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RISS 인기검색어
- 검색키워드
- 저자 : Alex Elvin (검색결과 4 건)
- 무료
- 기관 내 무료
- 유료
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Mass and Stiffness Distributions in Optimized Ungrouped Unbraced Frames
Alex Elvin,Richard Walls 한국강구조학회 2010 International Journal of Steel Structures Vol.10 No.3
This paper investigates the distribution of mass and stiffness in multi-storey, ungrouped, unbraced, optimized frames. Ungrouped structures are impractical to design and construct. However, optimized, ungrouped structures suggest how structural systems can be improved, and the loads can be carried more efficiently. The Virtual Work Optimization (VWO) method is used to minimize the weight of the structures considered. A 60-storey structure found in the literature is optimized to compare the distribution of mass and stiffness in grouped and ungrouped configurations. A parametric study of frames subjected to lateral loads, ranging in height from 5 to 30 stories, is carried out. Structures are designed to satisfy both strength and deflection criteria. Three different section databases are used for each case study to investigate whether the nature of discrete sections influences results. When ungrouped frames subject to lateral loads are optimized the total stiffness and mass per floor decrease approximately linearly with decreasing height, followed in some cases by a constant region of mass and stiffness, and a decrease in the foundation region. Distinct patterns emerge where members are stiffened on diagonal paths across the width of the structure. The distribution of mass in the frames suggests truss or megabrace behaviour.
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Optimizing Structures with Semi-Rigid Connections Using the Principle of Virtual Work
Alex Elvin,Johnnie Strydom 한국강구조학회 2018 International Journal of Steel Structures Vol.18 No.3
In this paper, the virtual work optimization method (VWOM) has been generalised to consider structures with semi-rigid connections. The VWOM is an automated method that minimizes the mass of a structure with a given geometry, multiple defl ection criteria and load cases, while adhering to Design code requirements. In the optimization process, members are selected from a discrete database to meet all strength and stiff ness criteria. Connections are modelled using rotational springs, allowing some moment transfer. The rotational stiff ness of each connection can be varied form rigid to pinned. The example of a pitched roof frame is used to explain the method. Two case studies are considered: (i) a three-storey two-bay and (ii) a four-storey three-bay offi ce building. The VWOM produced results up to 26.7% lighter than results in the literature. Furthermore, the structures were optimized for a range of rotational stiff ness, where all connections in the structure were assumed to have the same rotational stiff ness. Characteristic jumps in the optimized mass versus rotational stiff ness were observed.
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Alex Elvin,Johnnie Strydom 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.1
The Virtual Work Optimization Method (VWOM) is used to optimize tall buildings with semi rigid connections. The VWOM is an automated method that minimizes the mass of a structure with a given geometry, defl ection criteria and load cases, while adhering to building code requirements. Members are selected from a user defi ned database to meet strength and stiff ness criteria. The rotational stiff ness of connections can be specifi ed and varied, from rigid to pinned. The method is explained using an example of a two storey one bay steel frame with six members. Four case studies are presented: (i) a six storey two bay frame, (ii) a ten storey one bay steel building, (iii) a fi fteen storey three bay steel frame and (iv) a twenty four storey three bay building. The examples are compared to results found in the literature. Structures were optimized for a range of connection rotational stiff nesses. The VWOM obtained results up to 44.6% lighter than published work. Optimized results showed that in most cases the semi rigid connection produced the same results as the rigid connections. This is due to the rapid plateauing of the optimized mass as the connection stiff ness increases. Thus, the typical defi nition of semi rigid and rigid rotational stiff nesses (for example Eurocode 3) are both found on this plateau. If some members are lightly loaded, broad semi rigid and rigid bands can be produced. The eff ect in these cases is that structures with rigid connections are lighter than those with semi rigid connections as no compensation in the member stiff ness is required to meet defl ection criteria.
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Sand or grease? Corruption-institutional trust nexus in post-Soviet countries
Nazim Habibov,Elvin Afandi,Alex Cheung 한양대학교 아태지역연구센터 2017 Journal of Eurasian Studies Vol.8 No.2
This paper empirically tests several hypotheses about the nexus of corruption-institutional trust in Post-Soviet transitional countries of the former Soviet Union and Mongolia. We use two different indices of institutional trust to check the robustness of our analysis and estimate OLS and instrumental variable models with and without interaction terms. All things considered, our findings reject “greases the wheels” and “trust begets an honest political system” hypotheses. Instead, our findings support the “sand the wheels” hypothesis. Furthermore, a multiplicative interaction model suggests that the negative marginal effects of experienced corruption are higher in the environments where satisfaction with services is low. In addition, we found that increases in corruption erode trust at all levels of the societal institutions including political parties, government and financial institutions, international investors, non-profit organizations, and trade unions. This finding is important since it highlights the negative consequences of corruption on the development of broader level economic institutions and on civil society.
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