SEISMIC BEHAVIOR OF MULTI-STORY … shear is maximum in flat slab system and least in flat slab with...

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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.

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

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/m2. Floor finishes is taken as 1.2 kN/m2. 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



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 multi-

story 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.



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



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



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.



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



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



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



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. XIVth

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.

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