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International Journal of Engineering Research ISSN:2319-6890)(online),2347-5013(print) Volume No.5 Issue: Special 3, pp: 701-704 27-28 Feb. 2016

NCASE@2016 doi : 10.17950/ijer/v5i3/039 Page 701

A Review on Seismic Response of RC Building on Sloping Ground

S.D.Uttekar, C.R.Nayak

Civil Engg.Dept, Vidya Pratisthan College of Enigineering,Baramati. email: [email protected], [email protected]

Abstract- Seismic analysis is the calculation of the response of a structure to earthquakes. It is part of the process of structural design, earthquake engineering or structural assessment and retrofit in regions where earthquakes are prevalent. The aim of this paper to study the response of RC structure on slopping ground. To evaluate the response of building by using linear analysis and non linear analysis. The analysis will be carried out on SAP2000 with help of guidelines following code I.S 1893:2002 (part I),FEMA356. The seismic response on sloping ground is quite different as compare to seismic response on plain ground. In RC structure design we do not consider the effect of infiil wall on structure during earthquake. In addition to this infill walls have a considerable strength and stiffness and they have significant effect on the seismic response of the structural system. Necessity of analysis the seismic response of RC building on sloping ground because Lack of timely revisions of codes of practice and standards. Hill buildings are different from those in plains; they are very irregular and unsymmetrical in horizontal and vertical planes, and torsionally coupled. Due to the varied configurations of buildings in hilly areas, these buildings become highly irregular and asymmetric, due to variation in mass and stiffness distributions on different vertical axis at each floor. Such construction in seismically prone areas makes them exposed to greater shears and torsion as compared to conventional construction.

Keywords Response, Torsionally coupled. Linear analysis, Non-linear analysis, sloping ground

1. Introduction

The economic growth & rapid urbanization in hilly region has accelerated the real estate development. Due to this, population density in the hilly region has increased enormously. Therefore; there is popular & pressing demand for the construction of multi -storey buildings on hill slope in and around the cities. In some parts of world, hilly area is more prone to seismic activity; e.g. northeast region of India. codal provisions have proved unsafe and, resulted in loss of life and property when subjected to earthquake ground motions. Seismic analysis is the calculation of the response of a structure to earthquakes. It is part of the process of structural design, earthquake engineering or structural assessment and retrofit in regions where earthquakes are prevalent. During past earthquakes, reinforced concrete (RC) frame buildings that have columns of different heights within one storey, suffered more damage in the shorter columns as compared to taller columns in the same storey

The study of earthquake resistant building on slopes becomes popular to prevent the loss of life, property during earthquake ground motion

In RC structure design we do not consider the effect of infill wall on structure during earthquake. The masonry infill walls which are constructed after completion of reinforced concrete frames are considered as non-structural elements. Although they are designed to perform architectural functions, masonry infill walls do resist lateral forces with substantial structural action.

Necessity of seismic evaluation

• The building may not have been designed and detailed to resist seismic force.

• Lack of timely revisions of codes of practice and standards. • Many of the existing building are lacking in adequate

earthquake resistance because these are not designed according to modern codes and prevalent earthquake resistance practice.

• Different heights of columns are present in building on hilly slopes in a same storey, as a result more forces are attracted during earthquake ground motion by short columns and damage occurs

• Hill buildings are different from those in plains; they are very irregular and unsymmetrical in horizontal and vertical planes, and torsionally coupled. Hence, they are susceptible to severe damage when affected by earthquake ground motion.

2. Significance It is observed from past earthquakes that the buildings on slopes serve more damage and collapse occurs. This review paper aims to analyse the dynamic characteristics of these type of buildings with two different configuration such as a) Step back b) Step Back-Setback

3. Previous Study

B.G. Birajdar1, S.S. Nalawade considered two buildings on sloping ground and one building is on flat soil. The first two are step back buildings and step back-setback buildings; and third is the set back building. The slope is taken 27 degree with horizontal. Depth of footing was taken 1.75m below ground level and the block size was considered as 7 m x 5 m x 3.5 m.The properties of beam and column is shown in Table 1.



Table 1

S. M. Nagargoje and K. S. Sable considered same

configuration of building and first two configuration of building was resting on slope soil and third configuration was taken on flat soil. Block size is taken as 7 m x 5 m x 3.4 m. Footing depth was taken as 1.6m below ground level. The properties of beams and columns were taken is shown in Table 2.

