Uniform Damage Distribution Research Articles

Optimum lateral load pattern for seismic design of elastic shear‐buildings incorporating soil–structure interaction effects

SUMMARYRecently, several new optimum loading patterns have been proposed by researchers for fixed‐base systems while their adequacy for soil–structure systems has not been evaluated yet. Through intensive dynamic analyses of multistory shear‐building models with soil–structure interaction subjected to a group of 21 artificial earthquakes adjusted to soft soil design spectrum, the adequacy of these optimum patterns is investigated. It is concluded that using these patterns the structures generally achieve near optimum performance in some range of periods. However, their efficiency reduces as soil flexibility increases especially when soil–structure interaction effects are significant. In the present paper, using the uniform distribution of damage over the height of structures, as the criterion, an optimization algorithm for seismic design of elastic soil–structure systems is developed. The effects of fundamental period, number of stories, earthquake excitation, soil flexibility, building aspect ratio, damping ratio and damping model on optimum distribution pattern are investigated. On the basis of 30,240 optimum load patterns derived from numerical simulations and nonlinear statistical regression analyses, a new lateral load pattern for elastic soil–structure systems is proposed. It is a function of the fundamental period of the structure, soil flexibility and structural slenderness ratio. It is shown that the seismic performance of such a structure is superior to those designed by code‐compliant or recently proposed patterns by researchers for fixed‐base structures. Using the proposed load pattern in this study, the designed structures experience up to 40% less structural weight as compared with the code‐compliant or optimum patterns developed based on fixed‐base structures. Copyright © 2012 John Wiley & Sons, Ltd.

General Seismic Load Distribution for Optimum Performance-Based Design of Shear-Buildings

An optimization method based on uniform damage distribution is used to find optimum design load distribution for seismic design of regular and irregular shear-buildings to achieve minimum structural damage. By using 75 synthetic spectrum-compatible earthquakes, optimum design load distributions are obtained for different performance targets, dynamic characteristics, and site soil classifications. For the same structural weight, optimum designed buildings experience up to 40% less global damage compared to code-based designed buildings. A new general load distribution equation is presented for optimum performance-based seismic design of structures which leads to a more efficient use of structural materials and better seismic performance.

Seismic damage assessment of reinforced concrete frames with shear wall according to load pattern

Studies have shown that most structures subjected to strong ground motions fall into an inelastic state. Therefore, it is necessary to study the inelastic behaviour of structures undergoing such earthquakes. In this study, three reinforced concrete (RC) frames with shear wall are considered. The preliminary designs of these frames are based on equivalent static forces in accordance with six patterns of loading distribution (namely Uniform Building Code (UBC), National Earthquake Hazards Reduction Program (NEHRP), Iranian seismic code, modified rectangular, first mode and the first three modes). The aim of this study is to investigate the distribution of damage in accordance with these six load patterns. IDARC 2D software has been used to calculate maximum drift, hysteretic energy and structural damage index when subjected to severe earthquakes. The results show that the current seismic design based on strength principles, even considering uniform strength distribution, does not lead to a uniform distribution of hysteretic energy, drift and damage index in storey height. However, modified rectangular and the first three mode patterns show more uniform distribution of damage than the others.

Effect of Omnidirectional Proton Irradiation On Shielded Solar Cells

An analysis of the effects of low energy proton irradiation on the electrical performance of triple junction (3J) InGaP2/GaAs/Ge solar cells is presented. The Monte Carlo ion transport code SRIM is used to simulate the damage profile induced in a 3J solar cell under the conditions of typical ground testing and that of the omnidirectional space environment. The results are used to present a quantitative analysis of the defect, and hence damage, distribution induced in the cell active region by the different radiation conditions. The modeling results show that, in the space environment where the incident radiation is omnidirectional, the solar cell will experience a uniform damage distribution through the active region of the cell. The cases of directional spectrum irradiation and omnidirectional irradiation through very thin shielding are also considered. Through an application of the displacement damage dose analysis methodology, the implications of this result on mission performance predictions are investigated

Energy-based seismic design of buckling-restrained braced frames using hysteretic energy spectrum

An energy-based seismic design procedure for framed structures with buckling-restrained braces is proposed using hysteretic energy spectra and accumulated ductility spectra. The procedure is based on the premise that the gravity load-resisting elements, such as beams and columns, are designed to remain elastic during earthquake, and all the seismic input energy is dissipated by the buckling-restrained braces. The proposed design procedure requires hysteretic energy spectra and accumulated ductility spectra corresponding to various target ductility ratios. The cross-sectional area of braces required to meet a given target displacement is obtained by equating the hysteretic energy demand to the accumulated plastic energy dissipated by braces. The design procedure was applied to three- and eight-story framed structures with buckling-restrained braces. Twenty earthquake records were utilized to construct the spectra and to verify the validity of the design procedure. According to analysis results, the mean values for the top story displacement correspond well with the given performance target displacements. Also, the inter-story drifts turned out to be relatively uniform over the structure height, which is desirable because uniform inter-story drifts indicate uniform damage distribution.

