Civil Engineering Association

Property Modification Factors for Seismic Isolation Bearings

The report examines the problem of establishing values of properties of seismic isolation bearings in the analysis and design of seismically isolated bridges. These bounding values of properties are determined with the use of system property modification factors. The property modification factors account for the effects of history of loading, the environmental conditions, and aging on the properties of the isolation bearings. The procedure requires that the mechanical behavior of the bearings be understood at both the macroscopic and microscopic levels. The report focuses on the effects of aging in elastomeric bearings and sliding bearings. The nature of friction in sliding bearings is also discussed. Property modification factors are presented for the effects of aging, contamination, travel, temperature, and scragging for selected interfaces and elastomeric bearings. The values represent the basis on which the bounding analysis is described in the 1999 AASHTO Guide Specifications for Seismic Isolation Design. (Adapted from authors' abstract).

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Passive Energy Dissipation Systems for Structural Design and Retrofit

This monograph introduces the basic concepts of passive energy dissipation and discusses current research, development, design and code-related activities in the field. The authors provide basic definitions for passive energy dissipation systems and provide basic design principles governing their use. Mathematical modeling, recent developments, and modern applications of the following devices are covered in depth: Metallic Dampers, Viscoelastic Dampers, Tuned Mass Dampers, Friction Dampers, Viscous Fluid Dampers and Tuned Liquid Dampers. The final chapter in the monograph discusses semi-active control systems. Semi-active mass dampers and semi-active fluid dampers have been installed in buildings in Japan, and are discussed in some detail, along with current research in the field. Tables are provided in the appendices that detail application of passive energy dissipation systems in North America and active and semi-active systems in Japan.

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Viscous Dampers: Testing, Modeling and Application in Vibration and Seismic Isolation

A fractional derivative Maxwell model is proposed for viscous dampers which are used for vibration isolation of piping systems, forging hammers and other industrial equipment, as well as for vibration and seismic isolation of building structures. The development and calibration of the model is based on experimentally observed dynamic characteristics. The proposed model is validated by dynamic testing and very good agreement between predicted and experimental results is obtained. Some analytical results for a single-degree-of-freedom viscodamper system are presented. These results are useful to the design of vibration isolation systems. An equivalent viscous oscillator is defined whose response is essentially the same as that of the viscodamper isolator. The model is employed in the analysis of a base-isolated model structure which has been tested on a shake table.

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Seismic Performance of High-Rise Building Frames with Added Energy-Absorbing Devices

This report is concerned with a study of two different devices, a combination of tapered-plate energy absorber (TPEA) and viscoelastic dampers and a combination of TPEA and fluid dampers. It starts with a general review of the developments in various energy dissipating devices. Then a finite element formulation for fluid dampers is developed for this study. A comparison is made between numerical solutions and experimental results when a 2/5 scale steel structure is equipped with added viscoelastic dampers. The structural response of high-rise buildings mounted with three energy absorbing devices, tapered-plate energy absorber (TPEA), viscoelastic dampers, fluid dampers, and two combined devices, TPEA and fluid dampers and TPEA and viscoelastic dampers, respectively, have been investigated. Next, a parametric study of TPEA devices for high-rise buildings is conducted. The selected response parameters in this study include: 1) story shear force; 2) floor displacement; 3) base shear force; and 4) ductility ratio. Finally, two combined devices, TPEA and viscoelastic dampers and TPEA and fluid dampers are examined. Results show such combined devices provide a strong safe-failure mechanism as reliable energy absorbing devices. They also can sustain a wide range of loadings from minor to severe earthquake ground motion and wind loads. The combined devices can compensate for each other's shortcomings so that a satisfactory design for wind loads and seismic hazard mitigation of the structures can be achieved.

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Design and Retrofit Methodology for Building Structures with Supplemental Energy Dissipating Systems

This report focuses on two fundamental issues related to the design of nonlinear viscous dampers for building structures: structural velocities and equivalent viscous damping. It begins with an overview of the capacity-demand spectral design approach and includes various steps involved in the pushover analysis to determine the structural capacity. An alternative elasto-plastic analysis approach is also introduced. Fundamental considerations for the design of supplmental damping systems are reviewed and the design formulations for a pseudo-actual velocity transformation are given following a discussion of the differences between the two quantities. The proposed equivalent linear damping for the nonlinear [viscous nature] devices based on the equivalent power comsumption approach is presented. Finally, various phases involved in designing supplemental systems are given Design steps for 2 alternative device configurations are given. A retrofit design example of a 9-story flexible steel building is presented and the performance of the two alternative configurations is discussed.

