International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 4, April 2017, pp. 507 517 Article ID: IJCIET_08_04_057 Available online at http://www.iaeme.com/ijciet/issues.asp?jtype=ijciet&vtype=8&itype=4 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 IAEME Publication Scopus Indexed SEISMIC BEHAVIOR OF MULTI-STORY STRUCTURE WITH DIFFERENT TYPES OF SLABS Mahesh Bakale M. Tech Student, School of Civil & Chemical Engineering, VIT University, Vellore, Tamilnadu, India T.S. Viswanathan Associate Professor, School of Civil & Chemical Engineering VIT University, Vellore, Tamilnadu, India ABSTRACT The objective of this paper is to study the seismic behavior of different types of slab systems in various seismic zones, considering the varying number of stories. The paper deals with the four types of slab system i.e. Conventional beam slab system, Flat plate system, Flat slab with drop system, and Ribbed slab system. The seismic behavior of these slab systems is studied by modelling G+6, G+9 & G+12 multi-story structure in ETABS software package. The study comprises of comparison of story displacement and story shear. Key words: Equivalent linear static analysis, Response spectrum analysis, Story displacement, Story shear, ETABS. Cite this Article: Mahesh Bakale and T.S. Viswanathan, Seismic Behavior of Multi- Story Structure with Different Types of Slabs. International Journal of Civil Engineering and Technology, 8(4), 2017, pp. 507 517. http://www.iaeme.com/ijciet/issues.asp?jtype=ijciet&vtype=8&itype=4 1. INTRODUCTION Earthquake resistant design of RC buildings is a continuing area of research since the earthquake engineering has gained prominence across the globe. Earthquakes occurring in recent past have shown that poorly designed and constructed structures result in great destruction. Hence, there is a need to determine seismic response of tall buildings for designing earthquake resistant structures. The seismic behavior of the structure during the earthquake depends critically on parameters like shape of the structure, size of the structure, intensity of the earthquake along with the type of slab. Structures designed for gravity loads in general may not be able to sustain the horizontal vibrations of the earth. Hence it is necessary to ensure the adequacy of the structure against horizontal vibration of the earth. http://www.iaeme.com/ijciet/index.asp 507 editor@iaeme.com
Seismic Behavior of Multi-Story Structure with Different Types of Slabs 1.1. TYPES OF SLAB SYSTEMS Conventional slab system: Beam - Column system as shown in Fig 1. Flat plates: These type of slabs do not have beams, drop panels or column capitals. The slabs are directly supported on columns as shown in Fig 2. Flat slab with drop: These slabs are similar to flat plates but have drop panels or column capitals in addition as shown in Fig 3. Ribbed slab: A panel composed of a thin slab reinforced by ribs in one direction as shown in Fig 4. Figure 1 Conventional slab system Figure 2 Flat plate Figure 3 Flat slab with drop Figure 4 Ribbed slab 2. METHODOLOGY 2.1. MODELLING A regular and irregular G+6, G+9, & G+12 multi-story structures modelling is carried out in ETABS software package. Description of models Model a: Regular Conventional slab system structure Model b: Regular Flat plate system structure Model c: Regular Flat slab with drop system structure Model d: Regular Ribbed slab system structure Model e: Irregular Conventional slab system structure Model f: Irregular Flat plate system structure Model g: Irregular Flat slab with drop system structure Model h: Irregular Ribbed slab system structure http://www.iaeme.com/ijciet/index.asp 508 editor@iaeme.com
Mahesh Bakale and T.S. Viswanathan 2.1. SALIENT FEATURES OF THE STRUCTURE The following are the salient features adopted to study the seismic behavior of multi-story structure with different types of slabs. Type of structure is multi-story rigid frame. Seismic zones considered is III, IV & V. Soil type is Hard. Importance factor of the building is 1. Bay width is 7m in both directions. Floor to floor height is 3m. Concrete grade is M30. Steel grade is Fe500. Live load is taken as 2 kn/m 2. Floor finishes is taken as 1.2 kn/m 2. External wall load is 14 kn/m. Internal wall load is 10.5 kn/m. Thickness of slab is 270mm (Model a & Model e), 350mm (Model b & Model f), 250mm (Model c & Model g) & drop is 350mm, 270mm (Model d & Model h) & width of ribs is 150mm with spacing of 1m. The number of stories considered is G+6, G+9, and G+12. Size of beams 300x650mm (for Model a & Model e) & 300x500mm (for Model d & Model g). Size of columns is 700x700mm up to story 3 & 550x550mm up to story 7 for G+6 structure. Size of columns is 700x700mm up to story 5 & 550x550mm up to story 10 for G+9 structure. Size of columns is 700x700mm up to story 6 & 550x550mm up to story 13 for G+12 structure. Method of analysis Equivalent linear static analysis for zone III & Response spectrum analysis for zone IV & zone V. 3. 3-D VIEW OF STRUCTURES 3.1. REGULAR STRUCTURES A structure having simple regular geometry and uniformly distributed mass and stiffness in plan as well as in elevation. In our study we have considered regular multi-story structure with different types of slabs. Figure 5 Model a Figure 6 Model b Figure 7 Model c Figure 8 Model d http://www.iaeme.com/ijciet/index.asp 509 editor@iaeme.com
