EFFECT OF POSITIONING OF RC SHEAR WALLS OF DIFFERENT SHAPES ON SEISMIC PERFORMANCE OF BUILDING...

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International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 3, May–June 2016, pp. 373–384, Article ID: IJCIET_07_03_038 Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3 Journal Impact Factor (2016): 9.7820 (Calculated by GISI) www.jifactor.com ISSN Print: 0976-6308 and ISSN Online: 0976-6316

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EFFECT OF POSITIONING OF RC SHEAR

WALLS OF DIFFERENT SHAPES ON

SEISMIC PERFORMANCE OF BUILDING RESTING ON SLOPING GROUND

S.P.Pawar

PG Student, Department of Civil Engineering

SKN Sinhgad College of Engineering, Korti, Pandharpur, India

Dr.C.P.Pise

HOD and Associate Professor Department of Civil Engineering


Y.P.Pawar, S.S.Kadam, D. D. Mohite and C. M. Deshmukh

Assistant Professors, Department of Civil Engineering,


N. K. Shelar

Assistant Professors, Department of Civil Engineering,

Government College of Engineering, Karad, India

ABSTRACT

The buildings situated on hill slopes in earthquake prone areas are generally irregular, torsionally coupled. Hence, subjected to severe damage when affected by earthquake ground motion. Such buildings have mass &

stiffness varying along the vertical & horizontal planes, resulting the center of mass & center of rigidity do not coincide on various floors, they demand

torsional analysis, in addition to lateral forces under the action of earthquakes. This study compels with a studies on the seismic behavior of buildings resting on sloping ground with a shear walls. It is observed that the

seismic behavior of buildings on sloping ground differ from other buildings. The various floors of such buildings step backs towards hill slope. Most of the

studies agree that the buildings resting on sloping ground has higher displacement and base shear compared to buildings resting on plain ground and the shorter column attracts more forces and undergo damage when

subjected to earthquake. Step back building could prove more vulnerable to seismic excitation.

S.P.Pawar, Dr.C.P.Pise, Y.P.Pawar, S.S.Kadam, D. D. Mohite, C. M. Deshmukh and N. K. Shelar


Index terms: Seismic Performance, Sloping ground, Step back building with slope 100,200,300, Shear wall with different configuration

Cite this Article: S.P.Pawar, Dr.C.P.Pise, Y.P.Pawar, S.S.Kadam, D. D. Mohite, C. M. Deshmukh and N. K. Shelar, Effect of Positioning of RC Shear

Walls of Different Shapes on Seismic Performance of Building Resting On Sloping Ground. International Journal of Civil Engineering and Technology, 7(3), 2016, pp.373–384.

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=7&IType=3

1. INTRODUCTION

The scarcity of plain ground in hilly areas compels construction activity on sloping ground resulting in various important buildings such as reinforced concrete framed structures resting on hilly slopes. Since, the behavior of buildings during earthquake

depends upon the distribution of mass and stiffness in both horizontal and vertical planes of the buildings, both of which vary in case of hilly buildings with irregularity

and asymmetry due to step-back and step back-set back configuration. The presence of such constructions in seismically prone areas makes them exposed to greater shears and torsion as compared to conventional construction. In order to highlight the

differences in behavior, this may further be influenced by the characteristics of the locally available foundation material. Current building codes including IS: 1893 (Part

1): 2002 suggest detailed dynamic analysis of these types of buildings on different soil (hard, medium and soft soil) types. To assess acceptability of the design it is important to predict the force and deformation demands imposed on structures and

their elements by severe ground motion.

2. BUILDING DESCRIPTION

Number of storey: 6 Slab thickness: 120 mm

Floor height: 3.5 m Thickness of concrete shear wall: 200 mm

No of bay in x and y direction: 5 Spacing in x and y direction: 4 m

Live load: 4 kN/m2 Floor finish load: 1. 875 kN/m2

Grade of concrete: M20 Grade of steel: Fe415

Beam sizes: 300x500 mm Column sizes: 500x500 mm

Earthquake parameters

Type of frame: SMRF seismic zone: v

Response reduction factor: 5

Importance factor: 1

The models are analyzed on leveled as well as sloping ground with a varying slope V: H). The frames on leveled and sloping ground under consideration for present study is as shown in Fig. 1 and Fig. 2 and Fig. 3

Effect of Positioning of RC Shear Walls of Different Shapes on Seismic Performance of Building Resting On Sloping Ground


