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Report # 118 : Earring system (Shekanj) in dome-roof structures with unreinforced brick and adobe materials

by Nima T. Bekloo

This building structure derives its name from the four earrings that are constructed at the four corners of a rectangular building at the spring level of dome roof. This structural system was developed due to the lack of of wood and stone. It was widely constructed more than 3 thousand years ago, after the invention of the dome-roof structures in the Old Persian Empire (Ashkanian & Sasanian). The main problem with the dome-roof building was to transform the rectangular or polygonal plan of the group of walls into the circular plan at the spring level of dome roof. They used to construct the first row of dome and then construct another row on top of previous one with a little offset closer to the center of the dome circle and so on. That was too difficult to construct. This system was invented to resolve this problem. In this system, once the walls were constructed, four earrings (shekanj) built upon four corners of walls intersections, and then it was much easier to build a dome over these. It is an ideal system to resist vertical and gravity loads and transform them into horizontal and shear loads. For lateral loads, domes behave like trusses and distribute the load to the other parts of the structure creating a perfect load path.

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Report # 117 : Four arches (Char taaqi) with dome-roof structures, and unreinforced brick and adobe materials.

by Nima T. Bekloo

The ‘Four arches’ or Char Taaqi (in Persian) derives its name from the four arches that connects tops of four timber or masonry piers enclosing the space. It is an equilateral architectural unit consisting of four arches or short Barrel vaults between four corner piers, with a dome over the central square; this square and the lateral bays under the arches or barrel vaults together constitute a room of cruciform ground plan. This structural system developed about 2500 years ago, after earring system in the Old Persian Empire (Sasanian age). Main goal of this building system was to create wide openings at four side of the structure. This building system was used for special places that carry high population like fire temple (place where Persians worshiped the Fire God), mosque, bazaar and other public places. This is not that difficult to built a dome over four arches. Further, dome structures are ideal for large span structures against gravity loads as it transforms them into horizontal and shear loads. In addition, for lateral loads, domes behave like a truss and distribute the load to other parts of the structure developing a perfect load path. This construction system has been considered, the most prominent structural system in traditional Iranian architecture. These are basically monumental buildings developed close to desert where there was not enough construction materials that could take tensile stresses.

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Report # 160 : Combined and Confined Masonry Construction

by Arturo Tena-Colunga, Artemio Juárez-Ángeles, Victor Hugo Salinas-Vallejo

It is defined as combined and confined masonry structures those where the bearing/seismic walls are made by alternating courses of lightweight concrete blocks (inexpensive in Mexico) with courses of fired clay bricks (more expensive) and they are confined with cast-in place reinforced-concrete tie-beams and tie-columns (Figure 1). The impact of confining elements in masonry walls includes: a) enhancing their stability and integrity for in-plane and out-of-plane earthquake loads, b) enhancing their strength (resistance) under lateral earthquake loads and, c) reducing their brittleness under earthquake loads and hence improving their earthquake performance. Although combined masonry construction has historical background in Mexico and worldwide (i.e., Tena-Colunga et al. 2009), combined and confined masonry became popular in recent times by the initiative of the inhabitants of the central Mexican states of Puebla, Tlaxcala and Oaxaca. This modern version of combined and confined masonry has been used since the early 1990s. Different arrangements to combine and alternate brick courses with block courses have been used (Juárez-Angeles 2009, Salinas-Vallejo 2009), but the one that it is most commonly used is the one depicted in Figure 1, where three courses of clay bricks alternate with a course of concrete blocks. Usually, this type of construction is being used for housing in rural and urban regions of Mexico, but it has also being used for warehouses and apartment buildings up to three stories high. The most common floor systems used with combined and confined masonry are: a) cast-in-place reinforced-concrete slabs 10 to 12 cm thick and, b) precast beams with concrete block infill and concrete topping (cast-in-place) and, c) cast-in-place waffle flat slab with polystyrene infill. Because of the poor quality of the concrete blocks produced in the central regions of Mexico, combined and confined masonry walls have similar behavior but lower shear strength and ductility compared to traditional confined masonry walls made of fired clay bricks only (Tena-Colunga et al. 2009). Nevertheless, these structures have had good performances during moderate and strong earthquakes, such as the M=6.5 June 15, 1999 Tehuacán earthquake and the M=7.6 January 21, 2003 Tecomán earthquake.

