ANALYSIS AND DESIGN OF RAFT FONDATION
IJRET: International Journal of Research in Engineering and TechnologyeISSN: 2319-1163 pISSN: 2321-7308ANALYSIS AND DESIGN OF RAFT FONDATIONZia-abe Deen. S. Punekar1, M H Kolhar2, Anjum Algur3, Kushappa M K41Professor, Research centre Civil Engg Dept, SIET Vijayapur, Karnataka, IndiaAssociate Professor, Research centre Civil Engg Dept, SIET Vijayapur, Karnataka, India3Associate Professor, Research centre Civil Engg Dept, SIET Vijayapur, Karnataka, India4Assistant Professor, Research centre Civil Engg Dept, SIET Vijayapur, Karnataka, India2AbstractIn Recent Era due to enhanced aesthetic construction we couldn’t provide the regular spacing of the column so like we couldn’tprovide the Isolated footing or combined footing everywhere in every construction, hence it is very common nowadays in themarket to provide the Raft footing so it helps in reducing the cost, effort of excavation and prevents sliding of adjacent footing. Inthis study a 12-storey building having conventional slab has been analyzed using Etabs-13 and Safe-V12 for the parameters likemoment, Punching shear and deflection of the footing. The Multistory Model will be imported from ETABS to Safe for the analysisand design of the Raft footing.Keywords: Raft Foundation, SAFE-V12, Response Spectrum Analysis, Punching Shear, and . INTRODUCTION An earthquake is a manifestation of the rapid release ofstress in the form of waves during the process of brittlerupture of rock. Earthquakes are the natural disasters of agenerally unpredictable nature. Nowadays, high-risebuildings are the symbols of a modernized living standardbecause of the population growth. Among them, earthquakedisasters are not limited to structural damage andinjury/death of people under collapsed structures. Afoundation, the lowest part of a structure, is in direct contactwith ground and located below the ground level. It transmitsall the loads from super-structure to the supporting soil. So,foundation design for an earthquake resistance is one of themost important parts to be considered in the structuralanalysis and design. For foundations of such high risebuilding, normally raft foundation, pile foundation or piledraft foundation are used. The raft will be used foreconomical consideration. The raft foundation is a kind ofcombined footing that may cover the entire area under thestructure supporting several columns in one rigid body. 1.1 Raft FootingThe raft will be used for economical consideration. The raftfoundation is a kind of combined footing that may cover theentire area under the structure supporting several columns inone rigid body. Raft foundations (sometimes known as MatFoundations) are a large concrete slab which can support anumber of columns and walls. The slab is spread out underthe entire building or at least a large part of it which lowersthe contact pressure compared to the traditionally used stripor trench footings.To study the Dynamic performance of Raft footingsubjected various loadings.To study the behavior of the structure for theparameters like Moments, Punching Shear anddeflection in SAFEDesign of the Raft foundation and detailing the same. 3. METHODOLOGYThe following methodology is used to achieve the abovedefined objectives. In ETABS 9.7.4 Story building has been analyzed usingResponse spectrum method. Exporting the axial loads at the base of the column tothe SAFE V12.FZK text format. Modeling the raft foundation (Concrete area) in SAFEV12. And assigning the actual material properties. Strips to be drawn both in X & Y direction @ aninterval of 1ft keeping the strip width of 0.5 ft. Then its required to satisfy both One-way shear &Punching Shear. Analyze the model for the axial Loads derived from theETABS-9.7. Footing should be analyzed for envelope combinationswhich includes all the load combinations and design ofthe Raft foundation and detailing the same.NumberstoreyThicknessslabBeams2. OBJECTIVESIn this study, the seismic performance of Raft footing willbe investigated through Response spectrum analysis.ColumnsTable-1: Building Descriptionof 12- storeyof150mmB200X450M25, B200X600M25,B300X450M25, B300X600M25,B300X900M25, B300X750M25C300X1000M30, C650X1000M30,C800DiaM45Volume: 06 Issue: 10 Oct-2017, Available @ http://www.ijret.org14
