Comparison between flat and Conventionalslab of high rise buildings with varying geometry under seismic loadingcondition SOHAN LAL*M. Tech. Student of Patel Institute ofEngineering & Science Bhopal M.P.
com Prof. J. P. Gupta**H. O. D.
Of Civil Engg. Department**Email: [email protected] 1 ABSTRACT This paper focuses on comparative study in the behavior of high risebuilding structures under seismic loading condition and wind pressure by usingdifferent types of slabs in various types of geometries. The whole analysis isdone by taking conventional slab and flat slab in various geometries and variousfloors separately. The parametric studies comprise of maximum lateraldisplacement, beam shear, storey drift and axial forces generated in the beamand column. For these case studies we have created 18 models for conventionaltwo-way slabs and flat slab without shear wall in rectangular, hexagonal andoctagonal geometry.
The modelling is done in STAAD.pro V8i for seismic zonesIII and rectangular, hexagonal and octagonal geometries have considered foranalysis. Plan size of rectangle 16X28 m, Hexagonal 16 m in diameter, andoctagonal 12 m in diameter have considered.
The models have alsodeveloped for different number of floors taking G+9, G+15 and G+23 storey forall above geometries. Seismic loadings, wind loadings are considered separatelyto evaluate the performance of all the 18th modelsand conclusions have drawn on the best slab framing system. Hence a deep comparativestudy is done to identify the best slab system in seismic zone III. KEYWORDS:Flat Slab, Conventional Two Way Slab, RCC Structure, Design & STAAD.pro V8i1 INTRODUCTION There is an increasing demand forconstruction of high rise buildings due to urbanization and an ever increasingpopulation.
Earthquake and wind pressure are the biggest enemy of such tallstructures. These earthquake forces are hazard in nature and are thusunpredictable. The structure designers needs to analysing the structures underthe action of these seismic forces and varying wind intensity.
Thus a careful analysisis required of such loads, so as to evaluate the external forces on tallstructures with a clear perspective of the damage that is to be expected. The structures are analysed for variousearthquake intensities and wind intensities then apply check for various performingcriteria at each level. It is become an essential practice for the last some decadesoccurs in the century. Hence the seismic characteristics and windcharacteristics of buildings having same layout needs to be understood under variousdifferent intensities of earthquake. It is necessary to carry out seismicanalysis and wind analysis of the building structure using different methods for determination of seismic characteristicand wind characteristic in structure. The main objective of this paper is to analysisand comparison between flat slabs and conventional two way slabs usingSTAAD.
proV8i, to get the best slab system. The design involves various loadcalculations, beam shear, beam moment and nodal deflection and analysing thewhole structure by STAAD.pro V8i using Limit State Design method using IndianStandard Code of Practice (IS: 456-2000). The STAAD.pro features are tostate-of-the-art user interface, and powerful analysis and design engines. Itoffers visualization tools, modelling tools and advanced finite element &dynamic analysis capabilities. STAAD.
pro offers a very interactive userinterface which allows the users to draw the new frame section and input themember property, element property, supports and load values. Then according tothe specified assigned property of the structure, it analyses the structure andfinally designs the all members with reinforcement details for RCC frames. 2.1 STAAD-pro V8iSTAAD pro is the leading Structural analysisand Design Software developed in Yorba Linda, CA by Research EngineersInternational. In the late months of year 2005, Research engineer was broughtby Bentley Systems. The professional version STAAD.
PRO is few of the majorlyused structural design and analysis software. It is quite user friendly andsupports a number of steel, concrete and timber design codes. It can makeutilization of different manifestations of structural analysis from theconventional first order static analysis, second order p-delta investigationand geometrical non-linear analysis.2.2 FLOOR SYSTEMS:-Slabs are used as flat surfaces, usually horizontal in building, floors,roofs, bridges slab and many other types of structures. The slab may besupported on directly walls, on reinforced concrete beams usually cast monolithicallywith the slab, on structural steel beams, on directly columns, or on the groundsurface. Slabs may be classified in different 16 types used in differentstructures. Flat slab and conventional slab are one of them.
Which arediscussed below:- 2.2.1 FlatSlab Floor System-Flat slab is areinforced concrete element supported directly on concrete columns or on thedrop panels used above the columns.
There are no beams in a flat slab. Slab issupported directly on columns itself and all applied loads are transferred to directlycolumns. In flat slab construction there are a plain ceiling is obtained andhence it offers attractive appearance from architectural point of view. Theconstruction of flat slab is easy and economical compare to other beam slabs andrequires less formwork. And also required less time for construction compare toother beam slabs.
The light is diffuses better by plain ceiling and also lessvulnerable in the case of fire compare to other beam slabs The flat slab iseasier to construct. The thickness of Flat slab is provided minimum 8? or 0.2m. 2.2.
2 ConventionalSlab Floor System:-The slab which issupported with Beams is known as conventional slab. In conventional slab thethickness provided is small and depth of beam is provided large and hence all loadsare transferred to beams, to Columns and then finally to foundations. Itrequires more time for construction as formwork increases compared to the flatslab system. The thickness of conventional slab is provided as 5? to 6?or 150mm.
The main reinforcement is providedin conventional slab in one direction or in both direction according to lengthand breadth of Conventional Slab. Based on the length and breadth ofConventional Slab is classified into two types: These types of slabs are usedin constructing floors of multistory building. Classification of Conventional Slab:- One-Way Slab Two-Way Slab 2.3 OBJECTIVEOF STUDY:-Ø Analysisof multi storied RCC buildings with Flat slab &Conventional slab (G+9,G+15& G+23 Storey) having Rectangle, Hexagonal, Octagonal geometry, bySTAAD.pro V8i using Limit State Design method considering earthquake Zone IIIas per the Indian Standard code of practice IS 1893-2002 part-I: Criteria forEarthquake resistant structure.
Ø Tomodel different structures with aforementioned configuration and compare themusing design aids like STAAD.pro V8i. Ø Tocompare the seismic behavior of multi storied RCC building with Flat slab &Conventional slab for different earthquake intensities in terms of variousresponses such as, Beam Shear, Beam Moments, Maximum Nodal Deflection andMaximum Axial load on Columns. Ø Tofind the relationship between earthquake intensities and responses. Ø Tofind the best slab system for high rise buildings in different geometries.