t s  We carried out shear compression tests on 16 three-leaf stone masonry panels, before and after injecting NHL grout.  Non-injected panels underwent external leaf separation at lower displacement levels.  Injected walls presented enhanced behaviour and increased mechanical parameters.  The use of scaled specimens may be considered representative of the tested masonry.

a r t i c l e

i n f o

Article history: Received 4 April 2013 Received in revised form 21 November 2013 Accepted 23 November 2013 Available online 18 December 2013 Keywords: Stone masonry Grout injection In-plane cyclic tests Ductility Energy dissipation Viscous damping Stiffness degradation Reinforcement effectiveness

a b s t r a c t This paper presents an experimental campaign on multi-leaf stone masonry panels, scales 1:1 and 2:3, in both original conditions and strengthened with grout injections. The panels were subjected to horizontal in-plane cyclic loading combined with vertical loading for different pre-compression levels, and provided important information on failure mechanisms, maximum displacement capacity, shear strength and other mechanical parameters, such as shear modulus and tensile strength. Further analysis provided results on other parameters which mainly characterise the behaviour of three-leaf masonry under seismic loads, i.e., stiffness degradation, energy dissipation, and viscous damping. The main aim of this study was to gather information on the static and dynamic behaviour of three-leaf stone masonry structures in non-injected and injected conditions, in order to accurately characterise their mechanical behaviour. In particular, the effectiveness of injections of hydraulic lime-based grout as a reinforcement technique was assessed and validated. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction During an earthquake, a resistant masonry wall is subjected to both vertical loads (due to gravity and the vertical component of the seismic action) and horizontal loads as a consequence of inertia-restoring forces. Multi-leaf stone masonry is particularly susceptible to in-plane shear actions, due to its low tensile strength. In addition, if the quality of the inner leaf with respect to the external leaves is poor, and if there are no transversal elements connecting the leaves, detachment and out-of-plane collapse of external leaves very often occurs, as shown in Fig. 1.

⇑ Corresponding author. Tel.: +39 0498275355; fax: +39 0498275631. E-mail addresses: [email protected] (B. Silva), massimo.dallabenetta@ unipd.it (M. Dalla Benetta), [email protected] (F. da Porto), claudio.modena@ unipd.it (C. Modena). 1 Tel.: +39 0498275631; fax: +39 0498275631. 2 Tel.: +39 0498275613; fax: +39 0498275613. 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.11.084

In order to predict the seismic resistance of masonry, study of its shear capacity is therefore necessary, as well as evaluation of the effectiveness of grout injections, to prevent out-of-plane and in-plane collapse mechanisms. Grout injections have proved effective in improving the in- and out-of-plane behaviour of multi-leaf stone masonry. Shaking table tests on storey-high walls have recently also demonstrated the effectiveness of injections in delaying leaf detachment under seismic loads, significantly improving wall behaviour [1]. As regards behaviour under horizontal in-plane loads, Shear Compression (SC) tests are typically used, to determine shear and tensile strength, including shear modulus. Parameters such as ductility, energy dissipation and stiffness degradation can also be evaluated by testing specimens under cyclic loading, in conditions which buildings actually undergo during an earthquake. In this technique, specimens are subjected to a constant vertical (axial) load, simulating the pre-compression level acting on the building. Cyclic lateral displacements are then applied at increasing

150

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

Nomenclature A b E Ehys Einp Ewc,0 Ewc,s fgr ft fwt,0 fwt,s G Gexp Gexp

Gk Gw,0 Gw,s h H Hcr Hdu Hf Hmax K Kcr l p0 p t

cross-sectional area of wall shear stress distribution factor Young’s modulus dissipated energy input energy elastic modulus of non-injected walls elastic modulus of injected walls compressive strength of grout tensile strength experimental tensile strength of non-injected walls experimental tensile strength of injected walls shear modulus shear modulus corresponding to cracking limit state 30–60% experimentally obtained shear modulus, resulting from average of values ranging from 30% to 60% of maximum shear resistance theoretical shear modulus shear modulus of non-injected walls shear modulus of injected walls height of stone masonry panels horizontal resistance horizontal resistance corresponding to cracking limit state horizontal resistance corresponding to ultimate displacement limit state horizontal resistance corresponding to flexural cracking limit state horizontal resistance corresponding to maximum resistance limit state secant stiffness secant stiffness at cracking limit state length of masonry panel open porosity total porosity thickness of stone masonry panels

amplitudes step-wise. Walls can be tested as cantilevers with central vertical loading or as double fixed-end walls [2]. Since the early 1960s, several authors have carried out shear compression tests on multi-leaf stone masonry, both in the laboratory and on-site, before and after grout injection. The main results of such experimental results are listed in Table 1. The geometry, mechanical properties of the studied materials, and the mechanical properties of the masonry before and after grouting are shown. Shear compression tests on injected and non-injected multi-leaf stone masonry specimens show that diagonal cracks generally develop in mortar joints, in some cases also passing through the stone, particularly at higher pre-compression levels. With repeated

V w

a d du dcr df dHmax

D

ci qb qr

r00

rmax s sHmax

su,0 su,s l l0 ls m n ncr ndu nf nHmax

vertical load width of stone masonry panels boundary condition parameter horizontal displacement measured at top of panels ultimate displacement displacement corresponding to cracking limit state displacement corresponding to flexural cracking limit state displacement corresponding to maximum resistance limit state imposed displacement at top of wall shear strain evaluated on masonry panel apparent density real density vertical pre-compression compressive strength of panels average nominal shear strength evaluated on panels average nominal shear strength evaluated on panels at maximum resistance shear strength of non-injected walls shear strength of injected walls ductility ductility of non-injected walls ductility of injected walls Poisson ratio equivalent viscous damping equivalent viscous damping corresponding to cracking limit state equivalent viscous damping corresponding to ultimate displacement limit state equivalent viscous damping corresponding to flexural cracking limit state equivalent viscous damping corresponding to maximum resistance limit state

imposed lateral displacement, cracking becomes more extensive and, at maximum lateral resistance, vertical cracks appear as an effect of compression [1,3]. Cracking also occurs in the transversal sides, due to increased out-of-plane deformation of the external leaves, reducing the resistant section of the compressed walls. Experimental tests also show that the failure mechanisms of injected masonry walls submitted to in-plane cyclic loading are mainly governed by the slenderness ratio, pre-compression level, and masonry bond. As observed from the failure modes of masonry walls, separation of external and internal leaves is due to shear failure planes generated in the infill material, causing high horizontal pressure on the external leaves [4]. The main cause of the im-

Fig. 1. Out-of-plane failure of stone masonry walls without transversal connections due to horizontal seismic actions, L’Aquila, Abruzzo, Italy.

