In situ full-scale tests for old masonry elements: the out-of-plane response

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In situ full-scale tests for old masonry elements: the out-of-plane response A. Borri D.I.C.A. Department, University of Perugia, Italy M. Candela P.A.U. Department, University of Reggio Calabria, Italy R.

It was directed to rubble masonry, with particularly reference to L Aquila old masonry type.

The main masonry features are: no ordinary setting, small size of the stones, regular flattens made in bricks, no transversal links and stones contact; these marks are representative of the Italian

1 In situ full-scale tests for old masonry elements: the out-of-plane response A. Borri D.I.C.A. Department, University of Perugia, Italy M. Candela P.A.U. Department, University of Reggio Calabria, Italy R. Fonti D.I.S.T. Department, University of Naples Federico II, Italy ABSTRACT: Regarding to old masonry response under seismic actions, destructive testing campaign was planned. It was directed to rubble masonry, with particularly reference to L Aquila old masonry type. The 6 th April 29 Earthquake, strongly damaged L Aquila historical centre; in the hearth of the so-called red zone, a corner palace permanent damaged was chosen. The main masonry features are: no ordinary setting, small size of the stones, regular flattens made in bricks, no transversal links and stones contact; these marks are representative of the Italian smallest historical centres and European one. Consolidation approach detection is obviously hard; therefore, in order to research and obtain an effective strategy of intervention, strictly connected to the above masonry type, seven panels were selected. Five strengthening approaches were pointed out; starting from the common injections until more advanced methods like the reticolatus, without overlook the tradition techniques. This paper will be focused on the out-of-plane answer; in relation to consider the first collapse mode the primary cause of building breakdown, during earthquake. 1 L AQUILA CITY AFTER EARTHQUAKE 1.1 The site The destructive in situ testing campaign was performed involving one old Palace permanently damaged by L Aquila earthquake in L Aquila city. It is placed in Saint Peter Square, in the heart of the historical center (Figure 1). mechanical properties and in-plane and out-of-plane response. Figure 2. Italian Peninsula, Abruzzi region (in green), L Aquila city (historical centre map). Figure 1. Chosen building photo after the 6 th April 29 Earthquake. L Aquila is one of the Italian cities listed into UNESCO sites; it is the administrative centre of the Abruzzi region, (see Figure 2). During the 29 seismic activity a great part of its historical centre was damaged; in order to research and obtain an effective strategy of intervention, strictly connected to the old masonry local features, the above testing campaign for full-scale specimens were carried out. Seven panels were chosen as structural elements suitable as specimens. They were placed at the building first floor and tested in order to identify 1.2 L Aquila old masonry: the main features Before explain both testing campaign program and strengthening measures, it is really important point out L Aquila old masonry features. L Aquila built setting show several masonry typologies all closed into rubble masonry category (see Figure 3); but it follows that two of them are most representatives, respectively widespread in L Aquila city and in the neighborhood (Formisano et al. 212). Figure 3. Masonry typologies detection in relation to stonework failure

The first type constructive scheme takes into account no ordinary stones setting, with no regular shape and small size.

However some regular courses made by bricks and stones irregularity filled up by wedges elements can be identified.

Instead, the second typology show a masonry setting lacking in many mechanical features: stone size smallest, no transversal section links, no stretcher elements, no bricks layers, no contact between

The building chosen for the full-scale tests match the first masonry typology; therefore, the followings strategies were focused on this specific masonry type.

