Seismic Response Control of Structures using Liquid Column Vibration Absorber Considering Real Earthquake Ground Motions

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1 Seimic Repone Control of Structure uing iquid Column Vibration Aborber Conidering Real Ground Motion Debai Panda M. Tech Scholar National Intitute of Technology Agartala Agartala, India Dr. Rama Debbarma Aociate Profeor National Intitute of Technology Agartala Agartala, India Arka Mitra M. Tech Scholar National Intitute of Technology Agartala Agartala, India Abtract-- In thi paper the performance of iquid Column Vibration Aborber (CVA) to mitigate tructural vibration conidering different real earthquake time hitory data i invetigated. To evaluate the ignificance of the parameter like ma ratio, frequency tuning ratio, length ratio, blocking ratio and area ratio, on the effectivene of the CVA for different earthquake, a imilar parametric analyi i performed uing a time domain method. The reult of the tudy how that CVA i very much effective in reducing the tructural repone to eimic excitation and the parameter play ignificant role in the performance of CVA and ome of them are alo enitive to the nature of the excitation. Keyword- Real earthquake time hitory; liquid column vibration aborber; vibration control; parametric tudy; I. INTRODUCTION iquid damper become more popular in recent day to reduce the eimic repone of tructure, due to their low implementation cot, eaier handling and low maintenance cot, and like other paive device, they do not uually interfere with vertical and horizontal load path. One of thee device, the Tuned iquid Column Damper (TCD), uppre the input energy by the combined action of the movement of the ma in the U-haped container, the retoring force on the liquid due to gravity and the damping due to liquid movement through the orifice. Tuned iquid Column Damper (TCD), CVA i one type of TCD whoe vertical cro ection area i different from it horizontal cro ectional area. Sakai et al (1989) propoed the nonlinear mathematical expreion of the TCD. Watkin (1991) teted a different TCD, the liquid column vibration aborber (CVA). In recent year many experimental and theoretical tudie have been carried out on the evaluation of CVA performance in uppreing the tructural vibration. However mot of them have invetigated the performance of CVA under inuoidal loading, wind excitation, and relatively few tudie ha been carried out on the eimic performance of CVA (Chang and Hu 1998; Chakraborty et al. 11). In thi paper the performance of Tuned iquid Column Damper (CVA) to control the earthquake induced tructural vibration i invetigated uing different pat earthquake data. A imilar parametric numerical analyi, involving the effect of the parameter like ma ratio, frequency tuning ratio, length ratio, and blocking ratio i carried out for different eimic time hitory data, uing a time domain method (The Newmark-beta linear acceleration method) to deal with the nonlinearity of the governing equation, the variation of the different parameter are noted for different nature of the excitation. It i hown that the effectivene of CVA to reduce tructural diplacement and acceleration are very much dependent upon the nature of the earthquake but overall it perform exceptionally well for all earthquake. Although the parameter like ma ratio, frequency tuning ratio, length ratio, area ratio play ignificant role in the performance of CVA and ome of them are alo enitive to the nature of the excitation, few general concluion are made in which the CVA i more effective. II. THE EQUATION OF MOTION OF STRUCTURE AND CVA SYSTEM A CVA i a U-haped liquid column tube whoe vertical cro ection area i different from it horizontal cro ectional area i attached to the top of a primary tructure. A building i modeled a a SDOF tructure and a CVA i mounted on top of the primary tructure a hown in Fig. 1. The horizontal and vertical cro ection area, horizontal length, vertical height of liquid and the liquid ma denity (generally water) are repreented by A h, A v, B, h and ρ repectively. The total length of the liquid column i, = (B+h).The ma of the damper, m A B A h, ignoring the ma of the d h v liquid container, which can be included within the ma of the primary tructure. 51