Table 1 Mechanical parameters obtained in laboratory and in situ tests under shear–compression (the definition of the used symbols may be found in the symbols list). Author

Code

Geometry

Mechanical properties of masonry before and after grouting

Dimensions (cm3) fgr/ft (N/mm2) fwt,0 (N/mm2) fwt,s (N/mm2) r0 (N/mm2) su,0 (N/mm2) su,s (N/mm2) Ew,0 (N/mm2) Ew,s (N/mm2) K (kN/mm2) Gw,0 (N/mm2) Gw,s (N/mm2) l0 ls 32.5/1.9 32.5/1.9 32.5/1.9 32.5/1.9 32.5/1.9 32.5/1.9 32.5/1.9 32.5/1.9 32.5/1.9

0.02 0.04 0.04 0.11 0.12 0.08 0.08 0.08 0.12

0.12 – – 0.22 0.22 0.25 0.29 0.23 0.27

– – – – – – – – –

– – – – – – – – –

– – – – – – – – –

– – – – – – – – –

– – – – – – – – –

– – – – – – – – –

65 85 85 73 81 94 87 78 109

100 – – 125 165 – – 173 143

8.2 11 9.0 4.7 5.9 5.8 7.3 6.0 6.9

4.8 – – 3.1 4.7 – – 5.4 4.7

Tomazˇevicˇ and Apih [3]

A-1 A-2 B-1 B-2 C-1 C-2 D-1 D-2

32.5/1.9 32.5/1.9 19.7/1.6 19.7/1.6 6.8/0.6 6.8/0.6 12.8/1.7 12.8/1.7

– – – – – – – –

0.30 0.30 0.36 0.37 0.20 0.42 0.33 0.39

– – – – – – – –

– – – – – – – –

– – – – – – – –

– – – – – – – –

– – – – – – – –

64.69 83.85 48.85 52.31 53.85 57.98 57.25 60.89

– – – – – – – –

160 200 117 122 137 142 148 148

– – – – – – – –

2.6 3.4 2.2 2.4 2.6 2.5 3.1 3.1

Modena and Bettio [25]

1

100  50  100 100  50  100 100  50  100 100  50  100 100  50  100 100  50  100 100  50  100 100  50  100

2 3 4 5 6

– – – – – – – – – – – –

0.040 0.034 0.043 0.026 0.024 0.026 – – 0.028 0.028 – –

0.052 0.037 0.046 0.043 0.035 0.039 0.066 0.066 0.044 0.044 0.052 0.058

0.048 0.041 0.046 0.028 0.025 0.028 – – 0.030 0.030 – –

0.043 0.037 0.046 0.028 0.026 0.029 – – 0.031 0.031 – –

0.055 0.040 0.049 0.046 0.039 0.042 0.071 0.071 0.049 0.049 0.064 0.059

258.9 226.5 271.8 168.3 148.9 168.3 – – 181.2 181.2 – –

336.6 239.5 291.3 271.8 226.5 246 427.2 427.2 278.3 278.3 343 394.8

– – – – – – – – – – – –

43.10 37.80 45.30 28.00 24.80 28.00 – – 30.20 30.20 – –

56.10 39.90 48.50 45.30 37.80 41.00 71.20 71.20 46.40 46.40 57.2 65.8

– – – – – – – – – – – –

– – – – – – – – – – – –

Modena [26]a

Pognana (E) Castelletto Merizzo

– – –

– – –

– – –

– – –

– – –

0.114 0.072 0.061

0.237 – –

– – –

– – –

– – –

102 36 74

268 – –

5.7 – –

2.3 – –

Corradi et al. [27]a

B-T-04-OR V-T-07-IN P-T-15-OR

90  180  48 90  180  48 90  180  48

– – –

– – –

– – –

– – –

0.219 – 0.172

– 0.225 –

917 – 471

– 1814 –

– – –

546 – 216

– 450 –

– – –

– – –

Corradi et al. [28]a

TC-01-F TC-02-F

86  48  182 86  48  182 86.3  48  180 86.3  48  180

– – – –

– – – –

– – – –

0.147 0.272 0.184 0.268

0.083 – 0.089 –

– 0.412 – 0.196

1298 – 306 –

– 4153 – 1770

– – – –

38 – 65 –

– 281 – 196

– – – –

– – – –

Galasco et al. [29]

CS00 CS01 CS02 CT01 CT02

– – – – –

– – – – –

0.200 0.160 0.100 0.130 0.100

– – – – –

0.2 0.5 0.2 0.5 0.2

– – – – –

– – – – –

– – – – –

– – – – –

– – – – –

– – – – –

– – – – –

– – – – –

– – – – –

Mazzon [1]

R2 R4 S4 S2 S5 R5

146  122  32 91  123  32 93  138  32 145  137  32 92  127  33 93  138  33

12.8/3.8 12.8/3.8 12.8/3.8 12.8/3.8 12.8/3.8 12.8/3.8

– – – – – –

0.10 0.12 0.14 0.13 0.17 0.17

1.0 1.0 1.0 2.0 2.0 2.0

– – – – – –

0.40 0.28 0.28 0.53 0.42 0.40

– – – – – –

4057 2738 5513 6708 4640 4323

– – – – – –

– – – – – –

383 170 140 449 249 281

– – – – – –

– – – – – –

In situ experimental investigation.

151

a

– – – – – – – – – – – –

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

Tomazˇevicˇ and Sheppard [5] CAT I 100  60  265 CAT II 150  100  50 150  100  50 CAT III 150  100  55 150  100  55 150  100  55 150  105  55 150  105  55 150  105  55

152

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

proved behaviour of grouted walls is the increased shear bond strength of the grout interface. Higher stress levels may therefore be achieved by greater bond strength between internal and external leaves [4]. Although few experimental studies have been carried out so far on the tensile and shear strength of grouted multi-leaf stone masonry, available data show that, after grouting, strength is enhanced due to homogenisation. The mechanical parameters shown in Table 1 show that shear strength values between 0.026 N/mm2 and 0.219 N/mm2 for noninjected masonry and between 0.040 N/mm2 and 0.53 N/mm2 for injected masonry can be achieved, considering the various levels of pre-compression. Injected specimens have shear strength on average 1.5 times higher than that of non-injected ones. The shear modulus (G) of non-injected masonry specimens ranges between 24.8 N/mm2 and 546 N/mm2 and, for injected ones; the range is 37.8–450 N/mm2, on average 2.1 times higher. The compressive strength of the grout (fgr) clearly does not increase the strength of the wall proportionally. Shear compression tests with high-strength (cement-based) and medium/low-strength (lime-based) grout shows no correlation between the fgr/ft ratio of the grout with increased masonry strength. The shear compression tests of [5] in specimens injected with cement grout even showed that ductility (l) decreases on average by 59.0% of that of non-injected specimens. Lastly, it should be noted that experimental results are few and do not allow totally reliable predictions of grouting efficiency. According to these observations, a series of experiments was set up in order to: (i) test low-strength grout; (ii) obtain a complete set of data on this type of material; (iii) carry out comparisons of 1:1 and 2:3 specimens, and (iv) obtain constitutive laws. 2. Experimental programme

