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Report # 83 : Precast concrete panel apartment buildings

by Maria D. Bostenaru, Ilie Sandu

This multi-family urban housing construction type was built in Romania from the 1960s through the 1990s. The load-bearing system is a precast-reinforced-concrete large-panel construction. Buildings of this type are typically high-rises (10 or 11 stories), although there are also low-to medium-rise buildings (4 to 8 stories) with different structural details. In general, these buildings consist of a rectangular plan, with a honeycomb (“fagure”) layout, typically housing four apartments per floor. Wall panels are laid in both the longitudinal and the transverse direction. The panels are mechanically coupled at the base with continuous vertical reinforcement bars. This region is well-known as an earthquake-prone area, with the epicenter of damaging earthquakes close to Vrancea. Earthquakes with a Richter magnitude of over 7.0 occur, on average, every 30 years. Bucharest, the capital, is located around 150 km south of the epicenter and lies in the main direction of the propagation of seismic waves. The Bucharest area is located on the banks of the Dâmbovita and Colentina rivers, on non-homogenous alluvial soil deposits. During the earthquake of 4 March 1977 (Richter magnitude 7.2), over 30 buildings collapsed in Bucharest, killing 1,424 people. There was no significant damage reported to the buildings of this construction type in the 1977 earthquake. Consequently, this construction technique has continued to be practiced since the earthquake. The building described in this report was built after the 1977 earthquake and so far has not been exposed to damaging earthquakes.

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Report # 82 : Single-family wood frame house

by Carlos E. Ventura, Mehdi H. K. Kharrazi

Single-family wood frame construction represents the most common housing construction practice found throughout Canada and constitutes over 50% of the housing stock in British Columbia. A typical Canadian-style modern wood frame house consists of a concrete foundation, upon which a platform is constructed of joists covered with plywood or oriented-strand board (OSB) to form the ground-floor level of the house. This platform is connected directly to the foundation with anchor bolts, or alternatively, supported by a short wall, a so-called “cripple wall,” “pony wall,” or “stub wall,” which should be connected to the foundation with anchor bolts. On this base, the exterior and interior walls are erected, which consist of a horizontal sill plate with vertical timber studs with board or panel sheathing nailed to the studs on the outside of the building. The roof structure typically consists of prefabricated trusses, which are covered with sheathing and roof tiles (Rainer and Karacabeyli 2000). Because this is generally considered to be a non-engineered construction, the Canadian National Building Code does not usually require direct professional architectural or engineering involvement. Specific seismic construction requirements and calculation/design requirements for seismic resistance are currently not included in Part 9 of the Code, which addresses low-rise residential wood frame construction. There is no evidence of substantial damage to this type of construction in past earthquakes in Canada, which have occurred away from densely populated urban centers. However, recent experimental research studies (Earthquake 99 Project at the University of British Columbia), focused on seismic performance of wood frame construction, have revealed vulnerability in this type of construction to seismic effects, depending on the age and wood construction technology.

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Report # 80 : Low-strength dressed stone masonry buildings

by Ravi Sinha, Vijaya R. Ambati

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Construction of stone masonry buildings using easily available local materials is a common practice in both urban and rural parts of India. Stone masonry houses are used by the middle class and lower middle class people in urban areas, and by all classes in rural areas. In rural areas, these buildings are generally smaller in size and are used as single-story, single-family housing. In urban areas, these buildings are up to 4 stories high and are used for multifamily housing. This is a typical load-bearing construction, in which both gravity and lateral loads are resisted by the walls supported by strip footing. If the locally available stone is soft, dressed (shaped) stones are commonly used and can be chiselled at low- or moderate cost. Mud or lime mortar has been used in traditional constructions; however, more recently, cement mortar is being increasingly used. Because soft sandstone is readily available in the Kutch region of Gujarat in the western part of India, stone block masonry constructions are widely used for both single- and multi-story constructions. These houses are usually built by local artisans without formal training and the resulting constructions are structurally weak and incapable of resisting large seismic forces. In the Kutch region, which was affected by the 2001 Bhuj earthquake, this construction type is commonly used with a gable end timber roof truss or RCC roof slabs. Thousands of these houses collapsed in the 2001 Bhuj earthquake resulting in the deaths of large numbers of people. This construction type is inherently unsuitable for areas of moderate-to-high seismic hazard, such as the Kutch region of Gujarat.

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Report # 79 : Concrete shear wall highrise buildings

by John Pao, Svetlana N. Brzev

This concrete shear wall high-rise represents a contemporary residential and commercial construction commonly found in downtown areas of Canadian cities. This multi-family building contains 100 to 200 units and provides housing for 300 to 500 inhabitants. The height of these buildings is variable and usually ranges from 12 to 35 stories. The lateral load-resisting system consists of reinforced concrete shear walls and concrete floor slabs. The gravity load is carried mainly by concrete columns. Seismic detailing of shear walls in medium-to-high seismic regions is mandatory per the Canadian Concrete Code. Exterior walls are clad in stucco backed by cold-form steel framing or masonry veneer, steel/glazing panels, or precast panels. There is no report on the damage sustained by this building type in past earthquakes in Canada. However, because these buildings are designed according to state-of-the-art seismic codes, their seismic performance is expected to be satisfactory in an earthquake of design intensity (per the seismic design requirements of the National Building Code of Canada).

