Report #: 152

Report Date:

Country: ARGENTINA

Housing Type:

Housing Sub-Type:

Author(s): Noemi Graciela Maldonado, Dr. Miguel Eduardo Tornello , Ulugbek T. Begaliev

Last Updated:

Regions Where Found: This report describes a particular building on the campus of the Technological National University in Mendoza. While confined masonry is a typical construction type in the Mendoza region, representing 70% of the building stock, it is not typical to base isolate such buildings. Although base isolation devices are used extensively in others seismic regions of the world, in Argentina there are few examples. This first building was constructed with the aim of research and the excellent results obtained up to date indicate a potentialfor wider use.

Summary: Most of the Argentine Republic can be considered seismic. Greater Mendoza is an important socio-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. An investigation of the application of Basal Seismic Isolation(BSI) on a building 'Students House' belonging to the Technological National University (UTN) has been implemented and is described here. Research of the isolation system for near source motions has been done. The construction of three modules of student houses was completed in 2004, with confined masonry and reinforced concrete for three levels and prestressed slabs. Both buildings have accelerometers to register earthquake effects. The complex was 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 a 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 a fixed basebuilding.

Length of time practiced: Less than 25 years

Still Practiced: No

In practice as of: 11-13

Building Occupancy: Residential, 5-9 units

Typical number of stories: 3

Terrain-Flat: Typically

Terrain-Sloped: Never

Comments:

The building possesses two important characteristics. First, it is seismically isolated; and the secondly it has been constructe

Plan Shape: Rectangular, solid

Additional comments on plan shape: The building has three storeys. The plan of building is rectangular with dimensions, (7.60 x 8.20) m. The architectural configuration is the same in the three levels. In every storey two flats are developed for a maximum of three students in each. Every flat has one bathroom, one office and areas designated for bedrooms. The vertical circulation consists ofexternal (steel stairs) and they link two different buildings. The outer walls are of confined masonry and they are 18 and 27 cm thick. The 18 cm thick walls possess two steel bars inmortar joints. The structure has been designed to transfer the vertical and horizontal loads efficiently. The walls in the East-West direction are 30 cm thick, while the perpendicular walls are 20 cm thick. One of the walls of 30 cm of thickness possesses two windows on each level (dimensions 120 x 120 cm) which represents the 14 % of wall surface.The house reception area penetrates the perpendicular walls. The opening of (280×235) cm represents 33 % of wall surface.

Typical plan length (meters): 8.2

Typical plan width (meters): 7.6

Typical story height (meters): 2.6

Type of Structural System: Other

Additional comments on structural system: The vertical and lateral load-resisting system is reinforced masonry walls.

Gravity load-bearing & lateral load-resisting systems: The building is constructed of reinforced concrete and reinforced masonry. A layer of reinforced concrete is cast on the face of masonry walls. The foundations are spread footings joint with rigid concrete reinforced beams. The level of the foundation at its base is 200 to 250 cm. below the level of natural ground. All the beams and columns have been designed in reinforced concrete. The slabs are prestressed concrete slabs (thickness 24 cm) with a top layer of reinforcedconcrete (mesh 4.2 mm @ 25 cm) 4 cm thick to guarantee a monolithic and rigid structural diaphragm at floor and roof level. The masonry walls resist vertical and horizontal loads. Walls located in the North-South direction are 20 cm thick and they possess a steel mesh 4.2 mm on both faces in addition to horizontal reinforcement in the mortarbeds(2 6mm every five courses) The base-isolation system used in the building consists of four helicoidal steel spring packages located at the corners of the building, together with four viscous dampers. These types of devices are normally used to isolate industrial equipment or to filter vibrations from vehicular or railroad traffic. Steel springs havethe advantage of well known behavior, they are stable with time, independent of temperature, and have no creep andnot residual displacements. They have the disadvantage of low damping (2% of critical), and therefore it is necessary touse additional devices for increasing the damping. Because the load capacity of an individual helicoidal spring is limited,for moderate or large loads, the use of packages of springs is required. The number of springs per isolator depends on the static and dynamic demand imposed by service and seismic loads. In this case, because of asymmetry of loads, two isolators are composed of 30 springs, with a load capacity of 921 kN and the other two are composed of 28 springs for a force capacity of 860 kN. The structural system with isolators has natural horizontal frequencies between 1 and 2 Hz and natural vertical frequencies of 3 to 3.5 Hz. For earthquake input excitation the isolation system allows a dynamic motion composed of vertical, horizontal and swaying and rocking motions. Part of the horizontal excitation is transferred to swaying and rocking modes and it is dissipated by the isolation system thus reducing the seismic demands on the superstructure. The viscous damper comprises a container of viscous material. A piston attached tothe upper part is immersed into the viscous material generating viscous forces in three orthogonal directions. The isolation system formed by spring isolators and viscous dampers has linear stiffness in all directions and an almost linear damping as a function of velocity. The design of the viscous damper is a function of maximum and minimum velocity demand that can be expected at the location. The maximum velocities of the selected records are in the range of 0.20 to 1.70 m/s. Viscous damping can be modified easily by changing the number of internal cylinders. In this case, due to the impulsive characteristic of anticipated earthquakes, large damping ratios have been selected in order to control displacements, 26% in horizontal direction and 13% in vertical direction. With these values the horizontal displacements are limited to 150-200 mm and the vertical ones to 30-50 mm, which are compatible with thedisplacements the springs and dashpots are capable of undergoing.

