A Comparative Study of Seismic Response of Flat Slab Structure and Conventional RC Framed Structure

Transcription

1 Volume 3, Issue, 1 Available online at International Journal of Innovative and Emerging Research in Engineering e-issn: p-issn: 39-9 A Comparative Study of Seismic Response of Flat Slab Structure and RC Framed Structure Abhijit Salunkhe a and Dr.D.N.Shinde b a P.G. Student, Department of Civil Engineering, P.V.P.I.T. Budhgaon, Sangli, India b Associate Professor, Department of Civil Engineering, P.V.P.I.T. Budhgaon, Sangli, India ABSTRACT: s is system of construction is one in which the beams used in the conventional methods of constructions are done away with, have advantages over conventional such as economy in construction, its architectural appearance, flexibility and speed of the construction. However because of removal of beams from flat slab, lateral stiffness is considerably reduced hence flat slab more flexible to seismic loading as compare with conventional. This objective of this work is to compare the seismic behavior of flat slab with conventional R.C.C. Structure. This work also study effect on seismic performance of flat slab. Keywords: RC, Seismic response, Static analysis, Dynamic analysis. I. INTRODUCTION s is system of construction is one in which slab is directly rest on the column. The slab directly rests on the column and load from the slab is directly transferred to the columns and then to the foundation. To support heavy loads, the thickness of slab near the support with the column is increased and these are called drops, or columns are generally provided with enlarged heads called column heads or capitals [1]. These increasing thickness of flat slab in the region supporting columns provide adequate strength in shear and to increase the amount perimeter of the critical section, for shear and hence, increasing the capacity of the slab for resisting two-way shear and to reduce negative bending moment at the support. is preferred over conventional in construction due to their advantages in reducing storey height and construction period as compared with conventional, leading to reduction of construction costs. Provision of the flat slab building in which slab is directly rested on columns, have been adopted in many buildings constructed recently due to the advantage of reduced floor to floor heights to meet the economical and architectural demands []. Because of absence of deep beam building s which are more significantly flexible than conventional concrete than traditional s, thus becoming more vulnerable to seismic loading. Thus the seismic analysis of these s is necessary to know the vulnerability of these s to seismic loading. [3] The flat slab are more respond to seismic loading as compare with conventional hence additional measure are required to improve their seismic performance. Therefore, flat slab constructed in earthquake prone region additional measures should be taken such as provision of in order to reduce the seismic response of flat slab RC. II. METHODS OF DESIGN OF FLAT SLAB Following are the methods used for analysis 1. The direct design method. The equivalent frame method METHODS OF SEISMIC ANALYSIS A. Linear static analysis B. Linear dynamic analysis 7

2 Volume 3, Issue, 1 III. PROBLEM FORMULATION, MODELLING AND ANALYSIS Following are the models used for analysis Case 1)- i. storey Flat Slab RC having plan dimensions 3 m x3 m. ii. storey conventional RC Framed having plan dimensions 3 m x3 m. iii. storey flat slab with having plan dimensions 3 m x3 m. Case )- i. 1 storey Flat Slab RC having plan dimensions3 m x3 m. ii. 1 storey conventional RC Framed having plan dimensions 3 m x3 m. iii. 1 storey flat slab with having plan dimensions 3 m x3 m. Case 3)- i. 1 storey Flat Slab RC having plan dimensions 3 m x3 m. ii. 1 storey conventional RC Framed having plan dimensions 3 m x3 m. iii. 1 storey flat slab with having plan dimensions 3 m x3 m. All above model are analysed and comparison is made between these analyses. To know vulnerability of the to seismic loading [] Details of Modelling: i. Storey height -3.m ii. Plinth level-.m iii. Thickness of flat slab- mm iv. Thickness of drop is -7mm. v. Thickness of is- 1mm. vi. Size of column -.m to 1.m. vii. Size of beam -3mm to mm. Loading Details: 1. Gravity loadsi. Live load at typical floor- kn/m ii. Live load at top floor - kn/m iii. Floor finish load at typical floor -1. kn/m iv. Floor finish load at top floor -. kn/m. Detail of Earthquake loading- 1. Static analysis a. Location of zone- IV. b. The direction of excitation -X. c. Importance factor -1 d. Response reduction factors-. Dynamic analysisa. Location of zone- IV. b. The direction of excitation -X. c. Damping-%.

