Int. Journal for Housing Science, Vol.38, No.1 pp.37-42, 2014 Published in the United States

0146-6518/01/37-42, 2014 Copyright©2013 IAHS

AN IN SITU DIAGONAL COMPRESSION TEST FOR BRICK WALLS WITH DISPLACEMENT CONTROL ON THE TWO EXTERNAL LAYERS

Alberto FRANCHI, Pietro CRESPI and Paola RONCA Politecnico di Milano Department of Architecture

Built Environment and Construction Engineering (ABC) Milan, Italy

Flavio PIZZAMIGLIO

Consortium for Structural Engineering Constructions in Europe (CIS-E) Politecnico di Milano

Milan, Italy

ABSTRACT Present paper presents the technical specifications of an experimental equipment able to perform an in situ diagonal compression test on a masonry specimen with displacement control. It is, therefore, capable to evaluate ductility behaviour also after the peak load. In addition, the equipment is capable to evaluate the different mechanical behaviour of a masonry specimen made of two external layers and a central core with different mechanical characteristics. The application of that equipment is described with reference to a couple of masonry specimens located in an historical building, Palazzo Paone, at L’Aquila. Key words: Diagonal Compression Test, Masonry, Displacement Control.

Introduction Experimental techniques capable to evaluate mechanical characteristics of the in situ masonry structures have been studied and standardized since a long time. The necessity to evaluate compression, tension, shear resistance and stress-strain monotonic and cyclic constitutive law of specific masonry walls of the building under consolidation have increased the interest on in situ experimental techniques. These

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techniques have to be able to give precise answers to the demand of reliable knowledge of the material mechanical properties [1]. Diagonal tension test is one, if not the only, possibility in order to evaluate tensile and shear resistance of an existing masonry wall. This test has been standardized at international level [2, 3] and utilized-developed in several applications, like in [4, 5, 6, 7, 8, 9, 10, 11]. Modern non-linear analysis, particularly for seismic loadings, requires the experimental evaluation of the post peak degradation curve in order to adopt reliable analytical models. No in situ diagonal compression test has been done before under ‘displacement control’ (at least to the Authors’ knowledge) but, vice versa, the whole experimental program has been executed under ‘load control’. A different picture is available for in laboratory diagonal compression tests: there is a fairly large amount of tests made under displacement control [12]. Moreover historical masonry walls at L’Aquila exhibit two external layers (approximately 15 cm of thickness) which are connected by a central part which is less predictable as far as presence of mortar and size and type of aggregates. Therefore it is most likely to expect a non-homogeneous behaviour of the entire section of the wall, i.e. it is to be expected that the two external layers move with a certain independence one from the other. The equipment has been studied in order to control, independently, the two jack forces, which act on each masonry external layer. The Present paper presents the equipment adopted on order to perform a diagonal compression test on two specimen of Palazzo Paone, downtown L’Aquila. The building was damaged by the earthquake of 2009 and it has been one of the first buildings to be repaired and structurally improved with respect to seismic loadings. Construction Company, belonging to the Paterlini Group from Brescia, had adopted a specific product, to be injected into masonry walls, in order to improve mechanical characteristics of masonry walls. The aim of the test program was that to evaluate mechanical characteristics of the historical masonry walls, before and after injection of that specific mortar product.

Experimental Programme

Experimental programme has been organized according to the following steps: 1. Construction and collection of all equipment parts in the Testing Materials and

Structures Laboratory of the Politecnico di Milano. 2. Validation of the equipment and testing procedures on one masonry specimen

inside the Lab of Politecnico di Milano. 3. Transportation of the equipment by truck to L’Aquila. 4. Execution of one test on a non-injected masonry and, the day after, execution of a

second test on an injected masonry specimen. The masonry specimens have been obtained in a wall at the first floor of the building where the architects have decided to open a new door. The first specimen has been obtained in the upper part of the wall (Figure 2) while the second specimen in the lower part of the wall, after removal of the first specimen. Masonry was made, as typical in

An In Situ Diagonal Compression Test 39

L’Aquila, by rounded stones (max size 13-15 cm) connected by poor mortar. The thickness of the wall was 60 cm.

5. Elaboration of the experimental results and presentation of the final report.

Experimental Equipment Experimental equipment is composed of: 1 piston pump (Figure 1) with oil circuit at a pressure of 220 bar. The pump is able to feed two separate oil circuits separately; each circuit is made of one pipe for the oil which flows from the pump to the jack and a second pipe from the jack to the pump. Two servo valves are placed on each circuit: one on the line which goes from the pump to the jack and a second one on the line from the jack to the pump. Servo valves are of analogical type such to control both pressure and flow rate. 2 jacks, able to apply both tension or compression force; the piston has a central screwed hole which allows to screw in series a load cell, with a spherical joint for avoiding creation of inclined undesired force, and a steel bar. The 2 jacks (Figure 2), positioned externally at the two sides of the masonry wall, are placed on a steel loading shoe, which transmit the compression force from the two jacks to the masonry specimen. Two steel loading shoes (Figure 2), positioned, as usual for this type of test, at two opposites corners of the masonry specimen. Two steel bars (Figure 2), which are connected, at one extreme, to the jack and, at the other, to the opposite steel cap. Two displacement transducers (Figure 2) placed on one side of the specimen along the two diagonals. 1 PC (Figure 1) for the data acquisition.