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Response History Analysis of Structures with Seismic Isolation and Energy Dissipation Systems: Verification Examples for Program SAP2000

SAP2000 is a recently released commercial structural analysis program with capabilities for dynamic analysis of structures with isolation and energy dissipation systems. This report presents five verification examples in which results obtained by SAP2000 are compared to experimental results and to results obtained by programs 3D-BASIS and ANSYS. Three of the examples involve seismically isolated structures, of which, one was tested on the shake table under conditions resulting in bearing uplift. The other two examples involve structures with linear and nonlinear fluid viscous energy dissipation devices, which were also tested on the shake table. In general, SAP2000 produced results in excellent agreement with other analysis programs and in good agreement with experimental results, except for the case of the structures tested with nonlinear viscous damping devices. In this case, SAP2000 underpredicted the displacement response of the structure.

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Response Modification Factors for Seismically Isolated Bridges

The 1997 AASHTO "Guide Specifications for Seismic Isolation Design" specify response modification factors for the substructures of isolated bridges that are lower than those specified for the substructures of non-isolated bridges. This report presents the rationale behind these specifications and presents research results that lead to the establishment of appropriate response modification factors for isolated bridges. The research concentrated on the dynamic analysis of simple models of seismic-isolated and non-isolated bridges for a range of isolated system and substructure behaviors, and for seismic excitation characterized by AASHTO ground motion spectra for a range of soil conditions and acceleration coefficients. The study investigated the displacement ductility demands in the substructure of these bridges and established the appropriate value of the ductility-based portion of the response modification factors. This was achieved by comparing the displacement ductility ratio for the substructures of isolated and non-isolated bridges. The study concludes that response modification factors should be lower in the substructures of isolated bridges than in the substructures of non-isolated bridges because: (a) elastic or nearly elastic substructure behavior is required for proper behavior of the isolation system, and (b) isolated bridges exhibit more sensitivity in the substructure inelastic response due to variability in the seismic input.

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Recommended LRFD Guidelines for the Seismic Design of Highway Bridges

The Recommended Guidelines consist of specifications, commentary, and appendices developed to be compatible with the existing load-and-resistance-factor design (LRFD) provisions for highway bridges published by AASHTO. This two-volume set offers the Specifications in Part I and the Commentary and Appendices in Part II. The new, updated provisions are nationally applicable and cover all seismic zones, as well as all bridge construction types and materials. They reflect the latest design philosophies and approaches that will result in highway bridges with a high level of seismic performance. This report contains numerous innovative and updated requirements and procedures, including: state-of-knowledge seismic hazard maps developed by the USGS; recommended design earthquakes and performance objectives; guidance on assessment of liquefaction and design solutions; new soil factors and spectral shapes; seismic design requirements for steel bridges; “no analysis” design concepts; some seismic resisting systems and elements not permitted in the current AASHTO provisions; capacity spectrum design procedures; displacement capacity verification (“Pushover”) analysis; and cost comparisons and implications. Equations, figures, and tables appear throughout this report.

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Evaluation of Accuracy of Simplified Methods of Analysis and Design of Buildings with Damping Systems for Near-Fault and for Soft-Soil Seismic Motions

The effect of near-field and soft-soil ground motions on structures with viscous-damping systems was examined. Damping modification factors for damping ratios up to 100% of critical were obtained for sets of near-field and soft-soil ground motions and compared to the values presented in the 2000 NEHRP Recommended Provisions. A study was carried out for the ductility demand in structures with and without damping systems, where the damped buildings were designed for a smaller base shear than conventional buildings in accordance with the 2000 NEHRP Provisions. Nonlinear response-history and simplified methods of the 2000 NEHRP Provisions were used to analyze single-degree-of-freedom systems and 3-story moment frames with linear viscous and nonlinear viscous damping systems to acquire knowledge on the influence of near-field and soft-soil ground motions on the accuracy of simplified methods of analysis. An extensive use of figures is provided throughout the report.

Development and Evaluation of Simplified Procedures for Analysis and Design of Buildings with Passive Energy Dissipation Systems

This report presents the development and evaluation of simplified methods of analysis and design for buildings with passive energy dissipation systems. The work was conducted under the auspices of the Building Seismic Safety Council, Technical Subcommittee 12, Base Isolation and Energy Dissipation, for the year 2000 update of the "NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures." Topics presented in the report include development of extended damping coefficients for modification of response spectra for damping in excess of 5% of critical; development of relationships between elastic and inelastic displacement of yielding systems with energy dissipating devices; a study of displacement ductility demand in yielding structures with viscous damping systems; development of equivalent lateral force and modal analysis procedures for buildings with damping systems; and validation studies of the developed analysis procedures using 3- and 6-story structures with linear viscous, nonlinear viscous, solid viscoelastic and yielding damping systems.

