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A flat platestructural system transfersthe load directly to the columns without any beams.This type of structure is space-efficient and thus becoming popular among designers. To satisfy both architectural and financial requirements, flat plate technology has been used in many recently built buildings. Bangladesh National Building Code does not allowflat plate constructions for Seismic Design Category D due to substantial concerns about their seismic behaviour. Brittle punching shear failure due to the transfer of shear forces and unbalanced moments between slab and column in flat plate structures causes serious problems. Concrete shear walls with flat plate structures have been developed to get around the problem of handlingseismic/lateral loads. Shear walls make the structure stiffer and help to reduce seismic demand.
Although a flat plate-shear wall (FP-SW) dual structural system is being used in many countries, its characteristics and behaviour stillneed to be well understood. Limited research has been conducted on the seismic behaviourof this type of structure. The seismic parameters (response modification factor, ductility reduction factor and overstrength factor) of the FP-SW structural system are not mentioned in any recognized building codes. In recent years, some researchers have worked on the nonlinear seismic behaviour of the flat plate structure. This research work aims to observe its performance under the seismic load prescribed in BNBC 2020 andevaluate the seismic parameters for a flat plate frame-shear wall dual structural system.
In this study, 54 models havebeen generated by varying the aspect ratio of the plan of the building, number of stories, storey height and material strength for parametric study. The buildings are first designed as dual system frame structures with special moment resisting frames in the moderate seismic zone (Zone 2) as per BNBC 2020.Linear static analysis and nonlinear static pushover analysis have been conducted using ETABS 2016. The slabs of the buildings are modelled as layered shell elements. The nonlinear behaviour of the individual components is incorporated,and the target displacement has been calculated according to ASCE 41-13 ‘Displacement Coefficient Method’. Through a parametric study, it has been found that the value of the response modification factor (R) decreases with theincreasing height of the buildings andincreases with higher-grade materials. The structure shows more elastic deformation before the collapse.The position and proportion of the shear wall also play an important role in determining the response modification factor, R. In the caseof special detailing of columns and shear walls,the study recommendsusing the response modification factor, R as 3.5, overstrength factor, Ω as 2.50 and ductility reduction factor, Rµ as 1.40for FP-SW dual systems for SDC A, SDC B and SDC C.FP-SW dual systemis, however, not recommended for SDC D, SDC E and structures more than 50m high. |
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