Flat Slab System Research Articles

Fragility analysis of flat-slab structures

Flat-slab RC buildings exhibit several advantages over conventional moment-resisting frames. However, the structural effectiveness of flat-slab construction is hindered by its alleged inferior performance under earthquake loading. Although flat-slab systems are widely used in earthquake prone regions of the world, fragility curves for this type of construction are not available in the literature. This study focuses on the derivation of such fragility curves using medium-rise flat-slab buildings with masonry infill walls. The study employed a set of earthquake records compatible with the design spectrum selected to represent the variability in ground motion. Inelastic response-history analysis was used to analyze the random sample of structures subjected to the suite of records scaled in terms of displacement spectral ordinates, whilst monitoring four performance limit states. The fragility curves developed from this study were compared with the fragility curves derived for moment-resisting RC frames. The study concluded that earthquake losses for flat-slab structures are in the same range as for moment-resisting frames. Differences, however, exist. The study also showed that the differences were justifiable in terms of structural response characteristics of the two structural forms.

1985年メキシコ地震で被災した某鉄筋コンクリート学校建築の耐震性能に関する調査・検討

Introduction Two 4-story reinforced concrete buildings in Fig.2 suffered moderate damage to structures as well as severe damage to nonstructural elements during the 1985 Mexico Earthquake. One month after the earthquake, the buildings were inspected by the authors' team on the level of damage, properties of materials and vibrational characteristics of the buildings and the ground. The inspection was made as a part of activities of the technical mission to the Department of Federal District of Mexico sent by the Japanese Government through the Japan International Cooperation Agency (JICA). After the inspection, further studies were made on their seismic capacity and response so that their behavior during the earthquake and the proposed strengthening methods might be discussed in detail. The Buildings and Their Damage These buildings were constructed in 1982 and have been used as a school for medical students. They were structurally identical except six month different in the completion of construction and different concrete strength by core sampling test. The building W had higher strength (36MPa) than that of another (25MPa). They located at the Transition Zone (Fig.1) and the subsoil consisted of soft clay of 16m thick and of deeper layer of solid sand and other soils (Fig.3). A building consisted of moment-resisting frames of columns and flat slab system called "Losa Plana" (Fig.5). No structural wall was provided. Grouped longitudinal reinforcements were arranged at each corner of a column (Fig.4). The structural damage was concentrated on columns and beams which existed only in the sticking portion be approximately 1 cm or 0.33% to the story height which could lead to moderate or partially severe damage to structures, though it is much less than the yield displacement. The displacement at upper stories is minor. These results well agree with the feature of observed damage. 2) The response dispacement is higher by approximately 50% when subjected to the recorded motion of SCT. 3) The strengthening by concrete walls leads to very minor displacement even during the motions of 1.5 to 2.0 times the intensity of simulated motion. 4) When most columns are reinforced, the structure is able to resist even an earthquake of 2 times the intensity of the simulated motion without any brittle failure. Conclusions 1) It is presumed that the ground motion at the building site would have possessed the characteristics of shorter period and lower intensity compared with those in the Lake Zone. 2) The damage to structures, bond-splitting failure in one building and flexural failure in another, would have occurred because of the lack of lateral stiffness and capacity, the grouped reinforcement with thin concrete cover and the difference of concrete strength. 3) It is presumed that the maximum story drift during the earthquake would have been around 0.3%, which was much less than the yield displacement. 4) Their seismic performance will be significantly improved when they are strengthened by concrete walls or reinforcement of columns.

Stress Analysis of Historic Structures: Maillart's Warehouse at Chiasso

The significant architecture of any era is expected to include its large public buildings: the temples and arenas of the classical period, the cathedrals of the Middle Ages, and the transportation terminals and exhibition halls of our own time. Nevertheless, the main lines of architectural development pass through other construction as well: in residence, school, and office buildings, and even in granaries, mills, and warehouses. Early-20th-century examples from this last category often cited as important sources of modern architectural design include the Berlin AEG Turbine Factory of Peter Behrens (1909), the Bauhaus at Dessau of Walter Gropius (1926), and the Mobilier National, Paris, of August Perret (1931). The warehouse of the Magazzini Generali at Chiasso, designed by E. Brenni and Robert Maillart in 1924, is another industrial building that has attracted the interest of architectural historians.' But, in fact, it is not the warehouse building that is especially significant, although it does provide an excellent example of the mushroom-column and flat-slab floor system in concrete that Maillart originated in 1910. Rather, it is the framing of an attached reinforced-concrete storage shed that has commanded so much attention (fig. 1). This shed, attributed to Maillart, is relatively small (33 x 50 meters in plan) and is, in fact, hidden behind the main building, a peculiarity that seems