Seismic Isolation of Highway Bridges

More than 200 bridges have been designed or retrofitted in the United States using seismic isolation in the last 20 years, and more than a thousand bridges around the world now use this cost-effective technique for seismic protection. Intended to supplement AASHTO’s Guide Specifications for Seismic Isolation Design (1999), this manual presents the principles of isolation for bridges, develops step-by-step methods of analysis, explains material and design issues for elastomeric and sliding isolators, and gives detailed examples of their application to standard highway bridges. Design guidance is given for the lead-rubber isolator, the friction-pendulum isolator, and the Eradiquake isolator, all of which are found in use today in the United States. Guidance on the development of test specifications for these isolators is also given.

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Design and Retrofit Methodology for Building Structures with Supplemental Energy Dissipating Systems

From NISEE library.

This report focuses on two fundamental issues related to the design of nonlinear viscous dampers for building structures: structural velocities and equivalent viscous damping. It begins with an overview of the capacity-demand spectral design approach and includes various steps involved in the pushover analysis to determine the structural capacity. An alternative elasto-plastic analysis approach is also introduced. Fundamental considerations for the design of supplmental damping systems are reviewed and the design formulations for a pseudo-actual velocity transformation are given following a discussion of the differences between the two quantities. The proposed equivalent linear damping for the nonlinear [viscous nature] devices based on the equivalent power comsumption approach is presented. Finally, various phases involved in designing supplemental systems are given Design steps for 2 alternative device configurations are given. A retrofit design example of a 9-story flexible steel building is presented and the performance of the two alternative configurations is discussed.

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evelopment and Evaluation of Simplified Procedures for Analysis and Design of Buildings with Passive Energy Dissipation Systems

From NISEE library.

This report presents the development and evaluation of simplified methods of analysis and design for buildings with passive energy dissipation systems. The work was conducted under the auspices of the Building Seismic Safety Council, Technical Subcommittee 12, Base Isolation and Energy Dissipation, for the year 2000 update of the "NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures." Topics presented in the report include development of extended damping coefficients for modification of response spectra for damping in excess of 5% of critical; development of relationships between elastic and inelastic displacement of yielding systems with energy dissipating devices; a study of displacement ductility demand in yielding structures with viscous damping systems; development of equivalent lateral force and modal analysis procedures for buildings with damping systems; and validation studies of the developed analysis procedures using 3- and 6-story structures with linear viscous, nonlinear viscous, solid viscoelastic and yielding damping systems.

Passive Energy Dissipation Systems for Structural Design and Retrofit

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Property Modification Factors for Seismic Isolation Bearings

Performance of Seismic Isolation Hardware under Service and Seismic Loading

This report presents a comprehensive description of the current stage of knowledge on the behavior of hardware used in seismic isolation and in seismic damping systems. Particular emphasis is placed on the description of fundamental behavior under both nonseismic, service-type of loading conditions and under high-speed seismic conditions.Specific problems described and addressed in this report include the following: (a) Aging of elastomeric and sliding bearings, (b) effect of ambient temperature on the behavior of elastomeric and sliding bearings, © prediction and experimental verification of effects of frictional heating on the sliding bearings, (d) prediction and experimental verification of effects of hysteretic heating on the lead-rubber bearings, (e) analysis of elastomeric and sliding bearings, (f) design of elastomeric and sliding bearings based on principles of LRFD and ASD, (g) establishment of upper and lower bound values of properties of seismic isolation bearings for use in the analysis and design and (h) detailed new testing protocols for seismic isolators and dampers. The presented information may represent the basis for the development of contemporary Guide Specifications for Seismic Isolation Design.

Seismic Protection of Electrical Transformer Bushing Systems by Stiffening Techniques

