1 Building constructions characteristics and mechanical properties of confined masonry walls 1 in San Miguel (Puno-Peru) 2 3 Tarque Nicola (1)*, Pancca-Calsin Erika (2) 4 1 Pontificia Universidad Católica del Perú. GERDIS Research Group, Civil Engineering Division. 5 Av. Universitaria 1801, San Miguel, Lima, Peru. Email: sntarque@pucp.edu.pe 6 2 Universidad Peruana Unión. Autopista Héroes de la Guerra del Pacifico, Juliaca, Peru. Email: 7 erikapancca@upeu.edu.pe 8 * Corresponding author: sntarque@pucp.edu.pe 9 10 ABSTRACT 11 House self-construction and self-management are very common in different cities in Peru, which is 12 the case in several areas in the district of San Miguel (Puno). This is due to the lack of financial 13 resources to hire professionals to design and construct their houses. Therefore, many residents build 14 without technical guidance and materials without quality standards. As a result, the buildings in the 15 area have various construction pathologies that demonstrate their high seismic vulnerability, which 16 indicates that the guidelines established in the Peruvian Masonry Design Code NTE 070 are not 17 followed. Therefore, as a first step towards evaluating the seismic vulnerability of the houses in San 18 Miguel, it was decided to evaluate the construction pathologies and typologies by conducting a 19 survey. Subsequently, to characterize and evaluate the physical-mechanical properties of the 20 masonry walls, 24 piles and 24 small walls were built and tested. The materials tested were obtained 21 from the urban area of the same study place. According to the experimental tests, it was observed 22 that the axial compression and diagonal shear values of the prisms are lower than the minimum 23 values specified in the Peruvian Construction Code, and this would increase the seismic 24 vulnerability of the constructions. Therefore, many of the houses in the district could suffer 25 significant damage and even collapse in a seismic event. 26 27 mailto:sntarque@pucp.edu.pe mailto:erikapancca@upeu.edu.pe mailto:sntarque@pucp.edu.pe 2 Keywords: non-engineering buildings; construction pathologies; masonry prisms; experimental 28 tests, seismic vulnerability; damage survey, Puno 29 30 1. INTRODUCTION 31 In some Peruvian cities, there has been an exponential increase in population, consequently 32 increasing the need for housing. In addition, there is a lack of resources to acquire a finished house 33 or hire professionals to design and build confined masonry structures. As a result, many residents are 34 forced to build informally, that means, without technical supervision and with cheap materials of 35 questionable quality (Flores et al. 2019, Yacila et al. 2019, Blondet et al. 2006). 36 The confined masonry (CM) buildings are characterized by masonry walls (fired clay units) enclosed 37 with reinforced concrete (RC) elements along the four edges. These RC elements may avoid out-of-38 plane failure and improve the shear in-plane behaviour of the walls. Unlike unreinforced masonry 39 buildings (URM), where kinematic failure modes may be analyzed (i.e. Micelli et al. 2016), CM 40 walls are more likely to fail in-plane. Also, some reseachers have studied the use of confine elements 41 to strength URM walls built with other unit types (Khan et al. 2021, San Bartolomé et al. 2009). 42 The CM walls (built with fired caly units) are the main structural elements that provide lateral 43 stiffness to the dwellings against the action of earthquakes and transfer the loads coming from the 44 slab to the foundation (Varela-Rivera et al. 2019, Marques and Lourenco 2019). An appropriate 45 density of CM walls in a structure and both directions allows the building to perform well in seismic 46 events. Therefore, it is necessary to know the constructive flaws of the walls, the characteristics and 47 mechanical properties of the masonry, the variability in the mortar thicknesses (Reddy et al. 2009), 48 and the quality of its materials to estimate the structural safety of the assembly. Based on data from 49 national censuses and annual measurements that CAPECO (2018) conducted on the formal housing 50 market, it is estimated that the percentage of informally built housing in Peru between 2007 and 51 2014 in Lima is 68.5%. In addition, it is inferred that the percentage of informal housing would be 52 equal to or greater than 70% in the rest of the country (Zavala et al. 2019). 53 Seismic vulnerability is represented by the susceptibility of a structure to suffer damage (Vatteri and 54 D’ayala 2021, Preciado et al. 2020, Ranjbaran and Kiyani 2017). Vulnerability reflects the lack of 55 3 strength of a building to earthquakes, as indicated by Bommer et al. (1998), and depends on the 56 building design characteristics, the quality of materials and the construction technique (Kuroiwa 57 2002). 58 Blondet et al. (2004) conducted a study on analyzing the seismic vulnerability of informal CM 59 dwellings in the Peruvian coastal area. It is determined that if a house is average but the quality of 60 construction is poor (e.g. use of low-quality materials), then the seismic vulnerability can be 61 assessed as high. Likewise, these houses are built in stages, depending on the inhabitants’ 62 availability of economic resources. According to Sánchez et al. (2019), the progressive construction 63 and the use of low quality materials may infer in a high seismic vulnerability since there is not 64 engineering building planning for the future. Also, Hadzima-Nyarko et al. (2016), and Parammal and 65 D’Ayala (2021) studied the vulnerability of confined masonry buildings and agree that the seismic 66 capacity may decrease when there are more deficiencies in the construction (e.g. poor wall-column 67 connection, low wall density, unconfined walls, spacing of cross walls, etc). This is why houses with 68 severe structural, architectural and construction deficiencies make them vulnerable to natural 69 phenomena such as earthquakes (Ruiz-García and Negrete 2009, Sánchez et al. 2019, Zavala et al. 70 2019). 