Typical wall densities in direction 1: 4-5%

Typical wall densities in direction 2: 4-5%

Additional comments on typical wall densities: The typical span of the roofing/flooring system is 3.50 meters. The length in plan of a typical span is 3.50 meter in East-West direction and 2.50 meter in North-South direction. The walls in the East-West direction are 30 cm thick, while the perpendicular ones are 20 cm thick. One of the walls 30 cm thick possesses two windows on each level (dimensions 120 x 120 cm) that represent the 14 % of wall surface. The housing reception area is located in the the perpendicular walls. The opening of 2.80×2.35 m. represents a 33 % of the wall surface.

Wall Openings: A typical house has 6 to 10 windows per floor, with a total average size of 3.0 m2. The position of these openings is variable, but usually is approximately 0.8 to 1.0 m from the floor level in rooms and from 1.8 to 2.0 m in bathrooms.

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

Modifications of buildings: Typical modifications include closing off the balconies and demolishing the interior walls to rearrange the apartments or to change the use. Often, additional stories are added without a building permit and without taking into account the load-bearing capacity of the structure.

Type of Foundation: Other Foundation

Additional comments on foundation: The foundation consists of spread footings joined by continuous reinforced concrete foundation beams The level of foundation of the base is of (-200 to 250 cm) with regard to the level of the natural ground. The isolation devices are located on the rigid beams that connect the bases of the footings.

Type of Floor System: Other floor system

Additional comments on floor system: The floor system is comprised of prestressed concrete slabs (hollow core). They are 1.20 meters wide and 7.00 meters long. They are 24 cm thick with a top layer of reinforced concrete (mesh 4.2 mm @ 25 cm) 4 cm thick to guarantee a monolithic and rigid floor diaphragm. The roofing systems is the same as floor systems, both are composed of prestressed reinforced concrete plates. They are 1.20 meter wide and 7.00 meters long. They are 24 cm thick with a top layer of reinforced concrete (mesh 4.2 mm @ 25 cm) of 4 cm thick to guarantee a monolithic and rigid structural element at the roof level.

Type of Roof System: Roof system, other

Additional comments on roof system: The roof system is precast hollow core slabs.

Additional comments section 2: The seismic vulnerability in this building type is due to the fact that the ground floor is used for commercial purposes and the upper levels for residences. Sometimes heavy items are stored on the upper floors when the entire building is used for commercial activity. In a typical building of this type, there are no elevators and 1-2 fire-protected exit staircases. The only means of escape is the main entrance door; there is only one staircase in each building.

Who is involved with the design process?: EngineerArchitectTechnologist

Roles of those involved in the design process: The building was designed by architects and structural engineers. The diverse phases of building construction were inspected by two architects, two engineers and three students of engineering. The inspection was present from the beginning to the end of the works. The architects and engineers took part in all phases of the work, from the design to construction and completion. Also university civil engineering students collaborated in the design and constructionof the buildings.

Expertise of those involved in the design process: The expertise required for the design and construction of this type is available. Building designs were prepared by design institutes. The academic background of the designers is the same as for conventional construction. It is not required to have designers with high academic degrees e.g. M.Sc. and Ph.D. on theteam. Construction of base isolated buildings and the approval of the designs were controlled by research institutes (State Experts) like any other new construction performed in accordance with the Building Code requirements.

Who typically builds this construction type?: Builder

Roles of those involved in the building process: The buildings have been constructed for students' residences. The building with base isolation can be compared with the same building but a fixed base, located a few meters away. Three buildings have been constructed near each other, with equal construction characteristics but one with base isolation. The percentage of reduction of the accelerations measured on the roofs of the buildings were:Earthquake 2005/09/09, 66%; 2006/08/05, 82%; 2007/09/15, 85%, 2008/10/16, 80%; 2009/05/08, 77%; 2010/02/27, 84% and 2012/06/18, 69%.

