International Journal of Research and Innovation (IJRI)
International Journal of Research and Innovation (IJRI) 1401-1402
STUDY OF DYNAMIC BEHAVIOUR OF A MULTISTORIED RCC STRUCTURE WITH WATER TANKS AS LIQUID DAMPERS
Muhammed Mujahid Ali1, Mythili Rao2, Mohammed Ahmeduddin3 1 Research Scholar, Department of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad,India. 2 Assistant professor, Department of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad,India. 3 Civil & Structural engineer, LEAD (I) pvt Ltd,Hyderabad,India.
Abstract Sloshing liquid dampers (SLDs), popularly known as tuned liquid dampers (TLDs), are used as passive control devices for reducing structural vibrations resulting from wind and earthquake excitations in tall buildings and high-rise structures. In the present investigation, effectiveness of these TLDs has been studied for a building. A twenty-storied building has been considered as a representative of the structure. It is shown that the liquid sloshing is the most important design parameter, rather than, tuning of the fundamental sloshing frequency to the structure frequency for the liquid damper to be effective. Furthermore, the liquid damper design for multistory buildings is different from that for Single Degree Of Freedom (SDOF) structures, where not only the optimal tuning ratio of the liquid damper is different, but multiple dampers located at critical locations are required for effective control of floor accelerations. The investigation is performed using the linear dynamic analysis. Response spectrum method is used for analysis of the structure under dynamic loading. This is very useful tool of earthquake engineering for analyzing the performance of structures and equipment in earthquakes, since many behave principally as simple oscillators. Thus, if you can find out the natural frequency of the structure, then the peak response of the building can be estimated by reading the value from the ground response spectrum for the appropriate frequency. In most building codes in seismic regions, this value forms the basis for calculating the forces that a structure must be designed to resist. Finally, it is illustrated that TLDs, if appropriately designed, can be very effective in reducing overall forces, moments, base shears, time period and deformation of building structures for earthquake type base excitations. To perform this type of analysis the software used here is SAP. From its 3D object based graphical modeling environment to the wide variety of analysis and design options completely integrated across one powerful user interface, SAP2000 has proven to be the most integrated, productive and practical general purpose structural program on the market today. This interface allows us to create structural models rapidly without long delays. Complex Models can be generated and meshed with powerful built in templates. Integrated design code features can automatically generate loads with comprehensive automatic steel and concrete design code checks per design standards. The model is subjected to dynamic loads and the results compared are base shear, roof displacement, Time period. The selected model were subjected to linear dynamic analysis with and without TLD. Results obtained from calculations, analysis and investigations are the lateral roof displacements, base shears & time period. Base shear was found to be 15% less when a TLD is used, similarly lateral displacement and time period was found to be 14% and 8% less respectively when a TLD was applied on the structure. *Corresponding Author:
INTRODUCTION
Muhammed Mujahid Ali , Research Scholar, Department of Civil Engineering, Aurora's Scientific Technological and Research Academy, Hyderabad India.