Specimens were constructed according to a technique representing one of the most widespread structural systems applied to minor historical buildings throughout Europe. This type of masonry is characterised by many voids in the inner leaf. Panels were sized with a percentage of voids and a thickness ratio so that the effects of injections were clear-cut, but were at the same time sufficiently representative of real walls. The walls were constructed without any type of transversal connection between the leaves, i.e., the most unfavourable situation. The specimens were composed of two external leaves, each about 18 cm thick (1:1 scale) or 12 cm (2:3 reduced scale). They consisted of rough-shaped limestone blocks not more than about 25 cm long, arranged in sub-horizontal courses with mortar joint thickness varying from 1 to 7 cm (1:1 scale) and 1 to 4 cm (2:3 scale). The internal core, about 14 cm (1:1) or 9 cm (2:3) thick, was made with limestone fragments poured into non-compacted layers between the two external leaves. The materials chosen to construct the specimens combined the need to reproduce the conditions of historical walls (e.g., chemical and mechanical characteristics of mortar, composition of inner cores, etc.) and to use easily available local materials. Three types of calcareous stone (red stone, regular white stone, and irregular white stone) were taken from the Cugnano quarry in Belluno, north-eastern Italy. The lime mortar (T30V) was composed of a binder of natural hydraulic lime and lime putty (ratio 1:3), with a lime/sand ratio of 1:3 and a water/binder ratio of 0.35. 2.2. Strengthening Half of the three-leaf panels were strengthened with injections of the commercial FEN-X/B natural hydraulic lime grout [9], see Fig. 3, a special, high-fluidity mix with an exclusive base of Fenix NHL5, sulphate-resistant with a low water-soluble salt content, designed for consolidating stone masonry structures. Injections were carried out after mortar curing. First, in order to optimise the distribution of injection points and consequently of the mixture in the cores, a pre-defined triangular mesh of equilateral triangles with 30-cm sides were drawn, allowing dense distribution of holes so that the mixture could reach all points of the inner layers. Only one of the sides was injected; on the opposite side, control holes were drilled according to another similar mesh with 60 cm sides. The injection procedure was quite fast and easy to perform and, including preliminary preparation of walls and sealing of holes, lasted a total of about 2 h to cover 8 m2. The average quantity of grout injected was 82 lt/m2 for 1:1 scale walls and 47 lt/m2 for 2:3 walls. After the walls were cut, visual inspection confirmed that almost all the voids and cavities had been filled, and revealed good bonding between injection material and existing mortar. After construction, curing and strengthening, the walls were sawn into 16 panels and transported to the Building Materials Experimental Laboratory, University of Padova, for testing.

2.1. Test programme and specimens 2.3. Material properties Before characterising injected masonry walls under in-plane horizontal loads, behaviour in compression, under both monotonic and cyclic loads, was studied on specimens of the same type. The main experimental mechanical parameters resulting from simple compression tests are listed in Table 2. The complete results of this preliminary characterisation, including experimental and numerical analyses, are available in literature [6,7]. For the present experimental research, two series of stone masonry walls (F in full scale 1:1, S in reduced scale 2:3) were constructed, see Fig. 2. According to experience with previous experimental work [1,8], the walls were constructed as a whole and were later subdivided into individual panels for testing.

The whole experimental set-up was preceded by a preliminary phase, consisting of: (a) characterisation of the mechanical properties of stone, mortar and injected material; (b) examination of rheological and physical properties (fluidity and stability) of grout and mechanical characteristics of composite elements (cylinders) made of stone fragments (full scale 1:1, reduced scale 2:3) injected with grout, all of which are presented in Table 3. The results clearly showed that the grout presented greater strength than the mortar. However, physical compatibility between the two materials was observed by Young’s modulus, which was similar on both cases.

Table 2 Panels tested in shear compression (the definition of the used symbols may be found in the symbols list). Specimens

Condition

Scale

Slenderness

Dimension (t  l  h) (mm)

rmaxa (N/mm2)

Ea (N/mm2)

r00 (N/mm2)

r00 /rmax (N/mm2)

SCF1.0NI SCF1.25NI SCF0.75NI SCF0.5NI SCF1.0I SCF1.5I SCF1.25I SCF2.0I

Non-injected (NI)

1:1

1.2

100  50  120

2.49

2531

4.89

5203

1.00 1.25 0.75 0.50 1.00 1.50 1.25 2.00

40% 50% 30% 20% 25% 35% 30% 50%

SCS0.5NI SCS1.0NI SCS0.75NI SCS1.25NI SCS1.25I SCS1.0I SCS1.5I SCS2.0I

Non-injected (NI)

2.41

2392

4.28

5125

0.50 1.00 0.75 1.25 1.25 1.00 1.50 2.00

20% 40% 30% 50% 25% 20% 30% 40%

Injected (I)

Injected (I)

2:3

1.25

80  33  100

a This values correspond to average values resulting from simple compression tests performed on the same typology of walls and tested within the same experimental campaign, [19].

153

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

Wall C - 8 panels in scale 1:1

Wall E - 8 panels in scale 2:3

Fig. 2. Stone masonry walls.

Fig. 3. Consolidation procedure. (a) Drilling holes for grout injection. (b) Cleaning drilled holes with compressed air. (c) Grout injection. (d) Sealing holes with mortar.

As regards the rheological properties of the grout, although the efflux values measured according to ASTM [10] and Marsh cones [11] were very high compared with the norm, grout fluidity during injection was satisfactory. The procedure also showed good stability, with little bleeding and segregation. Visual observations showed that the grout satisfied the requirements of injectability into cylinders, with good interactions between grout and stone and an effective injection procedure with regard to void filling. Comparison of the mechanical properties of the materials with results from cylinders showed that the overall behaviour of masonry depends on the weakest component material – in this case, mortar – due to the high mechanical characteristics of the stone and the lower values obtained from the injected cylinders. However, the resistance of composite materials is much lower than that of grout.

the wall was measured with a magnetostrictive absolute position sensor (200 mm), which was also used for retro-activation of the actuators. Fig. 5 shows the instrumental scheme used for the various types of specimens. Pre-compression levels for all walls (0.5, 0.75, 1.0 and 1.25 N/mm2 for non-injected specimens; 1.0, 1.25, 1.5 and 2.0 N/mm2 for injected specimens, for both scales 1:1 and 2:3) were defined according to the failure fields corresponding to the most typical failure modes (shear, compression and flexural failure mechanisms) for these kinds of structural elements, subjected to both compression and in-plane horizontal loads, see Table 2. Failure fields were computed by theoretical analysis based on Eqs. (1)–(3), which are normally applied for strength prediction of brick masonry walls. Further calibration was performed for three-leaf stone masonry, e.g., the formulas predicting the shear failure mechanism proposed by Turnšek and Cacovic [14] and refined by Turnšek and Sheppard [15]:

2.4. Test set-up, instrumentation and procedure

H ¼lt Shear compression tests were performed on 16 panels in various conditions (non-injected – NI, injected – I), scales and pre-compression levels. Specimens were tested in a cantilever-type boundary condition, with a fixed base. A steel track allowed the free displacement of the upper part of the specimen, and two vertical actuators were connected to the sledge, sliding on a frictionless linear guide, fixed at the top of a horizontal steel beam for uniform vertical load distribution. Horizontal displacement was applied by a third actuator, fastened to a stiffening steel structure, and connected to the panel with a forked beam [12]. The hydraulic and control systems were those developed by da Porto [13]. Fig. 4a shows a general view of the test rig and Fig. 4b the control and acquisition system. The specimens were instrumented with 32 potentiometric displacement transducers, four to measure transversal deformation and monitor leaf separation, 24 to measure in-plane flexural and shear deformations, and four to measure base uplift and relative sliding between wall and base and also between masonry panel and reinforced concrete beams (top and bottom). Lateral displacement at the top of

ft b

sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1þ

 H ¼lt 1 " H ¼lt

r00

shear failure mechanism

ft

ð1Þ



r00 rmax  6h compression failure mechanism rmax l 

r00 r00  rmax rmax

2 # 

rmax 2h l

ð2Þ

flexural failure mechanism

ð3Þ

where H is the wall’s horizontal resistance, rmax is the compressive strength of panels, r00 is the average compression stress due to the vertical load, t is the thickness of stone masonry panels and b is the shear distribution factor, defined as follows:

b¼

h l



P1 b¼ 6 1:5

(

1 if

h l

1:5 if

61 h l

ð4Þ

P 1:5

Table 3 Average values of the mechanical characteristics of the materials and composite elements (the definition of the used symbols may be found in the symbols list).

rmax (N/mm2)

Material Stones

Mortar T30V Grout FEN-X/B Cylinders (stone fragments and grout) a b

Red Stone Regular white Irregular white

(1:1) (2:3)

93.4 163.8 189.9 3.8 12.5 3.4 3.5

Tensile strength evaluated by flexural tests. Tensile strength evaluated by indirect tensile (Brazilian) tests.

ft (N/mm2) a

17.3 16.1a 29.6a 1.4a 2.8a 0.5b 0.5b

E (kN/mm2)

m (–)

qb (kg/m3)

qr (kg/m3)

p0 (%)

p (%)

54.5 68.0 80.1 4.7 7.5 4.5 3.6

– – – 0.27 0.29 – –

2665 2657 2642 – 1871 2263 2216

2441 2405 3104 – – – –

1.3 1.4 1.2 – – – –

8.3 9.1 15.0 – – – –

154

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

Fig. 4. Shear–compression test. (a) Test rig. (b) Control and acquisition system.

Fig. 5. Instrumentation set-up for shear compression tests.

3. Experimental results 3.1. Failure modes

20 15 10

Displacement [mm]

where h and l are the height and length of the masonry wall [16,17]. After the preliminary phase of pre-compression, cyclic tests were carried out under displacement control, by application of a horizontal displacement history with increasing amplitudes and peaks, repeated three times for each displacement amplitude. The amplitudes were imposed at a frequency of 0.005 Hz, see Fig. 6. All tests were carried out up to failure of specimens, when a null value of lateral resistance was achieved, allowing the post-peak phase to be examined.

5 0 0

2000

4000

6000

8000

10000

12000

14000

-5 -10

During in-plane cyclic testing, the specimens exhibited various types of overall behaviour, according to their condition (injected/ non-injected), panel scale and applied vertical load. Four limit states, which can be used to idealise the behaviour of masonry panels [18], were observed, corresponding to changes in the way specimens resist the progressive increase of applied lateral displacement.  The first limit state is due to the opening of the first flexural cracks (Hf, df). Flexural cracking limit is defined by the appearance of horizontal cracks on the first mortar bed joint between specimen and lower concrete beam, or at the second mortar bed joint. This phenomenon occurred in all specimens at displacements of ±0.50–2.50 mm for non-injected panels and ±1.50–4.00 mm for injected ones, depending on applied precompression and scale.  After the opening of the first cracks, the overall behaviour of each panel differed according to its condition, scale and precompression level. The wall reaches the cracking limit state – Hcr, dcr. At this point, two different main behaviours were observed. One was the appearance of the first significant diagonally oriented shear crack, due to shear mechanisms; the other was a crack pattern due to rocking, with the development of

-15 -20

Time [s] Fig. 6. Example of applied displacement history.

sub-vertical cracks in the compressed toes due to bending. Both behaviours were observed in both scale panels at displacements of ±1.0–2.5 mm for non-injected panels and ±2.5–7.0 mm for injected ones.  Subsequently, loads were increased gradually until maximum load (Hmax) and the relevant displacement (dHmax) were reached, which represents the third limit state.  The last phase corresponds to the ultimate limit state, at which specimens attain maximum displacement du, corresponding to a value of residual lateral resistance Hdu. Fig. 7 shows four specimens (SCF1.0NI, SCF1.0I, SCS1.0NI, SCS1.0I) tested under compressive stresses of 1.0 N/mm2, and Fig. 8 shows the corresponding lateral force vs. displacement hysteresis curves (the whole series of crack patterns and hysteresis curves are found in literature [19]).

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

In all cases, the first cracks occurred at the interface between mortar and stone in the lower part of the specimens. However, patterns differed in each case, according to the condition of the wall (injected/non-injected), scale (1:1, 2:3) and applied pre-compression level. Cracking appeared earlier on the specimens tested with higher vertical loads. Non-injected panels 1:1, specimens SCF1.0NI, SCF1.25NI and SCF0.75I, developed mixed flexural/shear behaviour. However, due to the pre-compression levels, SCF1.25NI collapsed due to crushing at the compressed toe. SCF0.5NI displayed dominant flexural behaviour. All injected specimens in scale 1:1 exhibited rocking. SCF2.0I, which was the specimen tested at the highest pre-compression, developed diagonal cracking, followed by compression failure. Non-injected panels in scale 2:3 generally showed behaviour governed by flexural failure. SCS1.0NI was already damaged before it was tested. Injected 2:3 panels were influenced by rocking, except for SCS2.0I with a higher pre-compression level, which showed clear-cut flexural behaviour and collapse influenced by crushing, as wide transversal cracks appeared after maximum resistance had been reached, with cracking of the inner core. In all cases, non-injected panels showed leaf separation at lower displacements. Non-injected specimens failed due to buckling of the external leaves, whereas injected specimens showed extensive transversal cracking of cores after reaching maximum resistance, confirming panel homogeneity due to grout injections. 3.2. Horizontal load and displacement Fig. 9 compares limit states and idealised envelope curves of all tested specimens, and Fig. 10 summarises the average characteristic values of lateral force (H) and displacement (d) at the relative limit states in the various masonry types. The injected panels, in both scales, developed the first crack at almost double displacement, twice the lateral resistance, when compared with the non-injected panels. Non-injected 2:3 panels