Table 2

Building Configuration

Size of column Size of beam

Step back Buildings

STEP4 to STEP5 230x500mm STEP6to STEP7 230x650mm STEP8to STEP9 300x650mm STEP10to STEP11 300x850mm STEP12to STEP15 350x900mm

230x450mm

Stepback & Setback Building

STEPSET4 to11 230x475mm STEPSET12 to 15 350x900mm

230x450mm

4. Method of Analysis

B. G. Birajdar1, S. S. Nalawade1 took the materials isotropic, homogeneous in nature. Floor diaphragms are taken as rigid.M25 concrete was used and P-delta effects, creep & shrinkage effects were not considered. Axial deformation was considered for columns. Torsional effect was considered as per IS-1893:2002.Seismic analysis was performed byResponse Spectra Method as per IS 1893:2002.Ordinary moment resisting frame was taken for all these types of buildings in seismic zone III. Response reduction factor and importance factor was taken as 3 and 1 respectively.5% of damping was considered.

S. M. Nagargoje and K. S. Sable3 analysed the seismic behaviour of these building located in seismic zone III by Seismic Coefficient Method as per IS 1893:2002.Response reduction factor and importance factor was taken as 5 and 1

respectively. Minimun six modes were analysed for each type of building.

5. Storey Drift

B.G. Birajdar1, S.S. Nalawade1 observed that the along x direction time period and top storey displacement is increased for step back building as the height increases. Dynamic response i.e. fundamental time period, base shear ,top storey displacement for step back building along x direction is shown in Table 3.

Table 3

The value of fundamental time period estimated by empirical formula as per IS 1893:2002 is lower than the value of fundamental time period obtained in dynamic analysis.

The value of base shear, fundamental time period is higher in Y direction than the corresponding values when earthquake force acts in x direction. Time period in dynamic analysis is greater than that calculated by empirical formula as per IS 1893:2002.The value of normalized shear force in columns, base shear, top storey displacement, time period for



step back building along Y direction is shown in Table 4. Table 4

In case of Step Back Set Back Buildings, the value of base shear ratio obtained in X direction from dynamic and static analysis are almost same. Time period in dynamic analysis in X direction is greater than that calculated by empirical formula as per IS 1893:2002 for Step Back Set Back Buildings. The value of time period, base shear ratio, top storey displacement in X direction is shown in Table 5.

Table 5

In Y direction, variation of shear force is found less Significant. Time period in dynamic analysis of this type of building is not affected by the height of building. Uniform section for columns from top to bottom is sufficient. The value of time period, base shear ratio,top storey displacement in Y direction is shown in Table 6.

Table 6

S.M. Nagargoje and K.S.Sable3 observed the base shear, top storey displacement in X and Y direction for step back, step back-set back building is shown in Table 7, Table 8 respectively.

Table 7

Table 8 The relationship between displacement and storey of Step, Step-Set, Set buildings is observed and shown in Figure1

Figure 1



4. Conclusions

During earthquake, STEP back buildings are more vulnerable than other building configuration. 1. Extreme left short column at ground level are damaged most during earthquake in case of Step back and Step back-Set back buildings 2. Consider the effect infill wall during calculation of seismic response. In this review paper the effect of infill wall do not consider in calculation 3. Base shear is higher for Step back-Setback building and lower for Step back building. 4. Lateral displacement of top storey is maximum for Step back building. 5. On sloping soil Setback- Stepback building is favored.

REFERENCES

i. B.G. Birajdar, S.S. Nalawade (2004) "Seismic Analysis

Of Buildings Resting On Sloping Ground", 13th World Conference on Earthquake Engineering,Vancouver, B.C., Canada, Paper No. 1472. Pp.1-6

ii. S.M.Nagargoje and K.S.Sable (2012) "Seismic performance of multi-storeyed building on sloping ground", Elixir International Journal

iii. Satish Kumar and D.K. Paul., “Hill buildings configuration from seismic consideration”, Journal of structural Engg., vol. 26, No.3, October 1999, pp. 179-185.

iv. Saptadip Sarkar, Dr. K.C.Biswal (2010). "Design Of Earth- Quake Resistant Multi-Storied Rcc Building On A Sloping Ground." A Thesis Submitted In Partial Fulfillment Of The Requirements For The Degree Of Bachelor Of Technology In Civil Engineering Department of Civil Engineering National Institute of Technology Rourkela 2010

v. Dr. Suchita Hirde, and Ms. Dhanshri Bhoite Dept. of App. Mechanics Govt. College of Engineering Karad 415124 India,” Effect Of Modeling Of Infill Walls On Performance Of Multi Story Rc Building” International Journal Of Civil Engineering And Technology (IJCIET) Volume 4, Issue 4, July-August (2013), pp. 243-250

vi. Prabhat Kumar, Sharad Sharma and A.D. Pandey (2012) “Influence Of Soil-Structure Interaction In Seismic Response Of Step-Back Buildings” ISET GOLDEN JUBILEE SYMPOSIUM Indian Society of Earthquake Technology, PAPER No. C013

vii. Murthy C.V.R. Learning earthquake design. viii. IS 13920:1993,"Indian Standard Code of Practice for