In the past few decades, electrical substation equipment has shown vulnerable behavior under
strong earthquakes, resulting in severe damage to electric power networks. High voltage
bushings, which are designed to isolate and transmit electricity from a transformer to the high
voltage lines, are the most critical as well as the most vulnerable components of the electrical
substations. Rehabilitation of existing bushing structures and proper design of new ones could
considerably reduce potential damage to them. Several experimental and numerical studies
conducted to investigate the seismic performance of transformer bushing structures have shown
that improved seismic performance may be achieved for bushings mounted on a rigid base
compared to those mounted on actual transformer tanks (“as installed” conditions), which appear
to be very flexible.
This reports investigates the seismic response of bushing structures both “as installed” on a
flexible base and on a rigid base as well as attempts to identify feasible approaches of stiffening
the base of the transformer bushings as a measure to mitigate their vulnerability under strong
seismic excitation. Finite element models of four different high voltage transformers were used
for performing modal and linear dynamic time history analyses in order to compare the response
of the bushing structures “as installed” and on a rigid base as well as investigate the efficiency of
several stiffening techniques to ensure the integrity of the bushings during strong earthquakes. In
addition, a two stage experimental investigation, consisting of system identification testing and
shake table testing, was conducted to verify the response trends identified by the numerical
studies.
Both numerical and experimental studies clearly showed that the bushing structures “as
installed” are very vulnerable to seismic excitation as well as very flexible compared to the ones
mounted on a rigid base. Moreover, these studies showed that stiffening the base of the bushings
can be beneficial for their response against ground shaking. From the stiffening techniques
investigated, incorporating flexural stiffeners on the cover plate of the transformer tank appears
to be the most efficient approach.

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Extreme Load Combinations: A Survey of State Bridge Engineers

This report briefly describes the recent progress of the current research program at
MCEER sponsored by the Federal Highway Administration (FHWA) on the
establishment of multiple hazard design principles for highway bridges followed by a
more detailed discussion on one specific aspect of the study with respect to establishing a
limited number of extreme load combinations for detailed study. One of the primary
research tasks of the MCEER research program is to establish limit-state equations
involving multiple hazard load effects within the context of the Load and Resistance
Factor Design (LRFD) Specifications (AASHTO 2010), published by the American
Association of State Highway and Transportation Officials (AASHTO) (Lee et al, 2008).
This task compares the importance and design emphasis of the extreme loads as well as
extreme load combinations by investigating the current practice and issues in design. A
survey was conducted among the state bridge engineers that constitute AASHTO’s
Subcommittee on Bridges and Structures (SCOBS) to obtain their professional opinion
on design considerations that are appropriate for their region. The result is an important
reference for the establishment and simplification of extreme limit states.

Modeling and Seismic Performance Evaluation of High Voltage Transformers and Bushings

Detailed techniques for the modeling of the bushings are presented in this report along with a discussion on the sensitivity of interactions. Additional investigations were conducted to explore feasibility and approximations in analyzing simplified models in which the tank cover and the bushings are separated from the transformer. The report presents the sensitivity study onmodeling various boundary conditions in the simplified model in an effort to match the response of the bushings with the response obtained from the full model.
The report also presents the global amplification effects of the tank construction on the response of the tank cover at base of bushings, and the effects on the apparent dynamic properties of bushings. Recommendations for guidelines on modeling transformers and bushings can be derived from this work.

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Seismic Design and Analysis of a Precast Segmental Concrete Bridge Model

This report studies the response of a precast segmental bridge model, designed according to the Accelerated Bridge Construction (ABC) techniques, when subjected to earthquake induced loads. A prototype bridge system is selected [Megally et al., 2002] and modified to comply with the ABC requirements for precast segmental bridges. The segmental bridge model is then scaled down to a 1/2.39-scale experimental model. The superstructure of the scaled bridge model consists of a single-span single-cell box girder, and its substructure consists of two square hollow piers. By means of modern structural experimental techniques, such as shake table dynamic testing, the large-scale precast segmental bridge specimen will provide valuable information on the behavior of such systems under seismic loading.

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Performance Assessment of Conventional and Base-Isolated Nuclear Power Plants for Earthquake and Blast Loadings

The sample NPP reactor building studied in this report is composed of containment and internal structures with a total weight of approximately 75,000 tons. Four configurations of the reactor building are studied, including one conventional fixed-base reactor building and three base-isolated reactor buildings using Friction PendulumTM, lead rubber and low damping rubber bearings.

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LRFD-Based Analysis and Design Procedures for Bridge Bearings and Seismic Isolators

This report describes the development and application of analysis and design specifications for bridge bearings and seismic isolators that (a) are based on the LRFD framework, (b) are based on similar fundamental principles, which include the latest developments and understanding of behavior, and © are applicable through the same procedures regardless of whether the application is for seismic-isolated or conventional bridges.
Examples are presented of design of conventional elastomeric and PTFE spherical bearings and three examples of detailed design and analysis of the seismic isolation system of a bridge located in California utilizing lead-rubber, single Friction Pendulum and triple Friction Pendulum isolators. The seismic isolation design examples utilize the latest definition of seismic hazard in California and intent to serve as a guide to application of the technology to bridges in California.