Expertise of those involved in building process: The expertise required for the design and construction of this type is available. Building designs were prepared by design institutes. The academic background of the designers is the same as for conventional construction. It is not required to have designers with high academic degrees e.g. M.Sc. and Ph.D. on theteam. Construction of base isolated buildings and the approval of the designs were controlled by research institutes (State Experts) like any other new construction performed in accordance with the Building Code requirements.

Construction process and phasing: During construction typical building tools and equipment were used. The construction of this type of housing takes place incrementally over time. Typically, the building is originally designed for its final constructed size.

Construction issues

Is this construction type address by codes/standards?: Yes

Applicable codes or standards: This construction type is addressed by the codes/standards of the country. For reinforced concrete structures we applied the national code CIRSOC 201. To evaluate the effect of the earthquakes on the building we applied the Code of earthquake resistant Constructions of the Province of Mendoza, 1987. To evaluate the capacity of the masonry wall we applied the Code of earthquake resistant Constructions of the Province of Mendoza, also. Finally in order to compare results also there was used the national code INPRES-CIRSOC 103. The Province of Mendoza for many years, has used code different from the national code. Nevertheless in recent years the codes have been unified and have been adopted at a national level (INPRES-CIRSOC). The INPRES-CIRSOC codes provide regulations regarding design and construction for earthquake conditions. The local regulations, Code ofResistant Constructions of Mendoza have been enforced since 1987, in different town councils of the Province of Mendoza.

Process for building code enforcement: The enforcement of the building code for public buildings in Algeria is done by the Controle Technique de la Construction (CTC). After the architectural plans have been prepared, their conformity to the building codes (CBA93, RPA99, etc.) must be approved by the CTC. The approval is related to the phases of the construction and the quality of the building materials. However, code enforcement is not required by Planning Services for private housing. As a result, the construction can proceed with only architectural plans. There is no inspection or quality control enforced during the construction.

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: This type of construction is an engineered, and authorized as per development control rules. The municipality authorities examine and approve the projects (architectural, structure and installations). In Argentina the code on seismic isolation and dissipation of energy is in progress. Therefore to approve the construction of the building the authority used the code of Chile (NChOf273). Building permits are required to build this housing type.

Typical problems associated with this type of construction: These constructions are inherently very weak against earthquake loading.

Who typically maintains buildings of this type?: Owner(s)

Additional comments on maintenance and building condition: The maintenance is performed either by the owner (city) or (periodically) by a contractor a maintenance firm.

Unit construction cost: The unit construction cost of the building is of approximately $US 650. The entire area of the building is of approximately 185 square meters. In this area six flat are included. Therefore the entire cost of the building is of $US120–250. To the value of the building it is necessary to add the cost of the isolation devices. This cost is $US 20.000 approximately.

Labor requirements: Each housing unit in rural area takes around 8-12 man-months (counting skilled man-months only) for construction. Only one or two skilled artisans are used, while the remaining are unskilled workers.

Additional comments section 3: These buildings were constructed using the following construction materials:2. Exterior walls (2 layers); one layer is made using regular concrete and the other one is made of lightwight concrete (for the purpose of heat insulation).3. Interior walls are made of regular concrete.

Damage patterns observed in past earthquakes for this construction type: Recent ground motions in the region have been of low magnitude. In general they have not produced serious damage in buildings of this type. The accelerations registered in the base isolated building are, in most cases, up to four times less than that the registered in the same building but of fixed base. In the isolated building have been registered under the fixed base building accelerations. Earthquakes recorded in the following reductions are observed, for example in the earthquake 2005/09/09, 66%; 2006/08/05, 82%; 2007/09/15, 85%, 2008/10/16, 80%; 2009/05/08, 77%; 2010/02/27, 84% and 2012/06/18, 69%.

Additional comments on earthquake damage patterns: Walls: Out of plane collapse, Classical X shear cracking. Frames: Buckling of the storey.Roof/Floor:Total/partial collapse.Connections: Excessive rotations, shear failure of the welds, unsitting.

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: The building possess a low vulnerability index. The fact of having base isolation seismic implies that the building is not vulnerable to seismic loads. The structural configuration in plan and elevation of the building also reduces vulnerability. The materials also are adapted to control the vulnerability of the building.

Vertical irregularities typically found in this construction type: No irregularities

Horizontal irregularities typically found in this construction type: No irregularities

Seismic deficiency in walls: A conventional building of large panel concrete construction or brick masonryconstruction: poor quality of panel joints and inadequate masonry strength.