Ductile Detailing of Reinforced Concrete Structures Subjected to Seismic Forces",Bureau of Indian Standards,New Delhi.

ix. IS:1893 (I)-2002., “Criteria for Earthquake Resistant Design of Structures” BIS, New Delhi.

x. FEMA 356, “Prestandard and commentary for the seismic rehabilitation of buildings”, American society of civil engineers, Reston, Virginia, 2000.

xi. IS 456:2000,"Indian Standard Code of Practice for Plane and Reinforced concrete",Bureau of Indian Standards,New Delhi.

xii. SAP2000 V14.2.4, “Integrated finite element analysis and design of structures basic analysis reference manual”, Berkeley, CA, USA: Computers and structures INC, Aug. 2010.



Experimental Study of Seismic Behaviour of Multi-storied Framed Structure

connected with Viscous Fluid dampers and Lumped masses

P. K. Deshpande, Vaibhav Shelar College of Engineering, Karad 415124, Shivaji University, Kolhapur, Maharashtra, India

email: [email protected] Abstract- Current trends in construction industry demands taller and lighter structures, which are also more flexible and having quite low damping value. This increases failure possibilities and also problems from serviceability point of view. The dynamic response of building structures due to earthquakes is very important to Civil engineers. Structures expose to earthquake excited vibrations are damaging to their structures components. Vibration control is having its roots primarily in aerospace related problems such as tracking and pointing, and in flexible space structures, the technology quickly moved into civil engineering and infrastructure-related issues, such as the protection of buildings and bridges from extreme loads of earthquakes and winds. The number of tall buildings being built is increasing day by day. Today we cannot have a count of number of low-rise or medium rise and high rise buildings existing in the world. Mostly these structures are having low natural damping. So increasing damping capacity of a structural system, or considering the need for other mechanical means to increase the damping capacity of a building, has become increasingly common in the new generation of tall and super tall buildings. But, it should be made a routine design practice to design the damping capacity into a structural system while designing the structural system. Now-a-days several techniques are available to minimize the vibration of the structure. The aim of the present work is to study the effect of Viscous Fluid damper and Lumped Masses on the dynamic response of multi-stored frame structures under earthquake excitations and the seismic response of frame structure model (one bay and three storied) for frequency, Amplification factor and lateral forces at different floor along X and Y direction for following cases (Experimental analysis). a) Analysis without damper and without lumped mass applied to the model b) Analysis without damper and with lumped mass and c) Analysis without lumped mass and with damper. And the comparative study is made for above three conditions. The investigation is also carried out for effectiveness of the damping in terms of the percentage reduction in force of second & third floor with respect to first floor when dampers are connected diagonally.

Keywords Viscous Fluid Dampers, Lumped Masses, Amplification Factor, Lateral forces

1. Introduction

New civil engineering structures tend to be lighter, more slender and have smaller natural damping capacity than those of

their older counterparts. This trend has increased the importance of damping technology to mitigate earthquake and wind-induced vibrations. The control of structural vibrations produced by earthquake or wind can be done by various means such as modifying rigidities, masses, damping, or shape, and by providing passive or active counter forces. To date, some methods of structural control have been used successfully and newly proposed methods offer the possibility of extending applications and improving efficiency.

The control of structural vibrations produced by earthquake or wind can be done by various means such as modifying rigidities, masses, damping, or shape, and by providing passive or active counter forces. To date, some methods of structural control have been used successfully and newly proposed methods offer the possibility of extending applications and improving efficiency.

The selection of a particular type of vibration control device is governed by a number of factors which include efficiency, compactness and weight, capital cost, operating cost, maintenance requirements and safety.

2. Materials and Methods

2.1 Structural Model Details (Aluminum Structure)

Figure 2.1 Framed Structure The physical properties of different sections are shown in table 2.1 Section Materi

al Mass (m) Kg

Depth (D) mm

Width (B) mm

Length (L) mm

Material properties Young’s Modul

Mass Density (ρ)



us (E) GPa

kg/m3

Column Aluminum

0.269

10 25 400 69 2700

Slab Aluminum

1.418

12 150 300 69 2700

The viscous fluid dampers which were used in the experimental work are of mass 0.211 kg , which contains viscous fluid SAE 90. Along with this for measuring acceleration at each floor level 1 D accelerometer was installed. A lumped mass of 500 gm (Calibrated) was installed as per the range of shake table

2.2. Experimental Setup

2.3 Methodology

Following methodology will be adopted for proposed work: 1. Literature Survey will be made through journals, reference

books, technical magazines and also through internet & IS Codes.

