• Title, Summary, Keyword: Capability Reinforcement

Search Result 87, Processing Time 0.028 seconds

Mechanical Properties of Steel-Fiber Reinforced Concrete (강섬유보강콘크리트의 역학적 거동 특성)

  • 홍성구;권숙국
    • Magazine of the Korean Society of Agricultural Engineers
    • /
    • v.31 no.3
    • /
    • pp.81-91
    • /
    • 1989
  • The aims of this study were to determine mechanical properties of steel-fiber reinforced concrete under splitting tensile, flexural and compressive loading, and thus to improve the possible applications of concrete. The major factors experimentally investigated in this study were the fiber content and the length and the diameter of fibers. The major results obtained are summarized as follows : 1.The strength, strain, elastic modulus and energy obsorption capability of steel-fiber reinforced concrete under splitting tensile loading were significantly improved by increasing the fiber content or the aspect ratio. 2.The flexural strength, central deflection, and flexural toughness of steel4iber reinforced beams were significantly improved by increasing the fiber content or the aspect ratio. And flexural behavior characteristic was good at the aspect ratio of about 60 to 75. 3.The strength, strain, and energy absorption capability in compression were increased with the increase of the fiber content. These effects were not so sensitive to the aspect ratio. The energy absorption capability was improved only slightly with the increase of the fiber length. 4.The elastic modulus, transverse strains, and poisson's ratios in compression were not influenced by the fiber content. 5.The steel-fibers were considered to be appropriated as the materials covering the weakness of concrete because the mechanical properties of concrete in tension and flexure were significantly improved by steel-fiber reinforcement.

  • PDF

A Study on the Convergence of the Evolution Strategies based on Learning (학습에의한 진화전략의 수렴성에 관한연구)

  • 심귀보
    • Journal of the Korean Institute of Intelligent Systems
    • /
    • v.9 no.6
    • /
    • pp.650-656
    • /
    • 1999
  • In this paper, we study on the convergence of the evolution strategies by introducing the Lamarckian evolution and the Baldwin effect, and propose a random local searching and a reinforcement local searching methods. In the random local searching method some neighbors generated randomly from each individual are med without any other information, but in the reinforcement local searching method the previous results of the local search are reflected on the current local search. From the viewpoint of the purpose of the local search it is suitable that we try all the neighbors of the best individual and then search the neighbors of the best one of them repeatedly. Since the reinforcement local searching method based on the Lamarckian evolution and Baldwin effect does not search neighbors randomly, but searches the neighbors in the direction of the better fitness, it has advantages of fast convergence and an improvement on the global searching capability. In other words the performance of the evolution strategies is improved by introducing the learning, reinforcement local search, into the evolution. We study on the learning effect on evolution strategies by applying the proposed method to various function optimization problems.

  • PDF

Creating damage tolerant intersections in composite structures using tufting and 3D woven connectors

  • Clegg, Harry M.;Dell'Anno, Giuseppe;Partridge, Ivana K.
    • Advances in aircraft and spacecraft science
    • /
    • v.6 no.2
    • /
    • pp.145-156
    • /
    • 2019
  • As the industrial desire for a step change in productivity within the manufacture of composite structures increases, so does the interest in Through-Thickness Reinforcement technologies. As manufacturers look to increase the production rate, whilst reducing cost, Through-Thickness Reinforcement technologies represent valid methods to reinforce structural joints, as well as providing a potential alternative to mechanical fastening and bolting. The use of tufting promises to resolve the typically low delamination resistance, which is necessary when it comes to creating intersections within complex composite structures. Emerging methods include the use of 3D woven connectors, and orthogonally intersecting fibre packs, with the components secured by the selective insertion of microfasteners in the form of tufts. Intersections of this type are prevalent in aeronautical applications, as a typical connection to be found in aircraft wing structures, and their intersections with the composite skin and other structural elements. The common practice is to create back-to-back composite "L's", or to utilise a machined metallic connector, mechanically fastened to the remainder of the structure. 3D woven connectors and selective Through-Thickness Reinforcement promise to increase the ultimate load that the structure can bear, whilst reducing manufacturing complexity, increasing the load carrying capability and facilitating the automated production of parts of the composite structure. This paper provides an overview of the currently available methods for creating intersections within composite structures and compares them to alternatives involving the use of 3D woven connectors, and the application of selective Through-Thickness Reinforcement for enhanced damage tolerance. The use of tufts is investigated, and their effect on the load carrying ability of the structure is examined. The results of mechanical tests are presented for each of the methods described, and their failure characteristics examined.

