(2) Abstract. The main objective of this study was to decrease thermal transmittance (U value) of brick masonry, with minimum cost increase and without use of insulation materials. Within the framework of this study, three new ceramic bricks were developed in order to improve the thermal performance of commonly used brick masonry in Chilean buildings. Design restrictions that keep external dimensions of bricks (14 cm) and fulfil structural requirements of Chilean standards, a country with high seismic activity,. have been taken into account. Mathematical modelling and measurements of thermal and structural properties were carried out. The new types of bricks were manufactured by a local factory of ceramic products. Laboratory measurements showed that new masonry without stucco reached a U value between 1,64 W/m2K to 1,80 W/m2K, significantly lower than 2,22 W/m2K of the reference masonry. All structural requirements were fulfilled according to Chilean standards of gravitational and seismic loads.. Key words: ceramic bricks, brick thermal performance.. Resumen. El principal objetivo de este estudio es disminuir la transmitancia térmica de la albañilería de ladrillos respecto de las utilizadas en Chile previo a la aplicación de la II fase de Reglamentación Térmica a partir de enero de 2007, incrementando al mínimo el costo de este sistema constructivo y sin adicionar materiales aislantes térmicos. En el marco de este estudio se desarrolló un nuevo tipo de ladrillo cerámico con el fin de mejorar su comportamiento térmico al compararlo con otros ladrillos de idéntico material usado en el país. Las restricciones de diseño para el ladrillo contempla el no aumentar el espesor del muro (14 cm) y cumplir con los requerimientos. estructurales existentes en las Normas chilenas. Para el desarrollo del estudio se realizó una modelación matemática para predecir cualidades térmicas y el comportamiento estructural de las albañilerías con el nuevo tipo de ladrillo. Mediciones de laboratorio mostraron que la nueva albañilería sin estuco alcanzó una transmitancia térmica entre 1,64 W/m 2K y 1,80 W/m 2K, significativamente menor que 2,22 W/m 2K presentada en la albañilería de ladrillos cerámicos de referencia. Todas los requerimientos estructurales fueron cumplidos de acuerdo a lo que establecen las Normas chilenas sobre cargas gravitacionales y cargas sísmicas.. Palabras clave: ladrillo cerámico, comportamiento térmico. páginas: 24 - 35. ]. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. Revista de la Construcción Volumen 8 No 1 - 2009. [ 25.
(3) 1. Introduction In Chile, the Thermal Regulation for housing was ratified by law in March 2000. Its first stage included roofs requirements in 7 different heating degree-day zones. As the Regulation was ratified - prompted by the Ministry of Housing and Urbanism (MINVU) of the Republic of Chile -, studies for a second stage were initiated. This new stage sets demands concerning vertical envelope (walls and windows) and ventilated floors. These demands specify a maximum U-value for walls and ventilated floors as well as a maximum window size according to their thermal behaviour. Although it was important for the country to establish a Regulation of this kind, the required standards are far away from achieving energyefficiency in residential housing. In fact, in a large part of the country (including Santiago -33°26’S; 70°41’W- with 6 million inhabitants and 40% of the population of the nation) the standard wall U-value required is 1,9 W/m2k. The standard for Concepción and Talcahuano cities (36°35’S;72°02’W), areas that include urban surroundings and representing 8,1% of the national total inhabitants, was set at 1,7 W/m2 K. However, the standard for a third urban area of central Chile, with 1.540.000 inhabitants and encompassing Valparaiso (33°01’S;71°39’W), Viña del Mar and surrounding areas, was set at 3,0 W/m2 K . A higher standard was set for the south of the country, characterized for its cold climate, reaching 0,7 W/m2K in the southernmost city in Chile, Punta Arenas (53°00’S;70°58’W), with 117.000 inhabitants . In spite of its weaknesses, the second stage of the Regulation-applied from January 2007- has challenged the building sector to modify their construction systems, particularly those based on brick masonry and reinforced concrete, to be able to comply with the required wall standards for different weather zones. The present thermal quality standards in this kind of walls are insufficient to cover the regulation requirements within most of the national territory. However, most of the available systems are economically and technically unfeasible, and alternatives used in developed countries have not yet been massively introduced in Chile.. 