IJSRD - International Journal for Scientific Research & Development Vol. 4, Issue 05, 2016 ISSN (online):

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IJSRD - International Journal for Scientific Research & Development Vol. 4, Issue 05, 2016 ISSN (online): 2321-0613 Seismic Analysis of Multistorey Building with Floating Columns Ashish. G.

Student 2 Assistant Professor 1,2 Department of Civil Engineering 1,2 Institute of Technology, University of Gondar, Ethiopia Abstract The objective of the present work is to study the behavior of

1 IJSRD - International Journal for Scientific Research & Development Vol. 4, Issue 05, 2016 ISSN (online): Seismic Analysis of Multistorey Building with Floating Columns Ashish. G. Pakmode 1 Prof. Lakshmikant Vairagade 2 1 M.Tech. Student 2 Assistant Professor 1,2 Department of Civil Engineering 1,2 Institute of Technology, University of Gondar, Ethiopia Abstract The objective of the present work is to study the behavior of multistorey buildings with floating columns under earthquake excitations. Finite element method is used to solve the dynamic governing equation. Linear time history analysis is carried out for the multistorey buildings under different earthquake loading of varying frequency content. The base of the building frame is assumed to be fixed. Newmark s direct integration scheme is used to advance the solution in time. The project is aimed at arriving to suitable configuration, modeling, developing models for analysis and design of building with floating column. A through study of relevant specifications is also aimed in the project. STAAD PRO version 8 is used for analysis and design. Key words: Floating Column, Multistorey Buildings, STAAD PRO earthquake s magnitude, its focus depth, distance from the epicenter, characteristics of the pathway through which the seismic waves moves, and the soil strata on which the constructed structure stands. The major direction of ground vibration is usually flat or horizontal. I. INTRODUCTION Many metropolitan cities multistorey buildings in India today have open first storey as an unavoidable feature. This is primarily being adopted to hold parking or reception lobbies in the first storey. Whereas the total seismic base shear as veteran by a building during an earthquake is reliant on its natural period, the seismic force distribution is reliant on the distribution of stiffness and mass along the height. The behavior of a building during earthquakes depends critically on its general shape, size and geometry, in addition to how the earthquake forces are carried to the ground. The earthquake forces developed at divergent floor levels in a building need to be brought down along the height to the ground by the shortest pathway; any deviation or discontinuity in this load transfer path results in poor performance of the building. Buildings with erect setbacks (like the hotel buildings with a few storey wider than the rest) cause a abrupt jump in earthquake forces at the level of discontinuity. Buildings that have less columns or walls in a particular storey or with oddly tall storey tend to break or collapse which is initiated in that storey. Many buildings with an open ground storey proposed for parking collapsed or were severely damaged in Gujarat during the 2001 Bhuj earthquake. Buildings with columns that suspend or float on beams at an intermediate storey and do not go all the means to the foundation have discontinuities in the load transfer path. A. What is an earthquake? Earthquakes are defined as a sudden vibration of the earth's surface that occurs after a release of energy in the earth's crust. Since the earth's crust is made up of several plates that are constantly moving slowly, vibrations can happen which result in small earthquakes. The majority of earthquakes are small but are not eagerly felt. Superior and aggressive earthquakes are those which occur in a discharge of energy as the plates slide past or crash into one another. The characteristics such as strength, period, etc. of seismic ground shakes estimated at any location depend upon the Fig. 1: Earthquakes Reinforced concrete Special moment frames are used as fraction of seismic force resisting systems in buildings that are planned to resist earthquakes. Beams and columns in moment frames are proportioned and detailed in such a manner that they must oppose flexural, axial, and shearing actions that effects as a building sways through multiple displacement cycles during strong earthquake ground shivering. Special proportioning and detailing requirements are liable for frame, competent of resisting strong earthquake shaking without important loss of stiffness or strength. These moment-resisting frame is called as Special Moment Frame cause of these additional necessities, which improve the seismic resistance in contrast with less severely detailed Intermediate and Ordinary Moment Frames. B. What is column? A column is supposed to be a vertical part of a building starting from foundation level and transferring the load to the ground. Fig. 2: Column C. What is a Floating Column? The term floating column is also a vertical part of a building which (due to architectural plan/ site conditions) at its lower level or Termination Level rests on a beam which is a horizontal part. The beams in turn transmit the load to other columns below it. All rights reserved by 219

Fig. 3: Hanging or Floating Columns There are a lot of projects in which floating columns are adopted, mainly above the ground floor, where transfer girders are employed, so that extra open space is

The transfer girders have to be planned, designed and detailed properly, mainly in earthquake zones. The column is an intense load on the beam which supports it.

Floating columns are capable enough to take gravity loading but transfer girder must be of sufficient size (Stiffness) with very minor deflection.