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Report # 159 : Reinforced concrete buildings in Pakistan

by Yasir Irfan Badrashi, Qaisar Ali, Mohammad Ashraf

This report addresses reinforced-concrete buildings in Pakistan. Due to the rapid urbanization in Pakistan in the recent past and consequently the scarcity and inflated cost of land in the major cities, builders have been forced to resort to the construction of reinforced-concrete buildings both for commercial and residential purposes. It is estimated that reinforced-concrete buildings constitute 10 to 15% of the total building stock in the major cities of Pakistan and this percentage is on the rise. However, construction of reinforced concrete buildings in Pakistan is still in nascent stage with construction procedures lacking compliance with the established construction procedures. This report is based on survey of the building stock of 5 major cities in Pakistan and hence provides a realistic picture of construction of reinforced-concrete buildings in Pakistan. The statistics provided in this report are based on personal observation of the authors as well as opinion of professionals working in the construction industry who were interviewed in the course of this survey.

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Report # 156 : Typical Single-Story Residential Construction Practices in Trinidad and Tobago

by Richard P. Clarke, Rakesh Ramnath

Typical single-story residential construction in Trinidad and Tobago comprises 100 mm thick unreinforced clay tile or concrete block masonry (URM) load-bearing walls supporting the roof. The roofing is a 20 to 30 degree gable or hipped shape and is of approximately 0.2 to 0.5 kN/m2 in weight. It comprises galvanized steel sheets supported by timber laths or cold-formed steel Z-purlins, in turn supported by timber or structural steel rafters. The rafters are nailed or bolted to the top of the walls, without blocking between the rafters. The flexible roof cannot act as a diaphragm. The soil class ranges from IBC classes B to E. Given the significant seismic hazard for Trinidad and Tobago, (i.e. rock PGA in the range of 0.2g to 0.6g for 10% exceedance probability in 50 years), this form of residential construction is quite vulnerable.

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Report # 152 : Base Isolation of Confined Masonry

by Noemi Graciela Maldonado, Dr. Miguel Eduardo Tornello

Most of Argentine Republic territory may be considered seismic.Great Mendoza is an important social-economic area in the mid- western region and it has the greatest seismic risk in the country. In the last 200 years or so, there have been important earthquakes affecting building structures. Consequently, new techniques aimed at controlling vulnerability must be developed. Methodology: An investigation of the actual application of Basal Seismic Isolation (BSI) on a building ‘Students’ House’ belonging to the Technological National University (UTN) is implemented. Research of the isolation system for near source motions has been done. The construction of three modules of student houses has been done in 2004, with confined masonry and reinforced concrete for three levels and prestressed slabs. Both buildings have accelerometers to register earthquake effects. The complex is completed with a building of two levels for administration with confined masonry. The aim is to control BSI displacement. The strategy proposed was to add damping to the isolation system within certain limits and the results are compared to similar fixed base building. To control near source displacements, additional damping is an applicable and economic strategy. Although with this strategy there is increased acceleration , it is far less than in the case of fixed base building

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Report # 150 : Timber-reinforced Stone Masonry (Koti Banal Architecture) of Uttarakhand and Himachal Pradesh, Northern India