26 ]. Revista de la Construcción Volumen 8 No 1 - 2009. ]. Since the present U values of ceramic brick walls is slightly over the defined standards, the Ceramic Brick Industry has decided to avoid insulation materials on this type of walls, preferring the strategy of improving thermal behaviour of ceramic bricks. An experimental evaluation made within this research at the Laboratory of Building Physics of the Universidad de Bío-Bío” got U values from 2,0 to 2,48 W/m2K for different types of ceramic brick walls. In terms of building energy-efficiency and the thermal behaviour proposed by the Second Stage of the Regulation, these thermal insulation standards are considered precarious. Values established in this regulation are below U=1,9 W/m2K in 5 out of the 7 climatic zones of the country, as defined by the Ministerio de la Vivienda y Urbanismo . The need to introduce changes to the present masonry constructive systems brought about the development of the Project FONDEF D01-l1161, which was carried out by the Universidad del Bíobío, the Pontificia Universidad Católica de Chile, the Université Catholique of Louvain, Belgium, and a group of local companies. Funds were provided by FONDEF of CONICYT (National Commission for Scientific and Technological Research). The main objective of the project was to develop construction technologies to improve higrothermal performance of local brick masonry and concrete walls. This paper shows achieved innovations in the design and manufacturing of ceramic bricks, with improved thermal properties and decreased U-value. These improvements will permit its use in most of the country, fulfilling the requirements mentioned by the Second Stage of the Thermal Regulation. The project focused on the improvement of masonry thermal behaviour of bricks without the use of wall thermal insulation. Design restrictions were to keep the external dimensions of the bricks, and thus fulfil the structural requirements established by Standards in Chile, a highly seismic country. Thermal improved bricks were designed. Before producing them, its thermal behaviour was analyzed through finite elements. This theoretical analysis allowed selecting those bricks that were finally produced in a national industry. The final manufactured bricks were submitted to several lab measurements to study their thermal, as well as structural properties.. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. páginas: 24 - 35.
(4) 2. Background. made of non-porous ceramic bricks . Other studies of a porous clay brick with inner diagonal divider walls used on 40 cm thick walls, measured a U-value of 0,304 W/m2K .. Nearly a 100% of industrially produced hollow bricks made in Chile have 14 cm wide, and 29 cm length. The height changes from different manufacturers: from 7,1 to 14,0 cm. The hollowed space inside the bricks varies between 41,2% and 67,4%. Apparent density varies between 0,78 and 1,00 ton/m3.. Small size alveolus and their thickness play an important role in the reduction of heat transfer. In fact, in a study analyzing heat flow inside closed cavities with mortar, the heat transfer by convection was negligible when compared to opened cavities. The latter is the result of a mortar discontinuity, which is used to interrupt thermal bridges in a masonry wall . Big cavities help heat transfer, as shown by experiments and analysis of ceramic thermal-brick behaviour . A discussion of the negative effect of partial presence of mortar in the cavities, from a thermal point of view, was also provided in this study .. 2.1 Bricks Morphology. All ceramic bricks used in Chile have vertical perforations that comply with existing structural requirements due to the high seismic activity in the country. It is known that vertical perforated bricks have better structural performance compared to bricks with horizontal perforations . Practically all local bricks have simple orthogonal perforations with a significant number of straight transversal connections. In practice, these connections work as thermal bridges able to reduce the trajectory of the conduction flow through the thickness of the brick. This explains the low thermal quality of local masonry bricks. Figure 1 shows some ceramic bricks manufactured in Chile. Big perforations in the centre of the brick respond to the need of using this space to install concrete and structural steel bars in the wall. Bibliography shows bricks with a different morphology compared to those produced in Chile. For example, bricks with inner diagonal dividers are fully used in Europe, so as to increase the heat conduction trajectory. These divisions also allow alveolus of low thickness. Probably, their sizes are at a borderline of industrial manufacture feasibility. U-value of 0,46 W/m2K has been reached in a 40 cm thick wall. Figure 1 Bricks manufactured in Chile. 3. Methodology In order to improve thermal performance of perforated ceramic brick walls, as a first step, an experimental study of thermal behaviour of different brick masonry walls was carried out. U values of these walls, thermal conductivity of certain ceramic samples and equivalent thermal conductivity of different perforated bricks were obtained. As a second step, new morphological design of perforated bricks was defined, using the strategy of avoiding thermal bridges and increasing the trajectory of thermal conduction through inner walls of bricks. Geometrical restrictions for perforated ceramic bricks of Chilean Standards were considered. A numerical study with finite elements was made in order to define the first brick to be fabricated by a local industry. After fabrication of the first type of brick, U value of different wall samples were obtained, using a standard test method of ASTM C236 standard . Some structural properties of walls were also studied with laboratory standard methods. In order to improve some structural properties of the first type of brick, two new different designs were studied considering identical steps: numerical study with finite elements, fabrication, testing for obtaining U value of walls and testing for obtaining structural properties.. páginas: 24 - 35. ]. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. Revista de la Construcción Volumen 8 No 1 - 2009. [ 27.