2 B m y x B. The equation of motion of tructure with CVA The equation of motion of primary tructure with CVA can be written a m m x c x k x m m z r A By d d b h (4) k c Where, m, k, c are the ma, tiffne and damping of the primary tructure. Fig.1: Simplified CVA-tructure ytem. A. The equation of motion of CVA: Due to the earthquake motion the tructure-cva ytem i ubjected to bae acceleration z b. If the relative horizontal diplacement of SDOF ytem and the liquid urface diplacement i repreented by x and y, the equation of motion of liquid column will be 1 Aheey Ah y y ga hy AhB x zb (1) Normalizing the above equation by liquid ma in the container, A h ee yy g y y x zb () ee ee ee ee B Where p i the length ratio. (ength ratio i the length of the horizontal portion of CVA to it total length). Tuning d g ratio, where i the frequency of the damper where ee 1 pr 1 d ee and i the Av frequency of the primary tructure and area ratio r. A The co-efficient of head lo, i determined uing equation (3) (By Wu et al. 5) z b 1.6 (3) Where i the blocking ratio. h Simplifying the above equation p 1 x x x y 1 z b em Where, AhB A vh (ma ratio), c m and From Eqn. () and (5) b m em B h r p 1 em x x x y g p y y y 1 ee ee ee 1 p z ee III. NUMERICA STUDY For thi tudy a building i modeled a a SDOF tructure and a CVA i mounted on top of the primary tructure a hown in Fig. 1, ued for the analyi. The propertie of primary tructure are m = kg, k = N/m and damping ratio of tructure, %.The tructure ha a natural frequency f1 =.8333 Hz, which i tuned by frequency of the CVA. To know the impact of eimic excitation on the performance of CVA, ome pat earthquake ground motion record are elected for the analyi. The tructure i analyzed twice, once without CVA and again with a CVA attached to the top, ubjected to pat earthquake ground motion record varying with different parameter. The tructure without and with CVA i ubjected to previouly elected pat earthquake data of Park field earthquake (1966), E-Centro earthquake (194), Nepal earthquake (15), and Eatern turkey earthquake (11).for different ma ratio.. (5) (6) 5

3 The variation of diplacement of tructure with time conidering time hitory data of previouly elected earthquake uing CVA and have been hown in Fig. and Table-1, which how the effectivene of the damper in reducing peak tructural repone for different ma ratio. The reult how that the effectivene of the CVA to reduce the tructural diplacement very ignificant for ome earthquake record and for ome record the reduction are not that much effective. For 5% ma ratio and for Parkfield and Eatern turkey earthquake, the peak diplacement reduction are 55.91% and 58.53% while for ame ma ratio and for E-Centro and Nepal earthquake data, the reduction are 33.79% and 9.94%. Diplacement(m) Time(ec) Nepal N-S earthquake =% =5% (c)nepal earthquake (15). CVA Diplacement(m) Parkfield earthquake =% =5% Time(ec) CVA Diplacement(m) Eatern Turkey earthquake =% =5% CVA Time(ec) (d) Eatern turkey earthquake (11). Fig. : Variation of diplacement of tructure conidering real time hitory data of (a) Parkfield earthquake (1966), (b) E-Centro earthquake (194), (c)nepal earthquake (15),(d)Eatern turkey earthquake (11), for Ma ratio = 5%, Damping ratio of tructure=% and, ength ratio=.8. Diplacement(m) E Centro earthquake =% =5% Time(ec) CVA (b) E-Centro earthquake (194). The variation of tructural acceleration with time conidering time hitory data of Parkfield earthquake (1966), E-Centro earthquake (194), Nepal earthquake (15), and Eatern turkey earthquake (11), with CVA and are hown in Fig. 3 and Table-. From Fig. 3 and Table- one can ee that peak tructural acceleration reduction capacity i not that much ignificant, thi problem i important for acceleration enitive component, uch a non tructural component, although thi obervation need more extenive analyi for confirmation. The reult alo confirm that the effectivene of the CVA to reduce tructural repone i highly dependent upon the nature of the excitation but overall it perform exceptionally well for all earthquake. From Fig. and 3, it can alo be een that overall tructural diplacement and acceleration reduction capacity of CVA i very good. Table-1: Value of maximum diplacement of tructure without and with CVA and correponding effectivene of CVA taking tructural damping=%, frequency tuning ratio=1, blocking ratio=.1 and length ratio=.8 Maximum diplacement(m) % Reduction With CVA With CVA Without damper Ma ratio Ma ratio 1% 3% 5% 7% 1% 3% 5% 7% Parkfield % 4.75% 55.91% 6.79% El -centro N-S % 1.98% 33.79% 38.3% Nepal N-S % 6.18% 9.94% 34.9% Eatern turkey % 45.67% 58.53% 6.3% 53

