Assessment of Ribbed Slab Constructions Framed Only in One Direction Against Lateral Load Excitations

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Addis Ababa University


Nowadays construction of buildings using ribbed slabs, with hollow blocks, is common from low to high seismic regions of Ethiopia. When investigating some of the buildings constructed and being constructed using such slabs, framing only in one direction is being practiced. In recent years, numbers of earthquakes have also occurred in different parts of the country. The occurrence of these earthquakes has drawn increased attention towards the importance of seismic performance evaluation and improvement of existing structures to reduce seismic risk. In this thesis work, performance evaluation of three case study buildings, constructed using ribbed slabs with hollow blocks framing only in one direction is done using static nonlinear, pushover, analysis. During the conventional analysis of such buildings, the floor slabs are considered to act as a rigid diaphragm. Therefore, in this thesis, the three case study buildings are evaluated for rigidity of the diaphragms. The result of the performance evaluation proved that the buildings do not perform adequately to insure the safety of their dwellers at their earth quake design level. The result of diaphragm flexibility check has also shown that the stiffness of such slabs is not sufficient to act as a rigid diaphragm in the longitudinal direction of the ribs. To improve the performance of the evaluated case study buildings, the introduction of the missing beams were found not to be sufficient. Therefore, addition of shear walls with some defined cross sectional dimension and plan distribution are recommended in addition to the insertion of the missing beams. Keywords: Ribbed slabs, framing only in one direction, seismic performance evaluation, static nonlinear analysis, pushover analysis, diaphragm, diaphragm flexibility



Ribbed slabs; framing only in one direction; seismic performance evaluation; static nonlinear analysis; pushover analysis; diaphragm; diaphragm flexibility