(5) 4. Research 4.1 Thermal behaviour of present ceramic brick masonry walls in Chile In a first step, an extended experimental study allowed the determination of the thermal quality of ceramic brick walls available in Chile. This work was performed in the Laboratory of Building Physics, Universidad del Bío-Bío, Concepción, Chile. (Lab accredited by Chilean legislation). The universe included 105 identified masonry walls available in the market. This selection came from different wall models and materials according with official figures. Thirty types of masonry walls were selected from this universe, representing, statistically, 96% of masonry walls constructed in the country. Bricks of these walls were mainly manufactured by two of the most important ceramic brick industries of Chile. Both companies provide 85% of industrial bricks available in the national market. Apart from these, smaller manufacturers and one craftsman producer were included. The different bricks were 14 cm thick, 29 cm long, and their height varied from 7 to 14 cm. The joining mortar was 13 mm thick, and it was made of a normal dosage of sand and cement. For each of the 30 walls the U-value was measured according to the Guarded Hot Box method and following the ASTM C236 Standard . The Uvalue of all different walls varied from 2,00 and 2,48 W/m 2 K. Taking into account the relative frequency of each wall in the universe, the average U-value obtained was 2,27 W/m2K, ranging between 2,17 – 2,38 W/m2K and 95% of reliability. Equivalent thermal conductivity, λ eq (W/mK) of different local hollow bricks varies between 0,297 and 0,475 (W/mK), with an average of 0,394 (W/mK). The craft-made massive brick reached a thermal conductivity of 0,490 (W/mK).. a) Generating the less possible thermal bridges: by achieving a geometry which would give to structural bricks a minimum number of transversal inner dividing walls and a maximum number of longitudinal inner dividing walls. b) Generating a maximum thermal trajectory in the brick: by designing transversal inner-dividing walls with a geometry that forces conduction heat flow through a longer path compared to the thickness of brick. Based on the above concepts, and taking into account geometric restrictions imposed by the Chilean NCh 169 Of. 2001 standard , three types of brick were developed with geometry and physical properties that include: minimum thicknesses of inner dividing walls and header face; perforation percentages; maximum and minimum areas of alveolus and taking into consideration the manufacturing process conditions of the company involved in the industrial production (see table 1 below). In order to compare properties of the newly developed bricks, a Reference Brick (RB) was considered. This brick represents the most common type used in masonries in the country.. 4.3 Numerical modelling of bricks Heat flow was numerically modelled through finite elements in each preliminary version of bricks. The purpose of this exercise was to adjust the design and anticipate the brick’s thermal characteristics before producing them at an industrial scale.. Figure 2 Thermal trajectory (conduction) Structural Brick with Diagonal Inner Dividing Walls. 4.2. Morphological design of bricks to improve thermal performance The new proposal is based on two fundamental concepts (see Figure 2), which are mainly oriented to:. 28 ]. Revista de la Construcción Volumen 8 No 1 - 2009. ]. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. páginas: 24 - 35.
