Space Structures Principles and Practice

IranCivilCenter.com - The Construction Industry Portal of Iran ENERGY DISSIPATION SYSTEMS FOR SEISMIC RESISTANCE Ali Sehat Tabatabaei, MSc. Civil Engineering University of East London ABSTRACT - This research reviews four well-known energy dissipation devices (EDD) used in practical structural applications and the effect of viscous damper on the behaviour of steel frames. The response of the one, two and five storey steel frames has been investigated through a numerical analysis. The seismic response of the frame, the storey displacements, inter-storey drifts, bending moment in the structural members and natural periods of vibration with EDD and without EDD were calculated and compared. The results showed that the EDD can absorb a portion of the energy induced by the earthquake into the structure and control the displacement of the structural members. Keywords: Energy dissipation devices, Viscous dampers, Earthquake 1. INTRODUCTION Earthquake is on the most damaging disasters. Repairing an area that has experienced an earthquake is expensive and difficult process. Engineers have introduced different techniques to prevent a large amount of the damage typically caused by earthquakes. The energy dissipation devises (EDD) are recognised as a suitable technique to control the seismic response of the structures and reduce the damages caused by earthquake. EDD can absorb a portion of earthquake-induced energy in the structure and minimise the energy dissipation demand on the primary structural members such as beams, columns and walls. These devices can substantially reduce the inter-story drifts and, consequently, non-structural damage. In addition, lower accelerations and smaller shear forces lead to lower ductility demands in the structure components. Many researches have been done on EDD since they have been used to protect structures from dynamic effects (Soong and Dargush [1], Zhang and Soong [2]). Zhang and Soong proposed and extended the sequential seismic design method to find the optimal configuration of viscous dampers for buildings with specified story stiffness. They used an intuitive criterion to place additional dampers sequentially on the story at which the inter-story drift response is a maximum. There are many different types of EDD. Each of these devices has a unique way of dissipating energy and controlling vibrations. 2. ENERGY DISSIPATION DEVICES Metallic Damper is one of the most effective mechanisms available for the dissipation of the energy, induced a structure during an earthquake, through the inelastic deformation of metals. There are several types of Metallic dampers including Steel Crossing-bracing dampers Copyright © 2003-2006 Iran Civil Center, All rights reserved worldwide. Page 1 of 8 Bell-shaped Steel Dampers.IranCivilCenter. so the force-displacement curves of the devices are rectangular loops. Sumitomo Friction Dampers. and the piston may contain a number of small Copyright © 2003-2006 Iran Civil Center. The advantages of using friction damper over the other types of energy dissipation devices include: • These devices have high resistance to fatigue • Their behaviour is not significantly affected by load amplitude. the number of applied load cycles or variations in temperature • No fluid leaking problems Figure 2 Pall friction damper [4] Viscoelastic (VE) Dampers are used as energy dissipation devices in structures where the damper undergoes shear deformations. Honeycomb Dampers System (HDS). When installed to a structure. There are many different friction dampers include. A Viscous fluid damper generally consists of a piston in the damper housing filled with a compound of silicone or similar type of oil. All rights reserved worldwide. Figure 1 illustrates the Xshaped ADAS damper. They generally exhibit rigid plastic behaviour and their force response can be modelled by simple Coulomb friction. Figure 1 ADAS damper [ 3] Friction devices dissipate energy as heat. caused by the sliding of steel plates against each other. Lead Joint dampers and Lead extrusion Damper (LED. frequency.com . shear deformation and consequently energy dissipations take place when relative motions occur between the centre plate and the outer steel flanges. Page 2 of 8 . These devices can be installed in bracing system of the structural frame. A typical VE shear damper consists of steel plates covered by viscoelastic layers as shown in Figure 3. Pall Dampers (Figure 2).The Construction Industry Portal of Iran Added Damping and Stiffness (ADAS) dampers. Energy Dissipating Restraint (EDR) and Wall Friction Damper. IranCivilCenter. All rights reserved worldwide.The Construction Industry Portal of Iran orifices through which the fluid may pass one side of the piston to the other as shown in Figure 4 [6]. Page 3 of 8 . however. Different locations of the EDD in the frame have been considered. 