71 Vulnerability usually manifests itself through various pathologies that appear in buildings. Many 72 researchers have studied the seismic vulnerability of masonry buildings on a local and large scale 73 demonstrated the necessity for understanding the seismic behaviour of those buildings and their 74 relationship to their mechanical material properties (Ahmad et al. 2010, Blondet et al. 2006, Flores et 75 al. 2019, Hadzima-Nyarko et al. 2016, Lovón et al. 2018). González et al. (2008) understand 76 pathology as a systematic deficiency that occurs in most constructions because of the poor quality of 77 materials used in construction, construction errors that are not identified that way by the builders, the 78 lack of a culture of quality in the supervision, the lack of regulations and legislation in construction, 79 among others. Consequently, it is necessary to determine the quality of the CM constructions and the 80 properties of the materials that the houses are built with. 81 As in other cities in Peru, in the district of San Miguel in Puno, the application of construction 82 standards appears to be still incipient. Nevertheless, the population makes a considerable investment 83 4 in constructing their housing, even saving several years. Therefore, the houses must be safe in the 84 event of a seismic event. 85 Puno has gone through several experiences of earthquakes, such as those that occurred in 1928 86 (6.9Ms) and 2016 (6.3Mw), which caused damage to homes (making them uninhabitable) and even 87 caused collapses. Therefore, to predict the seismic response of residential masonry walls, it is 88 essential to study their physical-mechanical characteristics and properties (Quiroz et al., 2014). 89 Furthermore, to evaluate the mechanical behavior of a masonry wall, it is necessary to know its 90 mechanical properties through experimental tests (Perez-Gavilán et al. 2019, Almeida et al. 2014, 91 Binda et al., 2014). For this reason, this study evaluated the mechanical characteristics of piles and 92 walls built with typical bricks from the San Miguel area to verify whether they meet the 93 requirements of Peruvian standard NTE 070 (2006) and thus infer their seismic vulnerability. 94 95 2. EVALUATION OF THE HOUSES 96 2.1. Surveys in the study area 97 The study was carried out in the district of San Miguel, which belongs to the province of San Román 98 in the department of Puno and is home to approximately 65,500 people. Figure 1 shows the location 99 map of San Miguel at the national, departmental and provincial levels. In Puno, the buildings have 100 grown without specific planning due to the spontaneous union of neighbourhoods and urbanizations 101 in its surroundings. This uneven and disorganized growth had different consequences in several 102 aspects, such as the heterogeneity in the variety and uses of housing. Likewise, the lack of a political 103 organization and the lack of attention to basic needs and services forced the population of the 104 northern area to create the district of San Miguel in 2016. Approximately 12 340 out of 16 130 105 dwellings in San Miguel are made of clay brick (INEI 2018). In this research, 92 dwellings were 106 chosen to be evaluated and intended to represent the construction typology of the area. 107 Unfortunately, it was impossible to have a more significant number of surveys because many 108 villagers were afraid that this study was part of the local government's tax data update campaign. 109 Nevertheless, figure 2 shows some of the surveyed dwellings, where it can be noticed how these 110 dwellings grow without an adequate architectural order. 111 5 112 Figure 1. Location map of the district of San Miguel, Puno. 113 114 115 116 117 Figure 2. Some surveyed households in the district of San Miguel (Puno). 118 119 Fieldwork, office work and experimental trials were carried out. The fieldwork consisted in 120 obtaining information using survey sheets from one wall of the first level per dwelling. As shown in 121 Figure 3, the sheets consist of 2 pages whose format was divided into general data on the house, 122 structural characteristics and wall construction. The latter includes the evaluation of the masonry 123 unit (quality and aesthetics, dimensions and superficial condition), mortar construction joints 124 6 (thickness, quality and finish) and wall settlement (alignment, type of rigging, aesthetics, and finish). 125 Additionally, existing pathologies were noted: unconfined walls, non-uniform mortar joint thickness, 126 cracks in the walls, presence of salinity in the overlying walls, poor horizontal and vertical alignment 127 of masonry units, cracks in columns and confining beams, efflorescence in walls, low-quality 128 masonry units, poor mortar-unit interaction, cracks in the mortar, poor column-wall interaction, wall 129 construction at different times, exposed steel, existence or not of seismic joints, among others. 130 Moreover, observations, comments, construction schemes and photographs of masonry walls were 131 also added to the file. Finally, the sheets were filled out by hand at the time of the home visit. 132 133 134 Figure 3. Household survey sheets, in Spanish. 135 7 136 Figure 3. (Continuation) Household survey sheets, in Spanish. 137 138 The desk work consisted of the analysis of the survey sheets. The information collected in the field 139 was processed in report forms for each dwelling. The surveyed dwellings' characteristics (structural, 140 constructive, pathologies and typologies) were grouped, and a database was created. Subsequently, 141 to characterize and evaluate the physical-mechanical properties of the masonry walls of the houses, 142 laboratory work was carried out, which consisted of building and testing piles and walls. Before this, 143 control tests (classificatory and non-classificatory) were carried out on the masonry units and the 144 mortar. The tested materials were obtained from the same study site. 145 146 8 2.2. Construction typologies 147 Confined masonry (CM) walls are composed of clay brick walls surrounded by reinforced concrete 148 (RC) elements. Some walls may have only on the ground floor an RC plinth. Typically, the 149 longitudinal steel bars of the RC elements are composed of four bars of Φ ½”, with stirrups of Φ ¼”. 150 Details of typical dimensions of CM walls and their CM elements are shown in Figure 4. 151 152 153 Figure 4. Typical confined masonry wall’s configuration. 154 155 From the 92 houses evaluated, six typologies of walls were obtained, defined according to the 156 thickness of the vertical (J.V.) and horizontal (J.H.) mortar joints. The three most predominant pairs 157 (J.V. - J.H.) were selected to be characterized in the masonry prisms. Typology 01 (T1) with mortar 158 thickness (J.V. and J.H.) of 20mm, typology 02 (T2) with a thickness of 30mm and typology 03 (T3) 159 with a thickness of 40mm. These results are shown in Figure 5: T1 represents 25% of dwellings, T2 160 represents 58% of dwellings, and T3 represents 12%. An additional typology was considered a 161 reference standard (TP), with mortar thickness between 10 to 15mm as indicated in NTE 070 (2006). 