155

reached higher displacement values at lower lateral forces with respect to the 1:1 panels, and injected panels showed their first cracks at almost the same displacement, with higher lateral forces for 1:1. At maximum resistance, injected panels in both scales showed three times higher displacements at almost 2 times higher force than non-injected ones. Comparisons of 1:1 and 2:3 panels showed that non-injected 1:1 specimens showed maximum resistance which was 67% higher than in the 2:3 panels, with almost the same displacement. Instead, the injected 1:1 panels showed 20% higher displacement values than the 2:3 panels, and also a 100% increase in maximum lateral resistance, defining the rocking mechanism of the 1:1 panels compared with the flexural mechanism of the 2:3 specimens with higher pre-compression loads. During the final part of the tests, at the ultimate displacement limit state, similar behaviour was observed in all panels, their mechanical characteristics deteriorated, and wide cracks appeared on transversal sides. Therefore, the different failure mechanisms which developed during the first part of the test were always affected by compression. This was most obvious in specimens subjected to higher pre-compression levels. In general, specimen comparisons, in both scales and with the same pre-compression levels, showed that, the higher the vertical load applied, the lower the resulting displacement, particularly for injected elements. At maximum resistance, the difference between non-injected and injected 1:1 specimens, subjected to the same vertical load (r0), was that the injected ones exhibited 5–6 times more displacement at an average of 40% higher maximum resistance values. The same phenomenon was observed, with smaller percentage differences, in the 2:3 panels, 3 times higher displacement at an average of 27% higher maximum resistance values. The overall behaviour of the walls was also analysed by comparing the envelopes of hysteresis loops for each panel. As a general rule, the non-injected panels in both scales were characterised by lower horizontal forces and maximum displacement values, 1:1 specimens exhibiting larger values in terms of initial

Fig. 7. Crack patterns. (a) Specimen SCF1.0NI at failure. (b) Specimen SCF1.0I at maximum resistance. (c) Specimen SCS1.0NI at failure. (d) Specimen SCS1.0I after maximum resistance.

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

H [kN]

(a)

200 150

150

100

100

50

50

0 -12

-8

200

(b)

-4

0

4

8

12

H [kN]

156

0 -30

-20

-10 -50

-100

-100

-150

-150

-200

-200

100 75

75

50

50

25

25

-4

0

4

8

12

H [kN]

H [kN]

-8

20

30

10

20

30

100

(d)

0 -12

10

δ [mm]

δ [mm]

(c)

0

-50

0 -30

-20

-10

0

-25

-25

-50

-50

-75

-75

-100

-100

δ [mm]

δ [mm]

Fig. 8. Lateral force (H) vs. displacement (d) hysteretic curves. (a) SCF1.0NI. (b) SCF1.0I. (c) SCS1.0NI. (d) SCS1.0I.

Fig. 9. Comparison of limit state envelope curves for (a) full scale specimens (1:1) and (b) reduced scale specimens (2:3).

stiffness, maximum lateral resistance and maximum displacement. The higher pre-compressed specimens in both scales achieved higher maximum resistance with more brittle failure in the final phase. The degradation of lateral resistance and the displacement capacity of the panels provided important information to evaluate changes in overall behaviour. Indicators of resistance and displacement capacity were calculated as the ratios of the considered magnitude at two different limit states. Table 4 shows ratios Hcr/Hmax, Hdu/Hmax and Hdu/Hcr for acting horizontal force and ratios dcr/ dHmax, du/dHmax and du/dcr for deformation capacity.

Considering first the degradation of lateral resistance of all specimens, ratio Hcr/Hmax was almost the same for all panels, and the cracking limit state always occurred between 87% and 95% of the resistance force (cracking of damaged panel SCS0.5NI occurred at 55%). This means that, when the collapse mechanism of each specimen manifested, the maximum lateral resistance of the wall was not achieved, although residual resistance was very low. All specimens also exhibited a similar decrease after attaining maximum horizontal force. The second ratio, Hdu/Hmax, emphasises an average reduction of 13% for 1:1 non-injected panels and 10% for injected ones, and 20% (without SCS0.5NI) for 2:3 non-injected

157

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

Fig. 10. Average values of lateral force (H) and displacement (d) at limit states, (the definition of the used symbols may be found in the symbols list).

panels and 8% for injected ones, of the force measured when the specimen failed. It is worth noting that SCS1.25NI showed a reduction of 36% of its strength. Lastly, the third resistance indicator, ratio Hdu/Hcr, was closer to one in all specimens, indicating that the cracking limit state occurs at approximately the same level of resistance as the ultimate limit state. The results from the displacement capacity indicators showed different overall behaviour from those of the resistance indicators. A great difference was observed with respect to the values obtained from specimens subjected to different vertical loads. Considering the first displacement capacity indicator, ratio dcr/ dHmax, the average values obtained for the various types of walls were 0.48 and 0.38 for 1:1 non-injected and injected panels, respectively, and 0.47 and 0.43, respectively for 2:3 panels (without SCS0.5NI), non-injected and injected. These results underline the fact that non-injected panels in both scales reached the same average displacements in order to attain maximum resistance. However, for the 1:1 injected elements, greater displacement was necessary with respect to the 2:3 injected ones (11%). Although the difference between load at cracking limit and at maximum resistance was restricted in all types of walls, greater displacements were obtained for the injected specimens (in both scales). The average increase in displacement for the 1:1 panels was 21%, but

only 15% in 2:3 panels. Also with different vertical loads, these results indicate the lower displacement needed for the specimens under higher vertical loads, to reach maximum resistance. Further significant information came from ratio du/dHmax. As expected [20], a lower pre-compression level allows greater displacement before the wall collapses. However, the injected panels, in both scales, reached greater displacements at higher vertical loads before collapse. This phenomenon was due to the rocking and flexural mechanisms of the specimens. In general, non-injected specimens, in both scales, had higher ratios than injected ones (average values: 1.54 and 1.20 for 1:1 non-injected and injected, and 1.48 and 1.39 for 2:3 non-injected and injected – without SCS0.5NI). The percentage decrease in the displacement before collapse between non-injected and injected specimens was 20% for 1:1 scale, and 6% for 2:3. Additional information came from ductility indicator du/dcr, related to the failure mechanism. In the non-injected specimens in scale 1:1 (exhibiting shear failure), high values of ultimate ductility were obtained, due to low displacements at shear cracking limit dcr. Note, however, the lower value of SCF1.25NI compared with the others, due to the more brittle collapse of the specimen after higher vertical loads. In the case of injected specimens 1:1, governed by a rocking mechanism, those subjected to lower vertical stress had a greater du/dcr ratio, since the low vertical loads

Table 4 Resistance indicators and displacement capacity indicators for all the tested specimens (the definition of the used symbols may be found in the symbols list).

a

Specimens

r00 (N/mm2)