General
Published: November 22, 2015 Review Type: peer reviewed Volume: II, Issue : IV Citation: Muhammed Mujahid Ali , Research Scholar (2015) "STUDY OF DYNAMIC BEHAVIOUR OF A MULTISTORIED RCC STRUCTURE WITH WATER TANKS AS LIQUID DAMPERS"
Starting from the very beginning of civilization, mankind has faced several threat of extinction due to invasion of severe natural disasters. Earthquake is the most disastrous among them due to its huge power of devastation and total unpredictability. Unlike other natural catastrophes, earthquakes themselves do not kill people, rather the colossal loss of human lives and properties occur due to the destruction of man-made structures. Building structures are one of such creations of mankind, which collapse during severe earthquakes, and cause direct loss of human lives. Numerous research works have been directed worldwide in last few decades to investigate the cause of failure of different types of buildings under severe seismic excitations. Massive destruction of high-rise as well as low-rise buildings in recent devastating earthquake of Nepal in April, 2015 proves that also in develop227
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ing counties, such investigation is the need of the hour. Conventionally reinforced concrete tanks have been used extensively in residential and industrial facilities for several decades. The design of these structures is also being given attention considering parameters such as strength requirements and serviceability requirements. Conventional design is followed till date for the design of high rise structures with water tanks. Seismic activity prone countries across the world rely on “codes of practice� to mandate that all the constructions fulfill at least a minimum level of safety requirements against future earthquakes. The devastation caused by recent earthquakes highlights the necessity of adequate protection in buildings against earthquake damage. One effective way of providing earthquake protection for buildings is the use of external structural control devices. Unfortunately, widespread use of these devices in developing countries is prevented due to the prohibitive additional cost of these devices, relative to the cost of construction of a typical building. Thus, research focus is shifting towards the study of effective and economic control devices for earthquakes. The behavior of a building during earthquakes depends critically on its overall shape, size and geometry in addition to how the earthquake forces are carried to the ground. Design of civil engineering structures is typically based on prescriptive methods of building codes. Normally in the static case, the loads on these structures are low and result in elastic structural behavior. However, under a strong seismic event, a structure may actually be subjected to forces beyond its elastic limit. The devastation caused by recent earthquakes highlights the necessity of adequate protection in buildings against earthquake damage. One effective way of providing earthquake protection for buildings is the use of external structural control devices. Unfortunately, widespread use of these devices in developing countries is prevented due to the prohibitive additional cost of these devices, relative to the cost of construction of a typical building. Thus, research focus is shifting towards the study of effective and economic control devices for earthquakes. The vibration control system, named Tuned Liquid Damper (TLD), has been widely recognized as an effective damper for reducing the structural vibration due to earthquake, strong wind and other dynamic loadings (Modi., 1987 and Fujino., 1988). In this damper, the sloshing period of the TLD is tuned to the fundamental period of the structure. This damper exploits the hydrodynamic force of the liquid (water) to control the vibration of the structure. Need of Work It is known that, some of the fluid containers are damaged in many earthquakes. Damage or collapse of these containers causes some unwanted events such as shortage of drinking and utilizing water, uncontrolled fires and spillage of dangerous fluids. The new generation civil engineering tall structures are flexible, weakly damped and light weight. Tuned liquid dampers are used to control the structural vibration in such structures. Response spectra provide a very handy tool for engineers to quantify the demands of earthquake ground motion on the capacity of buildings to resist earthquakes. Data on past earthquake ground motion is generally in the form of time-history recordings obtained from instruments placed at various sites that are activated by
sensing the initial ground motion of an earthquake. The amplitudes of motion can be expressed in terms of acceleration, velocity and displacement. The first data reported from an earthquake record is generally the peak ground acceleration (PGA) which expresses the tip of the maximum spike of the acceleration ground motion (Figure 1). Although useful to express the relative intensity of the ground motion (i.e., small, moderate or large), the PGA does not give any information regarding the frequency (or period) content that influences the amplification of building motion due to the cyclic ground motion. In other words, tall buildings with long fundamental periods of vibration will respond differently than short buildings with short periods of vibration. Response spectra provide these characteristics.