3 Volume 3, Issue, 1 IV. RESULTS 1. Base shear - Base shear is the total design lateral force (V B) along any principal direction, which is determined by following expression Where V B =A hw Ah = Design horizontal acceleration spectrum W = Seismic weight of building. TABLE I BASE SHEAR COMPARISON of above models [] Model Case 1- storey Structure Linear static analysis Response spectrum analysis Structure with Case - 1 storey Structure Structure with Case 3-1 storey Structure Structure with From above result it is observe that flat slab are more flexible than conventional. The flexibility of flat slab can be reduced by providing.. Storey drift- Storey drift is computed as a difference between lateral displacement of one floors to the other floor. It is one of the important response quantity and which is indictor of structural performance of multi-storey buildings. According IS 193 (Part 1): maximum allowable storey drift in any storey due to minimum specified design lateral load factor 1. should not be exceed shall. times the storey height under consideration. For the analysis of all above model storey drift should not exceed 1.mm. Drift control is necessary to limit damage to interior partition, elevator and stair enclosure, glass and cladding system []. 9

4 Volume 3, Issue, 1 Comparison of Storey Drift for different cases Case 1- storey Conventiona l with shear wall with Figure 1. Linear Static Analysis Figure. Linear Dynamic Analysis. The plot of drift values shows that provision of imparts uniform stiffness to the flat slab and it reduces the drift values of mid-storey almost by %, thus proving the reliability of in case of multi-storey s. Case - 1 storey with with Figure 3. Linear Static Analysis. Figure.Linear Dynamic Analysis The plot of drift values shows that provision of imparts uniform stiffness to the flat slab and it reduces the drift values of mid-storeys almost by %, thus proving the reliability of in case of multi-storey s. Case 3-1 story with with Figure. Linear Static Analysis Figure. Linear Dynamic Analysis

5 Volume 3, Issue, 1 In case of 1 storey in zone IV, Storey drift of flat slab differs very much from conventional RC framed and exceed permissible values (storey drift being more than 1 mm) when analyzed by linear static analysis. Thus, multi-storey flat slab essentially demand lateral load resisting system such as in-plane in order to bring storey drift values within permissible limits. Comparison of Displacement for different cases Case 1 - storey R.C.framed with R.C.framed with Figure 7. Linear Static Analysis. Figure. Linear Dynamic Analysis Maximum displacement attained by flat slab with is much lesser than that in case of flat slab without. Both the analysis viz. linear static analysis and linear dynamic analysis emphasis that multistorey flat slab s are to be accompanied with the for better performance of flat slab during earthquake. Case -1 storey R.C.framed with 3 1 R.C.framed with Figure 9. Linear Static Analysis Figure1. Linear Static Analysis. Figure 9 and figure 1 shows the significant reduction in maximum displacement of flat slab after the application of. Case 3-1 storey 1

6 Volume 3, Issue, with opening with RC framed with Figure11. Linear Static Analysis. Figure1. Linear Dynamic Analysis Maximum displacement attained by flat slab with found to be reduced by more than % than that in case of flat slab without. Hence such a multi-storey having 1 numbers of storeys must be accompanied with lateral load resisting element such as to bring the displacement values to the desired level as in this case. V. CONCLUSION 1. For all case, flat slab without design base shear less as compare with conventional which is due to the flexibility of flat slab.. In case of flat slab storey drift is more as compare with conventional RC framed. This storey drift can be reduced by provision of to flat slab. 3. From analysis result it seen that displacement of the flat slab is more as compare with conventional.. The displacement of the flat slab is reduced by provision of. Format of Reference REFERENCES [1] Dr. U. Gupta, S. Ratnaparkhe, P. Gome, Seismic behavior of buildings having flat slabs with drops, IJETAE volume, October 1. [] S.Pahwa, V. Tiwari. M. Prajapati, Comparative Study of Flat Slab with Old Traditional Two Way Slab IJLTET, volume, July 1. [3] Navyashree K., T. Sahana, Use of flat slab in multi-storey commercial building situated in high seismic zone, International journal of research in engineering and technology. [] Dhanagar A.L.,Narule G.N. A comparative study of seismic response of flat slab and conventional International journal of latest trends in engineering and technology. [] Alkarani, R Ravindra., Evaluation of Punching Shear In Flat Slabs International Journal of Research in Engineering and Technology Nov. 13. [] Dr. V. Varghese, S. Bothara, Dynamic analysis of moment resisting frame building with and Grid slab, IJERA volume, July-August 1. [7] Prof. K. S. Sable, Er. V. A. Ghodechor, Prof. S B Kandekar, Comparative Study of Seismic Behavior of Multistory Flat Slab and Reinforced Concrete Framed Structures, IJCTEE, Volume, issue 3, June 1. [] IS 193 (Part 1), Criteria for Earthquake Resistant Design of Structure, BIS. [9] IS-:, Code of practice for plain and reinforced concrete, code practice fourth revision, Bureau of Indian Standards, New Delhi, July.