Report: 33

Building Type: Precast reinforced concrete frame building with cruciform and linear-beam elements (Series 106)

Country: Kyrgyzstan

Author(s): Ulugbek T. Begaliev, Svetlana Uranova, Manukovskiy V.

Last Updated:

Regions Where Found: Buildings of this construction type can be found in Bishkek (the capital of Kyrgyzstan). This type of housing construction is commonly found in urban areas.

Summary: Precast reinforced concrete frame buildings (series 106) were introduced in Kyrgyzstan around 1975. This type of apartment building is usually 9-stories high; less frequently, they may be 12 stories. The fundamental period of vibrations is typically in the range from 0.65-0.85 sec. Series 106 was developed by the Kyrgyz Design Institute for construction in seismically-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.

Length of time practiced: 25-60 years

Still Practiced: Yes

In practice as of:

Building Occupancy: Residential, 50+ units

Typical number of stories: 9-12

Terrain-Flat: Typically

Terrain-Sloped: 3

Comments:

Plan Shape: Rectangular, solid

Additional comments on plan shape: Typical shape of a building plan for this housing type is rectangular form with some modifications at the perimeter.

Typical plan length (meters): 18

Typical plan width (meters): 12

Typical story height (meters): 3

Type of Structural System: Structural Concrete: Precast Concrete: Moment frame

Additional comments on structural system: Lateral load-resisting system: The lateral load-resisting system is moment-resisting concrete frame. The load-bearing structure consists of a precast reinforced concrete space frame and precast floor slabs. The space frame (with column spans of 6 m) is constructed using two main modular elements: cruciform element and linear-beam element. The cruciform element consists of the transverse frame joint with half of the adjacent beam and column lengths. The longitudinal frames are constructed by installing the precast beam elements in-between the transverse frame joints. The precast elements are joined by welding of the projected reinforcement bars (dowels) and casting the concrete in-situ. Joints between the cruciform elements are located at the midspan of beams and columns, whereas the longitudinal precast beam-column connections are located close to the columns. The floor structure consists of precast reinforced concrete hollow-core slabs; reinforcement bars are projected from the slabs for achieving the anchorage to the beams. Gravity load-bearing system: The gravity load-bearing structure is moment resisting concrete frame.

Gravity load-bearing & lateral load-resisting systems:

Typical wall densities in direction 1: >20%

Typical wall densities in direction 2: >20%

Additional comments on typical wall densities: Not applicable-walls are not a part of load-bearing structure.

Wall Openings: Walls do not constitute a part of the load-bearing structure in moment-resisting space frame buildings. Typical size of windows is: 1.2m (height) X 1.5-2m (width), doors : 2m (height) X 0.9-1m (width). The overall area of window openings accounts for 30 to 40% of facade walls, while doors account for less than 10% of partition wall area.

Is it typical for buildings of this type to have common walls with adjacent buildings?: No

Modifications of buildings: Usually, modifications are made in non-structural (exterior and interior) walls.

Type of Foundation: Shallow Foundation: Reinforced concrete isolated footing

Additional comments on foundation: Buildings of this type have basement floor; frames at the basement are infilled with concrete block walls. The isolated footings are tied with the reinforced concrete foundation beams, which are acting as the foundation for basement walls.

Type of Floor System: Other floor system

Additional comments on floor system: Precast hollow core concrete slabs

Type of Roof System: Roof system, other

Additional comments on roof system: Precast hollow core concrete slabs

Additional comments section 2: Typical separation distance between buildings: 10 meters and more

Who is involved with the design process? EngineerArchitectOther

Roles of those involved in the design process: The Design Institute develops the design documentation. Design for this construction type was done completely by engineers and architects.

Expertise of those involved in the design process: Expertise related to design and construction of this type according to the legal sistem of Kyrgyz Republic was available. Designs for buildings of this type were prepared by specialized design institutes with experise in this type of construction.

Who typically builds this construction type? Builder

Roles of those involved in the building process: The construction is performed by builders. Engineers played a leading role in each stage of construction.

Expertise of those involved in building process:

Construction process and phasing: The construction company makes the precast elements and performs the assembly. Precast elements can be made in the factory (plant). The main equipment used for construction is: crane, welding equipment and concrete mixers. This building is not typically constructed incrementally and is designed for its final constructed size.

Construction issues: Poor quality of construction work resulting in inadequate load-bearing capacity of joints.

Is this construction type address by codes/standards? Yes

Applicable codes or standards: SNiP II-7-81. Building in Seismic Regions.Design code. The first code/standard addressing this type of construction was issued 1961; the most recent code/standard addressing this construction was issued 1981.

Process for building code enforcement: Building permit will be given if the design documents have been approved by the State Experts. State Experts check the compliance of design documents with pertinent Building Codes. According to the building by- law, buildings cannot be inhabited without the formal approval of a special committee. The committee gives the approval if design documents are complete and the construction has been carried out in compliance with Building Codes.

Are building permits required? Yes

Is this typically informal construction? No

Is this construction typically authorized as per development control rules? Yes

Additional comments on building permits and development control rules:

Typical problems associated with this type of construction:

Who typically maintains buildings of this type? BuilderOwner(s)Renter(s)

Additional comments on maintenance and building condition:

Unit construction cost: For load-bearing structures only about 180$/m2.

