Assessment of flat plate Construction without shear walls with respect to the effectiveness against lateral load resisting Capacity
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Date
2009-11
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Addis Ababa University
Abstract
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.
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(Structures Major