Static and Dynamic Pressures acting on tank wall
Seismic analysis of liquid-containing tanks differs from buildings in two ways: 1. During seismic excitation, liquid inside the tank exerts hydrodynamic force on tank walls and base. 2. Liquid-containing tanks are generally less ductile and have low redundancy as compared to buildings. Objective of Study The present work aims at the following objectives: 1. To evaluate targeted Displacements of Structure with Full tank and Empty Tank conditions separately and compare them. 2. To evaluate Base Shear of Structure with Full tank and Empty Tank conditions and compare them. 3. To evaluate Modal periods and frequencies of Structure with Full tank and Empty Tank conditions separately and compare them. Scope of Study Actually the knowledge of the rules governing the motion of the liquid in a tank is of basic importance for understanding the behavior of liquid-based devices and testing the reliability of the relevant simplified mechanical models. Recently, the popularity of TLDs as viable devices for structural control has prompted study of sloshing for structural engineering applications. The motion of liquids in rigid containers has been the subject of many studies in the past few decades due to its frequent application in several engineering disciplines [18]. Moreover, one should emphasize that the need for accurate evaluation of the sloshing loads is also required for the design of aerospace vehicles, in civil engineering applications for the design of water tanks and dams, for chimney’ installations (Figure 1), for problems relating to safety for tank trucks on highways and liquid tank cars on railroads, as well as in maritime applications where the effect of sloshing of liquids present on board, for e.g., liquid cargo or liquid fuel, 228
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can cause loss of stability of the ship as well as structural damage. 1. Using SAP 2000 software, considering the 20 storey RCC and structure of Height 63m and each floor height is 3m. 2. To consider parameters such as Displacement, Base Shear, and Time period for Seismic load in accordance with IS 1893:2002. 3. To compare the effect of TLD on proposed building. 4 The building studied is reinforced concrete with water tank positioned at the center of gravity of the building at the roof.
tion frequency is lower than the resonance frequency, the peak structural response typically increases with increasing water depth ratio. However, at the region of resonance (f/fs ≈ 1), the response amplitude reduces drastically upon attachment of the TLD.
REVIEW OF LITERATURE Bhosale Dattatray, G. R. Patil, Sachin Maskar[6] (2014): Use of Overhead Water Tank to Reduce Peak Response of the Structure. This paper presents analytical investigation carried out to study the use of over head water tank as passive TMD. The behaviour of the tank subjected to three earthquake data, namely, Elcentro, Bhuj, Washington was studied. The results shows if the tank is tuned properly it can reduce the peak response of structures subjected to seismic forces. Jitaditya Mondal, Harsha Nimmala, Shameel Abdulla, Reza Tafreshi[16] (2014): Tuned liquid damper. The aim of this paper is to show the effectiveness of a tuned liquid damper (TLD). TLD can be used in building structures to damp structural vibrations. A Tuned liquid damper is water confined in a container, usually placed on top of a building that uses the sloshing energy of the water to reduce the dynamic response of the system when it is subjected to excitation. Tejashri S. Gulve, Pranesh Murnal[28] (2013): Feasibility of Implementing Water Tank as Passive Tuned Mass Damper. This paper presents analytical investigation carried out to study the feasibility of implementing water tank as passive TMD. The behavior of the tank subjected to five earthquake data, namely, Elcentro, Bhuj, Kobe, Chichi and N-Palm was studied. The results show that TMD can reduce the peak response of structures subjected to seismic forces. Emili Bhattacharjee, Lipika Halder* and Richi Prasad Sharma[9] (2013): An experimental study on tuned liquid damper for mitigation of structural response. This paper investigates the performance of unidirectional tuned liquid damper (TLD) that relies upon the motion of shallow liquid in a rigid tank for changing the dynamic characteristics of a structure and dissipating its vibration energy under harmonic excitation. A series of experimental tests are conducted on a scaled model of structure tuned liquid damper systems to evaluate their performance under harmonic excitation. One rectangular and one square TLD with various water depth ratios are examined over different frequency ratios, and time histories of accelerations are measured by precisely controlled shaking table tests. The behavior of TLD is also studied by changing the orientation of the rectangular TLD subjected to the given range of harmonic excitation frequencies. The effectiveness of TLD is evaluated based on the response reduction of the structure. From the study, it is found that for each TLD, there exists an optimum water depth that corresponds to the minimum response amplitude, and the maximum control of vibration is obtained under resonance condition with the attachment of TLD. At the initial stage, when the excita-
Structural response of the structure with TLD and without TLD
