Physical and Numerical Approaches for the Optimal Insertion of Seismic Viscous Dampers in Shear-Type Structures

This article presents the results of an exhaustive parametric analysis which compares the performances offered by various systems (which lead to both classical and non classical damping matrices) of added viscous dampers in shear-type structures. The aim of the research work here presented is the identification of the system of added viscous dampers which maximizes the dissipative properties under an equal “total size” constraint. The choice of the systems of added viscous dampers considered in the comparison is carried out both using a numerical approach (based upon the use of genetic algorithms) and a physically based approach (based upon the properties of classically damped systems). The comparison is carried out through the numerical evaluation of the dynamic response of representative shear-type structures to both stochastic and recorded earthquake inputs. The results obtained using both approaches indicate that a damping system based upon the mass proportional damping component of the Rayleigh viscous damping matrix (referred to as MPD system) is capable of optimizing simultaneously a number of different performance indexes, providing the best “overall” damping performances. The MPD system is characterised by viscous dampers (a) which connect each floor to a fixed point and (b) which are sized proportionally to the corresponding floor mass.     

FRICTION DAMPED STEEL MOMENT-RESISTING FRAMES SUBJECTED TO LONG-DISTANCE EARTHQUAKES: INFLUENCE OF WELD FRACTURES

It has been generally accepted that steel moment-resisting frames behave in a ductile manner under seismic excitations. However, during the 1994 Northridge earthquake in California, weld fractures at the beam-to-column connections occurred in many steel buildings. Such brittle failures obviously precluded the traditional ductile-behaviour assumption and had a significant effect on the responses of steel moment-resisting frames. In this paper, the performance of a friction damping system for retrofitting steel moment-resisting frames was investigated under long-distance earthquakes. For this purpose, the 1985 Mexico City (SCT), the 1995 Bangkok, or the 1977 Romania ground motions, all scaled to a peak ground acceleration of 0.17 g, were considered in this study. Responses of the building under the 1940 El Centro N-S component were also included for comparison. The results of the study show that a friction damping system can reduce the seismic responses significantly. The devices can also prevent the total collapse and joint failures of the building equipped with friction dampers, while the one without dampers would collapse, even under a peak ground acceleration of only 0.17 g.     

STRENGTH REDUCTION FACTORS FOR DUCTILE STRUCTURES WITH PASSIVE ENERGY DISSIPATING DEVICES

In recent years, current seismic codes started contemplating the design of structures with passive energy dissipating devices. One important issue for the rational seismic design of these devices and the structure that contains them is the formulation of numerical methods to estimate their design seismic forces. From the study of the dynamic response of single-degree-of-freedom systems subjected to accelerograms recorded in Mexico during the last two decades, expressions to estimate the strength reduction factor that should be used to reduce the elastic design strength spectra for 5 percent damping, to establish the design seismic forces for structures having different combinations of plastic and viscous energy dissipating capacities, are formulated.     

Nonlinear Response of RC Framed Buildings with Isolation and Supplemental Damping at the Base Subjected to Near-Fault Earthquakes

The nonlinear seismic response of base-isolated framed buildings subjected to near-fault earthquakes is studied to analyze the effects of supplemental damping at the level of the isolation system, commonly adopted to avoid overly large isolators. A numerical investigation is carried out with reference to two- and multi-degree-of-freedom systems, representing medium-rise base-isolated framed buildings. Typical five-story reinforced concrete (RC) plane frames with full isolation are designed according to Eurocode 8 assuming ground types A (i.e., rock) and D (i.e., moderately soft soil) in a high-risk seismic region. The overall isolation system, made of in-parallel high-damping-laminated-rubber bearings (HDLRBs) and supplemental viscous dampers, is modeled by an equivalent viscoelastic linear model. A bilinear model idealizes the behavior of the frame members. Pulse-type artificial motions, artificially generated accelerograms (matching EC8 response spectrum for subsoil classes A or D) and real accelerograms (recorded on rock- and soil-site at near-fault zones) are considered. A supplemental viscous damping at the base is appropriate for controlling the isolator displacement, so avoiding overly large isolators; but it does not guarantee a better performance of the superstructure in all cases, in terms of structural and non structural damage, depending on the frequency content of the seismic input. Precautions should be taken with regard to near-fault earthquakes, particularly for base-isolated structures located on soil-site.     

