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Report # 104 : Adobe House

September 15, 2011 By

by Mehrdad Mehrain, Farzad Naeim

This building type is typically one or two stories and used for single-family housing. It is more predominant in the desert, in cold-weather, or other inhospitable climates. It has a large mass and basically no strength, particularly against out-of-plane wall forces. These buildings are the most seismically vulnerable. In the 2003 Bam earthquake, collapse of these buildings was widespread and contributed to many of the 43,000+ deaths. The typical mode of collapse is out-of-plane failure of the walls, resulting in loss of support for the roof. Adobe construction is widespread throughout Iran, and is used both by wealthy families in luxury residences, as well as by poor families in more modest dwellings.

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Filed Under: Adobe / Earthen, Asia & Mideast, Iran

Report # 114 : Stonework building with wooden timber roof

September 15, 2011 By

by Masoud N. Ahari, Alireza Azarbakht

Stonework buildings are a common type of rural construction in many parts of Iran (Figure 32). It is widely used in the mountainous areas because of the ease of attaining the building material. More than 71,000 stonework buildings were built in 1968-1972 in comparison to 54,000 brick masonry buildings in these years [1]. Unfortunately these buildings are often found in highly seismic parts of Iran (see maps on WHE webpage for Iran). Buildings of this type are up to two stories high, with height/width aspect ratio on the order of 0.3-0.5. The building materials consists of stone, wood, mud mortar and straw. The major elements of these systems are stonewalls which carry both gravity and lateral loads. These walls consist of stone or stone ballast with mud mortar and straw. For reasons of thermal insulation the thickness of these walls is not less than 50 centimeters (usually 70 centimeters). Details of wall are shown in Figures 11 to 20. The roof includes wooden joists and a set of secondary joists which are plastered with a thick layer of mud (Figures 21 and 22). Different views of this kind of building are shown in Figures 1 to 3. Also a typical building view, plan and layout are shown in Figures 4 to 10. Weak points of this construction type are: the presence of a heavy roof; inadequate behavior of the walls under out-of-plain forces (Figures 23 and 24); poor shear capacity of the mortar; inadequate connection between roof and walls; inadequate connection between intersecting walls; and lack of diaphragm action in floors and roof where the roof elements (wooden beams) do not work together in earthquakes and may collapse (Figures 25 and 27). In general, this kind of structure is frequently used as a house and stable in mountainous villages, but its earthquake performance is not acceptable. Any proper rehabilitation techniques may save many people’s lives.

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Filed Under: Asia & Mideast, Iran, Masonry, Stone Masonry

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

September 15, 2011 By

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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Filed Under: Asia & Mideast, Iran, Masonry, Unreinforced Masonry

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

September 15, 2011 By

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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Filed Under: Asia & Mideast, Iran, Masonry, Unreinforced Masonry

Report # 27 : Confined brick masonry building with concrete tie columns and beams

August 18, 2011 By

by Behrokh H. Hashemi, Faramarz Alemi, Mohsen G. Ashtiany

This is a typical confined brick masonry housing construction common in rural areas of Iran. This building type is often used as a single-family house. Brick masonry shear walls confined with concrete tie columns and beams provide earthquake resistance in both directions. This building type is expected to have good seismic performance.

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Filed Under: Asia & Mideast, Confined Masonry, Iran, Masonry

Report # 26 : Semi-rigid steel frame with “Khorjinee” connections

August 18, 2011 By

by Behrokh H. Hashemi, Mohsen G. Ashtiany

This housing type is commonly used for low-rise building construction in Iran, mainly for family apartment buildings. This structure is characterized with a special type of semi-rigid beam-to-column connection called “Khorjinee connection.” This connection consists of a pair of continuous beams spanning over several columns and connected to the column sides by means of angle sections. Beam and column are welded to the angle section. A major problem with the Khorjinee connection is that it is very difficult to improve the rigidity of the connection in the weak direction (the direction perpendicular to the connection) since the crossed beams are connected to the web of Khorjinee beams. Thus, in the weak direction of the frames, the connections are considered as pinned (hinges) and the bracing is used to resist seismic loads. However, in the Khorjinee direction, since the possibility of using the bracing is very limited, the frame is considered a rigid structure. Also, out-of-plane partial beam-to-column transfer of bending moment and early onset of failure in the angles are the most likely causes of failure for a building subjected to lateral earthquake loads. These buildings are vulnerable in earthquakes (e.g., 1990 Manjil earthquake).

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Filed Under: Asia & Mideast, Iran, Steel, Steel Braced Frame

Report # 25 : Steel frame with semi-rigid “Khorjini” connections and jack arch roof “Taagh-e-Zarbi”.

August 18, 2011 By

by Arzhang Alimoradi

This is a common type of urban/rural construction in many parts of Iran. It is widely used in the cities as a popular structural system for low-rise residential buildings because of the ease of construction and of erecting the frame. Buildings of this type are up to 5 stories high, with a height/width aspect ratio on the order of 1.5. This system consists of a special kind of steel framing with heavy brick infills as partitions. Roof girders are connected to the supporting columns by means of semi-rigid connections. Diaphragms may range from flexible to rigid depending on the detailing and the construction quality. The structure is extremely heavy because of the brick infills between the roof beams. The roof is constructed in the form of a shallow arch called a ‘jack arch’. Roofs, ceilings, and floors constructed in this way contributed to building failures and to an unusually high death toll in many recent earthquakes in Iran. As many as half the buildings completed in the early 1970s in Iran had jack arches. In a jack arch system, steel beams or a reinforced concrete joist system span the distance between the main girders across the length of the building. An arch made of small bricks connect the beams. Each arch rises only about ten centimeters. The ‘valleys’ of this wave-like surface are filled with mortar. The completed ceiling, roof, or floor is thick and heavy. Frequently the steel support beams are not tied together properly or are left untied (From: http://www.johnmartin.com/eqshow/647014_00.htm). Seismic vulnerability of this system is observed as medium to high. The dynamic behavior of the system in the two main perpendicular directions of the building plan differs significantly because of the differences in the stiffness and configuration of the connections in these two directions. Furthermore, ‘X’ bracings are usually used in the weak direction which further magnifies the non-uniform behavior of the structural system.

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Filed Under: Asia & Mideast, Iran, Steel, Steel Moment Frame