THEORY The problem of excessive response control is more pronounced for defense establishments as these are scattered and remotely located, house important and costly machines and equipment which are sensitive to vibration for normal functioning. Retrofitting or strengthening such structures with TLDs is an attractive and viable option as these are free from external energy dependence and regular maintenance. At the same time, these can easily be accommodated in existing structures and design parameters. Basic Principle Conventional anti-seismic approach relies on the inertialresisting capacity of the structure against earthquakes through a combination of properties such as strength, deformability and energy absorption. Damping the inherent energy dissipation capacity of such structure is very low (< 5 %). Very small part of energy is dissipated through elastic behavior. Under strong seismic excitation, these structures deform beyond the elastic limit, forming localized plastic hinges, resulting in localized damage, and thereby absorption of seismic energy. An alternate energy-based earthquake mitigation approach considers energy distribution within the structure. Time-dependent energy conservation relationship of a seismic event may be presented as E(t) = Ek(t)+ Es(t)+ Eh(t)+ Ed(t) where E(t) = absolute energy input from earthquake motion, Ek(t) = absolute kinetic energy , Es(t) = elastic strain energy (recoverable), Eh(t)= irrecoverable energy dissipated through inelastic, viscous and hysteretic actions, Ed(t)= energy dissipated by supplemental damping system and, t = time. In conventional structures Ed(t) is not present, the input energy from ground motion acceleration is transformed into kinetic and strain energies which are absorbed or dissipated through heat. The inherent energy dissipation
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capacity of the structure tries to dissipate the seismic input energy by hysteretic actions, causing damages to the structure. METHODOLOGY Hydrostatic pressure: The pressure applied by the liquid on the container under static condition. Hydrodynamic pressure: The pressure applied by the liquid on the container under dynamic condition. Impulsive liquid: Liquid in the bottom portion of the container which moves with the wall under dynamic loading. Convective Liquid: Liquid in the top portion of the container which undergoes sloshing and moves relative to the wall also known as sloshing liquid. Impulsive force: Force exerted by impulsive liquid on the walls of the water tank. It is summation of impulsive pressure on entire wall surface. Convective force: Force exerted by convective liquid on the walls of water tank. It is summation of convective pressure on entire wall surface.
Sl. No.
Variable
Data
1.
Type of structure
RCC Ordinary Moment Resisting Frame
2.
Number of storeys
20
3.
Floor Height
3m
4.
Dead Load applied on slabs
2kN/m2
5.
Live Load applied on slabs
2kN/m2
6.
Material used
Concrete: M20 Steel: FE415
7.
Size of column
380mm X 670mm
8.
Size of plinth beam
230mm X 300mm
9.
Size of typical beam
230mm X 450mm
10.
Thickness of wall
230mm
11.
Zone of building
V
12.
Importance Factor
2
13.
Response Reduction Factor
5
14.
Type of soil
II
Response Spectra: Response spectra are curves plotted between maximum response of SDOF system subjected to specified earthquake ground motion and its time period (or frequency). Response spectrum can be interpreted as the locus of maximum response of a SDOF system for given damping ratio. Damping: Buildings set to oscillation by earthquake shaking eventually come back to rest with time. This is due to dissipation of the oscillatory energy through conversion to other forms of energy, like heat and sound. The mechanism of this conversion is called damping. Seismic weight: The seismic weight of each floor is its full dead load plus appropriate amount of imposed load as specified. While computing the seismic weight of each floor, the weight of columns and walls in any storey shall be equally distributed to the floors above and below the storey. CASE STUDY OF BUILDING
Typical Plan View of the structure in SAP2000
Two similar buildings but with significantly different water conditions in water tank on the roof is modeled. One building is analysed considering empty tank and other building is analysed considering full water level in the tank i.e., full tank condition as shown in fig (representational images). The preliminary building data required for analysis assumed are presented in the following table.
Perspective view of Structure in SAP2000
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Results obtained from calculations, analysis and investigations are the lateral roof displacements, base shears & time period. RESULTS For ease, results are briefly described and classified into tabular format and graphical representation. Comparision of Base shear, joint displacements and time periods are presented in the below tables and graphical pictures. Comparision of Base Shear From the fig. 6.1 it is observed that in the full tank condition where the effect of sloshing is considered, the values of base reactions in the direction of X is less compared to the base reaction in empty tank condition, which explains the economical behavior of the structure under the liquid damper.
