Assessment of flat plate Construction without shear walls with respect to the effectiveness against lateral load resisting Capacity

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Addis Ababa University


The overwhelming social and economic impacts of recent earthquakes in the world have resulted in an increased awareness of the potential seismic hazard and the corresponding vulnerability of existing structures. Greater effort has been given to reasonable estimates, predictions and mitigation of the risks associated with these potential losses. As being one of the special reinforced concrete structural forms, flat-slab systems need further attention. We are living in an era when flat slab construction activity is booming due to many advantages it posses in terms of architectural flexibility, use of space, easier formwork and shorter construction time, However the structural efficiency of the flat-slab construction is hindered by its poor performance under earthquake loading. This undesirable behavior has originated from the insufficient lateral resistance due to the absence of deep beams or shear walls in the flat-slab system. Hence, the effectiveness of flat slab structures without shear walls or other stiffening mechanisms needs to be investigated against seismic hazard. Generally, flat-slabs can be designed by any procedure that satisfies equilibrium and geometric compatibility provided that every section has strength at least equal to the required strength (ACI-318). In this study various flat slab analysis methods that are pertinent to gravity and earthquake loading are reviewed along with different modeling techniques. Among many of flat slab analysis methods, Direct Design Method, Equivalent Frame Method and The finite analysis method are the most commonly used methods of analysis. And finally, FEM method is used to analyze flat slab buildings along with the effective beam width modeling method for gravity and seismic loading respectively. The regularity of the buildings in terms of mass and stiffness both in plan and elevation enabled the utilization of Assessment of flat slab Construction without shear walls with respect to the Effectiveness against lateral load resisting Capacity. AAU ,FoT, Department of Civil Engineering By :Eyob Tadesse two-dimensional analysis in the assessment of seismic response. Hence, in this study, the three dimensional flat-slab building is modeled as a series of two dimensional interconnected planar frames. For the modeling of the 2-D planar frames, the portion of the slab that will contribute to the frame analysis is determined as well as the width of the concealed beam within this slab portion. In this study different flat slab structures with different aspect ratios are modeled, analyzed and designed to satisfy strength requirements and these structures designed for strength are evaluated against drift capacity. Building layout in plan is kept constant while slab depth and building height are used as a variable by increasing the number of stories up to the attainment of the largest practical slab depth. Finally, Low to medium rise flat plate structures (G+1 - G+6 ) having medium spans , located in seismic zone 2 which are designed and analyzed in this study found to be effective in seismic hazards resistance. How ever, the outcome of this study articulate that flat plate structures with more than six numbers of stories constructed in seismic zone II need to be combined with shear walls or other stiffening mechanisms.



(Structures Major