Earthquake-resilient features in walls: Suitable wall thickness controls the distortion. Walls with horizontal and vertical steel to improve the ductility.

Seismic deficiency in frames: Lack of seismic resistance, as the structural elements are designed for gravity load only. The main deficiencies include: - column cross-section not sufficient to provide earthquake resistance. - absence of stirrups in beam-column joints. - lack of infilled masonry walls at the ground floor, thus creating a soft storey effect (see Fig. 10 and 11) -excessively large stirrup spacing in columns. - poor quality of materials and workmanship.Partial or total collapse of the building due essentially to excessive displacement (P-delta effect) at the ground floor level. The characteristic damage patterns include: failure of the top portion of columns at the ground floor level, development of plastic hinges in the columns (ground floor), crushing of columns due to axial compression, shear failure in column-beam joints.

Earthquake-resilient features in frame: The beams and columns have suitable steel shear reinforcement to allow for energy dissipation and to avoid brittle collapse.

Seismic deficiency in roof and floors: #NAME?

Earthquake resilient features in roof and floors: Possess 26 cm thicknesses to guarantee rigid diaphragms. High rigidity allows inertial forces to be distributed to the vertical resistant walls in an efficient way.

Other seismic deficiencies: Quality and precision in the construction of the Disengaging Reserve Elements

Other earthquake-resilient features: Disengaging Reserve Elements are effective in reducing seismic demand inthe building.

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

Additional comments section 5: The building was inaugurated in 2004 and therefore designed to a modern code. The building has had a good behaviour to vertical loads and to the small ground motions that have happened in the region.

Additional comments on seismic strengthening provisions: The most commonly used method for strengthening reinforced concrete frame buildings is reinforced concrete jacketing. The addition of new structural elements (such as shear walls or bracings) is rarely used. Construction of new shear walls is a common retrofit method for larger reinforced concrete frame buildings despite its high cost. (Forexample, this was done after the 1999 Ain Temouchent earthquake.) The addition of shear walls results in the increased lateral strength and stiffness of a building. As a result, seismic performance increases significantly as well. The walls are laid in a symmetrical manner to reduce torsional response. The bracing systems are not used very often.

Has seismic strengthening described in the above table been performed?: The first experience related to repairing and strengthening damaged buildings in Algeria was following the 1980 El Asnam earthquake (M 7.3). Also, some buildings strengthened after the previous (1954) El Asnam earthquake performed very well (without damage) in the 1980 Asnam earthquake. The methods described in Section 10.1 were applied. Other projects to strengthen damaged public buildings were undertaken after recent earthquakes such as the 1999 Ain Temouchent earthquake. The strengthening of buildings after the 2003 Boumerdes eq. has started but is not yet finished as of this writing (January 2004). The related seismic strengthening studies were entrusted to local engineering and design offices. The damaged elements were repaired with injection or with reinforced concrete jacketing. New structural elements (shear walls) were added only to the damaged structures of existing public buildingsto increase their lateral load resistance.

Was the work done as a mitigation effort on an undamaged building or as a repair following earthquake damages?: This work was done as the repair following the earthquake. In a few cases it was done specifically as part of a mitigation effort for a few undamaged strategic buildings in Algiers.

Was the construction inspected in the same manner as new construction?: The damaged construction is inspected in the same manner as the new construction.

Who performed the construction: a contractor or owner/user? Was an architect or engineer involved?: Owners build their own homes, and architects and engineers are never, or rarely ever, involved. In the aftermath of the 2003 Boumerdes earthquake, the repairing and strengthening operation was financed by the government andperformed by contractors and developers. In this case both the architects and engineers were involved.

What has been the performance of retrofitted buildings of this type in subsequent earthquakes?: Construction which was strengthened following the earthquakes which struck northern Algeria (Tipaza, 1989 and Ain Temouchent, 1999) was not affected by other earthquakes. The 2003 Boumerdes earthquake did not affect those areasso it is not yet known how retrofitted buildings will perform in future earthquakes. However, some vulnerability studies of the strengthened housing were completed, which concluded that strengthened buildings should perform well in future moderate earthquakes.

Dynamic Response of a Building with Base Isolation For Near Tornello M. E., Sarrazin A. M9th Canadian Conference on Earthquake Engineering. Paper No 1057. Ottaw a. Canada. 2007 1

CIRSOC 201. Reglamento Argentino de Estructuras de Hormigon.CIRSOCINTI 2005 1

INPRES-CIRSOC 103CIRSOCINTI 1982 1

Codigo de Construcciones Sismorresistentes de MendozaGobierno de MendozaCentro de Ingenieros 1987 1

Boumerdes earthquake report, 2003de Boumerdes,W.