Hcr/Hmax

Hdu/Hmax

Hdu/Hcr

dcr/dHmax

du/dHmax

du/dcr

SCF1.0NI SCF1.25NI SCF0.75NI SCF0.5NI Average

1.0 1.25 0.75 0.5

0.91 0.89 0.88 0.93 0.90

0.89 0.92 0.81 0.86 0.87

0.97 1.04 0.92 0.92 0.96

0.46 0.60 0.46 0.39 0.48

1.66 1.16 1.74 1.60 1.54

3.61 1.93 3.83 4.10 3.37

SCF1.0I SCF1.5I SCF1.25I SCF2.0I Average

1.0 1.5 1.25 2.0

0.87 0.93 0.89 0.95 0.91

0.79 0.99 0.94 0.89 0.90

0.90 1.06 1.06 0.94 0.99

0.33 0.46 0.26 0.49 0.38

1.09 1.22 1.21 1.28 1.20

3.34 2.65 4.71 2.60 3.32

SCS0.5NI SCS1.0NI SCS0.75NI SCS1.25NI Averagea

0.5 1.0 0.75 1.25

0.55 0.92 0.92 0.93 0.92

1.35 0.87 0.89 0.64 0.80

2.46 0.95 0.97 0.69 0.87

1.48 0.44 0.46 0.53 0.47

0.88 1.31 1.39 1.74 1.48

0.60 3.00 3.00 3.32 3.11

SCS1.25I SCS1.0I SCS1.5I SCS2.0I Average

1.25 1.0 1.5 2.0

0.91 0.90 0.91 0.93 0.91

0.94 0.89 0.94 0.92 0.92

1.03 0.99 1.03 1.00 1.01

0.38 0.26 0.49 0.60 0.43

1.56 1.17 1.57 1.26 1.39

4.11 4.56 3.20 2.11 3.50

Average value not including the damaged panel SCS0.5NI.

158

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

applied allowed rocking in SCF1.0I and SCF1.25I. Instead, those subjected to higher stresses – SCF1.5I and SCF2.0I – developed a smaller du/dcr ratio. The injected specimens in scale 2:3 showed the same phenomenon: SCS1.25I and SCS1.0I, subjected to lower vertical stress, had higher ratios, allowing rocking to take place, whereas SCS1.5I and SCS2.0I, with higher vertical stress, had lower ratios. Comparisons of the ductility of the non-injected and injected panels, in both scales, revealed a decrease of 1.5% for 1:1 injected panels (3.37 for non-injected and 3.32 for injected) but an increase of 12.5% for the 1:1 panels (3.11 for non-injected and 3.50 for injected).

3.3. Stiffness degradation, energy dissipation and equivalent viscous damping The seismic response of buildings is related not only to the strength and displacement capacity, i.e., ductility, of their structural elements, but also to the typical parameters of cyclic behaviour, such as stiffness degradation, energy dissipation capacity, and the viscous damping coefficient. Fig. 11 shows the relation between non-dimensional secant stiffness degradation K/Kcr (Kcr being secant stiffness at cracking limit state Kcr = Hcr/dcr) and measured displacement ratio d/dHmax. As already observed for masonry in general [2] and for multi-leaf stone walls in particular [1], the shape of stiffness degradation as a function of lateral displacement in a non-dimensional form generally follows a power law and is quite similar in all types of masonry walls. Distribution coefficients close to one were obtained by adjusting power law trend lines to the experimental data of each tested panel. Concerning stiffness degradation, a rapid decrease in all specimens subjected to lower vertical stress levels was observed. Injected panels clearly exhibited higher starting stiffness than noninjected ones, and a more rapid decrease due to rocking, whereas 2:3 injected specimens showed slower stiffness degradation. Non-injected 2:3 panels, compared with the corresponding 1:1 ones, had higher starting stiffness ratios, sustaining the decrease in stiffness and reaching a higher displacement ratio. Analysis of energy and related viscous damping provided useful information on overall wall behaviour. Fig. 12 and Table 5 show the energy ratios and equivalent viscous damping values for each panel and the average values at the various limit states. As regards energy dissipation, all non-injected specimens exhibited initial energy ratio (Ehys/Einp) higher than injected ones. Subsequently, the decrease in this ratio from the cracking limit

to the attainment of lateral resistance was almost the same for injected panels in both scales. Beyond this phase, increase was limited in all specimens, apart from the non-injected 2:3 ones, which showed a plateau up to failure. Higher values of ratio Ehys/ Einp were obtained for the non-injected specimens, but the absolute value of Ehys (dissipated energy) was higher for the injected ones, due to the greater displacement capacity reached after grout injection. Analysing the equivalent viscous damping (n), similar behaviour was reported as for energy, see Fig. 12b, non-injected panels showing greater values at initial damping and a substantial increase following the attainment of lateral resistance up to failure. The injected panels showed a much greater increase compared with the non-injected ones.

3.4. Mechanical parameters Shear compression tests also revealed important mechanical characteristics, in particular, tensile strength ft and shear characteristics such as maximum shear stress and sHmax and shear modulus G. Referential tensile strength ft of the masonry was evaluated with Eq. (1) [14], considering applied vertical stress r00 and panel geometry, when average shear stress at maximum resistance sHmax is known, see Table 6. sHmax is the nominal average shear stress at maximum resistance (horizontal load divided by horizontal crosssectional area) [21]. The average value of ft for the panels in scale 1:1 was 0.050 N/ mm2 in non-injected conditions and 0.170 N/mm2 the injected ones. For panels in scale 2:3, the ft values for non-injected (0.060 N/mm2) and injected (0.150 N/mm2) conditions were very similar to those obtained for 1:1 panels and matched the range of values found in literature [22] for uncut stone masonry with external layers of limited thickness and infill cores, in original conditions (ft from 0.0525 N/mm2 to 0.0765 N/mm2), injected with grout (ft ranging from 0.187 N/mm2 to 0.273 N/mm2). Analysis of mechanical properties showed that tensile strength ft was not significantly affected by the scale factor. However, due to its different mechanical definition, shear stress sHmax was obviously affected by pre-compression level. In any case, for non-injected masonry panels, average shear stress was found to be 0.185 N/mm2 and tensile strength 0.055 N/mm2 for injected panels, the estimated ft was 0.16 N/mm2 and sHmax 0.39 N/mm2. Shear modulus G was evaluated according to three methods. First, it was determined according to the effective stiffness, Eq. (5), of wall Kcr, in the boundary condition of a cantilever wall

Fig. 11. Stiffness degradation vs. normalised displacement. (a) Panels in scale 1:1. (b) Panels in scale 2:3 (the definition of the used symbols may be found in the symbols list).

159

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

(a)

(b)

100

50

90

45

80

40

70

35

60

30

50

25

40

20

30

15

20

10

10

5 0

0 0

0.5

1

1.5

2

2.5

3

3.5

0

0.5

1

1.5

2

2.5

3

3.5

Fig. 12. Energy dissipation (a) and equivalent viscous damping (b).