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Report # 78 : Reinforced concrete cast-in situ shear wall buildings (“OD”-type, with “fagure” plan)

by Maria D. Bostenaru, Ilie Sandu

This is typical urban multi-family housing practiced throughout Romania in the period from 1965 to 1989. There are many existing buildings of this type at the present time, with about 8,000 apartments in Bucharest alone. Concrete shear wall construction is commonly used for the residential construction and it accounts for over 60% of new housing. Buildings of this type are typically 10 or 11 stories high. The main load-bearing structure is a cast in-situ concrete shear wall structure supported by RC solid slabs. Each building block consists of several (5-6) identical building units (“tronsons” in Romanian) separated by means of seismic joints. The walls are continuous throughout the building height and orientated in two directions, with only one centrally located wall in the longitudinal direction and eight walls in the transverse direction. In addition, there are some lightweight concrete partition walls. This building plan is known as the honeycomb (“fagure”) plan. The buildings are often supported by mat foundations due to soft (alluvial) soil conditions. Many buildings of this type were designed according to the 1963 Romanian Building Code (P13-1963) which was updated in 1970 (P13-1970). The 1963 Code considered a magnitude 7 design earthquake for the Bucharest area. This region is well known as a seismically prone area, with the epicentre of damaging earthquakes close to Vrancea. Earthquakes with the Richter magnitude of over 7.0 occur once in 30 years. Bucharest, the capital, is located around 150 km south of the epicentre and lies in the main direction of the propagation of seismic waves. The Bucharest area is located on the banks of the Dâmbovita and Colentina river, on non-homogeneous alluvial soil deposits. During the earthquake of 4 March 1977 (Richter magnitude 7.2), over 30 buildings collapsed in Bucharest, killing 1,424 people. The buildings of “OD” type suffered damages of various extent in the 1977 earthquake, and one building unit (“tronson”) totally collapsed (that was the only shear wall building that collapsed in the FIGURE 1A: Typical Building Page 1 earthquake). Buildings with their longitudinal direction aligned parallel with the direction of seismic waves were most affected. The earthquake action in 1977 was mainly in NNE-SSV direction. Out of 167 building units (“tronson”s) of the “OD” type existing in Bucharest at the time of the 1977 earthquake, only 7 were lightly damaged; the remaining building units suffered a partial collapse (7 units) or damages (19 were significantly damaged, 72 were moderately damaged, and 61 were lightly damaged). According to the reports, damages to this construction type were due to inadequate wall density in the longitudinal direction, inadequate amount and detailing of wall reinforcement, lack of lateral confinement in the walls and in the boundary elements (“bulbs”) causing brittle concrete failure and buckling of reinforcement. In addition, the quality of concrete construction was found to be rather poor.

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Report # 77 : Buildings protected with “disengaging reserve elements” (vyklyuchayu-shchiesya svyazi)

by Jacob Eisenberg, Svetlana Uranova, Ulugbek T. Begaliev

This building type is characterized with a special system of seismic protection called “Disengaging Reserve Elements” (DRE). DRE are installed at the ground floor level of a building, which is typically a RC frame structure. The upper part of the building, usually 9 stories high, is a load-bearing wall structure, either of large-panel RC construction or brick masonry construction. DRE consist of a “rigid structure” (usually RC wall panel) connected to the adjacent RC frame members by means of disengaging restraints. Disengaging restraints are sacrificial reserve elements (fuses) that serve as restraints for the “rigid structures.” Typical restraints are steel plates joined together by means of rivets or steel bolts, steel bars, concrete prisms or cubes, etc. Initially, at the lower ground motion level, DRE and RC frame work together; at that stage, disengaging elements transfer lateral loads to rigid structures. DRE is an adaptive seismic protection system whose unique feature, the variable (self-adjusting) rigidity and periods of vibration during an earthquake, prevent resonance. This system is widely used in seismic-prone areas of Russia and Kyrgyzstan. Buildings of this type have not yet been exposed to the effects of damaging earthquakes.

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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 # 75 : Stone masonry apartment building

by Mohammed Farsi, Farah Lazzali, Yamina Ait-M

This is a typical residential construction type found in most Algerian urban centers, constituting 40 to 50% of the total urban housing stock. This construction, built mostly before the 1950s by French contractors, is no longer practiced. Buildings of this type are typically 4 to 6 stories high. The slabs are wooden structures or shallow arches supported by steel beams (jack arch system). Stone masonry walls, usually 400 to 600 mm thick, have adequate gravity load-bearing capacity; however, their lateral load resistance is very low. As a result, these buildings are considered to be highly vulnerable to seismic effects.

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Report # 74 : Uncoursed rubble stone masonry walls with timber floor and roof

by Yogeshwar K. Parajuli, Jitendra K Bothara, Bijay K. Upadhyay

This is a typical rural housing construction in the hills and mountains throughout Nepal. It is a traditional construction practice followed for over 200 years. These buildings are basically loose-fitting, load-bearing structures constructed of uncoursed rubble stone walls in mud mortar, with timber floors and roofs. They are expected to be extremely vulnerable to the effects of earthquakes due to their lack of structural integrity.

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Report # 73 : Unreinforced Brick Masonry Apartment Building

by Marjana Lutman, Miha Tomazevic

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.

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