2 and 5 storey steel frames without (bare frame) and with viscous dampers. • The damping force is out of phase with the displacement if dampers were installed in a structure in such a way that they have an inclined force.com . Finite element software (SAP2000 – Copyright © 2003-2006 Iran Civil Center. Figure 3 Viscoelastic damper [5] Figure 4 Fluid viscous damper [7] Fluid dampers have the following advantages: • The use of fluid dampers. The frames were subjected to earthquake loading using the EC8 simplified method (Simplified modal response spectrum analysis) [8]. 2 and 5 storey steel frames with and without dampers were performed and the results are given here. ANALYSIS OF STEEL FRAME WITH VISCOUS DAMPER The seismic analysis was performed on 1. reduced the story and base shears by 40% to 70% because of their pure viscous behaviour while other passive systems were not as effective in reducing base shear. 3. The analysis on the 1. The damper thus dissipate energy though the movement of a piston in a highly viscous fluid using the concept of flow of a liquid through an orifice. However.00% 0.8625 0. Table 2 Natural periods for bare frame and frame with damper Mode No. All the connections between beams and columns are assumed rigid connections.0055 0. has been considered in the analysis.00% 0.2072 0. Page 4 of 8 .2. All rights reserved worldwide. Figure 5 One-storey frame This frame modelled with and without the viscous damper with the properties shown in Table 1.0044 Reduction Ratio 32. It can be noticed that the displacements of the joints 2 and 4 in the bare frame are higher than the allowable limit required by clause 4.IranCivilCenter.024 cm).0054 0.00% 1.00% The displacement of the joint in the frame with the damper are reduced by over 50% comparing to the once in the bare frame as shown in Table 3.3. it does not have a significant effect on period for in the other modes.82% 0. Table 1 Properties of the added damper Element Weight (KN) Effective Stiffness (KN/m) Effective Damping (KN-S/m) D 50 2500 10 Table 2 presents the natural period of the frame with and without damper resulted from the modal analysis. one-storey steel frame as shown in Figure 5.The Construction Industry Portal of Iran Structural Analysis Programme) was used to carry out the analysis.208 0. Numerical studies on the bending moment of the column in the frame show a reduction of 25% in bending moment Copyright © 2003-2006 Iran Civil Center.2665 0.1 Analysis of One Storey Frame The simplest dynamic model. 1 2 3 4 5 Bare Frame Period (Sec) 1.(a) of Part 1.0044 Frame with Damper Period (Sec) 1. 3.com .2072 0.208 0.2 in EC8 (0. Adding the damper reduced the fundamental natural period by 32%. The Construction Industry Portal of Iran Joint Table 3 Joint displacement for both bare frame and frame with the damper 1 2 3 4 Output Case Displacement along X.44% <0. The maximum reduction is in the fundamental natural period by 27% and it occurred in Case 3 where two dampers were installed at both floors.024 Not OK Comments Reduction ratio <0.2 Analysis of Two-Storey Frame Analysis on the two-storey steel frame has been done in four different conditions as shown in Figure 7.554 0% 0.096 0% Case 2 Period Reduction (sec) ratio 2. bare frame (m) COMB1 COMB1 COMB1 COMB1 0 0.096 0% Case3 Period Reduction (sec) ratio 2.0276 Comments Displacement along X.021 0.019 0. In addition. 1 2 3 4 5 Bare frame Period (sec) 2.016 43.018 9.3% 45.1% 0.744 20.030 38.1% 0.024 Not OK >0.021 0.940 0.031 0.033 0.8% 0.564 12.482 14.024 OK 52.033 0.7% 10.4% 50.096 0% Table 5 presents the inter-storey drifts for the bare frame and 3 other cases.030 39. The natural periods reduced since the damper(s) is installed in the frame and it can be noticed from Table 4.019 0.9% 50. frame with damper (m) 0 0. D (b) Case 1 (a) Bare frame D D (c) Case 2 D (d) Case 3 Figure 6 2 storey steel frame Table 4 Natural period for different cases Mode No.034 0.096 Case 1 Period Reduction (sec) ratio 2.031 0.786 16.863 8.3% 5 6 0.024 OK 53.554 0.1% 0. The same damper that used in analysis for 1 storey frame was used for this frame.0279 0 0.545 0% 0.128 27.0% 10.0128 >0.017 43.3% 0.2% 0.44% 3.7% 0.917 0. Table 5 Analysis results for the 2 storey frame Interstorey drift (m) Reduction ratio Inter-storey drift (m) Reduction ratio Interstorey drift (m) Reduction ratio 2 3 0.554 0% 0.545 0% 0.8% 0.0133 0 0.018 9.6% Joint Bare frame Interstorey drift (m) Case 1 Case 2 Copyright © 2003-2006 Iran Civil Center.554 0% 0.9% 0.545 0% 0. the reduction ratios in the inter-storey drift for each case are provided. All rights reserved worldwide.1% 45.com .034 0.5% 0.545 0.IranCivilCenter. Case 3 Page 5 of 8 . it become stiffer therefore the natural periods reduced. this value is higher than the allowable limit by EC8 (0.24 19. Page 6 of 8 . Analysis for the bending moment in all for conditions show the bending moment in the column can be reduced by adding the damper between 25% . the inter-storey drifts at both floors are less than the allowable limit required by EC8 only in Case 3 and they have been reduced by over 43%.3 Analysis of Five-Storey Frame Analysis for a five-storey steel frame was performed in five different conditions. 