Table 5 Energy dissipation and equivalent viscous damping at the different limit states (the definition of the used symbols may be found in the symbols list).

a b

Specimens

r00 (N/mm2)

Ehys/Einp (%)

nf (%)

Ehys/Einp (%)

ncr (%)

Ehys/Einp (%)

nHmax (%)

Ehys/Einp (%)

ndu (%)

SCF1.0NI SCF1.25NI SCF0.75NI SCF0.5NI Averagea

1.0 1.25 0.75 0.5

45 72 59 55 59

12 16 13 27 14

11 66 50 44 42

10 16 10 36 12

23 61 47 40 44

10 16 11 63 12

33 60 54 46 49

17 16 24 89 19

SCF1.0I SCF1.5I SCF1.25I SCF2.0I Average

1.0 1.5 1.25 2.0

31 42 44 46 41

5 7 7 9 7

22 36 29 37 31

4 6 6 7 6

18 30 26 37 28

9 11 7 9 9

18 33 26 42 30

15 16 10 12 13

SCS0.5NI SCS1.0NI SCS0.75NI SCS1.25NI Averageb

0.5 1.0 0.75 1.25

81 75 63 75 71

28 21 15 18 18

67 52 49 61 54

20 9 12 13 11

59 47 46 51 48

14 13 12 12 12

52 45 46 51 47

12 14 17 27 19

SCS1.25I SCS1.0I SCS1.5I SCS2.0I Average

1.25 1.0 1.5 2.0

60 47 53 62 56

9 11 9 13 10

39 34 43 55 43

9 6 8 11 8

35 30 40 51 39

12 12 8 14 11

38 32 41 51 41

19 14 12 18 16

Flexural cracking

Cracking limit

Maximum resistance

Ultimate displacement

Average value not including the damaged panel SCF0.5NI. Average value not including the damaged panel SCS0.5NI.

Table 6 Tensile strength (ft) determined based on the experimental shear compression tests (the definition of the used symbols may be found in the symbols list). Specimens

sHmax (N/mm2)

r00 (N/mm2)

b

ft (N/mm2)

ft-average (N/mm2)

SCF1.0NI SCF1.25NI SCF0.75NI SCF0.5NI SCF1.0I SCF1.5I SCF1.25I SCF2.0I SCS0.5NI SCS1.0NI SCS0.75NI SCS1.25NI SCS1.25I SCS1.0I SCS1.5I SCS2.0I

0.23 0.21 0.15 0.15 0.34 0.43 0.42 0.52 0.11 0.25 0.20 0.28 0.39 0.34 0.39 0.44

1.0 1.25 0.75 0.5 1.0 1.5 1.25 2.0 0.5 1.0 0.75 1.25 1.25 1.0 1.5 2.0

1.2

0.07 0.05 0.04 0.06 0.15 0.16 0.18 0.18 0.04 0.02 0.08 0.09 0.17 0.16 0.14 0.14

0.05

1.25

0.17

0.06

0.15

160

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

Table 7 Shear modulus (G) determined according to the different approaches and for the different typologies of panels (the definition of the used symbols may be found in the symbols list). Specimens

E (N/mm2)

r00 (N/mm2)

Gexp (N/mm2)

Gexp

SCF1.0NI SCF1.25NI SCF0.75NI SCF0.5NI SCF1.0I SCF1.5I SCF1.25I SCF2.0I

2531

1.0 1.25 0.75 0.5 1.0 1.5 1.25 2.0

50.0 212.4 213.1 87.2 1140.0 1386.3 147.8 21.4

64.3 332.2 216.6 95.9 1116.6 1021.3 117.4 91.2

187.1 216.6 276.9 96.6 59.6 271.0 132.1 236.1

SCS0.5NI SCS1.0NI SCS0.75NI SCS1.25NI SCS1.25I SCS1.0I SCS1.5I SCS2.0I

2959

0.5 1.0 0.75 1.25 1.25 1.0 1.5 2.0

37.7 137.0 176.2 573.9 824.1 1496.8 289.4 582.8

52.2 121.9 166.9 429.3 791.0 1059.2 383.0 735.2

63.7 109.0 124.0 267.3 145.0 96.7 189.9 201.8

4966

5125

(a = 3.33) and in the hypothesis that the panel behaves as a homogeneous, isotropic material (Gk). The second and third methods make use of the experimental data, estimating G with Eq. (6). In the second method, shear modulus Gexp is considered to correspond to the cracking limit state. The third method estimates parameter Gexp 30–60%, considering the average of Gexp in the interval between 30% and 60% of maximum shear resistance [23,24].

kcr ¼

G A h k i 1; 2  1 þ a GEk ðhlÞ

s

Gexp ¼ P2 1 2

c

ð5Þ

ð6Þ

i¼1 i

where A is the cross-sectional area, h and l are the height and length of the specimen, E is the elastic modulus evaluated by vertical compression tests on the specimens, and s and ci are the average nominal shear stress and the shear strain evaluated on the masonry panel. Effective stiffness Kcr is the ratio between lateral resistance H and the corresponding displacement d, and can be experimentally evaluated from the envelope curves of the hysteresis loops. In this case, it was calculated as the secant value at the cracking limit state. Table 7 lists shear modulus values determined according to the various approaches. As regards evaluation of the shear modulus, the values corresponding to cracking limit state Gexp were higher than those obtained with shear modulus Gexp 30–60% (7% higher for 2:3 NI, 13% higher for 1:1 I, 17% higher for 2:3 NI, and 26% lower for 1:1 NI). The values obtained with these two methods were very different from those calculated with the first method (Gk) for the specimens on which failure was greatly affected by rocking (e.g., SCF1.0I, SCF1.5I and SCS1.0I) and, as such, cannot be considered as perfectly representative. 4. Conclusions Experimental shear compression testing was carried out on 16 three-leaf stone masonry panels in varying conditions (injected/ non-injected with grout), scales (full scale 1:1, reduced scale 2:3) and pre-compression levels (from 20% to 50% of rmax), to evaluate the effects of grout injections on cyclic in-plane horizontal loads. The main conclusions are as follows:  The overall behaviour of the panels was greatly influenced by the local position of the stones, mechanical characteristics, and pre-compression load. The more highly pre-compressed specimens achieved greater maximum resistance with more brittle failure at the final phase.

30–60%

(N/mm2)

Gk (N/mm2)

 Non-injected panels exhibited mainly shear mechanisms in specimens subjected to higher vertical loads, whereas lower pre-compressed specimens developed a flexural mechanism. Injected panels were influenced by a rocking mechanism.  In all cases, non-injected panels underwent leaf separation at lower displacement levels, specimens failing due to buckling of external leaves. Instead, injected specimens, in both scales, showed extensive transversal cracking after reaching maximum resistance, with cracking of the inner core, but no significant layer separation.  In injected panels, the first crack appeared at almost 2 times larger displacement values when compared with noninjected ones. At maximum resistance, injected panels exhibited 3 times higher displacement at almost 2 times higher force than the non-injected ones. A rapid decrease in stiffness in all specimens subjected to lower vertical stress levels was observed. Injected panels clearly had higher starting stiffness compared with non-injected ones, and a more rapid decrease due to rocking. Conversely, all non-injected specimens had a higher initial energy ratio Ehys/Einp than injected ones. In all types of mechanisms, the lower the applied pre-compression, the faster the decrease, until maximum lateral resistance was attained. Equivalent viscous damping showed similar behaviour to energy.  Analysis of mechanical properties revealed that, after grout injection, tensile strength ft increased 3 times and, in terms of experimental values (Gexp and Gexp30–60%) the shear modulus increased approximately 4.0 times; Gk remained more or less constant.  Changing the scale factor changed the influence of pre-compression on panel behaviour. The same collapse mechanisms for the same pre-compression values could not be reproduced in both scale 1:1 and 2:3 panels. However, in general, the use of scaled specimens may be considered representative of the type of masonry tested here.