IJRET: International Journal of Research in Engineering and TechnologyWallsSteelConcreteandeISSN: 2319-1163 pISSN: 2321-7308Wall200XVaries, Wall300XVaries,Wall400XVaries, Wall550XVariesFe500 and M25, M30Table-2: Design Loads and Seismic ParametersLive load3 kN/m²Floor finish1.5kN/m²Wall Loads17.5KN/m2, 12KN/m2ZoneIVImportance FactorI 1ResponseReduction R 5(SMRF)factorSBC300KN/m2Codes UsedIS-456-2000,IS-18932002,SP-164. BUILDING MODELSThe most important step in the Seismic Analysis of astructure is to create an appropriate mathematical model thatwill adequately represent its stiffness, mass distribution andenergy dissipation so that its response to earthquake couldbe predicted with sufficient accuracy. The frames have beenmodeled and analyzed using software ETABS-9.7. Beamsand columns are modeled as frame elements with centerlinedimensions. Supports at the base are assumed to be fixed.And raft foundation is modeled in Safe-V12 as a slabelement and SAFE provides an immensely capable yet easyto-use program for structural designers, providing the onlytool necessary for the modeling, analysis, design, anddetailing of concrete slab systems and foundations. UserInterface SAFE offers a single user interface to perform:Modeling, Analysis, Design, Detailing and Reporting.Fig- 1: Plan and 3D view of building5. RESULT AND DISCUSSIONThe selected frame models are analyzed using (Dynamic)Response Spectrum analysis. The results obtained from thisanalysis are such as Axial Loads from foundation level areexported from Etabs-9.7 and then imported in SAFE-V12.And modeled and analyzed in SAFE to study the behaviorof the structure for the parameters like Moments, PunchingShear and deflection in SAFE and designed the Raftfoundation and detailing the same.5.1 MomentsLayer-B (Grid- A) Moment 1043.07Kn-m, (from SAFE),Mu/bD2 1.287 Pt 0.316% Ast 2844mm2From Software same strip Ast 2500mm2.Volume: 06 Issue: 10 Oct-2017, Available @ http://www.ijret.org15
IJRET: International Journal of Research in Engineering and TechnologyeISSN: 2319-1163 pISSN: 2321-7308And in this case the image has been attached to show thatthe punching stress is lesser than the allowable stress. Hencewe know that to satisfy two way shear or punching shearτv τc i.e 0.1237 1.25. Hence punching shear is satisfied.Fig- 2(a): Moments on horizontal stripFig- 2(b): Area of steel on horizontal stripFrom the Above figures we can observe that the Area ofsteel obtained from the moment given from the Safe for theEnvelope combination is same as the Area of steel obtainedfrom the strips. So we can conclude that the design processin SAFE is for the Envelope combination.Fig- 3: Punching shear5.2 Punching ShearHere in this case we can observe that the Punching shear orthe other name is Two-way shear will be displayed forsmaller column or the columns assigned as line element.Because the in larger column there is no chances ofpunching the slab/footing at a single point. The load will beconverted as linear load.Volume: 06 Issue: 10 Oct-2017, Available @ http://www.ijret.org16
IJRET: International Journal of Research in Engineering and TechnologyeISSN: 2319-1163 pISSN: 2321-73085.3 DeflectionFig- 4: DeflectionEven though the Raft is on Grade we can expect a slightdeflection in the footing. In this we can observe that thedeflection of -16.5mm for this larger footing. Negativeindicates the hogging deflection.5.4 Design and DetailingDetailing is done using the area of steel obtained from theSAFE. Detailing will be like Top & Bottom reinforcementand again it will be like X direction & Y directionreinforcement.First layer has been provided through and throughT16@150c/c both ways in general. And second layer isprovided only where ever it is required.Volume: 06 Issue: 10 Oct-2017, Available @ http://www.ijret.org17
IJRET: International Journal of Research in Engineering and TechnologyeISSN: 2319-1163 pISSN: 2321-7308Fig-5: Detailing of Raft Foundation6. CONCLUSIONSCOPE FOR THE FUTURE STUDYIn this study we can conclude that the Raft footing is analyzedand designed for the envelope combination. That will be thecritical combination, obviously for one of the dynamiccombinations. Moment: From the above study it has been concludedthat the area of steel obtained from the moment givenfrom the safe for the envelope combination is same asthe area of steel obtained from the strips. So we canconclude that the design process in SAFE is for theenvelope combination. Punching Shear: It has been also concluded that themat/raft foundation is safe against punching shear ortwo way shear i.e. the punching shear ratio is less than1. Deflection: From above study we can also observe thatthere will be a slight hogging deflection in the raftfooting but it will not affect the building and also withinthe limit. Detailing & Casting: is quite simple compared toisolated footings. Excavation will be in one go and thepouring of concrete will be at a time this leads to savingin both the cost and time. We can compare the RAFT and ISOLATED footingsfor the same building to know the difference in terms ofcost.We can Analyze and design the Raft Foundation forTime-History Analysis.This study can further extended design the Raft or Matwith pile.REFERENCES[1]. THU ZAR AUNG1, DR. KAY THWE TUN,“Parametric Study on Foundation of Regular High-RiseR.C Building under Seismic Load” International journalscientific engineering and technology research, ISSN 23198885 Vol.03, Issue.10 May-2014, Pages: 2089-2095.[2]. Jay P. Chaliyawala, Hitesh K.Dhameliya,Hiten L.Kheni, “A REVIEW OF PERAMETRIC STUDY OFRAFT FOUNDATION” International journal of AdvanceEngineering and Research Development, Volume 1,Issue12, December -2014Volume: 06 Issue: 10 Oct-2017, Available @ http://www.ijret.org18