162 163 9 164 Figure 5. Distribution of walls according to the thickness of their joints. 165 166 2.3. Masonry wall pathologies 167 Vulnerability usually manifests itself through various pathologies that appear in buildings, ranging 168 from minor damage and inconvenience to the occupants to significant failures that can cause the 169 collapse of the dwelling or part of it (Astorga and Rivero 2009). Figure 6 shows the different 170 pathologies found in the studied dwellings. For example, Figures 6a and 6b show an inadequate 171 connection of the masonry units with the confining element since both elements have cracks or 172 separations. In addition, figures 6c and 6d show that some houses have cracks in their walls. These 173 cracks usually appear when there are differential settlements in the foundation due to low-strength 174 concrete or the deficient use of reinforcing steel in the confining elements (Mosqueira and Tarque 175 2005). Likewise, Figures 6e and 6f show mortar joint thicknesses more significant than 15 mm 176 (value recommended by NTE 070). 177 Moreover, these thicknesses are not homogeneous. Figures 6g and 6h show walls with efflorescence 178 damage, a crystalline deposit (saltpetre) generally white colour that develops in the masonry or on 179 the surface of the concrete, which, if not repaired, can increase and weaken the wall (Sathiparan and 180 Rumeshkumar 2018, Annila et al. 2018). Figures 6i and 6j show no confining beam for the wall, and 181 the columns are short due to the existence of windows. Finally, Figures 6k and 6l show the poor 182 quality of the workmanship used in the construction of many houses, which, according to Mosqueira 183 and Tarque (2005), can cause a reduction of up to 40% in the shear strength of the walls. 184 25% 58% 12% 5% 0% 10% 20% 30% 40% 50% 60% 70% Mortar joint thickness couples. T1 T2 T3 Others 10 a) b) c) 185 d) e) f) 186 g) h) i) 187 j) k) l) 188 Figure 6. Existing pathologies in analyzed dwellings. 189 Figure 7 shows the percentage of incidence of various pathologies observed, the most predominant 190 being the construction of walls with non-uniform mortar joint thickness (95%), houses with exposed 191 steel (92%), with efflorescence in the lower part of walls (64%), with poor vertical alignment of 192 bricks (63%), with the presence of cracks in mortars (62%), with the existence of salinity in overlays 193 (62%), with the poor horizontal alignment of bricks (61%), with lack of good brick-mortar 194 interaction (62%), with lack of good brick-mortar interaction (62%), with the presence of cracks in 195 the mortar (62%), with the existence of salinity in the overlay (62%), with the poor horizontal brick 196 alignment (61%), with lack of good brick-mortar interaction (59%), with deficient column-wall 197 interaction through notching (54%), with cracks in confining columns (53%), among others. 198 199 11 200 Figure 7. Existing pathologies in evaluated dwellings. 201 202 3. EXPERIMENTAL TESTS 203 A total of 100 control trials were performed on masonry units (20 samples of dimensional variation, 204 20 of warping tests, 20 of compressive strength tests, 20 of suction tests and 20 of absorption 205 percentage tests) and 48 tests on prisms (24 of axial compression in piles and 24 of diagonal shear in 206 walls). The masonry units (average dimensions 0.20m x 0.10m x 0.07m) were obtained from the 207 exact study location, handmade and produced by two different producers, here named as F1 and F2. 208 209 210 211 Non-uniform mortar joint thickness x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Houses with exposed steel x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Efflorescence in the lower part of walls x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Poor vertical alignment of bricks x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Presence of cracks in mortars x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Salinity in overlays x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Poor horizontal alignment of bricks x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Lack of good brick-mortar interaction x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Deficient column-wall interaction through notching x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Cracks in confining columns x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Brick spalling or peeling of layers x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Poor quality of the bricks due to their appearance x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Detachment of particles or spalling of mortar x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Efflorescence on the wall x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Hollowness in confining beams x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Poor quality of sand in the mortar for its appearance x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Poor wall-beam interaction x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Regular sized vertical cracks x x x x x x x x x x x x x x x x x x x x x x x x x x x Walls without load bearing wall beam x x x x x x x x x x x x x x x x x x x x x x x x x Vertical or diagonal cracks along the wall x x x x x x x x x x x x x x x x x x x Wall construction at different times x x x x x x x x x x x x x x x x Unconfined earthquake-resistant walls (portal frames) x x x x x x x x x x x x x x x Regular sized diagonal cracks x x x x x x x x x x x x Column construction at different times x x x x x x x x 100%0% 20% 40% 60% 80% 𝟗𝟓% 𝟗𝟐% 𝟔𝟒% 𝟔𝟑% 𝟔𝟐% 𝟔𝟐% 𝟔𝟏% 𝟓𝟗% 𝟓𝟒% 𝟓𝟑% 𝟓𝟎% 𝟒𝟗% 𝟒𝟏% 𝟒𝟏% 𝟑𝟒% 𝟑𝟐% 𝟐𝟗% 𝟐𝟕% 𝟐𝟓% 𝟏𝟗% 𝟏𝟔% 𝟏𝟓% 𝟏𝟐% 𝟖% 12 3.1. Control tests on the units 212 The objective of the tests was to classify and determine the properties of the masonry units used in 213 this study. The control trials included both classificatory and non-classificatory tests. 214 215 3.1.1. Qualifying tests 216 For the tests, two random groups of 10 masonry units were taken per producer (a total of 20). The 217 properties related to the classification of the masonry units, according to NTE 070 (2006), are the 218 dimensional variation, warping and compressive strength tests, which were performed according to 219 the NTP 399.613 Standard. 220 The percentage of dimensional variation defines the height of the mortar courses, since the greater 221 the variation in the heights of the units, the need arises to increase the joint mortar thickness beyond 222 what is strictly necessary to achieve good adhesion (Gallegos and Casabonne 2005). The standard 223 joint thickness should be around 10 mm. NTE 070 (2006) indicates that for every 3 mm increase in 224 joint thickness, the compressive strength of the masonry and shear strength decreases by 15%. 