FIG 1. PC for data acquisition (left) and pump with servo valves (right).

40 Franchi, Crespi, Ronca and Pizzamiglio

FIG 2. The second masonry specimen before (left), during the test (right).

Experimental Results Following Table 1 gives the results of specimen. A (the two sides of the wall are identified with number 1 and 2), not reinforced by mortar injection, and specimen B which has been reinforced with injected mortar. Figures 4 and 5 give diagrams of diagonal single jack load versus corresponding head piston displacement (Figure 4) and the 2 extensometer displacement (Figure 5). It is worth to remark: (i) Figure 4 shows that the 2 jacks forces on the external layers are almost equal in the reinforced injected specimen, while the opposite for the original specimen; (ii) injected specimen presents a strength and a ductility which is between 3 and 4 times the values registered for the original specimen.

Table 1. Single jack diagonal peak load and corresponding displacement.

Specimen Max Diagonal Force (kN)

Diagonal Displacement of the Jack Piston Head at the Peak

Force (mm) A1 34,43 22,12 A2 23,45 21,76 B1 80,36 38,71 B2 76,04 38,87

FIG 3. Cracks at peak load of the injected specimen.

An In Situ Diagonal Compression Test 41

FIG 4. Single jack diagonal force versus corresponding displacement.

FIG 5. Single jack diagonal load versus extensometer displacement (the transducers went out of service, and then removed, at the peak load).

Conclusion

An in situ diagonal compression test with displacement control on the two external sides of a masonry wall has been presented. The experimental equipment has been

42 Franchi, Crespi, Ronca and Pizzamiglio

developed in order to perform ‘in situ’ diagonal compression tests, with a reasonable cost and a limited damage to the entire masonry panel. Application to No.2 masonry specimen prepared and tested at Palazzo Paone in L’Aquila (summer 2012) has shown that it is possible to appreciate both the different behaviour of the two sides of the wall, if it exists, and the ductility post peak load. Original masonry and the same masonry injected with mortar have shown an increment of strength and ductility with a factor in the range of 3-4.

References

[1] Decreto Ministero Infrastrutture 14/01/2008–Norme Tecniche per le Costruzioni’.

[2] ASTM E 519:07 – Standard Test Method for Diagonal Tension (Shear) in Masonry Assemblages.

[3] UNI EN 1052-3:2003 – Metodi di prova per muratura – Determinazione della resistenza iniziale a taglio.

[4] Brignola, A.; Frumento, S.; Lagomarsino S.; Podestà, S. – Identification of Shear Parameters of Masonry Panels through the In Situ Diagonal Compression Test, in International Journal of Architectural Heritage, 3-2009, pp.52-73.

[5] Chiostrini, S.; Galano, L.; Vignoli, A. – On the Determination of Strength of Ancient Masonry Walls Via Experimental Tests, documento libero, 2000.

[6] M. Corradi, C. Tedeschi, L. Binda e A. Borri–Experimental Evaluation of Shear and Compression Strength of Masonry Wall Before and After Reinforcement: Deep Repointing, in Const. and Building Material, No.22,(2008), pp.463-472.

[7] Calderini, C.; Cattari, S.; Lagomarsino, S. – The Use of the Diagonal Compression Test to Identify the Shear Mechanical Parameters of Masonry, in Construction and Building Material, No.24, (2010), pp.677-685.

[8] Chiostrini, S.; Galano, L.; Vignoli, A. – In Situ Shear and Compression Tests in Ancient Stone Masonry Walls of Tuscany, Italy, in Journal of Testing and Evaluation, Vol. 31, (2003).

[9] Corradi, M.; Borri, A.; Vignoli, A–Experimental Study on determination of Strength of Masonry Walls, Const.,Building Material, No.17, (2003), pp.325-337.

[10] Borri, A.; Castori, G.; Corradi, M.; Speranzini, E.–Shear Behaviour of Unreinforced and Reinforced Masonry Panels Subjected to InSitu Diagonal Compression Tests, in Const. and Building Material, No.25,(2011),pp.4403-4414.

[11] Gallo Curcio, A. – Comportamento a taglio delle murature, in Sul consolidamento degli edifici storici, Roma, EPC LIBRI, (2007), pp.119-137.

[12] Balsamo, A.; Prota, A.; Jovinella, I.; Morandini, G.–Comportamento sperimentale di muratura di tufo rinforzata con FRG a base ecopozzolana, Realtà MAPEI No.104.