(6) Table 1 Properties of produced bricks. The heat flow was simulated under steady-state conditions, regarding the following mechanism of thermal transfer: Solid material: conduction through solid material (clay: λ = 0,49 W/mK). Cavities: conduction and radiation through perforations and alveolus, with λ = 0,025 W/mK in the case of thermal conductivity of the air and an emissivity range between 0,8 and 0,9 for cavity surfaces respectively. Convection was not considered because, as mentioned above, previous studies have established that this is negligible when perforations are small (still air) . Surfaces: external and internal surface convection and radiation were considered. Temperatures taken in account: internal 298 K and external 274 K; surface resistance Rsi = 0,12 m2K/W in the case of the internal surface and Rse = 0,05 m2K/W in the. case of the external surface, according with standard Chilean NCh 853 Of. 91 . Numerical modelling simulations for walls with each type of brick are shown in Table 1. U values for walls without steel reinforcement, as in confined masonry, were estimated. To estimate the thermal bridge impact due to steel bars, U values of reinforced masonry walls were also analyzed (see Figure 3). This case considers steel through big cavities within bricks, filled with cement mortar. In both cases, estimation of U value takes into account only the brick zone of the wall and not the foundation and bond beam. It is important to mention that Chilean thermal regulation of residential buildings does not specify thermal requirements for bond beam and foundations.. Figure 3 Reinforced concrete wall. páginas: 24 - 35. ]. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. Revista de la Construcción Volumen 8 No 1 - 2009. [ 29.
(7) Table 2 shows estimated U values of the four different masonry walls. In case of confined masonry (CM1 and CM2), mathematical modelling estimations showed lower U values than measured ones. These differences –less than 5%–, may be explained by the model’s own limitations. For example, it does not take into account the possibility of cement mortar incorporation into the cavities. According to other experiments carried out in this field , the impact of incorporating some cement mortar in perforations during construction process is thermally more relevant than an eventual airflow in the hollow cavities. According to figures of Table 2, U values of reinforced masonry are between 3 and 4% higher than respective confined masonry walls.. 4.4 Laboratory measurements of developed bricks An industry representing approximately 35% of the national brick market, fabricated the new brick in its structural version. Measurements, to determine Uvalue and mechanic properties of masonry specimens prepared with the 3 different types of bricks developed during this research, were carried out according to Chilean and international standards. Mechanical. properties were measured in the Material Laboratory of DECON of the Pontificia Universidad Católica de Chile and U values were measured at the Laboratory of Building Physics of the Universidad del Bío-Bío, Chile. The joining mortar thickness of masonry was 13 mm. Measurements did not consider stucco in walls. Wall thickness was 14 cm in all cases.. 5. Laboratory procedures and results 5.1 U-value Figure 4 shows the variation of U-value of a masonry wall with respect to the type of brick used. Version 2 of the DIDW&S (Diagonal Inner Dividing Walls & Structural) brick masonry reached a U-value that was 26% below the value of the Reference Brick (RB). All DIDW&S brick versions produced reduced U-values when compared to RB. These measurements were made in a calibrated hot box chamber according to ASTM C236 standard . Figure 4 shows that the three versions DIDW&S bricks have U-values below the requirements established by the Chilean Housing Regulations for Santiago and, version 2 (DIDW&S2) even fulfils those of the city of Concepción.. Table 2 Estimated U values of different masonry wall. 30 ]. Revista de la Construcción Volumen 8 No 1 - 2009. ]. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. páginas: 24 - 35.
(8) 5.2. Compression Strength of individual bricks. Figure 4 U-value Experiment results. Figure 5 shows that version 1 of DIDW&S bricks have a high compression strength compared with the RB. This is due to a significant increment of solid area, which gives a higher strength (from 54,4% goes up to 61,8%). All DIDW&S brick versions are above the required Chilean standard NCh 169 Of2001, for Grade 1 bricks . Measurements were made according to NCh 167 Of 2001 standard. (Construction-ceramic bricks tests) .. 5.3 Shear strength of the brick–mortar interface. Figure 5 Compression strength of individual bricks Experiment results. Figure 6 shows that all three versions of DIDW&S bricks have a higher bond compared to the RB. Best results are shown by versions 1 & 2. All DIDW&S brick versions fulfil the requirements of the Chilean Standard: NCh 169 for Grade 1 bricks. Measurements were made according to NCh 167 Of 2001. (Construction-ceramic bricks tests) .. 5.4. Walls’ Compression Strength. Note Grade1 brick: With minimum compression strength of 15 MPa. MqP: An industrial brick with a perforation percentage below 50%.. Figure 6 Shear Strength of the brick–mortar interface Experiment results. páginas: 24 - 35. ]. Figure 7 shows measurements results observed masonry prism samples exposed to compression. Results obtained for walls built with version 1 & 2 DIDW&S bricks are satisfactory. Values similar to those of the RB were reached. Measurements were made according to NCh 1928 Of 2003 standard. (Reinforced masonry-Requirements for structural design) . Figure 8 shows testing installation.. Figure 7 Prisms compression strength Experiment results. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. Revista de la Construcción Volumen 8 No 1 - 2009. [ 31.