225 Therefore, it is essential to know the dimensional variation. The test was performed on 20 units (F1 226 and F2) and consisted in measuring with a millimetre graduated ruler the three dimensions of the 227 unit (length, width and height) from the midpoints of the edges that limit each face. The warpage is 228 used to determine how concave or convex a masonry unit is. Values greater than 2 mm of warpage 229 can cause horizontal mortar joints to have hollows, hence, a poor bond between the unit and mortar 230 and lower shear strength of the wall. A total of 20 units (F1 and F2) were tested. The test consisted 231 of placing the surface of the unit on a flat table. Then, a metal ruler was placed on the diagonal of the 232 seating surface to measure the most bending part (concave or convex) using a graduated wedge. 233 Gumaste et al. (2006) indicate that the compressive strength of the brick can contribute between 25 234 to 50% of the shear strength of masonry walls. Twenty bricks (F1 and F2) were tested. The 235 compressive strength of the brick was obtained by dividing the breaking load by the gross area of the 236 brick. 237 238 239 13 3.1.2. Non-classificatory tests 240 These tests are more related to the construction procedure of masonry walls (Manchego and Pari 241 2016). For the tests, two random groups of 10 masonry units were selected, one group for each 242 producer of F1 and F2 masonry units. The suction measures the initial water absorption rate from the 243 bearing face of the masonry unit, a significant property to achieve adequate contact between the 244 mortar and the unit. For the present study, all 20 samples (F1 and F2) were tested. This property was 245 calculated as the relation between the unit's dry weight and the unit's weight after having placed it 246 for one minute inside a tray with a constant height of 3 mm of water to fill the voids of the seating 247 face of the unit with water. 248 The absorption percentage was performed to determine the amount of water contained in a masonry 249 unit, calculated through the weight of the masonry unit in dry conditions and the weight in saturated 250 conditions (after being immersed in water for 24 hours). This property is essential because the higher 251 the absorption percentage, the more porous the unit is and, therefore, the less resistant to weathering 252 (San Bartolomé 2008). 253 254 3.2. Tests on mortars 255 The compressive strength of the mortar influences masonry strength. Then, significant variability in 256 mortar strength causes variability in masonry strength (Jessop and Langan 2005). Mortar is made of 257 a mixture of fine aggregate and binders, to which a certain amount of water is added to provide a 258 workable and adhesive mixture (Manchego and Pari 2016). The mortar specimens were obtained 259 from the same mixture used for the construction of the prisms. Twelve cubes of approximately 50 260 mm on each side were formed. They were cured with water for 28 days and then tested in axial 261 compression. 262 263 3.3. Tests on masonry prisms 264 Piles and walls (prisms) are used to calculate the axial compressive strength and diagonal shear 265 strength of clay masonry, respectively. The prisms have to represent the walls as well as possible, so 266 they should be exposed to similar conditions and have the same variables (unit type, mortar dosage, 267 14 joint mortar thickness, rigging, workmanship, etc.) as the walls. To characterize the behaviour of the 268 handmade masonry walls, 48 prisms (24 piers and 24 walls) were built. In these prisms, 4 269 construction typologies were represented, the 3 typologies (T1, T2 and T3) that best represent the 270 walls of the houses (joint mortar thickness and cement dosage: sand), and the standard typology (TP) 271 with the characteristics indicated by NTE 070 (2006). For each typology, 3 specimens were built, 272 and each group was for handmade masonry units of the two producers (called F1 and F2). 273 Depending on the typology, the piles were built with 3 or 4 courses (heights between 0.30 and 0.38 274 m) and the slenderness was between 2.5 and 4. According to the NTP 399.605 (2013), the pile 275 slenderness should be between 1.3 and 5.0. 276 The small walls (called also wallets) were between 6 and 7 courses. The approximate dimensions of 277 the wall’s assemblies were 0.60 x 0.60 m, as suggested by the NTP 399.621 (2004). The ASTM 278 E519 (2021) standard suggests a minimum dimension of 1.20 x 1.20 m, but also permit walls with 279 less dimension if the testing equipment may not accommodate bigger walls. RILEM TC 76-LUM 280 (1994) considers small walls built with at least 4 courses and keeping as much as possible a squared 281 shape. Then, the adopted dimension here agrees with the revised standards. 282 The construction characteristics of the specimens of the standard typology (TP) were as follows: 283 joint mortar thickness between 10 to 15 mm and a mortar dosage of 1:4 (cement: sand). This 284 typology was built respecting the indications of NTE 070 (2006). Regarding typologies T1, T2 and 285 T3, these were built with a joint mortar thickness of 20mm, 30mm and 40mm, respectively, the three 286 of them with a mortar dosage of 1:7 (cement: sand), the dosage most commonly used in housing 287 construction in the study area. To analyze the influence of these variables, the following parameters 288 were kept constant: the type of rigging (head bond), which represents almost 95% of the walls of the 289 houses studied, the workmanship, the age of the specimens (28 days) and the testing technique. 290 Regarding the workmanship, the prisms were made by a local master builder to replicate the 291 construction reality as closely as possible. The construction procedure was as follows: before 292 construction, the units were wetted by immersing them in a bucket of water for one minute to avoid 293 too much water absorption of the mortar, prisms verticality was controlled with a plumb line and a 294 15 level, heights were controlled with a scantling (wooden ruler), the prisms were cured by watering 295 during the first 3 days as this is what is commonly done in the construction of informal dwellings. 296 The axial compressive tests and the diagonal compression tests were force-controlled due to 297 limitations in the laboratory. The load was applied trying to keep a rate velocity of 10 kN/min. Since 298 no LVDTs were placed on the samples to measure deformations, just the maximum strength in each 299 test was computed. 