Category: Kyrgyzstan

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Report # 76 : Load-bearing wall buildings protected with the “sliding belt” base isolation system

by Jacob Eisenberg, Svetlana Uranova, Marat Abdibaliev, Ulugbek T. Begaliev

Sliding belt is a base isolation system developed to protect buildings from seismic effects by reducing and limiting the level of seismic forces. The sliding belt system is installed at the base of the building between the foundation and the superstructure. The foundation is usually made of cast-in-situ concrete and the superstructure is typically a load-bearing wall structure, either a 9-story, large concrete panel system, or a 3-story brick masonry construction. Once the earthquake base shear force exceeds the level of friction force developed in the sliding belt, the building superstructure starts to slide relative to the foundation. The lateral load transferred to the superstructure is expected to be approximately equal to the frictional force that triggers the sliding of the structure. The sliding belt consists of the following elements: (a) sliding supports, including 2-mm-thick stainless steel plates attached to the foundation and 4-mm Teflon (PTFE) plates attached to the superstructure, (b) reinforced rubber restraints for horizontal displacements (horizontal stop), and (c) restraints for vertical displacements (uplift). A typical large panel building with plan dimensions 39.6 m x 10.8 m has 63 sliding supports and 70 horizontal and vertical restraints. The sliding belt scheme was developed in CNIISK Kucherenko (Moscow) around 1975. The first design application in Kyrgyzstan was made in 1982. To date, the system has been applied on over 30 buildings in Bishkek, Kyrgyzstan. All these buildings are residential buildings and are presently occupied. Base-isolated buildings of this type have not yet been exposed to the effects of damaging earthquakes.

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Report # 42 : Houses with mud walls and thatch roofs

by Svetlana Uranova, Ulugbek T. Begaliev

This building type is widespread in the rural areas of Kyrgyzstan, and also in some urban areas. It is a non-engineered construction. Due to its low cost, it is mainly used by poor people. Various building materials are used for this type of construction, e.g., clay and straw for the walls, wood for the roof structure, and stone for the foundations. In order to achieve adequate flexibility or plasticity, a small amount of clay is mixed with water. Straw is added to achieve an improved consistency. Small panel boards are used as formwork for casting mud walls. The walls are cast in lifts; a new lift is cast after the previous one has set. Windows and doors have wood lintels. Floors are made out of wood planks. Buildings of this type do not have any earthquake-resistant features and are considered to be highly vulnerable to seismic effects.

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Report # 41 : Two-story unreinforced brick masonry building with wooden floors

by Svetlana Uranova, Ulugbek T. Begaliev

This is a non-engineered construction practiced in Kyrgyzstan from 1920 to 1957. The load-bearing structure consists of unreinforced brick masonry walls and wooden floor beams. Brick masonry walls are usually constructed of mud mortar. Walls are usually perforated with rather large door and window openings. The wall length between the adjacent cross walls is on the order of 9-10 m. Wooden floor elements (beams) are not tied together and they do not behave as diaphragms. Based on the performance in past earthquakes, this building type is considered to be highly vulnerable to seismic effects.

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Report # 40 : Buildings with cast in-situ load-bearing reinforced concrete walls

by Svetlana Uranova, Ulugbek T. Begaliev, V. Manukovskiy

Buildings with cast-in-situ load-bearing reinforced concrete walls are widespread in many republics of the former Soviet Union. There are many such buildings in Kyrgyzstan in areas with a design seismicity of 8 and 9 on the MSK scale. The buildings with cast-in-situ walls are typically medium- to high-rise buildings (4-18 stories high; often 12-stories high). High-rise buildings of this type (9-18 stories high) have basements. The load-bearing structure consists of cast-in-situ reinforced concrete walls and precast reinforced concrete floor slabs. Floor slabs are either two-way solid slab structures, or, less often, hollow-core slabs. These buildings do not have any frame elements (columns and beams). Facade walls are usually made of lightweight (ceramsite) concrete. The buildings are supported by concrete strip or mat foundations. This building type is considered to be earthquake-resistant. Problems are mainly related to the quality of construction.

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Report # 39 : Reinforced concrete frame buildings without beams (seria KUB).

by Svetlana Uranova, Ulugbek T. Begaliev

Frame buildings without beams were introduced in the last decade of the Soviet Union (period 1980-1989) in some of the Soviet Republics: Kyrgyzstan, Tadjikistan, Caucasian region of Russia etc. This type of precast construction is known as seria KUB. This type of apartment buildings is usually 5-9 stories high; in some cases these buildings are 12 stories high. The load-bearing structure consists of precast reinforced concrete columns and slabs. Precast column elements are usually two stories high. Typically, column spans are equal to 6m. Precast slab elements are made of solid concrete without ribs, and the dimensions are: 3 m x 3 m X 0.16 m (length X width X thickness). Most buildings of this type have some kind of lateral load resisting elements, such as: cast-in-situ shear walls, or precast shear walls, or shear cross braces etc. All precast structural elements are combined in 3-D moment frame by means of a special joint system. Partitions are made of brick masonry or small concrete block masonry. This building type is considered to be very vulnerable in earthquakes. The seismic resistance of buildings of this type depends on the type of column-to-slab joints. Similar structures were damaged in the 1988 Spitak (Armenia) earthquake.

