Report: 73

Building Type: Unreinforced Masonry Building

Country: SLOVENIA

Author(s): Marjana Lutman, Miha Tomazevic

Last Updated:

Regions Where Found: Buildings of this construction type can be found in all Slovenian towns, and it constitutes up to 30 % of the entire housing stock in Slovenia. This construction type was also practiced in other countries in the region, in particular Montenegro and Macedonia, which were part of the former Yugoslavia. This type of housing construction is commonly found in urban areas.

Summary: This construction was commonly used for residential buildings in all Slovenian towns, and it constitutes up to 30% of the entire housing stock in Slovenia. The majority of these buildings were built between 1920 and 1965. They are generally medium-rise, usually 4 to 6 stories high. The walls are unreinforced brick masonry construction laid in lime/cement mortar. In some cases, the wall density in the longitudinal direction is significantly smaller than in the transverse direction. In pre-1950 construction, there are mainly wooden floor structures without RC tie-beams. In post-1950s construction, there are concrete floors with RC bond- beams provided in the structural walls. Roof structures are either made of wood (pitched roofs) or reinforced concrete (flat roofs). Since this construction was widely practiced prior to the development of the seismic code (the first such code was issued in 1964), many buildings of this type exceed the allowable number of stories permitted by the current seismic code (maximum 2 or 3 stories for unreinforced masonry construction). Buildings of this type have been exposed to earthquake effects in Slovenia. However, this construction type experienced the most significant damage in the 1963 Skopje, Macedonia, earthquake, which severely damaged or caused the collapse of many buildings.

Length of time practiced: 76-100 years

Still Practiced: No

In practice as of:

Building Occupancy: Residential, 20-49 units

Typical number of stories: 4-6

Terrain-Flat: Typically

Terrain-Sloped: 3

Comments: Currently, this type of construction is not being built. This housing construction was practiced in the period between 1920 and

Plan Shape: Rectangular, solid

Additional comments on plan shape: Typical shape of building plan is rectangular with length/width ratio ranging from 2.0 to 8.0. In the longitudinal direction, the building is usually divided into 2 to 5 segments. Each segment has its own entrance, staircase and elevator.

Typical plan length (meters): 25-90

Typical plan width (meters): 10-13

Typical story height (meters): 2.7-3

Type of Structural System: Masonry: Unreinforced Masonry Walls: Brick masonry in lime/cement mortar

Additional comments on structural system: The vertical load-resisting system is un-reinforced masonry walls. The gravity-load bearing structure consists of roof and floor structures and structural walls. In the case of an additional top floor built atop the original flat RC roof structure, there is a new timber pitched roof. The lateral load-resisting system is un-reinforced masonry walls. The lateral load-resisting system consists of exterior and interior brick masonry walls. Wall thickness varies from 380 mm (exterior and some interior walls) to 250 mm (the majority of interior walls). The mortar mix varies through the building height: pure cement mortar is used at the lowest two floors, composite lime/cement mortar is used for the middle portion and pure lime mortar for the upper floors. Due to large openings and longitudinal exterior walls, the lateral resistance in longitudinal direction is often significantly inferior as compared to the lateral resistance in the transverse direction. The lateral load transfer to load-bearing walls is accomplished through roof and floor structures. In the case of older buildings of pre-1950 construction characterized with wooden floor structures, the walls were not joined together by means of wooden or iron ties. In the case of newer buildings, all structural walls are tied together with RC edge beams of RC floors. The walls are supported by concrete strip foundations. The weakest link in this construction are usually wall-floor and wall-roof connections in case of timber floor construction.

Gravity load-bearing & lateral load-resisting systems: The mortar is made of lime or composite lime and cement mix

Typical wall densities in direction 1: 1-2%

Typical wall densities in direction 2: 5-10%

Additional comments on typical wall densities: The typical storey height in such buildings is 2.85 meters. The typical structural wall density is up to 10 %. 2.2-6% in longitudinal direction (typical distance between two adjacent walls ranges from 5.4-11.6 m), and 5.5-6.6% in transverse direction (typical distance between two adjacent walls ranges from 2.2-8.7 m).

Wall Openings: The buildings of this type are characterized by two longitudinal exterior walls with the majority of openings located in these walls, and two exterior walls in the transverse direction with a few smaller window openings or no openings at all. The average area of a window opening is 1.8 m# in longitudinal exterior bearing walls. The exterior walls in the transverse direction are characterized with smaller kitchen or toilet window openings of typical area less than 0.5 m#. The area of balcony door and window openings is approx. 4.0 m#. The door area in the exterior and interior load bearing walls is approximately 2.0 m#. The total area of openings is approximately equal to 30 % of the longitudinal exterior wall surface area.

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

Modifications of buildings: A few modifications have been carried out in these buildings. Since the majority of interior walls have been constructed as load bearing walls, no significant changes are observed. In some cases, an additional floor has been built atop the flat roof; the additional floor typically has a pitched roof.

Type of Foundation: Shallow Foundation: Reinforced concrete strip footing

Additional comments on foundation: Foundations are often made of unreinforced concrete.

Type of Floor System: Other floor system

Additional comments on floor system: Wood planks or beams with ballast and concrete or plaster finishing; The floor and roof structures are made of timber in pre-1950 construction.