300 301 3.3.1. Masonry piles 302 Masonry piles are prisms composed of bricks laid one on top of the other and joined with mortar, as 303 shown in Figure 8. 28 days after their construction, the piles were tested in axial compression. Only 304 forces were measured, but deformation was not measured. This test made it possible to determine the 305 strength of the walls to vertical loads, whose stress depends on the quality of the units, mortar and 306 unit-mortar interaction. 307 a) b) 308 Figure 8. Masonry piles, a) samples, b) test set up 309 Figure 9 shows that failure in the piles was the development of vertical cracks through the units and 310 mortar. 311 a) b) d) e) 312 Figure 9. Failure mode of the tested piles, a) TP, b) T1, c) T2, and d) T3. 313 16 The average pile dimensions and maximum compressive loads recorded during the tests are detailed 314 in Table 1. 315 316 Table 1.- Average pile dimensions by type and maximum supported load. 317 Typology Dimensions in mm Pmax (kN) Length Width Height TP 201 102 325 71.86 T1 201 104 348 74.42 T2 200 103 376 56.44 T3 200 102 292 61.62 318 3.3.2. Masonry walls 319 One of the most critical situations in which a wall can be subjected to shear is in the event of a 320 seismic effect, hence the importance of knowing the mechanical behaviour of the masonry under this 321 type of stress (Tena and Miranda 2003). The test to determine this behaviour consists in applying a 322 diagonal tension to a squared wall. Two steel loading shoes were used to apply the machine load to 323 the specimen (ASTM E-519 2021). Figure 10 shows the walls constructed in this research. The 324 construction process was similar to that of the piles. During the tests, only the acting forces were 325 measured, but not the deformation of the diagonals on the wall faces. 326 a) b) 327 Figure 10. Masonry walls, a) samples, b) test set up 328 329 17 The wall failure mode was mostly by diagonal cracking and breaking bricks and mortar, as shown in 330 Figure 11. The two wooden tables along two wall sides were placed to avoid the fall of the broken 331 pieces, but they did not have interaction with the walls during the tests. 332 a) b) 333 c) d) 334 Figure 11. Failure shape of the tested walls, a) TP, b) T1, c) T2, and d) T3. 335 336 Table 2 shows the dimensions of the tested walls and the average maximum load values for each 337 type. 338 339 Table 2.- Average dimensions of the walls by type and maximum load capacity. 340 Typology Dimensions in mm Pu (KN) Length Width Height TP 578 543 200 68.76 T1 548 610 200 56.35 T2 578 583 200 50.68 T3 630 632 200 39.67 341 342 343 344 18 4. RESULTS 345 346 4.1. Control tests (classificatory and non-classificatory) 347 From the results of the classification tests, F1 bricks are classified as Type IV according to their 348 dimensional variation of 3.41%, and F2 bricks as Type III with a dimensional variation value of 349 4.17% (NTE 070 2006). Standard ITINTEC 331.017 (1978) indicates that Type IV bricks are high 350 strength and durability, suitable for rigorous service conditions and subjected to moderate exposure 351 to the elements. Type III bricks are medium strength and durable, suitable for use in low exposure to 352 weathering conditions. 353 On the other hand, according to their warping, the masonry units of both producers F1 and F2 are 354 classified as Type V, according to NTE 070 (2006). The average values for F1 were 1.40 mm convex 355 and 1.20 mm concave, and F2 bricks were 1.40 mm convex and 1.50 mm concave. ITINTEC 331.017 356 (1978) states that Type V bricks are high strength and durability, suitable for use in very rigorous 357 service conditions, and can also be subjected to moderate exposure to weathering conditions in 358 contact with heavy rain, soil and water. 359 Regarding the characteristic strength to axial compression (f'b) of the masonry units, NTE 070 360 (2006) considers 4.90 MPa as the minimum value to be considered as type I brick. The F1 bricks do 361 not classify at this minimum since their f'b was 4.61 MPa on average. On the other hand, F2 bricks 362 (6.16MPa) do classify as Type I. Type I are bricks with meagre strength and durability, which can 363 only be used under minimum requirements (1 or 2-story houses) and avoiding direct contact with 364 rain or soil, according to ITINTEC 331.017 (1978). 365 From the non-classifying tests, which are more related to construction procedures, the suction values 366 must be between 10 and 20 gr/200cm2-min. From the values achieved in the tests, none of the units 367 is in this range. Therefore, it is recommended to water the units before setting, since, otherwise, 368 adverse effects could be generated when the unit absorbs water from the mortar. Regarding the 369 absorption test, the masonry units had values lower than the maximum value of 22% indicated by 370 NTE 070 (2006). About the saturation coefficient, units with values greater than 0.85 are too porous 371 and, therefore not very durable (San Bartolomé 1994). According to the results of the test, the 372 19 masonry units do not exceed the limit, which means that they are durable and, since they have a low 373 absorption percentage, they could also be exposed to the outdoors. 374 Despite the fact that the results of the qualification tests could be good in some aspects, the structural 375 quality of the units is poor given their low f'b value, whose result varies even from one producer to 376 another (F1 and F2). 377 378 4.2. Compression tests on mortars 379 To compare the quality of the mortar used to construct the masonry prisms, cubic specimens of 380 mortar with two different dosages were made and tested. For the 1:4 dosage (cement: sand), which 381 was used for the TP standard typology, a compressive strength (f'c) of 14.4 MPa was obtained. For 382 the 1:7 dosage commonly used for housing construction in San Miguel (T1, T2 and T3), an f'c of 8.2 383 MPa was obtained (43% lower than TP). San Bartolomé (1994) mentions that the poor quality of the 384 mortar can influence the compressive strength of the masonry by 10%. Therefore, the compressive 385 strength of the mortar should be similar to that of the unit. This is to avoid its failure by crushing and 386 giving homogeneity to the masonry. 387 388 4.3. Axial compression tests on piles 389 The axial compressive strength (fm) of the piles was calculated using the following equation: 390 𝑓𝑓𝑓𝑓 = 𝐶𝐶 ∗ 𝑃𝑃𝑃𝑃á𝑥𝑥 á𝑟𝑟𝑟𝑟𝑟𝑟 391 where C represents the coefficient of correction for slenderness that varies according to the height of 392 the pile and Pmax is the maximum load applied on the prism. The value of C in this study was 0.92 393 for TP and T1; 0.94 for T2; and 0.88 for T3. The characteristic strength to the axial compression of 394 the masonry (f'm) was obtained as the average value of the samples tested (by typology) minus one 395 times the standard deviation. 