2 The first type constructive scheme takes into account no ordinary stones setting, with no regular shape and small size. As a direct consequence of it, total absence of headers is noticed and lacks among the stones or thickness mortar joints can be pointed out. However some regular courses made by bricks and stones irregularity filled up by wedges elements can be identified. Therefore, regular flatten made in bricks and stretcher elements are present (see Figure 4a) (Ceradini 24) (Candela and Fonti, 21). Figure 4. Masonry sampling (1m x 1m); a) type one, L Aquila historical centre; b) type two, L Aquila surrounding area. Instead, the second typology show a masonry setting lacking in many mechanical features: stone size smallest, no transversal section links, no stretcher elements, no bricks layers, no contact between the bigger stones, no vertical and horizontal interlock (see Figure 4b.). All that makes hard strengthening approach detection. The building chosen for the full-scale tests match the first masonry typology; therefore, the followings strategies were focused on this specific masonry type. Regarding this first step two principal lacks were carried out: absence of headers and no contact among stones; they were all over posted like starting dates for strengthening approaches detection. 2 THE TESTING CAMPING 2.1 The testing program Two façade involved: Only first floor masonry elements - The panels selected are physically separated by a regular progression of windows, therefore, each masonry part closed to the openings was identified like a singular rigid block. Panel dimensions: wide 6cm, high 4cm, large - variable Seven panels were tested: Two panels were posted useful for masonry mechanical parameters characterization and behavior identification under horizontal actions (in plane and out-of plane tests in static conditions). Moreover, test with no destructive methods were applied. Five panels were strengthened with different approaches and finally tested out-of-plane in static conditions. University involved: Sergio Lagomarsino working group, University of Genoa, Italy Antonio Borri, University of Perugia, Italy Michele Candela, University of Reggio Calabria, University of Naples Federico II, Italy 2.2 The strengthening methods In order to provide different strengthening levels, the five reinforcement strategies take into account basic approach like injections or more advanced methods as artificial headers addition, without overlook tradition techniques. Starting from the no reinforced panel response, for out-of-plane mechanisms, the final goal is obviously improve panels resistance against horizontal actions in order to obtain the maximum possible resistance related to panel geometrical dimensions. The panels are considered rigid blocks. Following panel strategies of intervention overview show - according to fault adjustment improving (Borri et al. 212) (Fonti, 213) Panel n.4 Fault corrected: none; Strengthening method: Injections (See Figure 5a); Executive phases: 1) Panel drilling (n.17); 2) Anchors setting in the holes, pitch 6cm; 3) Masonry cleaning; 4) The injection. Grouting (lightweight mortar) was injected with light pressure near 2 bar. Figure 5. Specimen n.4; a) Masonry reinforcing with anchors; b)specimen n.1 - reinforcement approach: Reticolatus (external surface) and GFRP reinforced plaster (internal surface) Panel n.1 Fault corrected: no transversal section links; Strengthening method: Reticolatus ; The reinforcement approach applied use two different solutions for both internal and external surfaces. The last one surface was strengthened by the Reticolatus technique related to restoration criteria for no plastered masonry. Instead, second one use GFRP reinforced plaster, like show in Figure 5b. The transversal connections between the two differ solutions applied was realized by some little bars. A particular cable (Dyneema rope) was rolled around these tie elements; the rope setting follow the stones as a mesh. Therefore, bars connect the two meshes, one in GFRP and another in rope.

technique of headers addition to achieve a new one, in order to guarantee good transversal connection and re-establish regular stresses conditions.

The innovative header is made of lighten concrete with a T shape modeled in order to fill the empty areas by pushing metallic elements. (See Figure 1). a) 1,8m 1.8m b) Figure 6.

Executive phases: (Figure 6) 1) Panel drilling; the horizontal boreholes were placed full in wideness, four in numbers; 2) The header s built up; elements dimensions 3cm x 2cm made

3 Fault corrected: no transversal section links; Strengthening method: original header with Bossong system technology - injection anchors with sock; The strengthening idea begins from

This system patented by the Bossong Spa it s well-know namely injection anchors with sock.

The steel bars enclosed in a mesh fabric sleeve into which a specially developed grout is injected under low-pressure.

3;a)injection anchors with sock-as headers; b) Panel final result. Executive phases: 1) Panel drilling.

The sock mesh is a porous membrane designed in order to contain the aggregates that constitute the mixture, and allow cement flow into the sock.

The injection devices are designed according to anchors size and features, in this case the diameter is about 8 mm.