Seismic Behavior of Multi-Story Structure with Different Types of Slabs 3.2. IRREGULAR STRUCTURES Irregular buildings are broadly classified into Plan irregularities and Vertical irregularities. In these type of structures there may be uneven distribution of mass, strength and stiffness in plan as well as in elevation. In our study we have considered both plan and vertical irregular multistory structure with different types of slabs. Figure 9 Model e Figure 10 Model f Figure 11 Model g Figure 12 Model h 4. RESULTS AND DISCUSSIONS 4.1. REGULAR STRUCTURE 4.1.1. Story Displacement A graph is plotted with the story displacement as Y-axis and story height as X-axis for all the four models in the seismic zones III, IV & V. It is observed that the displacement increases as the height of the structure increases for all the four models. It was observed that story displacement is same in both X and Y direction for Model a, b, & c due to symmetry of the structures. In case of Model d, it was observed that the story displacement was more in Y direction compared to the X direction, it is because of ribs spanning parallel to the X direction increases stiffness and hence the story displacement decreases in X direction and the story displacement increases in Y direction. http://www.iaeme.com/ijciet/index.asp 510 editor@iaeme.com
Mahesh Bakale and T.S. Viswanathan Figure 13 Comparison of story displacements for Zone III Figure 14 Comparison of story displacements for Zone IV Figure 15 Comparison of story displacements for Zone V http://www.iaeme.com/ijciet/index.asp 511 editor@iaeme.com
Seismic Behavior of Multi-Story Structure with Different Types of Slabs 4.1.2 Story Shear It is the sum of design lateral force at all the levels above story under consideration. A bar graph is plotted for story shear with max. story shear as Y axis and no. of stories as X axis. The story shear increases with increase in the number of stories for all the four models. It was observed that the max. story shear for all the four models is similar in both X and Y direction. Figure 16 Comparison of story shear for Zone III Figure 17 Comparison of story shear for Zone IV Figure 18 Comparison of story shear for Zone V http://www.iaeme.com/ijciet/index.asp 512 editor@iaeme.com
Mahesh Bakale and T.S. Viswanathan 4.1.3 Summary for story shear and story displacements Table 1 Story shear & story displacement for Zone III Table 2 Story shear & story displacement for Zone IV 4.2. IRREGULAR STRUCTURE 4.2.1. Story Displacement In case of irregular structure, it was observed that story displacement in both X and Y direction were not same due unsymmetrical configuration of the structure. The story displacement increased as the height of the structure increases for all the four models. http://www.iaeme.com/ijciet/index.asp 513 editor@iaeme.com
Seismic Behavior of Multi-Story Structure with Different Types of Slabs Table 3 Story shear & story displacement for Zone V Figure 19 Comparison of displacements for Zone III Figure 20 Comparison of displacements for Zone IV http://www.iaeme.com/ijciet/index.asp 514 editor@iaeme.com
Mahesh Bakale and T.S. Viswanathan Figure 21 Comparison of displacements for Zone V 4.2.2. Story Shear The max. story shear in case of irregular structure was observed to be same in both X and Y direction. The story shear gets increased as the number of stories increases for all the four models. Figure 22 Comparison of story shear for Zone III Figure 23 Comparison of story shear for Zone IV http://www.iaeme.com/ijciet/index.asp 515 editor@iaeme.com
Seismic Behavior of Multi-Story Structure with Different Types of Slabs Figure 24 Comparison of story shear for Zone V 4.2.3. Summary for story shear and story displacements Table 4 Story shear & story displacement for Zone III Table 5 Story shear & story displacement for Zone IV http://www.iaeme.com/ijciet/index.asp 516 editor@iaeme.com
Mahesh Bakale and T.S. Viswanathan Table 6 Story shear & story displacement for Zone V 5. CONCLUSIONS The seismic behavior of multi-story structure considering various types of slabs system i.e. Conventional slab, Flat plate, Flat slab with drop, and ribbed slab system with varying number of stories in the structure is studied. The following are the major conclusions: 1. Story displacement is maximum in flat slab system and least in conventional slab system in all the seismic zones for both regular & irregular structure. 2. Story shear is maximum in flat slab system and least in flat slab with drop system in all the seismic zones for both regular & irregular structure. 3. Flat slab system story displacement is about 37% higher than conventional slab system for regular structure. 4. Flat slab system story displacement is about 24% higher than conventional slab system for irregular structure. 5. Flat slab system story shear is about 17% higher than flat slab with drop system for regular structure. 6. Flat slab system story shear is about 11% higher than flat slab with drop system for irregular structure. REFERENCES [1] Ahmad J. Durrani, S. T. (1994). Earthquake Response of Flat Slab Buildings, International Journal Engineering Research & Technology (IJERT), Journal of Structural Engineering, 117(4), 947-963. [2] Apostolska, R. N. (2014). Seismic Performance of Flat-Slab Building Structural Systems. XIV th World Conference on Earthquake Engineering. Beijing. [3] Bhina, M. R. (2014). Assessment of different aspects of RC flat slab building and its serviceability. Proceedings of International Conference on Architecture and Civil Engineering (ICAACE-14). Dubai. [4] Reddy, M. V. (2014). Comparative study of seismic analysis between conventional and flat slab with drop and without drop framed structures with different masonary infills, International Journal Engineering Research & Technology (IJERT), 3(10), 82-89. [5] Sashi K. Kunnath, N. P. (1991). Seismic Response of RC buildings with Inelastic floor Diaphragms. Journal of structural engineering, 120(3), 1218-1237. [6] IS- 1893- Part I: 2002, Criteria for Earthquake Resistant Design of Structures, Bureau of Indian Standards, New Delhi. [7] ETABS. (2015), Analysis Reference Manual, Computers and Structures, Berkely, California, USA. http://www.iaeme.com/ijciet/index.asp 517 editor@iaeme.com