Structural Analysis of a Multi-Storeyed Building using ETABS for different Plan Configurations

Structural Analysis of a Multi-Storeyed Building using ETABS for different Plan Configurations

Abhay Guleria

Undergraduate, Deptt. of Civil Engineering,

J.N.G.E.C. Sundernagar, Sundernagar, India

AbstractETABS stands for Extended Three dimensional Analysis of Building Systems. ETABS is commonly used to analyze: Skyscrapers, parking garages, steel & concrete structures, low and high rise buildings, and portal frame structures. The case study in this paper mainly emphasizes on structural behavior of multi-storey building for different plan configurations like rectangular, C, L and I-shape. Modelling of 15- storeys R.C.C. framed building is done on the ETABS software for analysis. Post analysis of the structure, maximum shear forces, bending moments, and maximum storey displacement are computed and then compared for all the analyzed cases.

Keywords- Structure Design, ETABS, High Rise Buildings, Plan Irregularity

1. INTRODUCTION

   Structural analysis means determination of the general shape and all the specific dimensions of a particular structure so that it will perform the function for which it is created and will safely withstand the influences which will act on it throughout its useful life. ETABS was used to create the mathematical model of the Burj Khalifa, designed by Skidmore, Owings and Merrill LLP (SOM). The input, output and numerical solution techniques of ETABS are specifically designed to take advantage of the unique physical and numerical characteristics associated with building type structures. ETABS provides both static and dynamic analysis for wide range of gravity, thermal and lateral loads. Dynamic analysis may include seismic response spectrum or accelerogram time history.

   This analysis mainly deals with the study of a rectangular, L, C and I shaped plan using ETABS. A 32m x 24m 15- storeys structure having 4m x 4m bays is modelled using ETABS. The height of each storey is taken as 3m, making total height of the structure 45m. Loads considered are taken in accordance with the IS-875(Part1, Part2), IS-1893(2002) code and combinations are acc. to IS-875(Part5). Post analysis of the structure, maximum shear forces, bending moments, and maximum storey displacement are computed and then compared for all the analysed cases.

2. MODELLING OF RCC FRAMES

   An RCC framed structure is basically an assembly of slabs, beams, columns and foundation inter-connected to each other as a unit. The load transfer mechanism in these structures is from slabs to beams, from beams to columns, and then ultimately from columns to the foundation, which in turn passes the load to the soil. In this structural analysis study, we have adopted four cases by assuming different shapes for the same structure, as explained below.

   1. Rectangular Plan

   2. L-shape Plan

   3. I-shape Plan

   4. C-shape Plan

   The building is 32m x 24m in plan with columns spaced at 4m from center to center. A floor to floor height of 3m is assumed. Plan of the building for all the cases is shown in the following figure.

   Units

   Fig 1: Plan (a) Rectangular (b) L shape (c) I shape (d) C shape of the Building

   TABLE 1

   Building Description
   Length x Width	32m x 24m
   No. of storeys	15
   Storey height	3m
   Beam dimensions	450x450mm
   Column 1-5 storeys dimensions	600x600mm
   Column 6-12 storeys dimensions	500x500mm
   Slab thickness	125mm
   Thickness of main wall	230mm
   Height of parapet wall	0.90m
   Thickness of parapet wall	115mm
   Support conditions	Fixed

   Material Specifications
   Grade of Concrete ,M30	fck= 30N/mm2
   Grade of Steel	fy= 415N/mm2
   Density of Concrete	c= 25kN/m3
   Density of Brick walls considered	brick= 20kN/m3

3. MATERIAL SPECIFICATIONS TABLE 2

4. LOADING

   Loads acting on the structure are dead load (DL), Live load and Earthquake load (EL).

   1. Self weight comprises of the weight of beams, columns and slab of the building.

   2. Dead load: Wall load, Parapet load and floor load (IS 875(Part1))

      1. Wall load= (unit weight of brick masonry X wall thickness X wall height)

         = 20 kN/m3 X 0.230m X 3m

         = 13.8 kN/m (acting on the beam)

      2. Wall load (due to Parapet wall at top floor)

         = (unit weight of brick masonry X parapet wall thickness X wall height)

         = 20 kN/m3 X 0.115m X 0.90m

         = 2.07 kN/m (acting on the beam)

   3. Live load: Floor load: 4kN/m2 and Roof load: 2 kN/m2 (IS 875 (Part 2) acting on beams

   4. Seismic Load: Seismic zone: V (Z=0.36), Soil type: I, Importance factor: 1, Response reduction factor: 5, Damping: 5%. IS 1893(Part-1):2002.

   Here Seismic load is considered along two directions EQlength and EQwidth

5. LOADING COMIBINATION

   The structure has been analyzed for load combinations considering all the previous loads in proper ratio. Combination of self-weight, dead load, live load and seismic load was taken into consideration according to IS-code 875(Part 5).