(9) Figure 8 Prism compression strength installation. Figure 9 Strength to prisms diagonal compression Experiment results. Figure 10 Strength to diagonal compression of wall testing equipment. 5.5 Strength to diagonal compression of walls Figure 9 shows that all three versions of DIDW&S bricks have a considerable higher level of shear strength compared with the RB testing samples. Average diagonal compression strength was 35% higher. Measurements were made according to NCh 2123 Of 2003 standard. (Confined masonryRequirements for structural design) . Figure 10 shows the testing equipment utilized in this standard. Prismatic resistance to compression strength and prismatic resistance to diagonal compression strength are fundamental tests to predict masonry wall performance under gravitational loads and/or seismic loads. According to results obtained by Lüders, Hidalgo y Diez [12,13], tests of lateral cyclical loads on bricks of RB type showed that maximum shear strength resistance is 34% lower than the one obtained by static load tests. Extrapolating this result to the DIDW&S brick masonry (without steel bars in both directions), maximum shear strength resistance under cyclical load would be around 0,61MPa.. 32 ]. Revista de la Construcción Volumen 8 No 1 - 2009. ]. 5.6 Strength to lateral impact Problems were observed when the units were exposed to lateral load during the storing process i.e. part of the bottom bricks were fractured while piling. This made necessary the study lateral mechanical properties; this is to say, under the action of perpendicular loads to the wall surface. Impact test were carried out and the bricks were exposed to uniform lateral load. Impact tests were directed to the centre and edges of the bricks. A 529 gr steel ball was dropped from different heights until fractures appeared.. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. páginas: 24 - 35.
(10) Figure 11 shows lateral load impact experiment results. When impact was applied to the edges, results of DIDW&S three versions were similar to those of the RB. Nevertheless, version 1 central area showed an important decrease to the impact strength. For this reason, the central area was reinforced, and this generated versions 2 & 3 of the DIDW&S bricks. Transversal inner dividing walls were introduced; these partially help to improve the impact strength, as shown by results from versions 2 & 3. In spite of this, the strength level at the centre did not reach the strength of the RB. A considerable improvement in performance would be expected if the lateral faces work as a slab, compared to performances where the lateral face works as a beam as in the case of lab measurements.. problems of the wall surface when exposed to normal loads. However, it is believed that a 2MPa strength to lateral load is sufficient to adequately resist normal loads on wall surfaces, which generally acts as a building structure. Moreover, strength to lateral load should considerably improve if external walls of bricks work as a slab while locked up by the mortar.. 5.8 Perforation percentage of analyzed units Figure 13 shows perforation % changes of all brick versions. All developed versions showed a lower perforation percentage compared with the RB. The increase in the amount of clay used is a disadvantage due to rises in direct costs of production. Figure 12 Strength to lateral load Experiment results. 5.7 Strength to transversal load A second measurement with the DIDW&S brick used a static and a uniform load over a lateral face, simulating a normal load over the wall surface (see following figure). Results are shown in Figure 12. Figure 12 shows that all three versions of the DIDW&S brick type have reduced strength to lateral load when compared with the reference brick (RB). Results obtained are 50% below those of the RB. Incorporating transversal inner brick dividing walls did not make a significant improvement with respect to lateral load strength. This brought about structural performance Figure 11 Strength to lateral impact Experimental results. páginas: 24 - 35. ]. Figure 13 Brick perforation percentage. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. Revista de la Construcción Volumen 8 No 1 - 2009. [ 33.