2. Structural requirements will be finalized to follow technical concept of framed Structure and it will be compatible with existing shake table .

4. Selection of material will be done from the recommendations of ARAI. 5. Fabrication of the framed structure of suitable size. 6. Examine the seismic behavior of model under excitation using

shake table along X direction ( longer side parallel to excitation) and Y direction ( shorter side parallel to excitation). the model was tested for fixed base acceleration " g " with varying frequencies ( in the range of 5 Hz to 60 Hz)

7. Comparison of lateral force for following cases a) Analysis without dampers and without lumped masses

applied to the model, b) Analysis without dampers and with lumped masses and c) Analysis without lumped masses and with dampers.

2.4 Experimental Analysis

The experimental work was carried on multi storied aluminum frame model (one bay three storied) to study the behavior in terms of acceleration and lateral force at each story level along X direction and Y direction respectively. Total 30

cases were performed, with 15 cases along X direction and 15 cases along Y direction. Following is the list of different cases: Table 2.4.1 Different types of conditions along X and Y Direction

Graphical variation of Frequency and Amplification factor Along X Direction: 1) Analysis without damper and without lumped mass applied to the model

.

Figure 2.4.A.1 Graph Frequency Vs Amplification Factor

2.i) Lumped masses on all floors (500gm on each floor)


Sr. No Different types of conditions

1 Without dampers and without Lumped masses 2 Without dampers and with Lumped masses i Lumped masses on all floors ii Lumped masses on 2nd and 3rdfloor iii Lumped masses on 1st and 2nd floor iv Lumped masses on 1st and 3rd floor v Lumped masses only on 3rd floor vi Lumped mass only on 2nd floor vii Lumped mass only on 1st floor 3 Without Lumped masses and with dampers i Dampers connected at all floors ii Dampers connected at 2nd and 3rd floor iii Dampers connected at 1st and 2nd floor iv Dampers connected at 1st and 3rd floor v Damper connected only at 3rdfloor vi Dampers connected only at 2ndfloor vii Damper connected only at 1st floor

Power Amplifi

Shake table

Excitation to Frame

Accelerometer Signature vibration control

Computer


NCASE@2016 doi : 10.17950/ijer/v5i3/040 07

3) Analysis without damper and without lumped mass applied to the model i) Dampers Connected at all floors


Along Y direction: 1) Analysis without damper and without lumped mass applied to the model

Figure 2.4.B.1 Graph Frequency Vs Amplification Factor

2. i) Lumped masses on all floors (500gm on each floor)

Figure 2.4.B.2 Graph Frequency Vs Amplification Factor

3) Analysis without damper and without lumped mass applied to the model i) Dampers Connected at all floors

Figure 2.4.B.3 Graph Frequency Vs Amplification Factor 2.5 Experimental Results Table 2.5.1: Percentage reduction in lateral force along X direction

Sr.

No

Different types of conditions % Reduction in

Lateral Force

SF wrt

FF

TF wrt

SF

1 Without dampers and without Lumped masses

20.5↓ 15.66↓

2 Without dampers and with Lumped masses i Lumped masses on all floors 19.45↓ 15.27↓ ii Lumped masses on 2nd and 3rdfloor 0 0 iii Lumped masses on 1st and 2ndfloor 29.33↓ 19.79↓ iv Lumped masses on 1st and 3rd floor 41.06↓ 27.37↓ v Lumped masses only on 3rd floor 27.1↓ 17.26↓ vi Lumped mass only on 2nd floor 9.93↓ 4.29↓ vii Lumped mass only on 1stfloor 40.25↓ 45.68↓ 3 Without Lumped masses and with dampers i Dampers connected at all floors 22.89↓ 15.92↓ ii Dampers connected at 2nd and 3rdfloor 23.22↓ 15.64↓ iii Dampers connected at 1st and 2nd floor 39.86↓ 20.45↓ iv Dampers connected at 1st and 3rdfloor 25.18↓ 14↓ v Dampers connected only at 3rd floor 21.88↓ 8.79↓ vi Dampers connected only at 2ndfloor 28.42↓ 24.41↓ vii Dampers connected only at 1st floor 31.74↓ 24.52↓