by Piyoosh Rautela, Girish Chandra Joshi, Yogendra Singh, Dominik Lang

Despite being located in a high seismic risk area, a region in the Himalayan states of Uttarakhand and Himachal Pradesh (Northern India) exhibits an elaborate tradition of constructing multistoried houses. In the Rajgarhi area of Uttarkashi district (Uttarakhand) a large number of intact buildings of the distinct construction type known as Koti Banal can be found. Koti Banal is the name of a village in the Yamuna Valley which represents the traditional knowledge and understanding of earthquake effects on buildings and their earthquake resistant design. Investigations suggest that the region had evolved this elaborate and magnificent earthquake-safe construction style as early as 1,000 years before present. This architectural style further demonstrates the existence of elaborate construction procedures based on principles somewhat akin to that of blockhouse construction. Many features of these buildings are considered as the basics of modern earthquake-resistant design. Generally, ornate multistoried houses with abundant use of wooden beams are characteristic of Rajgarhi area. For buildings of the Koti Banal architecture, locally available building materials such as long thick wooden logs, stones and slates were judiciously used. The height of these structures varies between 7 and 12 m above the base platform which consists of dry stones. These structures are observed to have four (Chaukhat) to five (Panchapura) stories. It is reported that especially buildings of the Koti Banal architecture withstood and performed well during many past damaging earthquakes in the region. In a report on the effects of the 1905 Kangra earthquake (M 7.8), Middlemiss (1910) already describes the well performance of these ?(..) top-heavy constructions? located along steep slopes of the Kangra-Kulu epicentral area, which differed ?entirely from the sun-dried brick-built structures of the Kangra Valley. The performance of these structures has also been corroborated by eye-witness accounts during the 1991 Uttarkashi earthquake which had a magnitude of mb 6.6 in an epicentral distance of 30 km during which many new buildings collapsed while these structures did not suffer any damage. The reasons that these buildings outlived so many centuries mainly lie in their structural configuration which clearly demonstrate that their builders already had the idea of dynamic earthquake actions, particularly out-of-plane failure of masonry walls. The buildings are further characterized by a number of advantageous design features such as regular plan shapes, the sensible use of locally available building materials, the integration of wooden beams over the total height of the building as well as small openings and the arrangement of shear walls.

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Report # 148 : Vivienda de Minifalda (Wooden houses with heavy bases)

by Dominik Lang, Alvaro Amador, Lisa Holliday, Claudio Romero L, Armando Ugarte

The term ‘minifalda’, translated ‘miniskirt’ refers to the building’s walls which consist of masonry or concrete in the lower part, while the upper part is made of a light wood construction (also ‘madera y concreto’). According to a recent population census carried out in 2005 (INEC, 2006), the total percentage of minifalda houses in Nicaragua was around 7% (8% in urban and 5.6% in rural areas). In the year 1998, minifalda represented 9.8% of the total houses in Nicaragua (12.8% in urban and 6.1% in rural areas; according to OPAS, 2001). Comparing the two numbers, it shows that the rate of this construction type on the total building stock in Nicaragua has reduced considerably. The combination of a more stable and consolidated base made of concrete or masonry and a light and flexible upper part of the walls made of wood frame construction, provides these houses with some advantages. However, the heavy roofs, which consist mostly of tiles, increase the vulnerability of the buildings especially during earthquake action.

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Report # 147 : Traditional Naga Type House

by Amir Ali Khan

The housing type is most common throughout the Northeast India which lies in the most severe seismic zone of the country (Zone V – corresponding to MSK IX). Majority of this type of houses are used for residential purposes. Typically these houses are built with light weight locally available material like bamboo, wooden planks, thatch etc. These housing types have traditional system of bamboo/wooden posts. Bamboo posts are inserted into the ground to act as compression members and are tied with horizontal bamboo/wooden girders with the help of bamboo ropes (cane) to give a proper shape and framing action. However, there is no protection of bamboo/wooden posts against decaying/termites or any other natural cause. The performance of these houses during the past earthquakes is unknown. However, during the discussions with local people about the performance of these houses in the past major earthquakes, it was noted that the majority of houses survived.

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Report # 145 : Pillar walaghar (URM infilled RC frame buildings)

by Yukta Bilas Marhatta, Jitendra K Bothara, Meen Bahadur Magar, Gopal Chapagain

This building type is widely constructed in the urban and semi-urban area of Nepal. It has all the characteristics of a vernacular building only with the exception that few of the construction materials are not local. It is one of the most emerging building typologies in Nepal. This is mostly non-engineered building typology. However, in urban areas sometimes competent structural engineers are also involved in the design. This technology was picked up after its relatively better performance during 1988 Udaypur earthquake which recorded M6.4 on Richter scale, that severely hit eastern Nepal. In this type of building a lightly reinforced frame is constructed first and then infill walls are erected later between columns. Though not usual, sometimes walls are constructed first and columns and beams later. These buildings serve multifunctional purposes such as residential, commercial, official, religious, educational, etc. These buildings are highly vulnerable to earthquake because of deficient detailing, inferior construction materials and the inadequate technology employed. Despite the use of modern materials of construction there is an ever growing risk to life and property due to potential earthquake attack. This building type, if designed and constructed properly, is suitable for low rise buildings up to 3 to 4 stories high. It is necessary to disseminate simple techniques of earthquake resistant measures for these buildings to the grass-root level.

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