An Exploratory Study on the Relationship between Organizational Performance and Information Systems' Support on the Internal Capability of Organizations (기업의 내부능력에 대한 정보시스템 지원과 기업성과간의 관련성 연구)

  • Yoon Jong-Soo;Yoon Jong-Wook;Kim Yoo-Jung;Park Seung-Bong
    • The Journal of Information Systems
    • /
    • v.15 no.3
    • /
    • pp.55-85
    • /
    • 2006
  • The purpose of this study Is to investigate what types of internal capabilities are mainly supported by information system applications that have been introduced in organizations during the last three years, and to examine the relationships between information systems' support on internal capabilities and organizational performance are differed with the organizational size and the type of industry. This study is also to suggest a few research propositions that can be applied to empirical studies dealing with the relationship between organizational performance and information systems' support on organizational capabilities in the future. To accomplish these research purposes, this study performed a survey and 101 responses were used for statistical analysis. The research results are as follows: First information systems' applications introduced into organizations during the most recent 3-year period, were mainly used to support the production/service capability, leading to an improvement of both the product and the service and reinforcement of task efficiency in the organizations. Second the support of information systems' applications on the production and service capability of organizations influenced organizational performance in a positive manner. Third, the relationship between organizational performance and support of information systems on organizational capabilities was partially differed by organizational size and the type of industry, the organization is involved in. Fourth, two research propositions that can be applied for empirical studies in the future were suggested with regard to the relationship between organizational performance and support of information systems on organizational capabilities, based on the statistical analysis.

  • PDF

Direct Tensile Behavior of Steel.Fiber Reinforced Concrete (강섬유콘크리트의 직접인장 거동 특성)

  • 이신호;고재군
    • Magazine of the Korean Society of Agricultural Engineers
    • /
    • v.29 no.4
    • /
    • pp.124-131
    • /
    • 1987
  • The aims of this study was to determine the mechanical properties of steel-fiber reinforced concrete under direct tensile loading, and also to insestigate the mechanism fiber reinforcement in order to improve the possible applications of steel-fiber reinforced concrete. In this study the major variables of experimental investigation were fiber conntents, and the lengths and diameters of fibers. The major results obtained are summarized as follows : 1. The strength, elastic modulus and energy absorption capability of steel-fiber reinforced concrete under direct tensile loading were improved as increasing of fiber contents. 2. The direct tensile strength of steel-fiber reinforced concrete was not influenced by the lengths of fiber, but was decreased as increasing of fiber diameters. 3. The direct tensile strength of steel-fiber reinforced concrete was not influenced by the fiber aspect-ratio, but this was because the fiber contents were below the critical value of fiber content. 4. The correlation of direct tensile strength and combined parameter, Vf l/d, was not good. 5. Mutiple cracking and post-crack resistance were investigated at stress-strain curves in direct tensile test. 6. The effect of fiber reinforcement can be influenced by fiber orientation and the bond strength between fiber and matrix. 7. The improvement of mechanical properties of steel-fiber reinforced concrete under direct tensile loading can be theoretically explained by the concept of composite materials.

  • PDF

Repeated Loading Tests of Reinforced Concrete Beams Containing Headed Shear Reinforcement (Headed Shear Bar를 사용한 콘크리트 보의 반복 하중 실험)

  • 김영훈;윤영수;데니스미첼
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • /
    • pp.512-517
    • /
    • 2003
  • The repeated loading responses of four shear-critical reinforced concrete beams, with two different shear span-to-depth ratios, were studied. One series of beams was reinforced using pairs of bundled stirrups with $90^{\circ}C$ standard hooks, having free end extensions of $6d_b$. The companion beams contained shear reinforcement made with larger diameter headed bars anchored with 50mm diameter circular heads. A single headed bar had the same area as a pair of bundled stirrups and hence the two series were comparable. The test results indicate that beams containing headed bar stirrups have a superior performance to companion beams containing bundled standard stirrups, with improved ductility, larger energy adsorption and enhanced post-peak load carrying capability. Due to splitting of the concrete cover and local crushing, the hooks of the standard stirrups opened, resulting in loss of anchorage. In contrast, the headed bar stirrups did not lose their anchorage and hence were able to develop strain hardening and also served to delay buckling of the flexural compression steel. Excellent load-deflection predictions were obtained by reducing the tension stiffening to account for repeated load effects.

  • PDF

Opportunistic Spectrum Access Based on a Constrained Multi-Armed Bandit Formulation

  • Ai, Jing;Abouzeid, Alhussein A.
    • Journal of Communications and Networks
    • /
    • v.11 no.2
    • /
    • pp.134-147
    • /
    • 2009
  • Tracking and exploiting instantaneous spectrum opportunities are fundamental challenges in opportunistic spectrum access (OSA) in presence of the bursty traffic of primary users and the limited spectrum sensing capability of secondary users. In order to take advantage of the history of spectrum sensing and access decisions, a sequential decision framework is widely used to design optimal policies. However, many existing schemes, based on a partially observed Markov decision process (POMDP) framework, reveal that optimal policies are non-stationary in nature which renders them difficult to calculate and implement. Therefore, this work pursues stationary OSA policies, which are thereby efficient yet low-complexity, while still incorporating many practical factors, such as spectrum sensing errors and a priori unknown statistical spectrum knowledge. First, with an approximation on channel evolution, OSA is formulated in a multi-armed bandit (MAB) framework. As a result, the optimal policy is specified by the wellknown Gittins index rule, where the channel with the largest Gittins index is always selected. Then, closed-form formulas are derived for the Gittins indices with tunable approximation, and the design of a reinforcement learning algorithm is presented for calculating the Gittins indices, depending on whether the Markovian channel parameters are available a priori or not. Finally, the superiority of the scheme is presented via extensive experiments compared to other existing schemes in terms of the quality of policies and optimality.