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Report # 38 : Prefabricated concrete panel buildings with monolithic panel joints

by Svetlana Uranova, Ulugbek T. Begaliev

Prefabricated concrete panel building construction with monolithic panel joints has been practiced throughout the former Soviet Union (including Kyrgyzstan) since 1965. This type of prefabricated construction is known as seria 105. Apartment buildings of this type are usually 5-9 stories high. The foundations are made of cast in-situ reinforced concrete. Steel dowels are provided in the foundations to ensure anchorage of steel rebars located in the panels and in the panel joints. The load-bearing structure in large panel buildings consists of reinforced concrete panels combined to form a box-type rigid system by means of special joints. This building type is considered to be one of the most earthquake-resistant construction types in the former Soviet Union.

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Report # 36 : Single-family brick masonry house

by Ulugbek T. Begaliev, Svetlana Uranova

This housing type represents a very popular single-family housing construction practice followed in Kyrgyzstan in the recent past. Approximately 80% buildings of this type, mostly those constructed after 1990, do not comply with the Building Code requirements. These are low-rise (1- to 2-story high) buildings with a complex plan and wall layout. The main load-bearing system consists of brick masonry walls in cement mortar partially confined with reinforced concrete posts and beams; columns are provided only at some wall corners and intersections. Rigid brick masonry walls have low load-carrying capacity. Wall thickness is either 380 mm or 510 mm. SNiP (Building Code) includes provisions for the horizontal wall reinforcement (welded wire mesh at the wall corners) and the provision of reinforced concrete columns at the wall corners. The floor system consists of precast reinforced concrete hollow-core slabs with typical slab panel dimensions of 5.86 m length X 1.2 m width. Reinforced concrete bond beam (belt) is constructed at the building perimeter at the floor level to provide the confinement and diaphragm action for seismic load effects. Complex building geometry and irregular wall distribution results in the significant torsional effects during earthquakes due to the eccentricity between the centre of mass and centre of stiffness. These buildings are located in the regions of high seismic hazard, which had experienced earthquakes of intensity VIII, IX or higher (per the MSK scale) in the past. This type of construction is expected to demonstrate poor seismic performance, due to the poor quality of masonry walls and complex layout resulting in torsional effects.

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Report # 35 : Traditional wood frame construction (yurta)

by Ulugbek T. Begaliev, Svetlana Uranova

This type of building is the national traditional dwelling of the Kyrgyz people. It is a light portable construction. The bearing structure of a yurta is a special wood frame, consisting of wood poles. The wood frame is covered by felt tension cloth. The floors are traditionally covered with felt rugs (koshma). Yurtas can be easily disassembled and moved to new places. They are warm in winter and cool in the summer. The buildings have only one door and one opening in the roof. Yurtas are circular in plan. The diameter is usually 4 m#6 m. This type of building is used at the present time by shepherds, particularly during the summer, for celebrations and funerals, and as temporary buildings during extreme situations in Kyrgyzstan. The yurta is a very light structure, has a symmetrical plan, and has good seismic resistance.

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Report # 34 : Buildings with hollow clay tile load-bearing walls and precast concrete floor slabs

by Ulugbek T. Begaliev, Svetlana Uranova

Buildings of this type are characterized with load-bearing masonry walls and precast concrete floors. Typical buildings of this type are 3 to 4 stories high and they are characterized with two longitudinal walls and several cross walls. There are many existing buildings of this type in Kyrgyzstan, and most of them were constructed in the 1960s. This construction practice was banned after 1966, due to the code provisions that required restriction of the size of the cores in hollow clay tiles (blocks). The exterior walls are made of hollow clay masonry tiles (blocks). In some cases there are two wall wythes: the exterior wythe made of hollow clay tiles and the interior wythe made of solid clay bricks. The floor system consists of precast reinforced concrete hollow core slabs. Buildings of this type were built in the areas with high seismic design intensity (8, 9 and higher on the MSK scale). This building type is considered to be rather vulnerable to seismic effects.

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Report # 33 : Precast reinforced concrete frame building with cruciform and linear-beam elements (Series 106)

by Ulugbek T. Begaliev, Svetlana Uranova, V. Manukovskiy

Precast reinforced concrete frame buildings (series 106) were introduced in Kyrgyzstan around 1975. These apartment buildings are usually 9 stories high; less frequently they may be 12 stories. The fundamental period of vibrations is typically in the range of 0.65-0.85 sec. Series 106 was developed by the Kyrgyz Design Institute for construction in earthquake-prone areas. Several buildings of this type (about 15 in total) were built in the capital city Bishkek (design seismicity 8 on the MSK scale). The load-bearing structure consists of a precast reinforced concrete space frame and precast floor slabs. Partition walls are constructed using clay-brick masonry units or small concrete blocks. Buildings of this type have not yet been subjected to major earthquakes. These buildings are not considered to be highly vulnerable to earthquake effects, provided that the construction quality, particularly with reference to the joints, is satisfactory. It should be noted that precast frame buildings of a different type (Series 111) performed very poorly in the 1988 Spitak (Armenia) earthquake.

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