396 Figure 12 shows a summary of the 24 results obtained from the axial compressive strength tests on 397 masonry piles. As can be seen, the f'm values obtained for TP did not reach the recommended value 398 by NTE 070 for handmade bricks (3.40 MPa), even though an adequate mortar was used in this 399 20 typology. It can be pointed out that this typology is the closest to the value recommended by the 400 Peruvian standard. The f'm results obtained for the other typologies (T1, T2 and T3) are lower than 401 the minimum recommended value. Therefore, the poor construction quality of the masonry walls in 402 San Miguel is demonstrated. 403 404 Figure 12. Characteristic strength to axial compression in TP, T1, T2 and T3 piles. 405 406 According to values obtained for typologies T1, T2 and T3, it can be deduced that the characteristic 407 strength to axial compression in piles is inversely proportional to the joint mortar thickness; that is, 408 as the mortar joint thickness increases, the axial compression strength decreases. As shown in Figure 409 13, the f'm value of TP (thickness e= 10 mm and mortar 1:4) is 90% of the standard f'm; of T1 (e= 20 410 mm), between 80 and 88% of the standard; of T2 (e= 30 mm), between 67 and 70% of the standard; 411 and T3 (e= 40 mm), 68% of the minimum specified value in the standard. It is also indicated that the 412 mortar used in TP had a compressive strength of 14.4 MPa, and in the others of 8.2 MPa. 413 414 Figure 13. Variation of f'm according to TP, T1, T2 and T3 mortar joint thickness. 415 416 3.09 2.95 2.29 2.24 3.12 2.72 2.39 2.30 3.40 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 TP T1 T2 T3 f'm (M Pa ) Constructive Typologies F1 F2 NTE 070 (Handmade masonry) 60% 70% 80% 90% 100% 0 10 20 30 40 50 f' m / f 'm (s ta nd ar d) Mortar joint thickness (mm) F1 F2 Mean 21 4.4. Diagonal compression tests on walls 417 ASTM E-519 (2021) and the NTP 399.621 (2004) standards defines the test method for determining 418 the diagonal tensile strength (vm) assuming uniform shear stress conditions. In this case, the 419 diagonal tensile and shear strength are the same. These standards recommends the following 420 equation for evaluating the diagonal tensile (shear) strength: 421 𝑣𝑣𝑣𝑣 = 0.707 ∗ 𝑃𝑃𝑢𝑢 𝐴𝐴𝑛𝑛 422 where Pu is the maximum force supported by the wall and An is the area of one side of the 423 specimen. The characteristic strength of the masonry to shear obtained from diagonal compression 424 wall tests (v'm) was obtained as the average value of the tested specimens (by typology) minus one 425 time the standard deviation. 426 It is important to mention that RILEM TC 76-LUM (1994) stablishes that the stress state is not 427 uniform along the diagonal of the wall. Then, there are different equations to compute the tensile and 428 shear strength. The first is obtained as 0.5 Pu/An, and the second as 0.88 Pu/An (Brignola et al. 2008). 429 As Crisci et al. (2020) mention, the tensile strength of masonry walls is lower than the one computed 430 with ASTM E-519 (2021), while the pure shear strength is higher. 431 Figure 14 shows the results obtained from the diagonal tensile strength tests on masonry walls 432 following the ASTM E-519 (2021) and NTP 399.621 (2004), no deformation gauges were used. 433 Even though the TP walls were built with a good quality mortar and respecting the thickness of the 434 joints, their v'm value did not reach the minimum value recommended by NTE 070 (2006) for 435 handmade bricks (0.50 MPa). The diagonal tensile (shear) strength values of the other typologies are 436 well below the recommended minimum. This situation is of concern since v'm is a direct value to 437 evaluate the seismic capacity of confined masonry housing. It is essential to mention that the v'm for 438 industrial bricks is 0.80 MPa according to the standard. In case to use RILEM TC 76-LUM (1994) 439 standard, the computed tensile strengths will be less than the ones reported in Figure 14. 440 22 441 Figure 14. Diagonal tensile (shear) strength characteristic for TP, T1, T2 and T3 walls 442 computed with ASTM E-519 (2021) and NTP 399.621 (2004). 443 444 Similar to piles, it can be deduced that the characteristic strength to diagonal shear in walls is 445 inversely proportional to the thickness of the mortar joint; that is, as the thickness of the joint mortar 446 increases, the diagonal shear strength decreases. Figure 15 shows that the v'm value of TP (e= 10 447 mm) is around 77% of the v'm of the standard; of T1 (e= 20 mm) 60% of the standard; of T2 (e= 30 448 mm) between 54 and 58% of the standard; and T3 (e= 40 mm), between 38 and 42% of the minimum 449 value specified in the standard. 450 451 Figure 15. Variation of v'm according to TP, T1, T2 and T3 mortar joint thickness. 452 453 5. CONCLUSIONS 454 Of all the surveyed houses, 25% have walls with joint thicknesses of 20 mm, 58% with 30 mm, 12% 455 with 40 mm, and 5% variable. In addition, the inhabitants use handmade bricks for construction. The 456 10 most common construction problems in these houses are walls with non-uniform mortar joint 457 0.38 0.30 0.29 0.19 0.39 0.31 0.27 0.21 0.50 0.00 0.10 0.20 0.30 0.40 0.50 0.60 TP T1 T2 T3 v' m (M Pa ) Constructive Typologies F1 F2 NTE 070 (Handmade masonry) 30% 40% 50% 60% 70% 80% 90% 100% 0 10 20 30 40 50 v 'm / v 'm (s ta nd ar d) Mortar joint thickness (mm) F1 F2 Mean 23 thickness, exposed steel, efflorescence in the lower part of walls, poor horizontal and vertical 458 alignment of bricks, presence of hollowness in mortar, salinity in overlays, lack of good brick-mortar 459 interaction, deficient column-wall interaction through notching, and hollowness in confining 460 elements. This demonstrates the lack of professional counselling during the design and construction 461 of housing in San Miguel and Puno in general. 