(11) 6. Conclusions Experimental and numerical methods have been used to improve the thermal performance of ceramic bricks normally used in Chile. This thermal improvement was made considering structural requirements and geometric restrictions imposed by Chilean standards. Manufacturing feasibility of the new bricks was also taken into account. To prevent significant increases in cost of masonry, thickness of new bricks is 14 cm, as actual bricks manufactured in the country. Masonry walls with new bricks of identical external dimensions showed a lower thermal transmittance (U value) than a reference wall constructed with a ceramic brick normally used in the country. Laboratory measurements showed that the new masonry reached a U value between 1,64 W/m2K to 1,80 W/m2K, significantly lower than 2,22 W/m2K of the reference masonry. The U value decrease was achieved by increasing the trajectory of thermal conduction with diagonal inner dividing walls within the bricks. This diagonal trajectory creates small cavities in bricks, where. 34 ]. Revista de la Construcción Volumen 8 No 1 - 2009. ]. convection heat-transfer is practically negligible. In other words, geometry of alveolus and dividing walls of bricks generate an important impact in thermal performance of brick masonry. Structural results - even if they show a reduction of some mechanical properties compared with the reference brick masonry- widely fulfil the present constructions standards of masonry in Chile. Results show that all three new developed bricks fulfil the Chilean 2007 Thermal Regulations for Santiago and Valparaíso. In one case (version 2 of DIDW&S), U value allows fulfilment of requirements of not only Santiago and Valparaiso, but also Concepción. These cities are the most important urban centres of Chile. It is important to mention that diagonal compression resistance of DIDW&S brick masonry – a fundamental property for seismic design - is higher than the RB manufactured in Chile. Therefore, bricks developed within this research are expected to show an appropriate performance under horizontal cyclical events. Nevertheless, dynamic tests are recommended to verify such assessment.. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. páginas: 24 - 35.
(12) References. 7.. Instituto Nacional de Normalización. NCh 169.Of2001 Standard. Building Construction - Ceramic Bricks Classification and requirements.. 1.. Instituto de la Construcción. Manual de Aplicación de la Reglamentación Térmica. Instituto de la Construcción. Santiago de Chile. 2006.. 8.. 2.. B. Lancarrierre, B. Lartigue; F. Monchoux. Numerical study of heat transfer in a wall of vertically perforated bricks: influence of assembly method. Energy and Building 35 (2003) 229-237.. Instituto Nacional de Normalización. NCh 853.Of1991 Standard. Thermal conditioning - Thermal envelope of buildings - Thermal resistance and transmittance calculation.. 9.. Instituto Nacional de Normalización. NCh 167.Of2001 Standard. Construction. Ceramic Bricks - Test.. 3.. J.P. Oliva. L’isolation écologique. Conception, matériaux, mise en œuvre. Terre vivante. Mens, France. 2001. 10. Instituto Nacional de Normalización. NCh 1928. Of2003 Standard. Reinforced Masonry – Requirements for Structural Design.. 4.. K. Ghazi Waliki, Ch Tanner. U-value of a dried wall made of perforated porous clay bricks. Hot box measurements versus numerical analysis. Energy and Building 35 (2003) 675-680.. 11. Instituto Nacional de Normalización. NCh 2123. Of2003 Standard. Confined Masonry – Requirements for Structural Design.. 5.. M. Sait Söylemez. On the effective thermal conductivity of building bricks. Building and Environment 34 (1999) 1-5.. 6.. American Society for Testing Materials. ASTM C 236. Standard Test Method for Steady-State Thermal Performance of Building Assemblies by Means of a Guarded Hot Box.. páginas: 24 - 35. ]. 12. Hidalgo P.; Jordán R.; Lüders C. Comportamiento sísmico de edificios de albañilería armada diseñados con las normas chilenas. Departamento de Ingeniería Estructural DIE-Nº 85-1. Escuela de Ingeniería, Pontificia Universidad Católica de Chile. Enero 1985. Santiago, Chile. 13. Lüders C.; Hidalgo P. Modos de falla en muros de albañilería armada sometidas a cargas horizontales cíclicas. 3a Conferencia Latinoamericana de Ingeniería Sismorresistente. Septiembre 1984. Guayaquil, Ecuador.. Bustamante, W. - Bobadilla, A. - Navarrete, B. Vidal, S. - Saelzer, G.. [. Revista de la Construcción Volumen 8 No 1 - 2009. [ 35.