With the growing urbanisation and rise in the prices of land, the vertical displacement of human dwellings has gone up by many folds. Most of the buildings constructed in the recent years have seen a rapid growth in their height. This also resembled a new feature in these buildings which has increased total area of space or the space required for parking and lobbies i.e. the provision of soft storey or flexible storey. These soft storey or flexible storey in a building is the opened plinth level without infill walls. These soft storey or flexible storey in a building finds most of their uses in allocation for parking, lobbies and sometime to avoid artificial flooding. It has become an unavoidable feature in the multi-storey RC buildings. But the influence of provision of soft storey or flexible storey in buildings has never been positive as it creates large amount of instability between adjacent ground floor and the upper floors.
Influences of soft storey or flexible storey in building
As stated earlier, the influence of soft storey or flexible storey in a building has never been positive in the sense of resistant to the horizontal earthquake forces. This type of floor actually creates separation between the adjacent upper floors and the ground floor during the time when horizontal forces are in action. The soft storey at this time displaces greater as compared to the upper unit of floor thus they are also termed as flexible storey. One of the most significant influences of soft storey is that it contributes to the causes of the collapse of RCC frame building. Most of the buildings that has been built across various towns and cities has found a relevant cause of collapse, i.e. the soft storey tends to create a large difference in the stiffness values in between the ground and upper storey of the building by many times. Thus, the upper storey tends to move almost together as a single block, and most of the horizontal displacements of the building occur in the soft storey or flexible storey itself.
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Provision to soft storey or flexible storey
1.By stiff column at open ground storey : The effects of stiffness is very important as if the setting of the stiffening elements at structure and their geometrical specifications are not opted accurately, the structure may undergo amplify against the earthquake waves and the structure may be subject to fracture and may even lose its practical aspects. If the stiffness of structure elements in multi-storey structures alters, it can precipitate the vibration of structural modes shape. Stiffness of a column means resistance to deformation- the larger is the stiffness, larger is the force required to deform it. In this study, the seismic vulnerability of buildings with soft first storey is shown with the help of core-study. The drift and the strength demands in the first storey columns are very large for buildings with soft ground storeys. Thus, it is important to incorporate the stiff column at open ground storey.
2.By provide adjacent infill wall panel at each corner of open ground storey in building frame : Masonry infill is normally considered as non-structural elements and their stiffness contributions are generally ignored in practice. Masonry infill has several advantages like good sound and heat insulation properties, high lateral strength and stiffness. These help to increase the strength and stiffness of RC frame and hence to decrease lateral drift, energy dissipation capacity due to cracking of infill and friction between infill and frame. This in turn increases redundancy in building and reduces bending moment in beams and columns. Masonry infill has disadvantages like very high initial stiffness and compressive strength. This also induces torsional effect in the structure if not symmetrically placed. While analyzing multi storey buildings, designers usually neglect the contribution of masonry infill in resisting loads. They consider only dead weight of masonry and analysis is done by bare frame method.
The present study has been carried out the effect of masonry infill at adjacent side of each corner of the open ground storey for 12 storied building using SAP 2006 software.
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International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 3, Issue 2, March -April 2013, pp.461-468 461 | P a g e ‘ ‘Influence of Provision of Soft Storey in RC Frame Building for Earthquake Resistance Design’’