Comparative Study of Structural Responses of Floating Column and Non-Floating Column Structural Frames

I. INTRODUCTION

A typical Column is a vertical structural member which support to horizontal structural members by means of their weights, moments, and shear force, axial load etc., to keep the structure in safe condition and transfer these loads to the ground. But now a day‘s some columns are designed in such a manner that it does not reach to the ground, because of various architectural aspects. In those cases the columns transfer above loads as a point load on a beam. This type of column is termed as Floating column. This Point load increases too much bending moment on beam so that area of steel required will be more in such cases. While earthquake occurs, the building with floating columns damages more as compared to the building without any floats columns because of discontinuity of structure & load transfer path. The overall size, shape and geometry of a structure play a very important roll to keep structure safe while earthquake occurs. As theory and practical study on buildings says that, earthquake forces developed at different floor levels in a building needs to be brought down along the height to the ground by the shortest path; any deviation of discontinuity in this load transfer path results in poor performance of the building. In Earthquake analysis the main response parameters are storey displacement, Storey drift, storey shear. These parameters are evaluated in this paper and critical position of floating column building is observed. In this critical position the effect of increasing section of beam and column in irregular building and regular building has been observed. The Response of a structure to the ground vibration is a function of the nature of foundation soil; materials, form, size and mode of construction of structure; and the duration and characteristics of ground motion. IS 1893 (part I):2002 specifies the various criteria for design of structure considering earthquake zones, type of structure, soil type, Importance factor of structure, response reduction factor etc. The basic criteria of earthquake resistant design should be based on lateral strength as well

• By using floating columns large functional space can be provided which can be utilizing for storage and parking. • In some situations floating columns may prove to be economical in some cases. • The floating column is important for dividing the rooms and some portion can raise without whole area

• Not suitable in high seismic zone since abrupt change in stiffness was observed. • Required large size of girder beam to support floating column. • Floating columns leads to stiffness irregularities in building. • Flow of load path increases by providing floating columns. The load from structural members shall be transfer to the foundation by the shortest possible path.

• The objective of the present work is to study the behaviour of multi-storey buildings with and without floating columns under earthquake excitations. • Seismic Coefficient Method is carried out for the multi-storey buildings under different load combination. The base of the building frame is assumed to be fixed. • To study of Internal floating columns & Alternate floor floating columns observation of displacement at various nodes. • To know the axial forces at various nodes due to provision of External floating columns. • To observe the effect of storey drift on structure due to floating column. Case 1: RC Building without floating columns Case 2: RC Building with Internal floating columns Case 3: RC Building with External floating columns

A RCC medium rise building of G+14 stories with floor height 3m subjected to earthquake loading in Zone II, III, IV, V has been considered .In this regard, ETAB software have been considered as tool to perform. Hence in this chapter we will discuss the parameters defining the computational models, the basic assumptions and the geometry of the selected building considered for this study. Displacements, axial forces, shear force, bending moment. Have been calculated for different columns and beams to find out the effect in the building.

1. Length of building -26 m 2. Width of building-26 m 3. Storey Height of building – 3m 4. Total height of building – 45 m 5. Dimension of column - 0.8x0.5 m for zone v 6. Dimension of beam - 0.5x 0.3 m for zone v 7. Thickness of slab – 150 mm 8. Dead load on building for 0.23m thick wall - 14 kN/m 9. Dead load on building for 0.15m thick wall – 9kN/m 10. Live load on building -3 kN/m2 11. Response Spectra - As per IS 1893 (Part-1): 2002 14. Response reduction factor a. For SMRF - 5 15. Seismic load as per zone factor and Response Reduction Factor a. Earthquake load in X –Direction 16. Earthquake load in Z –Direction b) Assumption 1. The material is homogeneous and isotropic. 2. All columns supports are considered as fixed at the foundation. 3. Tensile strength of concrete is ignored in sections subjected to bending. 4. The maximum target displacement of the structure is calculated in accordance with the guidelines given by IS Code for maximum roof level lateral drift and displacement. 5. The building is designed by according to I.S. 456:2000 for Dead Load and Live load.

