Special Issue on Design and Analysis of Structures with Seismic Damping Systems

Special Issue on Design and Analysis of Structures with Seismic Damping Systems Michael D. Symans Guest Editor; and, Associate Professor, Rensselaer Polytechnic Institute, Dept. of Civil and Environmental Engineering, Troy, NY 12180.

E-mail: [email protected] edu The papers in this special issue focus on the theme of design and analysis of structures with seismic damping systems, the intent being to provide a summary of current research activities within the general ? eld of seismic energy dissipation systems.The special issue originated within the ASCE-SEI Task Committee on Supplemental Damping Systems for Seismic Applications, a committee serving under the ASCE-SEI Committee on Seismic Effects. Two members of the task committee, Finley A. Charney and Andrew S. Whittaker, were particularly helpful in developing the special issue, assisting with its early development, and the soliciting manuscript reviews.

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Their efforts are gratefully acknowledged. In addition, the general membership of the Seismic Effects Committee supported the efforts of the task committee by serving as reviewers for many of the manuscripts.Their collective efforts are sincerely appreciated. The special issue begins with a lead paper, “Energy Dissipation Systems for Seismic Applications: Current Practice and Recent Developments,” which is coauthored by a mix of academicians and practitioners Symans, Charney, Whittaker, Constantinou, Kircher, Johnson, and McNamara . The lead paper provides an overview of current practice and recent developments in the application of passive energy dissipation systems for seismic protection of structures, with particular attention given to the application of such systems within the framing of building structures.

Furthermore, emphasis is given to descriptions of viscous, viscoelastic, metallic, and friction damping systems, including recent applications of such systems. In the paper “Design Formulations for Supplemental Viscous Dampers to Building Structures,” Hwang, Huang, Yi, and Ho examine the accuracy of existing design formulas for determining the damping coef? cients corresponding to a speci? ed added damping ratio. They conclude that the effect of ? exural deformations of a building is as signi? cant as the shear deformations and that neglecting ? xural deformations leads to inaccurate damping ratios. New design formulas are presented that account for both ? exural and shear deformations, providing more accurate predictions of the damping ratio contributed by linear viscous dampers and ensuring a more conservative design for buildings that employ nonlinear viscous dampers. In “Comparison of Methods for Computing Equivalent Viscous Damping Ratios of Structures with Added Viscous Damping,” Charney and McNamara demonstrate that the approach used to compute modal damping ratios can have a signi? cant in? ence on the computed values and that the axial ? exibility of toggle-brace linkages can result in reduced system damping as the damping constant of the damper increases, a phenomenon that is readily observed through examining complex-valued mode shapes.

In their paper “Seismic Protection of Frame Structures by Fluid Viscous Damped Braces,” Sorace and Terenzi present results from experimental testing of two three-story building frames, one constructed of steel and the other of reinforced concrete, each containing a bracing system employing ? uid viscous dampers.The method by which the damping coef? cient of the dampers was selected is discussed and evaluated by comparing the target response with the experimentally measured response. An analytical study entitled “Fluid Dynamics and Behavior of Nonlinear Viscous Fluid Dampers” is presented in the paper by Hou. In this study, the dynamics of the ? uid ? ow are evaluated through solving the Navier-Stokes equations, and the shear-thinning effect and viscoelasticity of the ? uid are considered. Comparisons with experimental data show that both the nonlinear viscous and restoring force behavior can be captured.The seismic response of a three-story reinforced concrete frame with viscous wall dampers is investigated by Lu, Zhou, and Yan in their paper “Shaking Table Test and Numerical Analysis of RC Frames with Viscous Wall Dampers.

” In addition, the effect of the wall dampers on the seismic performance of a partially damaged reinforced concrete frame is examined. The test results demonstrate that the viscous wall dampers add signi? cant damping while also providing some increase in stiffness, reducing the test structure displacements, and in some cases, increasing accelerations.Blasetti, Hoffman, and Dinehart and Dinehart, Blasseti, and Shenton study the application of viscoelastic materials to woodframed shear walls in their companion papers “Simpli? ed Hysteretic Finite-Element Model for Wood and Viscoelastic Polymer Connections for Dynamic Analysis of Shear Walls ” and “Experimental Cyclic Performance of Viscoelastic Gypsum Connections and Shear Walls,” respectively. First, a simpli? ed approach to modeling complex hysteretic behavior, such as is found in wood framing connections, is developed in which combinations of basic elements found in commercial ? nite-element analysis software are used.This approach is then used to model the behavior of a shear wall that employs a viscoelastic material between the wood framing and gypsum sheathing in lieu of conventional screw connections. Experimental tests demonstrate that shear walls that use the viscoelastic material have signi? cantly larger energydissipation capacity and stiffness.

In the ? rst of a set of companion papers, Christopoulos, Tremblay, Kim, and Lacerte discuss the development of a new bracing system in “Self-Centering Energy Dissipative Bracing System for Seismic Resistance of Structures: Development and Validation. The bracing system can undergo large deformations without damage while providing a ? ag-shaped hysteretic response with full recentering capability. The experimental results validate the design and behavior equations that are developed. In their second paper, “Seismic Response of Multistory Buildings with SelfCentering Energy Dissipative Steel Braces,” Tremblay, Lacerte, and Christopoulos evaluate the seismic response of a series of steel-framed buildings containing the new bracing system and JOURNAL OF STRUCTURAL ENGINEERING © ASCE / JANUARY 2008 / 1 compare the performance with the same buildings incorporating buckling-restrained braces.Zhu and Zhang, in their paper “Seismic Analysis of Concentrically Braced Frame Systems with Self-Centering Friction Damping Braces,” present a new bracing system that has selfcentering capability and dissipates energy via friction.

Nonlinear dynamic analyses of steel-braced frames are performed, both with the new bracing system and with buckling-restrained braces. In the paper “Seismic Response Evaluation of Posttensioned Precast Concrete Frames with Friction Dampers,” Morgen and Kurama investigate the seismic response of unbonded posttensioned precast moment frames that incorporate friction dampers at the beam-column joint.Seismic response analyses show that the dampers provide signi? cant energy dissipation to the frame while the posttensioning provides self-centering capability. Comparative studies are performed between frames incorporating the new friction damper system and framing having more conventional beam-column joints. Ghosh and Basu examine the seismic performance of a liquid column damper in their paper “Seismic Vibration Control of Nonlinear Structures Using the Liquid Column Damper. ” The damper is modi? ed from a conventional liquid column damper so that it has a broader range of applicability.

Numerical simulations are performed to evaluate the effectiveness of the damper. In their paper “Experimental and Theoretical Investigation of Equivalent Viscous Damping of Structures with TLCD for Different Fluids,” Colwell and Basu describe an experimental investigation of the damping characteristics of three different ? uids that are utilized within a tuned liquid column damper. Numerical simulations are then performed to evaluate the effectiveness of the different ? uids in suppressing the response of structures subjected to base excitation. The ? al paper in this special issue, “Feasibility Study of Passive Electromagnetic Damping Systems,” examines the potential application of an electromagnetic damper for passive control of dynamic structural response. In this paper, Palomera-Arias, Connor, and Ochsendorf analytically show that the hysteretic response of the proposed damper is similar to that of an ideal dashpot but with a time delay.

Further, the authors evaluate the physical and economic viability of the damper as a structural control device. 2 / JOURNAL OF STRUCTURAL ENGINEERING © ASCE / JANUARY 2008

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