Support & Column Positions
Calculation of Tank Capacity No. of liters per capita per day consumption as per IS 1172 â&#x20AC;&#x201C; 1993 = 150litres Estimated no. of persons occupying the building = 600nos. Total no of liters consumed per day = 150 X 600 = 90,000 liters =90 m3 Minimum volume of water tank required for consumption purpose = 90m3 Calculation of Tank Dimensions Considering Water Depth ratio as 0.5 h/L=0.5 Assuming Height of water as 5.6m H=0.5*L=5.6 L=11.2m L*B*h=90 11.2*B*5.6=90m3 B= 1.44m Minimum size of water tank required is 11.2*1.44*5.6 = 90.32m3 Considering size of tank as per availability of space = 9.52*6.85*5.6 = 365.19m3 Total volume of water = 9.52*6.85*5.6 =365.19m3
Base Shear in the direction of X
Discussion on result it is observed that the base shear value is decreased from 613kN to 526kN which is almost 15% decrease in the base shear value. Displays the Base shear of the structure in both the cases of Empty and Full Tank, mainly comparing the Base shear values in the earthquake condition in Y direction. The graph clearly displays the change in the structures base shear when a TLD is used.
RESULTS AND DISCUSSION The model is subjected to dynamic loads and the results are compared in terms of base shear, roof displacement, Time period. The selected model were subjected to linear dynamic analysis with and without water containing in the water tank. The sloshing of water was calculated manually and load was applied on the dummy beam modeled at the location of the centroid of the trapezium formed by the water pressure. Two cases were considered for observing the behavior of the structure and the base shear, roof displacements and time periods were observed in two different directions namely X and Y direction according to SAP 2000.
Base Shear in the direction of Y
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Comparision of Joint Displacements
Results for Empty Tank Condition
Joints at the roof of the structure i.e., ends of water tank are considered for observing the change in the displacement values in seismic conditions in both X and Y directions. Absolute displacements of the joints are reduced under damping condition resulting in the decrease of the relative displacement of the structure.
Above graphs shows the base reactions of the entire structure in difference load cases which have developed by analyzing the structure without water loading i.e., Empty tank condition. Joint displacements for top most joints i.e., for roof of water tank are checked for the effect on structure and presented in the above graphs and tables for each load cases. Time periods for 12 modes are also checked. Results for Full Tank Condition
Joint Displacements in the direction of X for EQ X Load Case
Similarly, Joint displacements for the same joint numbers are compared in the Y direction and results are observed. Fig. 6.4 compares the displacement values of the roof joints in Y direction for Damping and without TLD case.
Above graphs also shows the base reactions of the entire structure in difference load cases which have developed by analyzing the structure with water loading i.e., Full tank condition. Joint displacements for top most joints i.e., for roof of water tank are checked for the effect on structure and presented in the above graphs and tables for each load cases. Time periods for 12 modes are also checked. Average displacement change is 14% by using the TLD on the structure. And the time period value is decreasing by 8% by applying the TLD. Base reactions are shown in the below table Summary This chapter copes with the numerical study and presentation of results of response spectrum analysis for the buildings under study; the results are then compared and are represented in the form of graphs and tables. The results were studied and based on the study, the conclusions were drawn. The detail conclusions for the present study are given in the next chapter. Conclusions 1. The percentage difference in base shear obtained from response spectrum for empty tank and full tank case is 15 percent.
Discussion on result From above figures and tables for joint displacement, it is observed that for every joint there is an average decrease in the displacement value by 14% when a TLD is used.
2. The percentage difference in Joint displacements obtained from response spectrum for empty tank and full tank case is 14 percent. 3. The percentage difference in time periods obtained from response spectrum for empty tank and full tank case is 8-9 percent. 4. Based on the results it can be concluded that when water tank sloshing load is analyzed and considered as a TLD in application on the structure against the earthquake load it effectively reduces the overall behavior of the structure resulting in economic and safe design. 5. From this study, it has been found that TLD can successfully be used to control the response of the structure. During the life of the building, if there is no seismic activity, the structure will behave as an elastic system, unaffected by the presence of the dampers.