Type of Roof System: Roof system, other

Additional comments on roof system: The floor and roof structures are made of timber in pre-1950 construction.

Additional comments section 2: When separated from adjacent buildings, the typical distance from a neighboring building is 30 meters.

Who is involved with the design process? EngineerArchitect

Roles of those involved in the design process: Architects and engineers designed buildings of this type. Architects are in charge of the architectural design, and structural engineers are in charge of the structural design, construction process and supervision.

Expertise of those involved in the design process:

Who typically builds this construction type? Other

Roles of those involved in the building process: The buildings of this type were built by builders. Sometimes they also live in buildings of this type.

Expertise of those involved in building process: It used to be a very common type of residential construction. As a result, design and construction expertise was good. The construction foreman was usually a technician; however the supervision was carried out by an engineer.

Construction process and phasing: The construction was usually carried out by a government-owned construction company. After the stabilization of the ground floor, the foundations and the basement walls are constructed of cast-in-situ concrete. The brick walls are built manually atop the floor structure. Hollow clay tile floor is usually constructed spanning in the transverse direction of the building. Hollow clay tiles are first placed on the shuttering. Subsequently, the longitudinal steel bars in the ribs, transverse steel bars for the RC topping, and the bond beam reinforcement are placed. Finally, the concrete topping is poured atop the masonry. Concrete and mortar is prepared using machine mixers. The construction of this type of housing takes place in a single phase. Typically, the building is originally designed for its final constructed size. The buildings were originally designed for a certain height. If the owners decide to build an additional floor atop the existing building, the load-bearing capacity of the upper floor structure needs to be verified. Building permits are required for any structural expansion and renovation.

Construction issues:

Is this construction type address by codes/standards? Yes

Applicable codes or standards: National Seismic Code for Buildings (1981). The year the first code/standard addressing this type of construction issued was 1964. The first code including design vertical load, wind and seismic load was the Preliminary National Building Code (1948). After the catastrophic earthquake in Skopje (in former Yugoslavia) in 1963, the first Seismic Code addressing this type of construction was issued (1964). In addition to the National Seismic Code for Buildings, Eurocode 8 is being used at the present time.

Process for building code enforcement: Since the buildings were built as public residential buildings, the building codes have been enforced. The design, construction and supervision were carried out with consideration of the National Building Code. The design of a building was approved by the state authorities. After the construction, building had to pass technical verification in order to get the use and occupancy permit.

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? Owner(s)

Additional comments on maintenance and building condition: The owners need to retain a house management company to coordinate and organize the building maintenance.

Unit construction cost: Total value per m# of an apartment area estimated in 1966 was 80 $US/m#. The current market value of apartments in these buildings is much higher (500 - 1000 $US/m#), depending on the building location.

Labor requirements: The design of a building took about 3 - 4 months. Typically, several buildings of the same type were built at the same site, and the construction took 1 - 2 years for a team of about 50 skilled workers.

Additional comments section 3:

Patterns of occupancy: One family occupies one housing unit. Each building typically has 12-60 housing unit(s). Number of housing units depends on the size of the building; it varies from 12-60 units in each building. There are typically 4 - 10 housing units per floor.

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: Ratio of housing unit price to annual income: 5:1 or worse The prices are expressed in US$. Smaller apartments (50 m#) may cost US$ 30.000, and the annual income for a person may be US$ 5.000. Larger apartments (70 m#) may cost US$ 45.000, and the annual income for a person may be US$ 8.000. Economic Level: For Poor Class the Housing Unit price is 30000 and the Annual Income is 5000. For Middle Class the Housing Unit price is 45000 and the Annual Income is 8000.

Typical Source of Financing: Owner financedInvestment poolsOther

Additional comments on financing: Other: Government-owned housing foundation.

Type of Ownership: RentUnits owned individually (condominium)

Additional comments on ownership:

Is earthquake insurance for this construction type typically available?: Yes

What does earthquake insurance typically cover/cost: The whole area of Slovenia has been divided into the two “seismic insurance zones”. The residential buildings are divided into two categories depending on the age of construction: older buildings, built before or in 1965, and the newer buildings, built in 1966 or later. For the higher seismic zone, the annual insurance rate is 0.105 % of the building value for older buildings and 0.07 % for the newer buildings. For the lower seismic zone, the annual insurance rate is 0.07 % and 0.045 % of the building value for older and newer buildings respectively.

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:

• Guidelines and Procedures Used to Eliminate the Impact of the Earthquake in the So Jones,B.G. Proc. Social and Economic Aspects of Earthquakes, Eds. Jones,B.G. and Tomazevic,M., Ljubljana-Ithaca, 1982, Institute for Testing and Research in Materials and Structures - Cornell University, pp. 413-423 1982

• Report on Mitigating and Consequences of the Earthquake of Bovec of April 12, 1998, Ljubljana Adm. for Civil Protection and Disaster Relief (in Slovene) 1998

• The Seismic Resistance of Historical Urban Buildings and the Interventions in their Floor Systems: an Experimental Study Tomazevic,M., Lutman,M. and Weiss,P. The Masonry Soc. j., 12 (1), Boulder, 1993, The Masonry Soc., pp. 77-86 1993

• Earthquake-Resistant Design of Masonry Buildings Tomazevic.M. Series on Innovation in Structures and Construction - Vol.1, Imperial College Press, London 1999