Plan Ground slope 100

Figure 1 Building frame on sloping ground

Ground slope 200 Ground slope 30

0

Figure 2 and 3 Building frame on sloping ground

3. MODELLING AND ANALYSIS

In the present study lateral load analysis as per the seismic code for the bare Frame and concrete Shear wall structure is carried out and an effort is made to study the

effect of seismic loads on them and thus assess their seismic vulnerability by performing response spectrum analysis. The analysis is carried out using SAP 2000 V

15.2.2 analysis. Concrete frame elements are classified as beam and column frames. Columns and beams are modelled using three dimensional frame elements. Slabs are modelled as rigid diaphragms. The beam column joints are assumed to be rigid. Using

Software, analyses are carried on six storied building models on sloping ground with a different slope which are as follows: 100,200 and 300. To improve the seismic response

of building different shear walls configurations are chosen as shown in fig 4 to Fig 8. In every model, position of shear walls is decided to keep the building symmetrical about both the principal axes to avoid undue torsion. Length of shear walls and no of

columns in both directions is kept same to keep the structure symmetrical in both principal directions in plan.

Load Combinations

The following load combination has been used for the calculating the member forces

and for comparing its results as per IS 1893 (Part 1): 2002.

1.5 (DL + IL)



1.2 (DL + IL ± EL)

1.5 (DL ± EL)

0.9 DL ± 1.5 EL

4. METHOD OF ANALYSIS

The IS 1893 (Part 1): 2002 recommends 3D modeling for dynamic analysis (Response

Spectrum analyses and Time History analyses) of irregular buildings higher than 12m in zone IV and V, and those greater than 40m in height in zone II and III. 3D analysis including torsional effect has been carried out by using response spectrum method for

this study. Dynamic response of these buildings, in terms of base shear, fundamental time period, roof displacement and member forces is presented, and compared within

the considered configuration of shear walls as well as with model without shear walls on sloping ground and at different slopes, efficient positioning of shear walls configuration to be used is suggested. Three columns A, B and C as shown in Fig. are

considered for comparison of member forces in the present study.

The seismic analysis of all buildings is carried by Response Spectrum Method in

accordance with IS: 1893 (Part 1): 2002. As per codal provisions dynamic results are normalized by multiplying with a base shear ratio Vb/VB , where Vb is the base shear evaluation based on time period given by empirical equation and, VB is the base shear

from dynamic analysis , if Vb/VB ratio is more than one. Damping considered for all modes of vibration was five percent. For determining the seismic response of the

buildings in different directions for ground motion the response spectrum analysis was conducted in longitudinal and transverse direction (X and Y). The other parameters used in seismic analysis were, severe seismic zone (IV), zone factor 0.36,

importance factor 1, special moment resisting frame (SMRF) for all models with a response reduction factor of 5. The default number of modes (i.e. 12) in software was

used and the modal responses were combined using CQC method. The response spectra for medium soil sites with 5% damping as per IS 1893 (Part1):2002 is utilized in response spectrum analysis.

The following models of building are considered on sloping ground.

W 10 without shear wall W 20 without shear wall

S 10 with straight shape shear wall S 20 with straight shape shear wall L10 with L-shape shear walls L 20 with L-shape shear walls

C10 with channel shape shear wall C 20 with channel shape shear wall

T10 with T-shape shear walls T 20 with T-shape shear walls

W 30 without shear wall

S 30 with straight shape shear wall

L 30 with L-shape shear walls

C 30 with channel shape shear wall

T 30 with T-shape shear walls



Figure 4 Building without shear wall on sloping ground

Figure 5 Building with straight shape shear walls on sloping ground

Figure 6 Building with L-shape shear walls on sloping ground



Figure 7 Building with T-shape shear walls on sloping ground

Figure 8 Building with Channel shape shear walls on sloping ground

5. RESULTS AND DISCUSSION

The results of present study are categories as follows

From the results obtained in present study it is observed that the buildings on slopes are more vulnerable to seismic activity. The building on slopes shows the different behavior in two principal directions as presented in this study. The base shear of

buildings on slopes for different shear walls configuration is increased by approximately 50% along the direction parallel to slope whereas it is increased by 30-

45% in other transverse direction as shown in Fig.9 and Fig.10 compared to model 1.The lateral displacement observed in the direction parallel to slope is more as compared to displacement in transverse direction. Hence displacement in x direction

is only shown in fig.11and Fig.12. The reduction in lateral displacement is observed similar to that of models on leveled ground due to provision of shear walls in both

directions. The time period of shear walled model get reduced by 50-60% as compared to model 1.The time period and lateral displacement observed is minimum for model 2 (straight shape) among all the configurations. The seismic performance of

building on slope is as presented in Fig.13, and Fig.14



Figure 9 Variation of base shear for building of without shear wall on sloping ground with varying slope