   TABLE 3

6. MODELLING IN ETABS

   Fig 2: 3-D View of the 15-storeys Rectangular-shape building

   VII. USING THE TEMPLATE

   Fig 3: 3-D View of the 15-storeys L-shape building

   Fig 4: 3-D View of the 15-storeys I-shape building

   Fig 5: 3-D View of the 15-storeys C-shape building

7. RESULTS AND DISCUSSIONS

   TABLE 4

   Max B.M. and Shear Force of Beam
   Forces	Rectangular	L-shape	I-shape	C-shape
   B.M. My	92.99	97.38	101.54	99.74
   B.M. Mz	0.11	1.56	0.64	1.12
   Shear Force Fy	161.09	159.18	158.18	159.27

   Max B.M. and Shear Force of Column
   Forces	Rectangular	L-shape	I-shape	C-shape
   Axial Force Fx	399.265	453.41	400.40	435.03
   Shear Force Fy	88.16	87.68	91.96	90.59
   Shear Force Fz	90.11	86.15	95.23	87.59
   B.M. My	181.93	172.35	174.40	173.63
   B.M. Mz	182.11	172.24	173.64	172.39

   Storey Overturning Moments for different Plan Configurations

   Fig 6: StoreyHeight Vs Overturning Moments

   The figure shows that the overturning moment varies inversely with storey height. In case of rectangular plan, a moment produced is higher than other shapes. Storey overturning moment decreases with increase in storey height for all cases.

   Comparison of Storey Shear for 1st, 5th, 10th, 15th storey for different configurations

   Fig 7: Graph of Storey Shear for different Plan configurations

   As per above fig. it has been concluded that the storey shear decreases with the increase in storey height. Storey shear is less in L-shape building among all the cases.

   Fig 8:Graph of Storey Shear for 5th Storey

   Roof Displacement Vs Height of the Building

   TABLE 6

   STOREY	LATERAL DISPLACEMENT (mm)
   	Rectangular	L-shape	I-shape	C-shape
   0	0	0	0	0
   1	1.37	1.30	1.27	1.37
   2	3.41	3.58	3.51	3.41
   3	5.95	6.29	5.85	6.05
   4	8.49	9.11	8.29	8.59
   5	11.12	12.03	10.93	11.32
   6	13.76	15.07	13.76	14.24
   7	16.78	18.32	16.49	17.37
   8	19.51	21.57	19.41	20.39
   9	22.24	24.72	22.15	23.22
   10	24.59	27.64	24.49	25.85
   11	26.83	30.46	26.93	28.49
   12	28.88	32.95	28.88	30.63
   13	30.15	34.91	30.34	32.49
   14	31.61	36.86	31.71	34.15
   15	32.39	38.16	32.78	35.02

   Above table shows that the storey displacement increases with the increase in storey height. Displacement in rectangular shape building is less than other cases.

   Max Lateral Drift for various storey heights

   STOREY	LATERAL DRIFT (mm)
   	Rectangular	L-shape	I-shape	C-shape
   0	0	0	0	0
   1	3.9	3.8	3.8	3.8
   2	7.3	7.3	7.2	7.4
   3	8.1	8.4	8.1	8.4
   4	8.2	8.7	8.4	8.8
   5	8.2	8.9	8.5	9
   6	9.5	10.04	9.7	10.03
   7	9.4	10.01	9.6	10.01
   8	9.0	9.8	9.3	9.9
   9	8.5	9.4	8.9	9.5
   10	7.9	8.8	8.3	9.0
   11	7.1	8.0	7.6	8.3
   12	6.2	7.2	6.7	7.4
   13	5.1	6.1	5.6	6.3
   14	3.7	4.8	4.3	5.0
   15	2.3	3.7	3.1	3.9

   TABLE 7

   C

   paper and are not topically subordinate to each other.

   Fig 9: Graph of Storey Drift Vs Storey height

   Fig 9: Mode Shape for 12th mode for (a) Rectangular (b) L-shape (c) I- shape (d) C-shape of the building

8. CONCLUSIONS

The analysis of the multi-storeyed building reflected that the storey overturning moment varies inversely with storey height. Moreover, L-shape, I-shape type buildings give almost similar response against the overturning moment. Storey drift displacement increased with storey height up to 6th storey reaching to maximum value and then started decreasing. From dynamic analysis, mode shapes are generated and it can be concluded that asymmetrical plans undergo more deformation than symmetrical plans. Asymmetrical plans should be

adopted considering into gaps. The Fig. 9 shows that asymmetrical plans undergo more deformation and hence symmetrical plans must be adhered to.

ACKNWOLEDGMENT

This case study would not have been possible without the able guidance of Prof.RL Sharma, Director JNGEC, S.P.Guleria (H.O.D.), Madhu Sharma, Assistant Professor, and Tarun Goel, Assistant Professor, Civil Engineering. I extend my heartfelt thanks to our worthy faculty.

REFERENCES

1. Poonam, Anil Kumar and A. K. Gupta, Study of Response of Structural Irregular Building Frames to Seismic Excitations, International Journal of Civil, Structural, Environmental and Infrastructure Engineering Research and Development, Vol.2,

   Issue 2 (2012) 25-31

2. B. K. Sanghani and P. G. Patel, Behaviour of Building Component in Various Zones, International Journal of Advances in Engineering Sciences, Vol. 1, Issue 1(Jan. 2011)

3. P. Prashanth, S. Anshuman, R.K. Pandey, Herbert Arpan, Comparison of design results of a Structure designed using STAAD and ETABS Software, INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING, Volume 2, No 3, 2012

4. Salahuddin Hammad, Habib Saqib, Rehman Talha , Comparison of design of a building using ETABS V 9.5 & STAAD PRO, 2005

5. Bureau of Indian Standards: IS-875, part 1 (1987), Dead Loads on Buildings and Structures, New Delhi, India.

6. Bureau of Indian Standards: IS-1893, part 1 (2002), Criteria for Earthquake Resistant Design of Structures: Part 1 General provisions and Buildings, New Delhi, India.