IIIIIIVVIIIIIIVVIIIIIIVVIIIIIIVVSMRFSMRFSMRFSMRFSMRFSMRFSMRFSMRFSMRFSMRFSMRFSMRFSMRFSMRFSMRFSMRFFxFxFxFxFxFxFxFxFxFxFxFxFxFxFxFx1.5(DL+EQX)03747.213878.714103.754409.353798.753932.454161.274472.003651.493788.504022.994341.423939.514103.004320.994647.981.5(DL+EQX)13504.463623.093826.114101.813552.843673.503880.004160.423416.573540.143751.644038.833658.663805.304000.814294.071.5(DL+EQX)23255.203360.063539.513783.203300.633407.403590.123838.243175.563284.883471.993726.083448.323580.673757.144021.841.5(DL+EQX)33001.903093.093249.143461.053043.993136.933295.993511.992930.253025.463188.413409.693207.423324.393480.363714.311.5(DL+EQX)42745.722823.692957.113138.302784.322863.893000.053184.972681.772763.332902.923092.482948.573050.233185.783389.111.5(DL+EQX)52487.462552.852664.742816.702522.512589.352703.732859.062430.882499.462616.832776.222694.812781.652897.433071.101.5(DL+EQX)62227.822281.422373.142497.702259.292314.192408.142535.732178.262234.672331.222462.322427.652500.342597.272742.651.5(DL+EQX)71967.432010.162083.292182.591995.302039.182114.292216.281924.561969.742047.062152.072149.072208.642288.052407.171.5(DL+EQX)81706.871739.771796.071872.521731.111765.021823.051901.851670.371705.371765.271846.611876.021923.201986.102080.441.5(DL+EQX)91447.361471.931513.981571.081467.831493.201536.601595.551416.391442.441487.021547.561596.591633.081681.741754.741.5(DL+EQX)101188.961206.561236.691277.601205.981224.331255.751298.421164.321183.341215.901260.111311.671339.181375.851430.861.5(DL+EQX)11931.49943.25963.37990.70944.96957.39978.681007.58912.76925.80948.12978.431030.771049.941075.511113.861.5(DL+EQX)12675.34682.43694.58711.07685.13692.79705.89723.68662.09670.25684.21703.18747.32759.59775.95800.491.5(DL+EQX)13420.92424.57430.82439.30426.88430.93437.85447.25412.70417.10424.64434.88464.38471.52481.04495.331.5(DL+EQX)14167.52168.86171.16174.28169.50171.02173.63177.17163.94165.65168.58172.56171.06173.75177.34182.73

1. With the provision of Internal floating columns & Alternate floor floating columns may increase in axial force & shear force at all floors. 2. It is observed that Internal floating columns & External floating columns increases the torsion values at all floors for all zones 3. It is observed that provision of Alternate floor floating columns there is reduction in the Torsion values 4. With the provision of Internal floating columns there is increase in moment at corner column but reduction in moment at intermediate column at all floors. For Alternate floor floating columns the result were exactly opposite to the results obtained in Internal floating columns 6. Provision of External floating columns may decrease displacement at various nodes 7. Provision of floating column increases torsion in beam at all floors for all zones 8. Due to the increase in the value of bending moment in the beams adjacent to the floating columns up to 4th floor the size of the beam increases hence increases in overall quantity of steel & concrete of the structure 9. The quantity of steel and concrete gets increase as compared to the individual cases due to floating column so floating column may be provided at appropriate places as per requirement of the plan 10. Placement of Internal or External floating column may result development of additional forces on adjoining beams and columns adequate checks should be carried out before designing the structure. Precaution must also be taken for smooth transfer of lateral forces to ground

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PG Student, Civil Engineering Department, SVERI‘s College of Engineering, Pandharpur, Maharashtra