이력에너지 스펙트럼을 이용한 비좌굴 가새골조의 내진설계

본 연구에서는 단자유도계 시스템에서 작성한 이력에너지 스펙트럼과 누적된 변위 연성비 스펙트럼을 이용하여 비좌굴 가새골조의 내진설계법을 제안하였다. 먼저 목표 연성비에 해당하는 이력에너지 스펙트럼과 누적된 연성비 스펙트럼을 작성하였다. 주어진 목표 변위를 만족하기 위하여 필요한 가새의 단면적은 이력에너지 요구량과 가새에 의하여 소산된 누적 소성에너지를 같다고 하여 산정하였다. 스펙트럼을 작성하고 설계절차의 유효성을 검증하기 위하여 20개의 지진기록을 이용하였다. 제안된 방법에 따라 설계된 3층과 8층 비좌굴 가새골조의 해석결과에 따르면 최상층 변위의 평균값이 성능 목표 변위에 잘 부합됨을 알 수 있다. 또한 층간변위는 구조물 높이에 따라 비교적 일정하였는데 이것은 손상 분포가 일정하기 때문에 바람직하다. 그러므로 제안된 에너지 설계법은 기존 강도설계법의 대안으로 비좌굴 가새골조의 신뢰할만한 설계법이라고 할 수 있다. In this study seismic design procedure for buckling-restrained braced frame systems was proposed using hysteretic energy spectrum and accumulated ductility spectrum constructed from single degree of freedom systems. The hysteretic energy spectra and accumulated ductility spectra corresponding to target ductility ratio were constructed first. The cross-sectional area of braces required to meet a given target displacement was obtained by equating the hysteretic energy demand to the accumulated plastic energy dissipated by braces. Twenty earthquake records were utilized to construct the spectra and to verify the validity of the design procedure. According to analysis results of three- and eight-story buckling-restrained braced frame structures designed using the proposed method, the mean values for the top story displacement correspond well with the given performance target displacements. Also, the inter-story drifts turned out to be relatively uniform over the structure height, which is desirable because uniform inter-story drifts indicate uniform damage distribution. Therefore if was concluded that the proposed energy-based method could be a reliable alternative to conventional strength-based design procedure for structures with buckling-restrained braces.

Seismic safety improvement of damage-controlled reinforced concrete frames

Conventional aseismic design methods for reinforced concrete (R/C) frames all but disregard the state of damage over the entire building frame. This paper introduces an automated damage-controlled design method for R/C frames which aims at a uniform damage distribution throughout the building frame, as measured by the individual member damage index. The accuracy of the basic hysteretic model and the damage model for R/C members is verified by reproducing the experimental load-deformation curves of one-bay one-story frames. Application of this design method to various frame structures indicates that (1) regardless of the structural properties or input earthquake characteristics, damage-controlled frames generally survive more severe earthquake excitations and suffer less damage than conventionally designed frames, and (2) member yielding strength in the lower stories of damage-controlled frames is larger than that for conventionally designed frames, while the trend is opposite in the upper stories.

Arc-Erosion Studies of Matrix-Strengthened Silver-Cadmium Oxide

A matrix-strengthening agent has been added to Ag-CdO material in order to reduce it's susceptibility to arc erosion. The matrix-strengthening agent, added to Ag-CdO as an additional oxide component, was chosen to enhance the wetting of liquid silver on the Ag-CdO surface. The erosion characteristics of Ag-CdO containing various matrix-strengthening additives have been investigated under static-gap conditions and in switching devices. The statlc-gap erosion measurements showed a lower material loss rate for Ag-CdO materials that euntained a matrix-strengthening additive compared to conventional Ag-CdO. The lowest erosion rate was obtained with a material containing the additive exhibiting the lowest interfacial energy against silver. Electron microscopy of the eroded surface of matrixstrengthened Ag-CdO revealed a smooth surface morphology indicative of good wetting between molten silver droplets and the contact surface. The erosion characteristics of materials containing the two most promising additives GeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and Ta <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> 0 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> were evaluated in switching devices. Even though the material loss rate of the matrix-strengthened Ag-CdO was higher than that of conventional Ag-CdO under some test conditions, the surfaces of the matrix-strengthened materials consistently showed a uniform distribution of damage over the contact surface in contrast to the more severe localized damage observed on the conventional Ag-CdO contacts. Metallographic sections of the tested contacts revealed a significant reduction in thermal stress cracking for materials containing the additive. The reduced cracking tendency and more uniform erosion pattern are shown to result in extended cycle life under heavy arcing conditions for matrix-strengthened Ag-CdO compared to conventional Ag-CdO.

Paper 19: Conditions Producing Concentrated Erosion in Large Steam Turbines

The paper presents the results of intrascope observations and instrument traverses in the final stages of three large steam turbines and describes the processes controlling the distribution of erosion on the moving blades. Concentrations of eroding water are shown to be produced by complex steam flows in the final stage which redistribute the water depositing on the surfaces of fixed blades. Of the three turbines considered, each has a different redistribution process, two leading to concentrated erosion, the third to a more uniform distribution of damage. In the former two turbines, it was found that the concentrations of water could be dispersed by small fences fitted to the fixed blade trailing edge, this simple modification promising to extend significantly the operating life of the moving blades.