Over-Strength, Ductility and Response Modification Factor of Small-Size Reinforced Concrete Moment Frame Buildings (소규모 철근콘크리트 모멘트골조 건축물의 초과강도, 연성도 및 반응수정계수)

  • Kim, Taewan;Chu, Yurim;Park, Hong-Gun;Shin, Yeong Soo
    • Journal of the Earthquake Engineering Society of Korea
    • /
    • v.20 no.3
    • /
    • pp.145-153
    • /
    • 2016
  • Small-size buildings are not designed by professional structural engineers in Korea. Therefore, their seismic performance can not be exactly estimated because their member sizes and reinforcement may be over- or under-designed. A prescriptive design criteria for the small-size buildings exists, but it also provides over-designed structural members since structural analysis is not incorporated, so it is necessary to revise the prescriptive criteria. The goal of this study was to provide an information for the revision, which is seismic performance and capability of small-size reinforced concrete moment frame buildings. For the study, the state of existing small-size reinforce-concrete buildings such as member size and reinforcement was identified by investigating their structural drawings. Then, over-strength, ductility and response modification factor of the small-size reinforced concrete moment frame buildings were estimated by analytical approach along with seismic performance check. The result showed that they possess moderate over-strength and ductility, and may use slightly increased response modification factor.

An experimental and numerical investigation on the effect of longitudinal reinforcements in torsional resistance of RC beams

  • Khagehhosseini, A.H.;Porhosseini, R.;Morshed, R.;Eslami, A.
    • Structural Engineering and Mechanics
    • /
    • v.47 no.2
    • /
    • pp.247-263
    • /
    • 2013
  • It is evident that torsional resistance of a reinforced concrete (RC) member is attributed to both concrete and steel reinforcement. However, recent structural design codes neglect the contribution of concrete because of cracking. This paper reports on the results of an experimental and numerical investigation into the torsional capacity of concrete beams reinforced only by longitudinal rebars without transverse reinforcement. The experimental investigation involves six specimens tested under pure torsion. Each specimen was made using a cast-in-place concrete with different amounts of longitudinal reinforcements. To create the torsional moment, an eccentric load was applied at the end of the beam whereas the other end was fixed against twist, vertical, and transverse displacement. The experimental results were also compared with the results obtained from the nonlinear finite element analysis performed in ANSYS. The outcomes showed a good agreement between experimental and numerical investigation, indicating the capability of numerical analysis in predicting the torsional capacity of RC beams. Both experimental and numerical results showed a considerable torsional post-cracking resistance in high twist angle in test specimen. This post-cracking resistance is neglected in torsional design of RC members. This strength could be considered in the design of RC members subjected to torsion forces, leading to a more economical and precise design.

Finite element analysis of shear critical prestressed SFRC beams

  • Thomas, Job;Ramaswamy, Ananth
    • Computers and Concrete
    • /
    • v.3 no.1
    • /
    • pp.65-77
    • /
    • 2006
  • This study reports the details of the finite element analysis of eleven shear critical partially prestressed concrete T-beams having steel fibers over partial or full depth. Prestressed concrete T-beams having a shear span to depth ratio of 2.65 and 1.59 and failing in the shear have been analyzed using 'ANSYS'. The 'ANSYS' model accounts for the nonlinear phenomenon, such as, bond-slip of longitudinal reinforcements, post-cracking tensile stiffness of the concrete, stress transfer across the cracked blocks of the concrete and load sustenance through the bridging of steel fibers at crack interface. The concrete is modeled using 'SOLID65'-eight-node brick element, which is capable of simulating the cracking and crushing behavior of brittle materials. The reinforcements such as deformed bars, prestressing wires and steel fibers have been modeled discretely using 'LINK8' - 3D spar element. The slip between the reinforcement (rebar, fibers) and the concrete has been modeled using a 'COMBIN39'-non-linear spring element connecting the nodes of the 'LINK8' element representing the reinforcement and nodes of the 'SOLID65' elements representing the concrete. The 'ANSYS' model correctly predicted the diagonal tension failure and shear compression failure of prestressed concrete beams observed in the experiment. The capability of the model to capture the critical crack regions, loads and deflections for various types of shear failures in prestressed concrete beam has been illustrated.