Assessment of the Role of Drop Panel on Post Yield Performance of Flat Plate Framing System
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Date
2020-09
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Addis Ababa University
Abstract
Flat plate is among the commonly used flooring systems, simplicity in construction formwork set up and architectural freedom made this system very ideal and most practiced. Its use is limited to resisting vertical loading, its role as a primary lateral load resisting system is pulled back by its poor performance during cyclic earthquake loading. This poor performance; development of brittle punching shear hinge at a slab-column connection is the main reason for the system to be prohibited for use as a primary lateral load resisting system. Flat plate framing system uses a beamless plate for vertical load transfer and bracing of building. Connection capacity of this framing system is very small owing to the fact that beams are absent at connections. Unbalanced moment at the slab-column connection compromises the shear capacity at the shear critical region. This compromised shear capacity will result in a brittle punching shear failure during an earth quake loading. To overcome this connection failure, moment-shear interaction at slab-column connection needs to be properly modelled and be accounted for in analysis and design. Using eccentric shear model to analytically model moment-shear interaction at a slab-column connection, the role of drop panels in post yield response of flat plate framing system acting as a primary lateral load resisting system is studied. For this purpose 3-storey and 6-storey buildings were used as model buildings. A static nonlinear pushover analysis is used to compare post yield performances of these building models with and without drop panels. Out puts of nonlinear analysis showed that a drop panel helped avoid a brittle punching shear failure at slab-column connection. Drop panels on both model buildings have made yielding of flexural reinforcement to occur before punching shear failure, thus insuring a global ductile failure. Both the 3-story and 6-story model buildings have shown an increased base shear coefficient and roof drift ratio due to drop panels at slab-column connection. It is learnt that drop panels did not change the early stiffness of both building models. It is also learnt that early strength loss and sudden loss of stability on model buildings were improved by using drop panels at slab-column connection.
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pushover analysis, eccentric shear model, drop panel, punching shear