IJRET: International Journal of Research in Engineering and TechnologyeISSN: 2319-1163 pISSN: 2321-7308[3]. NithyaChandran J, AbhilashRajan, Soni Syed, “Seismicanalysis of building with underground storiesconsidering soil structure interactions” InternationalJournal of Emerging Technology and AdvancedEngineering,Website:www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 4, Issue 11,November 2014)[4]. Haytham Adnan Sadeq Mohammed SaleemTaha,“Structural Design of Raft Foundation” Qatar UniversityCollege of Engineering (Course: Design Of ReinforcedConcrete Structures)[5]. SagarSatishTayade, Mukund M. Mahajan, “Foundationin Refilled Soil” International Journal of InnovativeResearch in Science, Engineering and Technology, Volume3, Special Issue 4, April 2014[6]. IS 456-2000, “Plain and reinforced concrete-code ofpractice”, bureau of Indian standards, new delhi[7]. IS 875 (Part-I,II,III):1987, “code of practice for designloads for buildings and structures”[8]. IS 1893 (Part-I):2002, “Criteria for Earthquake resistantdesign of structures, general provisions for buildings[9]. SP-16 “Design Aids for Reinforced concrete to IS-4561978.[10]. ETABS-9.7 Manuals and Tutorials[11]. SAFE-V12 Manuals and Tutorials[12]. www. Wikipedia/Raft Foundation.comBIOGRAPHIESMr. Z.S.PUNEKAR presently he isworking as professor in civil engineeringdepartment of Secab Institute OfEngineering And Technology VijaypurIndia.Mr. M.H.KOLHAR presently he isworking as Associate professor in civilengineering department of Secab InstituteOf Engineering And Technology VijaypurIndia.Mrs. ANJUM ALGUR presently She isworking as Associate professor in civilengineering department of Secab InstituteOf Engineering And Technology VijaypurIndia.Mr. KUSHAPPA M K presently he isworking as Assistant professor in civilengineering department of Secab InstituteOf Engineering And Technology VijaypurIndia.Volume: 06 Issue: 10 Oct-2017, Available @ http://www.ijret.org19
analysis and design. For foundations of such high rise building, normally raft foundation, pile foundation or piled-raft foundation are used. The raft will be used for economical consideration. The raft foundation is a kind of
analyses of un-piled and piled raft foundations with sandy soil. For the un-piled raft, the normalized settlement parameter (IR) for the raft sizes of 8mx8m and 15mx15m ranged as 1.03-1.17mm and 0.66- 0.83mm respectively. In the case of the piled raft with raft thickness of 0.25, 0.40, 0.80, 1.50, 3.0m, the corresponding maximum settlements
, respectively. Raft foundations fail when the resistance of the raft is less than the action caused by the applied load. The raft resistance is measured using the design moment strength M c while the raft action is measured by the external bending moments M e as shown in Figure 1. The raft limit state function is given by the following equation:
As with any foundation system, a design of a piled raft foundation requires the consideration of a number of issues, including: 1. Ultimate load capacity for vertical, lateral and moment loadings 2. Maximum settlement 3. Differential settlement 4. Raft moments and shears for the structural design of the raft 5.
these systems can be combined and one can have a more efficient, safe and economical design. Thus, piled raft foundation system is one of those combined systems. In designing raft foundations, engineers frequently encounter situations in which the bearing capacity of the raft is quite adequate, but the settlements are estimated to be excessive.
the design requirements, piled raft foundations come out as an economical foundation option under such circumstances. Different methods of analysis of piled raft foundations have been developed, but there is only limited information about comparative performances of the piled raft foundation under various parameters.
the relationship between raft thickness and the number of design parameters, including soil type [9-10]. 3 TYPES OF FOUNDATION The most common forms of deep foundations are piles, pillars and caissons. The mechanism for shifting the weight to the ground is basically the same in these types of foundations. Raft.
Piled raft foundations provide an economical foundation option for circumstances where the performance of the raft alone does not satisfy the design requirements. Under these situations, the addition of a limited number of piles may improve the ultimate load capacity and reduce the settlement [1]. Katzenbach et al. [2] termed piled
Introduction to Magnetic Fields 8.1 Introduction We have seen that a charged object produces an electric field E G at all points in space. In a similar manner, a bar magnet is a source of a magnetic field B G. This can be readily demonstrated by moving a compass near the magnet. The compass needle will line up