462 From the results of axial compression in piles and diagonal compression in walls, it can be 463 concluded that the strength values are inversely proportional to the thickness of the mortar joints; 464 this means that the greater the thickness of the joint, the lower the strength value of the masonry. In 465 axial compression, masonry built with handmade bricks and joint thicknesses of 20, 30 or 40 mm 466 reduces its axial strength by 15, 32 and 35%, concerning the minimum value of 3.40 MPa specified 467 by the Peruvian standard. For diagonal compression, the same joints show a shear strength reduction 468 in the walls of 40, 45 and 60%, concerning the standard's minimum value of 0.50 MPa. Although in 469 masonry with a joint thickness of 10 mm and a mortar with a cement:sand ratio of 1:4, the masonry 470 strength values are below the minimum values recommended by the standard. In addition to the 471 construction problems identified during the surveys, it can be deduced that the houses in San Miguel 472 have a high seismic vulnerability and could fail and even collapse in case of an earthquake. These 473 results demonstrate the high seismic vulnerability of buildings in San Miguel and the urgent need to 474 implement training campaigns for the proper construction of seismic-resistant housing, study 475 massive forms of seismic reinforcement, and improvement of existing housing, thus mitigating the 476 seismic risk in Puno. 477 478 ACKNOWLEDGMENTS 479 The authors express their gratitude to Eng. Herson Pari, Eng. Ruben Sosa and Eng. Holger Lovon 480 for their support during the tests at the Universidad Peruana Unión, Juliaca. 481 482 483 484 485 24 REFERENCES 486 • Ahmad, N., Crowley, H., Pinho, R., Ali, Q. (2010). "Displacement-based earthquake loss 487 assessment of masonry buildings in Mansehra city, Pakistan". Journal of Earthquake 488 Engineering, 14 (S1), 1-37. https://doi.org/10.1080/13632461003651794 489 • Almeida, C., Guedes, J., Arêde, A., and Costa, A. (2014). “Shear-compressive experimental 490 behaviour of one-leaf stone masonry walls in north of Portugal”. Proceedings of the Second 491 European Conference on Earthquake Engineering and Seismology, Estambul, Turkey. 492 • Annila, P., Lahdensivu, J., Suonketo, J., Pentti, M., and Vinha, J. (2018). “Need to repair 493 moisture- and mould damage in different structures in finnish public buildings”. Journal of 494 Building Engineering, 16, 72-78, https://doi.org/10.1016/j.jobe.2017.12.010. 495 • ASTM E519 / E519M-21, Standard Test Method for Diagonal Tension (Shear) in Masonry 496 Assemblages, ASTM International, West Conshohocken, PA, 2021, www.astm.org. 497 • Astorga, A. and Rivero, P. (2009). “Patologías en las Edificaciones”. Centro de Investigación en 498 Gestión Integral de Riesgos, Venezuela. 499 • Binda, L., Baronio, G., Penazzi, D., Palma, M., and Tiraboshi, C. (2014). “Caratterizzazione Di 500 Murature in Pietra in Zona Sismica: Data-base Sulle Sezioni Murarie e Indagini Sui Materiali”. 501 Proceedings of the 9th Convegno Nazionale Ingegneria Sismica, Torino, Italy. 502 • Blondet, M., Tarque, N., and Velasquez, J. (2006). “Seismic risk assessment of informally built 503 confined masonry dwellings in Peru”. Proceedings of the First European Conference on 504 Earthquake Engineering and Seismology, 627. 505 • Blondet, M., Dueñas, M., Loaiza, C., and Flores, R. (2004). “Seismic vulnerability of informal 506 construction dwellings in Lima, Perú: preliminary diagnosis”. Proceedings of the 13th World 507 Conference on Earthquake Engineering, 2122. 508 • Bommer, J., Salazar, W., and Samayoa, R. (1998). “Riesgo sísmico en la Región Metropolitana 509 de San Salvador”. Programa Salvadoreño de Investigación sobre desarrollo y medio ambiente, 510 San Salvador. 511 https://doi.org/10.1016/j.jobe.2017.12.010 25 • Brignola, A., Frumento, S., Lagomarsino, S., and Podestà, S. (2008). “Identification of shear 512 parameters of masonry panels through the in-situ diagonal compression test”. International 513 Journal of Architectural Heritage, 3 (1), 52–73, https://doi.org/10.1080/15583050802138634. 514 • Cámara Peruana de la Construcción CAPECO (2018). “Construyendo formalidad”. 515 Construcción e Industria, Julio-Agosto de 2018. 516 • Crisci, G., Ceroni, F., and Lignola, G. P. (2020). “Comparison between Design Formulations 517 and Numerical Results for In-Plane FRCM-Strengthened Masonry Walls”. Applied Sciences, 10 518 (14), 4998, https://doi.org/10.3390/app10144998. 519 • E.070 (2006). “Reglamento Nacional de Edificaciones: Albañilería”. Ministerio de Vivienda, 520 Construcción y Saneamiento-SENCICO, Lima, Perú. 521 • Flores, E., Diaz, M., and Zavala, C. (2019). “Development of fragility function for typologies of 522 confined masonry dwelling in Metropolitan Lima and Callao cities”. Earthquake engineering 523 design and evaluation, 29 (2), 151-158, http://dx.doi.org/10.21754/tecnia.v29i2.717. 524 • Gallegos, H. and Casabonne, C. (2005). “Albañilería Estructural”. Lima - Perú: Fondo Editorial 525 de la Pontificia Universidad Católica del Perú. 526 • González, R., Aguilar, J., and Gómez, C. (2008). “Patologías constructivas de viviendas en 527 Chiapas”. Lacandonia revista de Ciencias de la Universidad de Ciencias y Artes de Chiapas, 2 528 (1), 73-86. 529 • Gumaste, K., Nanjunda, K., Venkatarama, B., and Jagadish, K. (2006). “Strength and elasticity 530 of brick masonry prisms and wallets under compression”. Material and Structures, 40(2) 241-531 253, https://doi.org/10.1617/s11527-006-9141-9. 532 • Hadzima-Nyarko, M., Pavico, G., and Lesic, M. (2016). “Seismic vulnerability of old confined 533 masonry buildings in Osijek, Croatia”. Earthquakes and Structures, 11 (4), 629 – 648, 534 https://doi.org/10.12989/eas.2016.11.4.629 . 535 • INEI, Instituto Nacional de Estadística e Informática. (2018). “Perú: Crecimiento y distribución 536 de la población total, 2017”. Lima, Perú: Censos nacionales 2017: XII de población, VII de 537 vivienda y III de comunidades indígenas. 538 https://doi.org/10.1080/15583050802138634 https://doi.org/10.3390/app10144998 http://dx.doi.org/10.21754/tecnia.v29i2.717 https://doi.org/10.1617/s11527-006-9141-9 https://doi.org/10.12989/eas.2016.11.4.629 26 • Jessop, E. and Langan, B. (2005). “Influence of mortar cube strength variability on the measured 539 compressive and flexural strengths of clay masonry prisms”. Proceedings of the Vth 540 International Brick Masonry Conference, 2, 163 - 170. 541 • Khan, F. Z., Ahmad, M. E. and Ahmad, N. (2021). “Shake table testing of confined adobe 542 masonry structures”. Earthquakes and Structures, 20(2), 149-160. 543 https://doi.org/10.12989/eas.2021.20.2.149 544 • Kuroiwa, J. (2002). “Reducción de desastres: Viviendo en armonía con la naturaleza”. Lima, 545 Perú: Programa de las Naciones Unidas para el Desarrollo (PNUD). 546 • Lovon, H., Tarque, N., Silva, V., and Yepes-Estrada, C. (2018). “Development of Fragility 547 Curves for Confined Masonry Buildings in Lima, Peru”. Earthquake Spectra, 34 (3), 548 https://doi.org/10.1193/090517EQS174M. 549 • Manchego, J. and Pari, S. (2016). “Análisis experimental de muros de albañilería confinada en 550 viviendas de baja altura en Lima, Perú”. M.S. thesis, Pontificia Universidad Católica del Perú, 551 Lima, Perú. 552 • Marques, R. and Lourenço, P. (2019). “Structural behaviour and design rules of confined 553 masonry walls: Review and proposals”. Construction and Building Materials, 217, 137-155, 554 https://doi.org/10.1016/j.conbuildmat.2019.04.266. 