3.24 3000 5000 7000 100 100 100 Modal analysis for this frame has been carried out and it shows a significant reduction for the natural period in some cases as shown in Table 7. Analysis results for the bending moment for the columns of this frame show a reduction up to 46% in bending moment in columns Copyright © 2003-2006 Iran Civil Center. D2 D2 D2 D1 (a) Bare frame D3 D3 D3 D3 (b) Case 1 (c) Case 2 (e) Case 3 (f) Case 4 Figure 7 Different cases for five-storey frame Table 6 Properties of the dampers Damper Name Weight (KN) Effective Stiffness (KN/cm) Effective Damping (KN-s/cm) D1 D2 D3 19.38%.024m. Comparing Case 2 and Case 3 shows the need of a damper where the inter-storey drifts is higher than 0.The Construction Industry Portal of Iran Analysis results for two-storey frame show that the inter-storey drift is within the EC8 allowable limit at the same floor at which the damper is installed. The maximum reduction ratio for the natural period is 20%. in the 1st mode of vibration of the Case 4. Three different dampers with different properties were used in the analysis.com . depending on the properties of the dampers and their location in the frame.24 19.IranCivilCenter. the inter-storey drift reduced considerably in case 4 at which dampers are installed in X bracing. which occurred. Moreover. Although. All rights reserved worldwide. The inter-storey drifts in all storeys are acceptable by EC8 requirements only in Case 3 as it shown in Table 9.024m) at the 3rd floor. Table 6 presents the properties of these dampers. It can be noticed that by adding the damper(s) to the frame. shown in Figure 8. 20% 1. 118 (5).9% 21. T.022 0.704 0.buffalo. 5.3% 34.50% 7.Slide 6) Copyright © 2003-2006 Iran Civil Center.036 0.IranCivilCenter.296 Case 2 Reduction ratio 7. All rights reserved worldwide.020 0.7% 29. With the proper distribution of the dampers in the frame. G. 6.eng.10% 8.40% 13. A.com .014 0. Journal of Structural Engineering. viscous dampers slightly reduce the bending moment resistance demand for the structural member of the frame. ISBN 0-471-96821-8 [2].60% Period (sec) 3.282 Reduction ratio 20.4% 2.023 Reduction ratio 15.016 0.70% 0.021 Reduction ratio 23. (1997).962 1.029 0.178 0.664 0. Ciupala for her support and her guidance for this project.686 0.8% 14.032 0.032 0.022 0. the effect of the viscous damper at different locations the steel frames has been investigated.The Construction Industry Portal of Iran Table 7 Natural period of the frame Mode No.024 0. Page 7 of 8 .6% Case 2 Interstorey drift (m) 0.2% 29.6.00% Period (sec) 2.282 0. T.F.20% Storey Table 8 Analysis results for five-storey frame 1 2 3 4 5 4.026 Case 1 Interstorey drift (m) 0.421 0. REFERENCES [1].60% 12.0% 19.9% 33.243 1.60% 8.5% 31.016 0.672 0.292 Case 4 Reduction ratio 16.60% 3.016 0.40% 4.0% 14.021 0.M. 1375-1392.7% 0.295 Case 3 Reduction ratio 13.10% 9.115 1.703 0.234 0.178 0.023 0. ACKNOWLEDGMENT I would like to appreciate Dr.016 0.1% Case 3 Interstorey drift (m) 0.ppt#311. (http://civil. John Willey & Sons Ltd.025 0.Zhang.019 0.311 Case 1 Period (sec) 3.T.449 0.032 0.394 0. Moreover.10% 4.453 0.448 1. In addition.H.9% 47. EDD significantly increase the resistance of the structure components to the dynamic loads and they are effective in reducing the seismic response of structures.T.10% 5.00% Period (sec) 3. Passive energy Dissipation Systems in Structural Engineering.10% 2. Bare frame Interstorey drift (m) 0.edu/technion/Lecture5_12_Devices_and_Models.033 0.732 1.20% 6.023 Reduction ratio 16.10% 5. University of Buffalo.416 0. 1 2 3 4 5 Bare frame Period (sec) 3.1% CONCLUSIONS One of the objectives of this research was to introduce different types of energy dissipation devices used for structural applications.3% 34.8% 11.50% 8. Soong (1992). R. engineers can control the storey displacements in the frame and therefore the inter-storey drift can be reduced within the EC8 allowable limit.4% Case 4 Interstorey drift (m) 0.026 Reduction ratio 15.123 0.1% 37.Soong.017 0.4% 50.Dargush. Seismic design of viscoelastic dampers for structural applications [3]. (1996).com/discussion/7551.IranCivilCenter. Gaithersburg. Passive Energy Dissipation Devices for Seismic Applications [8]. Buffalo. (1996) Copyright © 2003-2006 Iran Civil Center. Concordia University. [7]. M. Report NISTIR 5923. Experimental and analytical investigation of seismic response of structures with supplemental fluid viscous dampers. NEER 92-0032. B.The Construction Industry Portal of Iran [4]. M. A. http://www. NY.htm) [5]. (1992).Sadek.html [6]. D.M.designcommunity.Mohraz.Taylor. Design provisions for earthquake resistance of structures. All rights reserved worldwide.com .ca/department/About_Department. C. R. National Centre for Earthquake Engineering Research. Chung. Symans. Page 8 of 8 .W.bcee. Constantinou. F. Department of Building Civil and Environmental Engineering (http://www.concordia. National Institute of Standards and Technology. Eurocode8.