Table2.5.2 Percentage reduction in lateral force along Y direction

Sr. No

Different types of conditions % Reduction in Lateral Force



SF wrt FF

TF wrt SF

1 Without dampers and without Lumped masses

3.13↓ 23.54↓

2 Without dampers and with Lumped masses

i Lumped masses on all floors 38.59↓ 24.88↓ ii Lumped masses on 2nd and 3rd

floor 41.53↓ 32.53↓

iii Lumped masses on 1stand 2nd floor

60↓ 28.93↓

iv Lumped masses on 1st and 3rd floor

7.9↓ 15.33↓

v Lumped mass only on 3rd floor 13.43↓ 18.45↓

vi Lumped mass only on 2ndfloor 22.67 ↑ 22.61↓

vii Lumped mass only on 1st floor 58.16↓ 34.99↓

3 Without Lumped masses and with dampers

i Dampers connected at all floors 15.94 ↑ 37.54↓ ii Dampers connected at 2nd and

3rd floor 22.59↓ 22↓

iii Dampers connected at 1stand 2nd floor

6.5↓ 30.43↓

iv Dampers connected at 1stand 3rd floor

15.2 ↑ 24.14↓

v Dampers connected only at 3rd floor

45.52↓ 13.52↓

vi Dampers connected only at 2nd floor

17.21↑ 26.65↓

vii Dampers connected only at 1st floor

3.84↓ 31.89↓

As per the results obtained, following points were observed. 1. Due to presence of lumped masses and viscous fluid dampers, there is significant increase in amplification factor along X direction and reduction in amplification factor along Y direction. 2. Due to presence of lumped masses, there is increase in lateral force along X direction and Y direction. 3. Due to presence of viscous fluid dampers, there is significant reduction in lateral force along Y direction 2.6 Equation

The force/velocity relationship for this kind of damper can be characterized as F= C.V. α where F is the output force, V the relative velocity across the damper, C is the damping coefficient and α is a constant exponent which is usually a value between 0.3 and 1.0. Fluid viscous dampers can operate over temperature fluctuations ranging from –40°C to +70°C. 3. Conclusion Multistoried framed structure model (G+2) has been tested for the seismic behavior under excitation using shake table along X direction ( longer side parallel to excitation) and Y direction ( shorter side parallel to excitation). the model was tested for fixed base acceleration " g " with varying frequencies ( in the

range of 5 Hz to 60 Hz) . From the experimental study following conclusions can be drawn. 1) It is observed that there is reduction in lateral force due to presence of viscous fluid dampers. This will lead to improvement in performance level of the structure. 2) The location of dampers has significant effect on response of

the framed structure. It is advisable to provide dampers on all floors.

REFERENCES i. U. Frahm, Device for damping of bodies, US Patent No.

989, 958, 1911. ii. J. Ormondroyd, J.P. Den Hartog, The theory of dynamic

vibration absorber, Transactions of the American Society of Mechanical Engineers 50 (1928) 9–22.

iii. J.E. Brock, A note on the damped vibration absorber, Transactions of the American Society of Mechanical Engineers Journal of Applied Mechanics 13 (1946) A–284.

iv. J.P. Den Hartog, Mechanical Vibrations, 3rd Edition, McGraw-Hill, New York, 1947.

v. E. Hahnkamm, Versammlung der SchiffbautechnischeGesellschaft, Berlin, 1935.

vi. S.H. Crandall, W.D. Mark, Random Vibration in Mechanical Systems, Academic, New York, 1963.

vii. G.B. Warburton, Optimum absorber parameters for various combinations of response and excitation parameters, Earthquake Engineering and Structural Dynamics 10 (1982) 381–401.

viii. H.C. Tsai, G.C. Lin, Optimum tuned mass dampers for minimizing steady-state response of support-excited and damped systems, Earthquake Engineering and Structural Dynamics 22 (1993) 957–973.

ix. D. Holmes, Listing of installations, Engineering Structures 17 (1995) 676–677.

J. Morison, D. Karnopp, Comparison of optimized active and passive vibration absorber, Proceedings of the 14th Annual Joint Automatic Control Conference, Columbus, OH, 1973, pp. 932–938.

x. R.A. Lund, Active damping of large structures in winds, in: H.H.E. Leipholz (Ed.), Structural Control, North-Holland, New York, 1980.

xi. J. Chang, T.T. Soong, Structural control using active tuned mass dampers, American Society of Civil Engineers Journal of Engineering Mechanics Division 106 (1980) 1081–1088.

xii. F.E. Udwadia, S. Tabaie, Pulse control of single degree of freedom system, American Society of Civil Engineers Journal of Engineering Mechanics Division 107 (1981) 997–1009.

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