3 2.2.3 Panel n.2 Fault corrected: no transversal interlock; Strengthening method: Traditional technique with original headers ; The strengthening idea starts from the traditional reinforcement technique of headers addition to achieve a new one, in order to guarantee good transversal connection and re-establish regular stresses conditions. The headers regarding their bigger dimensions can tie panel from side to side. The innovative header is made of lighten concrete with a T shape modeled in order to fill the empty areas by pushing metallic elements. (See Figure 1). a) 1,8m 1.8m b) Figure 6. Specimen n.2 a) technique applied design; b) photo of pushing metallic elements; b) final result. Executive phases: (Figure 6) 1) Panel drilling; the horizontal boreholes were placed full in wideness, four in numbers; 2) The header s built up; elements dimensions 3cm x 2cm made about lighten concrete; 3) Setting of the T headers; 4) Setting of the pushing metallic elements Panel n.3 Fault corrected: no transversal section links; Strengthening method: original header with Bossong system technology - injection anchors with sock; The strengthening idea begins from the improvement of drilling techniques, which allow the embedding of reinforcement steel anchors inside masonry walls with a minimum impact. This system patented by the Bossong Spa it s well-know namely injection anchors with sock. It the special sock wraps the metal bar and guarantees the total control of injection and to create a strong mechanical interlock a long all over the section. The steel bars enclosed in a mesh fabric sleeve into which a specially developed grout is injected under low-pressure. Therefore, the injection anchors with sock arrange artificial headers perfectly bonded to masonry inner surfaces (Figure 7a). Figure 7. Specimen n.3;a)injection anchors with sock-as headers; b) Panel final result. Executive phases: 1) Panel drilling. The horizontal boreholes were placed full in wideness with variable length from 56 to 8 mm and diameter 6 mm; 2) Bars setting. bars, type GBOS, diameter 6 mm and 5 mm placement. The sock mesh is a porous membrane designed in order to contain the aggregates that constitute the mixture, and allow cement flow into the sock. chemical bond with the substrate is guarantee. 3) Very smallest nylon tube was used in order to give the injection. The injection devices are designed according to anchors size and features, in this case the diameter is about 8 mm. At the end, thirteen headers were added into the panel with a pitch of 65cm in the horizontal direction and 7cm in vertical one. (See Figure 7b) Panel n.5 Fault corrected: no transversal section links and no contact among stones Strengthening method: Traditional technique - headers setting and mortar joints replacement. The strengthening idea (Fonti, 213) start from Abruzzi local structural engineering features for old masonry constructions. The Abruzzi built widespread employ wooden elements for masonry connections and building safety against horizontal actions. Therefore, some wooden headers were placed in order to obtain the mechanical interlocks (in transversal section); instead, little bricks elements were placed in order to increase compression resistance for vertical loads and avoid the modification of the hinge position during panel overturning under horizontal loads. Executive phases: (See Figure 8) 1) Panel drilling. The horizontal boreholes were placed full in wideness with 4 holes diameter 2mm; 2) Replacement of the mortar joints with little bricks elements; 3) Setting of the wooden headers and wooden wedge-elements in order to reestablish regular stress condition.

3.1.2 Specimen n.4: Injection The comparison between the two experimental curves for specimens n.4 and 6 shows very similar response. (See Figure 1) 45 Curva Pannello n.3 4 Uy Pannello n.

25 2 198 15 166 267 13 237 1 83 5 3 THE OUT OF- PLANE TESTS 3.1 The pull-out tests According to the panels placement possibility, the specimens were tested by monotonous forcecontrol or cyclic tests.

Regarding the monotonous tests, the setup adopted use metallic anchor and cable positioned in the geometrical panel dimensions centre, in order to apply horizontal force.

6 The comparison between the no reinforced global panel force-displacement constitutive curve and the theoretical one show no codified response for L Aquila masonry: three-linear curve trend with no

Specimen n.4 and 6 force-displacement constitutive curve comparison The force-displacement constitutive curve recognized for panel n.

with significant horizontal displacements increasing without strength one until the maximum displacement of 13mm. 3.1.3 Specimen n.3 The comparison between the experimental response of the panels n.

with significant horizontal displacements increasing without strength one until the maximum displacement equal to 25mm and the corresponding force value equal to 166daN.