2 Fig. 3: Hanging or Floating Columns There are a lot of projects in which floating columns are adopted, mainly above the ground floor, where transfer girders are employed, so that extra open space is available in the ground floor. These open spaces may be necessary for assembly lobby or parking purpose. The transfer girders have to be planned, designed and detailed properly, mainly in earthquake zones. The column is an intense load on the beam which supports it. As far as analysis is concerned, the column is often assumed pinned at the base and is consequently taken as a point load on the transfer beam. Floating columns are capable enough to take gravity loading but transfer girder must be of sufficient size (Stiffness) with very minor deflection. Looking further, of course, one will continue to make buildings attractive rather than repetitive. However, this need not be done at the cost of poor performance and earthquake safety of buildings. Architectural features that are unfavorable to earthquake reaction of buildings should be avoided. If not, they must be minimized. When irregular features are incorporated in buildings, a significantly higher level of engineering effort is required in the structural design and so far the building may not be as good as one with simple architectural features. Hence, the structures already finished with these kinds of discontinuous members are rare in seismic regions. But those structures cannot be demolished, rather study can be completed to strengthen the structure or some corrective features can be suggested. The columns of the primary storey can be made stronger, the rigidity of these columns can be increased by retrofitting or these may be provided with bracing to reduce the lateral deformation. II. OBJECTIVE AND SCOPE To Analyze the behaviour of building for various floating combinations by dynamic analysis. To compare normal and floating column building with parameter such as the displacement by considering I.S code loading and load combination. III. MODELING AND ANALYSIS The building considered in the present report is G+6 storied R.C framed building of symmetrical rectangular plan configuration. Complete analysis is carried out for dead load, live load & seismic load using STAAD PRO. Response spectra method of seismic analysis is used. All combinations are Considered as per IS 1893:2002. Typical plan of building is shown in Fig.3.1 A. Building Properties Fig. 4: Plan of G+ 6 structures 1) Site Properties Details of building:: G+6 RC structure Outer wall thickness:: 230mm Inner wall thickness:: 230mm Floor height ::3 m Height of parapet wall ::0.8 m Thickness of parapet wall:: 230 mm 2) Seismic Properties Seismic zone:: II Zone factor:: 0.1 Importance factor:: 1.5 Response Reduction factor R:: 3 Soil Type:: medium Material Properties Material grades of M25 & Fe415 were used for the design. B. Loading on Structure Dead load: self-weight of structure Weight of 230mm wall: kn/m² Weight of parapet wall: 3.5 kn/m² Live load: 4 kn/m² Roof Live load: 1.5 kn/m² Wind load: Not considered Seismic load: Seismic Zone II C. Preliminary Sizes of Members Column:: 450mm x 600mm Beam:: 250mm x 400mm Slab thickness:: 125mm D. Model Type Type I: No float. Type II: float type I Type III: float type II Type IV: float type III (mix of Type I & II). 1) No Float All rights reserved by 220

3 4) Float 3 Seismic Analysis of Multistorey Building with Floating Columns 2) Float 1 Fig. 5: No Float Fig. 8: Float 3 3) Float 2 Fig. 6: Float 1 IV. RESULTS The results are obtained and presented in terms of critical structural response such as displacement in the building structure with and without float Models due to the applied seismic or earthquake load. The variations of the critical structural response for column C1, C5, C9 & C13 due to I.S code load combinations are presented below. Fig. 7: Float 2 All rights reserved by 221

6 Fig. 9: Results [7] Sekulovic Miodrag, Salatic Ratko and Nefovska Marija, Dynamic analysis of steel frames with flexible connections, Journal of computer and structures, Volume 80, Issue 11, Page no: , Volume 80, [8] Vasilopoulosa A.A and Beskos D.E., Seismic design of plane steel frames using advanced methods of analysis, Soil Dynamics and Earthquake Engineering Volume 26, Issue 12, December 2006, Pages V. DISCUSSIONS Parametric study is carried out on Building structure with & without floating columns for various I.S code load combinations using Staad Pro. In this paper the change in displacements of selected columns i.e. C1, C5, C9 & C13 are compared. The results obtained for C1, C5, C9 & C13 are presented in the form of graphs. VI. CONCLUSIONS The comparative study for the various columns combinations i.e. C1, C5, C9 & C13 is done for various load combinations given in I.S code. It has been seen that in the load combinations where seismic or earthquake loadings are not present the displacement of structure having no floating columns is comparatively less than the structure having floating columns. On the other hand where the earthquake or seismic load are present in the combinations given in I.S code the displacement of no float structure is comparatively greater than the structure having floating columns. ACKNOWLEDGMENT The journalist would like to prompt their sincere thanks to the G.H.R.A.E.T college of Engineering for giving Guidance and technical support to get done this research. REFERENCES [1] Balsamoa A, Colombo A, Manfredi G, Negro P & Prota P (2005), Seismic behavior of a full-scale RC frame repaired using CFRP laminates. Engineering Structures 27 (2005) [2] Bardakis V.G., Dritsos S.E. (2007), Evaluating assumptions for seismic assessment of existing buildings.soil Dynamics and Earthquake Engineering 27 (2007) [3] Brodericka B.M., Elghazouli A.Y. and Goggins J, Earthquake testing and response analysis of concentrically-braced sub-frames, Journal of Constructional Steel Research, Volume 64, Issue 9, Page no: ,2008. [4] Mortezaei A., Ronagh H.R., Kheyroddin A., (2009), Seismic evaluation of FRP strengthened RC buildings subjected to near-fault ground motions having fling step. Composite Structures 92 (2010) [5] Niroomandia A., Maherib A, Maheric Mahmoud R., Mahini S.S. (2010) Seismic performance of ordinary RC frames retrofitted at joints by FRP sheets. Engineering Structures 32 (2010) [6] Ozyigit H. Alper, Linear vibrations of frames carrying a concentrated mass, Mathematical and Computational Applications, Vol. 14, No. 3, pp , All rights reserved by 224

Seismic Analysis of Multistorey Building with Floating Column

Seismic Analysis of Multistorey Building with Floating Column Mohammed Sameer Ahmed M.Tech Student ABSTRACT In present scenario buildings with floating column is a typical feature in the modern multistory