4 6.5. Acceleration(m/ec ) CVA Parkfield earthquake =% =5% Time(ec) Acceleration(m/ec) Nepal N-S earthquake =% =5% Time(ec) CVA (c)nepal earthquake (15). 6 Acceleration(m/ec ) CVA E Centro earthquake =% =5% Time(ec) Acceleration(m/ec) Eatern turkey earthquake =% =5% CVA Time(ec) (b) El Centro earthquake (194). (d) Eatern turkey earthquake (11). Fig. 3: Variation of acceleration of tructure conidering real time hitory data of (a) Parkfield earthquake (1966), (b) E-Centro earthquake (194), (c) Nepal earthquake (15), (d) Eatern turkey earthquake (11), for ma ratio=5%, Damping ratio of tructure=%, ength ratio=.8. Table-: Value of maximum acceleration of tructure without and with CVA and correponding effectivene of CVA taking tructural damping=%, frequency tuning ratio=1, blocking ratio=.1 and length ratio=.8 Maximum tructural acceleration(m/ec ) % Reduction With CVA With CVA Without damper Ma ratio Ma ratio 1% 3% 5% 7% 1% 3% 5% 7% Parkfield % 6.7% 9.74% 13.14% El -centro N-S % 1.66%.73% 3.78% Nepal N-S % 3.18% 6.11% 9.47% Eatern turkey % 31.67% 38.6% 41.5% Ma ratio i the mot important parameter influencing the effectivene of CVA in reducing the tructural diplacement. Ma ratio can be defined a the ratio of the ma of the damper to the ma of tructure. It i evident from Table-1 and Fig. 4 that CVA with higher ma ratio i more effective in uppreing the tructural diplacement. To incorporate higher ma and to maintain the liquid column hape the CVA can conit of mall diameter tube of ame length, a the natural frequency of CVA depend only on it length. Much higher value of ma ratio i not effective a they add to the inertial load on the tructure due to bae excitation. Alo a higher ma ratio i impractical due to the pace requirement. And much higher ma ratio alo increae the overall loading in tructure, in real life application. In the range of ma ratio.5 to.7 CVA can effectively reduce the tructural diplacement without hampering the overall loading condition. 54

5 Fig. 5 how the influence of length ratio in peak liquid and tructural diplacement. If the value of length ratio i increaed gradually the value of maximum tructural diplacement i gradually reduced, and the liquid diplacement i increaing..1.9 Max.diplacement(m) iquid(=3%) iquid(=5%) iquid(=7%) E Centro Structure(=3%) Structure(=5%) Structure(=7%) Max. diplacement(m) Parkfield =% =4% ength ratio,p (b) E-Centro earthquake (194). Fig 5: The influence of length ratio on the maximum diplacement of tructure and liquid for 3% and 5% and 7% ma ratio conidering real time hitory data of (a) Parkfield earthquake, (b) E-Centro earthquake Max. diplacement(m) Ma ratio, (%) E Centro =% =4% Ma vratio, (%) Max. diplacement(m) iquid(=3%) iquid(=5%) iquid(=7%) Structure(=3%) Structure(=5%) Structure(=7%) E Centro Blocking ratio, (b) E-Centro earthquake (194). Fig. 4: Variation of maximum Diplacement of tructure with ma ratio for % and 4% damping ratio of tructure conidering real time hitory data of (a) Parkfield earthquake (1966), (b) E-Centro earthquake (194). With a higher length ratio CVA can reduce the maximum tructural repone more efficiently. Thi i becaue the ma of the horizontal part of the CVA i the only effective ma of CVA acting on the tructure. However length ratio i limited by the liquid diplacement bounded value, caue with higher increae of the liquid diplacement there i the chance of being out of tuned a a reult the efficiency of the CVA will reduce. Fig. 6 how that with increae in blocking ratio the liquid diplacement i decreaing while the tructural diplacement i increaing. Though the coefficient of head lo i depend upon the blocking ratio but the higher value of blocking ratio i not coniderable a with increae the blocking ratio the movement of liquid will decreae a a reult energy diipation by movement of liquid ma will