4 3.1.2 Specimen n.4: Injection The comparison between the two experimental curves for specimens n.4 and 6 shows very similar response. (See Figure 1) 45 Curva Pannello n.3 4 Uy Pannello n.3 limite Pannello n.3 Umax Pannello n.3 35 Curva Pannello n.6 Uy Pannello n.6 limite Pannello n.6 3 Umax Pannello n.6 Figure 8. Specimen n.5. a) Schematic plan for wooden headers setting; b) Panel final result THE OUT OF- PLANE TESTS 3.1 The pull-out tests According to the panels placement possibility, the specimens were tested by monotonous forcecontrol or cyclic tests. No axial load has been applied. Regarding the monotonous tests, the setup adopted use metallic anchor and cable positioned in the geometrical panel dimensions centre, in order to apply horizontal force. The main marks obtained are the following (Borri et al. 212): (from the no-reinforced to the best) Specimen n.6 no reinforcement Specimen n.6 The comparison between the no reinforced global panel force-displacement constitutive curve and the theoretical one show no codified response for L Aquila masonry: three-linear curve trend with no frail behavior it s generally noticed. Gradual development of relevant horizontal displacements after the maximum strength is recognized Uy Umax14 16 Umax 18 2 Spostamenti (mm) Figure 1. Specimen n.4 and 6 force-displacement constitutive curve comparison The force-displacement constitutive curve recognized for panel n.4 take into account a starting linear trend from to 9mm that show a pseudo-elastic behavior with corresponding strengths values respectively equal to 47daN and 162 dan (Uy). with significant horizontal displacements increasing without strength one until the maximum displacement of 13mm Specimen n.3 The comparison between the experimental response of the panels n.3 and 6 shows a very similar trend curve with different resistance values (Figure 11). Figure 11. Specimen n.3 and 6 force-displacement constitutive curve comparison. Figure 9. Specimen n.6. force-displacement constitutive curve From to 4mm pseudo-elastic behavior is identified with corresponding strengths values respectively equal to 47daN and 83daN(Uy). with significant horizontal displacements increasing without strength one until the maximum displacement equal to 25mm and the corresponding force value equal to 166daN. (See Figure 9) In fact, from to 8mm a pseudo-elastic behavior is noticed with corresponding strengths values respectively equal to 49daN and 198 dan (Uy). This last is more than double, in front of the specimen n.6. After the elastic limit nonlinear response is noticed, two different line segments could be distinguished: growing and plateau with significant horizontal displacements increasing until the maximum displacement of 163mm. the maximum strength recognized is equal to 267daN. Therefore, in global panel response the artificial headers gave a little improvement contribution. This is mainly due to excess in number of them; in fact

during the panel overturning they could be recognize as weak points. (See Figure 12) Figure 12. Specimen n.3 experimental work out-of-plane test, photo. 3.1.4 Specimen n.

5 during the panel overturning they could be recognize as weak points. (See Figure 12) Figure 12. Specimen n.3 experimental work out-of-plane test, photo Specimen n.2 The force-displacement constitutive curve recognized for panel n.3 is ever-grooving; it take into account a starting linear trend from to 7mm that show a pseudo-elastic behavior with corresponding strengths values respectively equal to 15daN and 279 dan (Uy). with both significant increasing of horizontal displacements and strength values until the maximum displacement 87mm and relative strength value equal to 426 dan (See Figure 13). Note: In order to make a comparison all values listed were prorated to masonry specimens reduced in largeness to 1m Specimen n.1 The force-displacement constitutive curve recognized for panel n.1 is ever-grooving. It take into account a starting linear trend from to 5mm with corresponding strengths values respectively equal to 115daN and 299 dan (Uy) (See Figure 15). with both significant increasing of horizontal displacements and strength values until the maximum displacement 154mm and relative strength value equal to 415 dan , ,64 231,12 212, ,34 163,71 144,45 327,42 394,35 375,57 385,2 p 415 Curva limite elastico (Uy) limite 356,31 limite ultimo (Umax) trilineare Curva limite elastico (Uy) limite limite ultimo (Umax) trilineare Uy Umax Spostamento (mm) Figure 15. Specimen n.1 - force-displacement constitutive curve By comparing panel n.1 and 2 analogue responses were noticed (See Figure n.16) Uy Umax Spostamenti (mm) Figure 13. Specimen n.2 - force-displacement curve It is obviously evident that the addition of artificial headers, good in number, could realize very well interlock in the transversal section avoiding partially hinge position modification during panel overturning under horizontal force (See Figure 14). Therefore, a perfect rigid-block behavior was experimental noticed (See Figure 2); however, it was no taken in advance of all panel weight force against horizontal loads Uy Umax Umax Spostamenti (mm) Figure 14. Specimen n.2 and 6 force-displacement constitutive curve comparison 13 Curva Pannello n.2 Uy Pannello n.2 limite Pannello n.2 Umax Pannello n.2 trilineare Pannello n.2 Curva Pannello n.6 Uy Pannello n.6 limite Pannello n.6 Umax Pannello n.6 trilineare Pannello n Curva Pannello n.2 Uy Pannello n.2 limite Pannello n.2 Umax Pannello n.2 Curva Pannello n.1 Uy Pannello n.1 limite Pannello n.1 Umax Pannello n Uy Umax Umax Spostamento (mm) Figure 16. Specimen n.1 - force-displacement constitutive curve. 3.2 Cyclic test: the panel n.5 The specimen n.5 was test by applying alternate horizontal action with loading and unloading cycles. The force-control tests was carry out with no axial load applied. The setup adopted use an horizontal actuator of 5 kn, in order to apply the alternated loading conditions to the panel which is free to roll on the top. The actuator was anchored by a steel beam placed in the geometrical panel dimensions centre. The mark obtained is the following: The cycles were five in numbers with growing step 3cm by 3cm. latest overturning phase was performed.

