Category: RC Moment Frame

by Maria D. Bostenaru

Such buildings generally range from 10 to 17 storeys in height with the ground floor being used for commercial purposes, whilst the upper floors house residential units. The vertical load bearing structure consists of moment-resisting reinforced-concrete frames which also generally serve as the lateral load-resisting system. However, when larger spans are encountered, reinforced-concrete structural walls are included to provide a dual structural system. Masonry infills built from lightweight concrete masonry units provide architectural space delineation. The seismic performance of such buildings constructed prior to 1977 varies from no damage to complete collapse. To date damage has usually been attributable to conceptual and construction mistakes.

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by Maria D. Bostenaru

This urban housing construction was practiced in Romania from 1907-1945, but predominantly in the 1930s, in the capital city of Bucharest. These buildings are mid- or high-rise (5-10 upper floors), often with two basements. Although there are several functional variations according to the usage and combination of flats, offices, and shops, this report discusses exclusive housing use. The number of housing units is variable. While smaller mid-rise buildings may contain one large luxury unit on each floor, taller buildings may include as many as eight small one-room flats, sometimes without a kitchen. The shape of the plan, containing L, U, H, or forms that cannot be described geometrically, and the elevation of the building are highly irregular. Upper floors may have recesses in the facade and may have corner towers. The load-bearing structure is RC skeleton designed for gravitational loads only. Columns are unevenly distributed so that beams at least one end are supported as secondary beams. Some beams are supported by columns with inadequate reinforcement or reduced sections of the RC members impede the formation of moment-resisting frames. The facade walls have solid clay brick masonry infill and improve the seismic behavior. The beneficial effect of masonry infill is influenced by the wall thickness, the size/position of openings in walls and the position of the partition wall to the frame. Staircases and elevators weaken the structure by introducing concentrated holes in flexible, thin RC slabs. Bucharest is located on alluvial soil deposits on river banks. Sandy ground or high levels of underground water have often presented problems for the foundation of buildings. Damaging earthquakes (M>7.0), centered in Vrancea, recur three times every century. These buildings were affected by the 1940 and 1977 earthquakes, but performed well relative to their high vulnerability. Out of the 61 buildings heavily damaged in the 1977 earthquake, 28 were of this type but were high-rise (7-9 floors).

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by Maria D. Bostenaru, Ilie Sandu

This is a post-World War II variant of the well-known Romanian ‘inter-bellum’ building. This urban housing construction was practiced in Romania over a rather short period of time after World War II until nationalization in 1947. Buildings of this type are still in use, mainly as apartment buildings. They are typically 7 to 11 stories high and the main load-bearing structure consists of a reinforced concrete space frame with reinforced concrete diagonal bracings. The floor structure consists of RC solid slabs and beams cast-in-place. The frames are infilled with brick masonry walls (typical wall thickness 140 mm or 280 mm). These buildings were designed according to the temporary guidelines issued in 1941 by the Ministry of Public Works (MLP) and based on German recommendations. This region is well known as a seismically prone area, with the epicenter of damaging earthquakes close to Vrancea. Earthquakes of Richter magnitude over 7.0 occur once in 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-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. It should be noted that although buildings of this construction type experienced severe damage (mainly cracking in the columns and the brick masonry infill walls) collapse was not reported. After the 1977 Vrancea earthquake, the damaged buildings were repaired and strengthened. One of the buildings described in this contribution was retrofitted by strengthening the existing columns with new reinforced concrete jackets and by replacing the existing brick masonry infill walls with new lightweight concrete block walls. The diagonal bracings were removed as a part of the retrofit. Another example shows a triangular-shaped building with the original bracing preserved during the retrofit.

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