555 • Micelli, F., Cascardi, A., and Marsano, M. (2016). “Seismic strengthening of a theatre masonry 556 building by using active FRP wires”. In Brick and Block Masonry: Proceedings of the 16th 557 International Brick and Block Masonry Conference (pp. 753-761). Padova, Italy: CRC Press, 558 https://doi.org/10.1201/b21889. 559 • Mosqueira, M. and Tarque, N. (2005). “Recomendaciones técnicas para mejorar la seguridad 560 sísmica de viviendas de albañilería confinada de la Costa Peruana”. M.S. thesis, Pontificia 561 Universidad Católica del Perú, Lima, Perú. 562 • NTP 399.605 (2013), Norma Técnica Peruana. “Unidades de albañilería. Método de ensayo para 563 la determinación de la resistencia en compresión de prismas de albañilería”. 564 https://doi.org/10.12989/eas.2021.20.2.149 https://doi.org/10.1193/090517EQS174M https://doi.org/10.1193/090517EQS174M https://doi.org/10.1193/090517EQS174M https://doi.org/10.1016/j.conbuildmat.2019.04.266 https://doi.org/10.1201/b21889 27 • NTP 399.613 (2005), Norma Técnica Peruana. “Unidades de albañilería. Métodos de muestreo y 565 ensayo de ladrillos de arcilla usados en albañilería”. 566 • NTP 399.621 (2004), Norma Técnica Peruana. “Unidades de albañilería. Método de ensayo de 567 compresión diagonal en muretes de albañilería”. 568 • Parammal Vatteri, A. and D’Ayala, D. (2021). “Classification and seismic fragility assessment 569 of confined masonry school buildings”. Bulletin of Earthquake Engineering, 19, 2213–2263, 570 https://doi.org/10.1007/s10518-021-01061-9. 571 • Perez-Gavilan, J., Flores, L., and Alcocer, M. (2019). “An Experimental Study of Confined 572 Masonry Walls with Varying Aspect Ratios”. Earthquake Spectra, 31, 945-968, 573 https://doi.org/10.1193/090712EQS284M. 574 • Preciado, A., Ramirez, A., Santos, J., and Rodriguez, O. (2020). “Seismic vulnerability 575 assessment and reduction at a territorial scale on masonry and adobe housing by rapid 576 vulnerability indicators: the case of Tlajomulco, Mexico”. International Journal of Disaster 577 Risk Reduction, 44 (101425), https://doi.org/10.1016/j.ijdrr.2019.101425. 578 • Quiroz, L., Maruyama, Y., and Zavala, C. (2014). “Cyclic behavior of Peruvian confined 579 masonry walls and calibration of numerical model using genetic algorithms”. Engineering 580 Structures, 75, 561-756, https://doi.org/10.1016/j.engstruct.2014.06.035. 581 • Ranjbaran, F. and Kiyani, A. (2017). “Seismic vulnerability assessment of confined masonry 582 buildings based on ESDOF”. Earthquakes and Structures, 12 (5), 489-499, 583 https://doi.org/10.12989/eas.2017.12.5.489. 584 • Reddy, B., Lal, R., and Rao, K. (2009). “Influence of Joint Thickness and Mortar-Block Elastic 585 Properties on the Strenght and Stresses Developed in Soil-Cement Block Masonry”. Journal of 586 Materials in Civil Engineering, 21(10), 535-542, https://doi.org/10.1061/(ASCE)0899-587 1561(2009)21:10(535). 588 • RILEM TC. 1994. 76-LUM. Diagonal tensile strength tests of small wall specimens, 1991. In 589 RILEM, Recommendations for the Testing and Use of Constructions Materials. London: E& 590 FN SPON, 488–489. 591 https://doi.org/10.1007/s10518-021-01061-9 https://doi.org/10.1016/j.ijdrr.2019.101425 https://doi.org/10.1016/j.ijdrr.2019.101425 https://doi.org/10.1016/j.engstruct.2014.06.035 https://doi.org/10.12989/eas.2017.12.5.489 https://doi.org/10.12989/eas.2017.12.5.489 https://doi.org/10.12989/eas.2017.12.5.489 https://doi.org/10.1061/(ASCE)0899-1561(2009)21:10(535) https://doi.org/10.1061/(ASCE)0899-1561(2009)21:10(535) 28 • Ruiz-García, J. and Negrete, M. (2009). “Drift-based fragility assessment of confined masonry 592 walls in seismic zones”. Engineering Structures, 31 (1), 170-181, 593 https://doi.org/10.1016/j.engstruct.2008.08.010. 594 • San Bartolomé, A. (1994). “Construcciones de Albañilería”. Fondo Editorial de la Pontificia 595 Universidad Católica del Perú, Lima, Perú. 596 • San Bartolomé, Á. (2008). “Comentarios a la Norma E.070 ALBAÑILERÍA”. SENCICO, Lima 597 - Perú. 598 • San Bartolomé, Á., Delgado, E., and Quiun, D. (2009). “Seismic Behaviour of Two Story Model 599 of Confined Adobe Masonry”. Proceedings of the Eleventh Canadian Masonry 600 Conference.Toronto, Canada. 601 • Sánchez, V. M., González, R., Castañeda, G., García, C. M., and Aguilar, J. A. (2019). 602 “Characterization of pathologies in housing structures. A case study in the city of Tuxtla 603 Gutierrez, Chiapas, Mexico”. Journal of Building Engineering, 22, 539–548, 604 https://doi.org/10.1016/j.jobe.2019.01.014. 605 • Sathiparan, N. and Rumeshkumar, U. (2018). “Effect of moisture condition on mechanical 606 behavior of low strength brick masonry”. Journal of Building Engineering, 17, 23-31, 607 https://doi.org/10.1016/j.jobe.2018.01.015. 608 • Tena, A. and Miranda, E. (2003). “Comportamiento mecánico de la mampostería”. 609 Edificaciones de mampostería para vivienda. Fundación ICA, 4, 103-132. 610 • Varela-Rivera, J., Fernandez-Baqueiro, L., Gamboa-Villegas, J., Prieto-Coyoc, A., and Moreno-611 Herrera, J. (2019). “Flexural Behavior of Confined Masonry Walls Subjected to In-Plane Lateral 612 Loads”. Earthquake Spectra, 35 (1), 405-422, https://doi.org/10.1193/112017EQS239M. 613 • Vatteri, A. and D’Ayala, D. (2021). “Classification and seismic fragility assessment of confined 614 masonry school buildings”. Bulletin of Earthquake Engineering, 19, 2213-2263, 615 https://doi.org/10.1007/s10518-021-01061-9. 616 https://doi.org/10.1016/j.engstruct.2008.08.010 https://doi.org/10.1016/j.jobe.2019.01.014 https://doi.org/10.1016/j.jobe.2018.01.015 https://doi.org/10.1193/112017EQS239M https://doi.org/10.1193/112017EQS239M https://doi.org/10.1007/s10518-021-01061-9 https://doi.org/10.1007/s10518-021-01061-9 https://doi.org/10.1007/s10518-021-01061-9 29 • Yacila, J., Salsavilca, J., Tarque, N., and Camata, G. (2019). “Experimental assessment of 617 confined masonry walls retrofitted with SRG under lateral cyclic loads”. Engineering Structures, 618 199, 109555, https://doi.org/10.1016/j.engstruct.2019.109555. 619 • Zavala, C., Diaz, M., Flores, E., and Cardenas L. (2019). “Damage limit states for confined 620 masonry walls based on experimental test”. Journal TECNIA, 29 (2), 135 – 141, 621 https://doi.org/10.21754/tecnia.v29i2.715. 622 https://doi.org/10.1016/j.engstruct.2019.109555 https://doi.org/10.21754/tecnia.v29i2.715