Time periods for Empty tank and Full tank condition
6. The water tank lies at the roof of the structure, and as they require no extra space they can be used without any problem. Inspection and periodic testing are not required. When there is no seismic activity there is no action in the tank, which can support its design static load indefinitely, so there are no problems of wear or fatigue. 7. Particular water level is to be maintained in the water tank by placing the exit pipe at some elevation which 232
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makes sure that required water level for damping is always available.
10. Epstein, H.I (1976), “Seismic design of liquid storage tanks”, J.Struct. Div. ASCE, 102, 1659-1673.
8. Apparently, TLD is a very attractive proposition for structural response control during a seismic event, but the major limitations hindering the application of TLDs are:
11. Fujino y, sun lm, pacheco bm, chaiseri p (1992). “tuned liquid dampers (tld) for suppressing horizontal motion of structures.” Journal of engineering mechanics, asce 1992; 118(10): p. 2017-30.
i) The physical phenomenon of water sloshing is not fully understood. Effects of wave breaking in the process of sloshing may be a potential source of analytical and design error; and ii) Prevalent methods for TLD design involve many approximations, which should be addressed through rigorous analytical and experimental studies.
12. G. P. Mavroeidis, b. Zhang, g. Dong, a. S. Papageorgiou, u. Dutta, and n. N. Biswas (2008). "The great 1964 prince william sound, alaska, earthquake": estimation of strong ground motion.
9. The major advantages which may be attributed to the tuned liquid dampers are: i) Low initial cost; ii) Low or no maintenance cost; iii) Ease of frequency tuning; iv) No limit for vibration amplitude ; v) Easy applicability for existing buildings and; vi) No mass or weight addition to the structure as water required for building purposes may also serve the damping requirement.
13.H.kosaka,t.noji,h.yoshida,e.tatsumi, h.yamanaka&a.k.agrawal (2010). "Damping effects of a vibration control damper using sloshing of water", vol 14.Hanson, R. D. (1973). "Behavior of liquid-storage tanks, in The Great Alaska earthquake of 1964: Engineering", National Academy of Science, Washington D.C., 331-339. 15.Hous ner, G.W. (1957). Dynamic pressures on accelerated Fluid Containers. Author
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Muhammed Mujahid Ali, Research scholar, Department of Civil Engineering. Aurora's Scientific, Technogical and Research academy. Hyderabad, India.
4. Banerji P, Murudi M, Shah AH, Popplewell N. (2000) “Tuned liquid dampers for controlling earthquake response of structures.” Earthquake Engineering Structural Dynamics 2000; 29: 587-602. 5. Baratta A, Corbi O, Orefice R (2004), Tuned Liquid Dampers for structural Applications: Experimental Evidence, Proceeding of the 4th International Conference on Engineering Computational Technology, Lisbon, 2004. 6. Bhosale Dattatray, G. R. Patil, Sachin Maskar (2014), "Use of Overhead Water Tank to Reduce Peak Response of the Structure", ISSN: 2278-3075, Volume-4 Issue-2
Mythili Rao. Assistant professor, Department of Civil Engineering, Aurora's Scientific, Technological and Research academy,Hyderabad, India.
7. Chaiseri, P., Fujino, Y., Pacheco, B.M. and Sun, L.M. (1989). Interaction of tuned liquid damper and structure: theory, experimental verification and application. J. Structural Engg./Earthquake Engg. Proc. JSCE 6:2, 273-282. 8. Doğangün A, Livaoğlu R, (2004), "Hydrodynamic pressures acting on the walls of rectangular fluid containers", Structural Engineering and Mechanics, vol:17, 2, 203214.
Mohammed Ahmeduddin Civil & Structural engineer, LEAD (I) pvt Ltd,Hyderabad, India. (External Guide)
9. "Emili Bhattacharjee, Lipika Halder and Richi Prasad Sharma (2013), ""An experimental study on tuned liquid damper for mitigation of structural response"", Structural Engineering 2013, 5:3"
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