6 Table 1. Specimen n.5 test. cycles Maximum strength number (dan) Tot n: 5 Positive Negative Displacement (mm) Positive Negative I II III IV V Overturning The trend curve that interpolates the experimental maximum values filled in Table n.1 is described by a three-linear force-displacement constitutive curve. It take into account a starting linear trend from to 25mm with corresponding strengths values respectively equal to 24daN and 59 dan (Uy). The panel shows a starting rigidity very similar to the no reinforced one; this occurrence is mainly due to the reinforcement method aims. It was developed according to old masonry traditional techniques in order to guarantee seismic improvement with no constitutive curve trend changing. In fact, the resistance values and relative displacements result increased until the top strength of 787daN with a corresponding displacement of 14mm. Therefore, after the elastic limit strong nonlinear response is noticed with significant increasing of both horizontal displacements and strength values until the maximum displacement of 24mm recognized during the turning phase. (See Figure 17) Ciclo I Ciclo II Ciclo III Ciclo IV Ciclo V Inviluppo fase negativa Inviluppo fase positiva retta massimo Uy Ribaltamento retta Y Umax -161 Figure 17. Specimen n. 5-Cyclic test Spostamento (mm) The response shows a symmetrical answer with asymptotic trend. By comparing the specimen s n.6, 2 and 5 it is possible notice that mortar joints replacement gave a strong contribute during first collapse mode mechanism activation in order to obtain the maximum efficiency of the panel against seismic failure FINAL REMARKS The final result of the experimental work consisting in two main outcomes: (i) identification of mechanical properties of individual stone elements inside the panel and (ii) derivation of force-displacement constitutive curves for global panels. Therefore, the following experimental evidences pointed out (Fonti, 213): different response for out-of-plane test were noticed, according to both masonry setting panel deviation from the rule of art and specific strengthening measures adopted; the above observations are referred to masonry resistance value checked during panel overturning under static horizontal loads; the check of header elements contribution in the out-of-plane collapse mechanisms and the importance of mortar joints replacement by small stone elements, in order to increase the compression resistance and to avoid the modification of the hinge position during panel overturning under horizontal loads; no possibility to consider masonry perfectly unilateral and infinitely resistant to the compression. The introduction of an additional parameter the shape interlock is proposed. As a final remark: the comparison with the available technical literature reference about masonry mechanical models showed a significant gap between the experimental force-displacement constitutive curve and the theoretical ones. 5 REFERENCE Borri, A., Candela, M., Fonti, R. (212). Old masonry structures in L'Aquila historical centre: retrofitting strategies and full scale tests. The assessments, Proc. of 15th World Conference on Earthquake Enginnering, Lisbon, September 212. Candela M., Fonti R. (21). The Solid Springer rule - behavior under dynamic stress. In: Proc. of COST ACTION C26 Final Conference, Urban Habitat Constructions under Catastrophic Events. Naples, vol. 1, p Ceradini, V. (24) Codice di pratica per la sicurezza e la conservazione degli insediamenti storici dell Area Grecanica. Gangemi: Roma. Formisano, A Fonti, R. Mazzolani, F.M. (212) The historical centre of Poggio Picenze after L Aquila earthquake: behavior and strengthening of masonry aggregate-walls In the Proc. of 8th SAHC 212. Wroclaw, Oct 212. Fonti, R. (213) La Statica delle Murature in pietra grezza. PhD Thesis in Construction Enginnering, Naples.

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