decreae. Max. diplacement(m) iquid(=3%) iquid(=5%) iquid(=7%) Structure(=3%) Structure(=5%) Structure(=7%) Parkfield Max.diplacement(m) Parkfield % (iquid(=3%)) % (iquid(=5%)) % (iquid(=7%)) % (Structure(=3%)) % (Structure(=5%)) % (Structure(=7%)) Blocking ratio, (b) E-Centro earthquake (194). Fig. 6: The influence of blocking ratio on the maximum diplacement of tructure and liquid for 3%, 5% and 7% ma ratio conidering real time hitory data of (a) Parkfield earthquake, (b) E-Centro earthquake Moreover from Fig. 5 and Fig. 6 it can be concluded that in the range of length ratio.7 to.8 and blocking ratio.1 to.3 the CVA i more efficient. Fig. 7 how that with increae in area ratio the liquid diplacement a well a the tructural diplacement i decreaing. A the liquid and tructural diplacement decreaing, the efficiency of CVA will increae and there i le chance of being out of tuned and could be a poible advantage when headroom i retricted. From Fig. 7 it can be concluded that in the range of area ratio 1.5 to the CVA i more efficient ength ratio,p 55

6 Max. diplacement(m) Parkfield iquid(=3%) iquid(=5%) iquid(=7%) Structure(=3%) Structure(=5%) Structure(=7%) Max. diplacement(m) El Centro % (=3%) % (=5%) % (=7%) Max. diplacement(m) E Centro Area ratio,r iquid(=3%) iquid(=5%) iquid(=7%) Structure(=3%) Structure(=5%) Structure(=7%) Area ratio,r (b) E-Centro earthquake (194). Fig. 7: The influence of area ratio on the maximum diplacement of tructure and liquid for 3%, 5% and 7% ma ratio conidering real time hitory data of (a) Parkfield earthquake, (b) E-Centro earthquake It i very important that CVA hould be tuned properly with the tructural frequency for better performance. The optimal tuning ratio not only depend upon the ma ratio and the damping of tructure but alo depend upon the nature of the excitation. Although the influence of the tuning ratio on the effectivene of the damper i different for different earthquake nature, and lightly change with the change of ma ratio, till, it can be een from Fig. 6 that in the range of tuning ratio,.9 to 1.1 the CVA i more efficient in controlling the tructural repone. Max. diplacement(m) Parkfiela % (=3%) % (=5%) % (=7%) Tuning ratio, Tuning ratio, (b) E-Centro earthquake (194). Fig. 8: Variation of max. Diplacement of tructure with tuning ratio for % damping ratio and 3%, 5% and 7% ma ratio conidering real time hitory data of (a) Parkfield, (b) E-Centro earthquake. IV. CONCUSIONS The reult of the tudy how that with the proper deign parameter CVA i efficient to reduce peak tructural diplacement due to the eimic excitation while the peak acceleration reduction capacity i comparatively le, but overall tructural diplacement and acceleration capacity i very efficient. The tudy alo how that the parameter play ignificant role in the performance of the CVA and ome of the parameter are alo enitive to the nature of the excitation, ome imilaritie i found in the nature of the behavior of the damper due to different type of earthquake excitation, which i very helpful in deigning the damper for real life application. Although the tructural diplacement and acceleration reduction capacity of CVA are highly depend on the nature of the excitation but overall it perform exceptionally well for all earthquake, by tanding out the maximum tructural diplacement and alo rapid repone decay. Thi i very beneficial in real life, by enhancing occupant comfort and afety in flexible building with low intrinic tructural damping. REFERENCES [1] Sakai F, Takaeda S. Tamaki T. [1989] Tuned liquid column damper new type device for uppreion of building vibration, Proceeding of the International Conference on High-rie Building, Nanjing, China, pp [] Watkin, R. D. [1991] Tet on a liquid column vibration aborber for talltructure, Proc. Int. Conf on Steel and Aluminium Structure, Singapore, [3] C.C Chang, C.T. Hu [1998] Control performance of liquid column vibration aborber, Engineering Structure, (7), [4] Wu, J.-C., Shih, M-H., in, Y-Y, Shen, Y-C. [5] Deign guideline for tuned liquid column damper for tructure reponding to wind, Engineering Structure 7, [5] Chakraborty, S., Debbarma, R. [11] Stochatic earthquake repone control of tructure by liquid column vibration aborber with uncertain bounded ytem parameter, Structural Safety, 33,