Labor requirements: For load-bearing structures, a team of 10 workers would take 9 to 12 months

Additional comments section 3:

Patterns of occupancy: Each floor has 2-4 housing units. One family occupies one housing unit. In general, 36 to 120 families occupy one building (depending on the number of building units and stories in a building).

Number of inhabitants in a typical building of this construction type during the day: >20

Number of inhabitants in a typical building of this construction type during the evening/night: >20

Additional comments on number of inhabitants:

Economic level of inhabitants: Low-income class (poor)Middle-income class

Additional comments on economic level of inhabitants: 40% poor, 50% middle class

Typical Source of Financing: Owner financedPersonal savings

Additional comments on financing: This is the present situation. Before 1990 the source of financing was the government. Now, all new and existing apartment buildings are private.

Type of Ownership: RentOwn outrightUnits owned individually (condominium)

Additional comments on ownership:

Is earthquake insurance for this construction type typically available?: No

What does earthquake insurance typically cover/cost:

Are premium discounts or higher coverages available for seismically strengthened buildings or new buildings built to incorporate seismically resistant features?: No

Additional comments on premium discounts:

Additional comments section 4:

Damage patterns observed in past earthquakes for this construction type: Buildings of this type have not been subjected to the effects of damaging earthquakes. Precast frame buildings that were affected by strong earthquakes in the former Soviet Union (e.g. 1988 Spitak, Armenia earthquake) had linear precast elements (i.e. no cruciform members), and the joints were located in zones of maximum seismic moment. It should be noted that the precast frame buildings affected by the 1988 Spitak earthquake (Series 111) are different from precast frame buildings (series 106) described in this contribution. The main difference is in the cruciform elements, larger joint areas, and location of critical joints away from the highly stressed areas of beams and columns-these are all positive features of the Series 106 described in this contribution (see also Table 5.2).

Additional comments on earthquake damage patterns:

The main reference publication used in developing the statements used in this table is FEMA 310 “Handbook for the Seismic Evaluation of Buildings-A Pre-standard”, Federal Emergency Management Agency, Washington, D.C., 1998.

The total width of door and window openings in a wall is: For brick masonry construction in cement mortar : less than ½ of the distance between the adjacent cross walls; For adobe masonry, stone masonry and brick masonry in mud mortar: less than 1/3 of the distance between the adjacent cross walls; For precast concrete wall structures: less than 3/4 of the length of a perimeter wall.

Additional comments on structural and architectural features for seismic resistance:

Vertical irregularities typically found in this construction type: Other

Horizontal irregularities typically found in this construction type: Other

Seismic deficiency in walls: Walls are not lateral load-resisting structures. Poor quality of walls, and wall-column and wall-floor joints.

Earthquake-resilient features in walls:

Seismic deficiency in frames: Poor quality of joints between the precast frame elements; damage to joints expected

Earthquake-resilient features in frame: Joints of columns are located at the column mid-height (where seismic bending moment=0). Joints for gravity load-bearing beams are located at the mid-span (where seismic bending moment=0).

Seismic deficiency in roof and floors:

Earthquake resilient features in roof and floors:

Seismic deficiency in foundation:

Earthquake-resilient features in foundation:

For information about how seismic vulnerability ratings were selected see the Seismic Vulnerability Guidelines

Additional comments section 5: This is a moment-resisting frame structure. The fundamental vibration period is relatively low, on the order of 0.65-0.85 sec (considering that there are no shear walls in buildings of this type). Structures of this type are designed for earthquake effects according to the 1981 Building Code and therefore are not expected to be very vulnerable to earthquake effects. This structure is characterized with special construction details for precast frames; such details are not present in other precast frame systems found in the Post Soviet Union, like precast frame of Series 111 which performed very poorly in the 1988 Spitak, Armenia earthquake. Important construction details characteristic of this construction type are: 1. A larger size of cast in-situ joint (approximately 50 cm long). In this way, installation of the reinforcement bars, welding, and casting of concrete is largely facilitated as compared with similar systems (characterized with smaller joint sizes). This is particularly important if non-plastic (i.e. less workable) concrete mixture is used (which is a common case). However, the quality of in-situ construction is considered to be generally poor. 2. Cruciform member joints are located in the low-stressed portions of the beams and columns (away from the beam-column joints) - at the beam midspan and at the column midheight. Beams spanning in the longitudinal direction are loaded only due to lateral load actions, e.g. winds or earthquakes; joints in these beams are located near the columns, in the highly stressed beam zones.

Additional comments on seismic strengthening provisions:

Has seismic strengthening described in the above table been performed? N/A

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages? N/A

Was the construction inspected in the same manner as new construction? N/A

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved? N/A

What has been the performance of retrofitted buildings of this type in subsequent earthquakes? N/A

Additional comments section 6:

• Seismic Hazard and Buildings Vulnerability in Post-Soviet Central Asia Republics. Edited by Stephanie A. King, Vitaly I. Khalturin and Brian E. Tucker. Kluwer Academic Publishers, P.O. Box 17, 3300 AA Dordrecht, The Netherlands. (Proceeding of the NATO Advanced Research Workshop on Earthquake Risk Management Strategies for Post-Soviet Central Asian Republics. Almaty, Kazakhstan, 22-25 October 1996)

• Building and Construction Design in Seismic Regions. Handbook. Uranova S.K., Imanbekov S.T. KyrgyzNIIPStroitelstva, Building Ministry Kyrgyz Republic.Bishkek.1996.