Figure 10 Variation of base shear for building of with a shear wall on sloping ground with varying slope

Figure 11 without shear wall Figure 12 Straight shape shear wall

Lateral displacement of building on sloping ground



Figure 13 without shear wall Figure 14 Straight shape shear wall

Variation of time period on sloping ground

6. MEMBER FORCES

The shear forces and bending moments in columns also get reduced same as to model

on sloping ground due to shear wall. The member forces such as axial forces, shear forces and bending moment are presented in Fig.15, to Fig.20 respectively. The buildings on slope are subjected to torsion when subjected to lateral load. Hence the

torsional moments are also compared. These torsional moments get reduced by 75-90% as shown in Fig.21, 22

Figure 15 Axial Forces for building without shear wall on sloping ground



Figure 16 Axial Forces for building with shear wall on sloping ground

Figure 17 Shear Forces for building without shear wall on sloping ground

Figure 18 Shear Forces for building with shear wall on sloping ground



Figure 19 Bending Moment for building without shear wall on sloping ground

Figure 20 Bending Moment for building without shear wall on sloping ground

Figure 21 Tortioal Moment for building without shear wall on sloping ground



Figure 22 Tortioal Moment for building with shear wall on sloping ground

7. CONCLUSIONS

From the present study the following conclusions are drawn

1. There is significant improvement observed in seismic performance of building on slopes by providing shear walls with different configurations since lateral displacement and member forces reduces considerably in building due to provision of shear walls.

2. For buildings on slopes shortest column on higher stiffness. The base shear and displacement is more along the slope than in other transverse direction.

3. The straight shape (or rectangular) shear walls configuration proves to be better among all configurations for resisting the lateral displacement.

4. The L-shape shear walls configuration is effective during seismic activity because the member forces developed in this configuration are less as compared to other configurations on sloping ground whereas on plane ground this configuration has approximately same member forces for all configurations. Also for this configuration base shear is Minimum among all configurations on leveled ground.

5. Use of T-shape shear walls gives more lateral displacement and member forces for buildings on slopes as compared to other configurations.

REFERENCES

[1] S. K. Hirde and Ms. S. T. Charjan, (2009), Effect of various positions of reinforced concrete shear walls on seismic performance of building having soft bottom storey, ISSE Journal, 11(1)

[2] B. G. Birajdar, S. S. Nalawde, (2004), Seismic analysis of buildings resting on sloping ground, 13th World Conference on Earthquake Engineering, Vancouver, B.C., Canada, Paper No. 1472.

[3] Prabhat Kumar, Sharad Sharma et al, (2012), Influence of soil-structure interaction in seismic response of step back buildings. ISET Golden jubilee symposium Indian Society of Earthquake Technology, Department of Earthquake Engineering Building IIT Roorkee, Roorkee, Paper No. C013. October 20–21.

[4] S.M.Nagargoje and K.S. Sable, (2012), Seismic performance of mult i-Storeyed building on sloping ground, Elixir International Journal

[5] S. A. Halkude, Mr. M. G. Kalyanshetti et al, (2013), Seismic Analysis of Buildings Resting on Sloping Ground with Varying Number of Bays and Hill Slopes, International Journal of Engineering Research 2(12).



[6] Prabhat Kumar, Ashwani Kumar et al, (2014), Comparison of Seismic Response of Buildings on Slopes, National conference on emerging trends in engineering science & technology (NCETEST-2014) March 29th -30th, College of Engineering Roorkee (COER), Roorkee, India.

[7] R. M. Sawant, Junaid Khan, Jabeen Khan and Satish Waykar, Behavior of High Strength Fiber Reinforced Concrete under Shear. International Journal of Civil Engineering and Technology, 6(4), 2015, pp.46–54.

[8] Reshma Chandran, Unni Kartha G and Preetha Prabhakaran, Comparative Study on Solid and Coupled Shear Wall. International Journal of Civil Engineering and Technology, 5(12), 2014, pp.117–133.

[9] Anila Anna Samson, Preetha Prabhakaran and Dr. Girija K, Performance of Shear Wall Building during Seismic Excitations. International Journal of Civil Engineering and Technology, 5(12), 2014, pp.73–84.

[10] IS 1893 (Part I): (2002), Criteria for Earthquake Resistant Design of Structures, Part I General Provisions and Buildings, Bureau of Indian Standards, New Delhi.

EFFECT OF POSITIONING OF RC SHEAR WALLS OF DIFFERENT SHAPES ON SEISMIC PERFORMANCE OF BUILDING...

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