Direct Displacement-Based Design of Glulam Timber Frame Buildings

We introduce a direct Displacement-Based Design methodology for glued laminated timber portal frames with moment-resisting doweled joints. We propose practical expressions to estimate ultimate target displacement and equivalent viscous damping, and we demonstrate that these expressions provide prior values that are close to those obtained a posteriori using a more refined model. Applied to case studies, the method yields base-shear forces lower than those obtained using the force-based approach of Eurocode 8. This is due to the high dissipation capacity of the specific connection technology, which apparently is conservatively accounted for in the q-factor of Eurocode 8.     

Energy Intensity in Light of China's Economic Transition

Two economic geographers examine the impacts of economic transition on the efficiency of energy use in China, the second-largest energy consumer in the world. Following a brief review of reform and deregulation in China's energy sector, they proceed to systematically test the relationship between economic transition (conceptualized as a triple process of marketization, decentralization, and globalization) and energy intensity using a panel data set. The statistical units of analysis are China's 30 provincial-level administrative regions, facilitating the investigation of spatial variations in energy intensity. Journal of Economic Literature, Classification Numbers: O53, P20, Q40, Q43. 9 figures, 5 tables, 62 references.     

The Clean Energy Dilemma in Asia: Observations on Russia and China

Two American economic geographers and prominent specialists, respectively, in the energy industries and resources of Russia and related economic developments in China, evaluate and supplement the material presented in the preceding paper on the clean energy dilemma in Asia (Wilbanks, 2008). The paper covers changes in the relationship between energy consumption and economic growth globally as well as in Russia and China, Russian oil and gas exports to Asia (more specifically to China), the development of energy resources and production in China, and energy intensities in both countries.     

China's Energy Security: Challenges and Priorities

In a companion paper to the essays comparing China's and India's economic rise (Prime, 2009) as well as India's energy security (Dadwal, 2009), two specialists on China's energy industries review the country's challenges posed by the need to dramatically increase energy use in order to support economic growth while coping with pressures to reduce environmental impacts from emissions of greenhouse gases. After reviewing the current mix of fuels in the economy and discussing each major energy resource (in terms of proven reserves, production, consumption, and foreign import requirements), the authors focus on measures undertaken by the Chinese government and corporations to improve access to vital supplies. The paper covers efforts to enhance the country's energy security, which include diversifying sources of oil supply, purchasing oil and gas concessions and financing of energy infrastructure development in African and Central Asian countries, instituting reforms to encourage more efficient energy use, and developing alternative energy sources. Journal of Economic Literature, Classification Numbers: O130, P280, Q400. 7 figures, 2 tables, 82 references.     

Displaying the future: techno‐nationalism and the rise of the consumer in Postwar Japan

This paper explains how, in the aftermath of World War II, a type of techno‐nationalism emerged that linked being Japanese to science and technology and the increased consumption of electrical appliances. By closely examining official exhibitions, we can see how the state and private sector strongly encouraged this techno‐scientific dreaming. Dazzling displays highlighted how the peaceful atom would help lead the nation to achieve high economic growth. At the same time, through the judicious purchase of labor saving appliances, consumers could reconcile the need to spend with the need to save.     

Security and the shaping of identity for nuclear specialists

Atomic energy developed from 1940 as a subject shrouded in secrecy. Identified successively as a crucial element in military strategy, national status and export aspirations, the research and development of atomic piles (nuclear chain-reactors) were nurtured at isolated installations. Like monastic orders, new national laboratories managed their specialist workers in occupational environments that were simultaneously cosseted and constrained, defining regional variants of a new state-managed discipline: reactor technology. This paper discusses the significance of security in defining the new subject in the USA, UK and Canada – wartime allies with similar political traditions distinct but trajectories in this field during the Cold War. The intellectual borders and content of the subject developed differently in each country, shaped under the umbrella of secrecy by disparate clusters of expertise, industrial traditions, and national goals. The nascent cadre was contained until the mid 1950s by classified publications and state-sponsored specialist courses. The early context of high security filtered its members and capped enduringly both their professional aspirations and public engagement.