Acknowledgements The first author would like to thank the FCT (Fundação para a Ciência e a Tecnologia – Foundation for Science and Technology) of Portugal. This work was carried out under EU Contract FP7ENV-2009-1-GA244123: ‘New integrated knowledge-based approaches to the protection of cultural heritage from earthquake-induced risk – NIKER’. Research was also partially supported by the Reluis Project and Executive Programme of Co-operation in the Field of Science and Technology, between the governments of Italy

B. Silva et al. / Construction and Building Materials 53 (2014) 149–161

and Japan. Thanks are due to Tassullo S.p.A. (Italy) for providing the basic materials. Specimens were built at ESEV (masonry school, Verona, Italy) and were tested at the Laboratory of Structural Material Testing, University of Padova. The authors would also like to thank engineers S. Santunione and N. Secchiero for their work as part of their graduation theses.

References [1] Mazzon N. Influence of grout injection on the dynamic behaviour of stone masonry buildings. PhD Thesis. Università degli Studi di Padova. Padova, Italy; 2010. [2] Tomazˇevic M. Earthquake-resistant design of masonry buildings. London (Great Britain): Imperial College Press; 1999. [3] Tomazˇevicˇ M, Apih V. The strengthening of stone-masonry walls by injecting the masonry-friendly grouts. Eur Earthq Eng 1993;6(1):10–20. [4] Toumbakari EE. Lime-pozzolan-cement grouts and their structural effects on composite masonry walls. PhD thesis. Katholieke Universiteit Leuven, Belgium; 2002. [5] Tomazˇevicˇ M, Sheppard PF. The strengthening of stone-masonry buildings for revitalization in seismic regions. In: Proceedings of 7th European conference on earthquake engineering; 1982. p. 275–82. [6] Silva B, Pigouni E, Valluzzi MR, da Porto F, Modena C. Assessment of the effectiveness of grout injection on the consolidation of 3-leaf stone masonry walls through the use of NDT and DT. In: Proceedings of SAHC conference, Wroclaw, Poland; 2012. [7] Silva B, Dalla Benetta M, da Porto F, Valluzzi MR. Compression and sonic tests to assess effectiveness of grout injection on three-leaf stone masonry walls. Int J Archit Heritage, 8(3), 2014, 408-435. [8] Valluzzi MR. Comportamento meccanico di murature consolidate con materiali e tecniche a base di calcea. PhD Thesis. University of Trieste, Trieste, Italy (in Italian); 2000. [9] Tassullo SpA. Tassullo Trento, Italy; 2012. Available at: . [10] ASTM C939, 1994. Flow cone method. Standard test method for flow of grout for preplaced-aggregate-concrete. [11] Miltiadou AE. Grouting as a method for the repair of masonry monuments. MSc thesis. Institute of advanced architectural studies, University of York, York, Great Britain; 1985. [12] Mosele F. In-plane and out-of-plane cyclic behaviour of reinforced masonry walls. PhD thesis. Università degli Studi di Trento; 2009. [13] da Porto F. In-plane cyclic behaviour of thin layer joint masonry walls. PhD thesis. Università degli Studi di Trento; 2005.

161

[14] Turnšek V, Cacovic F. Some experimental results on the strength of brick masonry walls. In: Proceedings of 2nd international brick masonry conference, Stoke-on-Trent, Great Britain; 1971. p. 149–56. [15] Turnšek V, Sheppard P. The shear and flexural resistance of masonry walls. In: Proceedings of research conference on earthquake engineering, Skopje, Republic of Macedonia; 1980. p. 517–73. [16] Benedetti D, Tomazˇevicˇ M. Sulla verifica sismica di costruzioni in muratura. Ingegneria Sismica 1984;I:9–16 (in Italian). [17] Decreto Ministeriale 14/01/2008 (NTC 2008). Norme Tecniche per le Costruzioni (Italian). [18] Abrams DP. Performance based engineering concepts for unreinforced masonry building structures. Prog Struct Mat Eng 2001;3:48–56. http:// dx.doi.org/10.1002/pse.70. [19] Silva B. Diagnosis and strengthening of historical masonry structures: numerical and experimental analyses. PhD Thesis. University of Brescia, Italy; 2012. [20] Vasconcelos G, Lourenço P. In-plane experimental behavior of stone masonry walls under cyclic loading. J Struct Eng 2009;135(10):1269–77. [21] Bernardini A, Modena C, Turnšek V, Vescovi, U. A comparison of laboratory test methods used to determine the shear resistance of masonry. In: Proceedings of 7th world conference on earthquake engineering, vol. 7, Istanbul, Turkey; 1982. p. 181–184. [22] Circolare. ‘‘Istruzioni per l’applicazione delle ‘nuove norme tecniche per le costruzioni’’ di cui al decreto ministeriale 14 gennaio 2008. GU n. 47 del 26–22009 - Suppl. Ordinario n.27. n. 617; 2009 (in Italian). [23] Bosiljkov V. Experimental and numerical research on the influence of the modified mortars on the mechanical properties of the brick masonry. PhD thesis. University of Ljubljana, Slovenia; 2000. [24] Bosiljkov V, Totoev Y, Nichols J. Shear modulus and stiffness of brickwork masonry: an experimental perspective. Struct Eng Mech 2005;20(1). [25] Modena C, Bettio C. Experimental characterization and modelling of injected and jacketed masonry walls. Nice, France: Italian–French Symposium Strengthening and Repair of Structures in Seismic Areas; 1994. p. 273–82. [26] Modena C. Interpretazione dei risultati ottenuti dalle prove in sito nell’ambito delle tre convenzioni con gli istituti di ricerca di Firenze e Milano e modellazione del comportamento strutturale dei componenti rinforzati. Convenzione di ricerca tra la Regione Toscana e il Dipartimento di Costruzioni e Trasporti dell’Università degli Studi di Padova; 1999 (in Italian). [27] Corradi M, Borri A, Vignoli A. Experimental study on the determination of strength of masonry walls. Constr Build Mater 2003;17(5):325–37. [28] Corradi M, Tedeschi C, Binda L, Borri A. Experimental evaluation of shear and compression strength of masonry walls before and after reinforcement: deep re-pointing. Constr Build Mater 2008;22(4):463–72. [29] Galasco A, Penna A Magenes G. Caratterizzazione meccanica di muratura in pietra. Parte seconda: prove cicliche di taglio-compressione su pannelli di grandi dimensioni. Technical report, Università degli Studi di Pavia. Allegato 4.2-UR01-2; 2009 (in Italian).