• Title/Summary/Keyword: Steel Cover

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Genetic algorithm based optimum design of non-linear steel frames with semi-rigid connections

  • Hayalioglu, M.S.;Degertekin, S.O.
    • Steel and Composite Structures
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    • v.4 no.6
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    • pp.453-469
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    • 2004
  • In this article, a genetic algorithm based optimum design method is presented for non-linear steel frames with semi-rigid connections. The design algorithm obtains the minimum weight frame by selecting suitable sections from a standard set of steel sections such as European wide flange beams (i.e., HE sections). A genetic algorithm is employed as optimization method which utilizes reproduction, crossover and mutation operators. Displacement and stress constraints of Turkish Building Code for Steel Structures (TS 648, 1980) are imposed on the frame. The algorithm requires a large number of non-linear analyses of frames. The analyses cover both the non-linear behaviour of beam-to-column connection and $P-{\Delta}$ effects of beam-column members. The Frye and Morris polynomial model is used for modelling of semi-rigid connections. Two design examples with various type of connections are presented to demonstrate the application of the algorithm. The semi-rigid connection modelling results in more economical solutions than rigid connection modelling, but it increases frame drift.

Effect of Reinforcing Bar on Rayleigh Wave Propagation on Concrete Structures

  • Kim, Jae-Hong;Lee, Kang-Wook
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.3 no.2
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    • pp.159-164
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    • 2015
  • This paper presents results on a study of the Rayleigh wave scattering in concrete with a steel bar using transient elastic waves. To study the characteristics of the scattered waves induced by a steel bar in concrete, a three-dimensional finite element method was adopted. A case for elastic wave propagation parallel to the steel bar is discussed. The effect of the cover thickness and steel bar diameter on the Rayleigh wave was studied. To confirm the numerical investigations, a concrete specimen containing a steel bar was made, and corresponding transient elastic wave experiments were conducted. It is believed that the result of this study can serve as an important reference in a nondestructive evaluation of concrete with a steel bar.

The Evaluation of Stability for Hook-type Bonding Method of Pile Foundation and Cap (훅타입 말뚝두부보강 기초의 안정성 평가)

  • Lee, Heunggil;Oh, Sewook
    • Journal of the Korean GEO-environmental Society
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    • v.8 no.3
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    • pp.41-49
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    • 2007
  • The typical bonding methods which connect steel pipe pile and spread footing is bolted bonding method using +type cover plate for reinforcing a head of steel pipe pile. In this paper, stability of spread footing in pile foundation have been evaluated by loading test of +type cover plate for reinforcing a head of pile and hook type bonding method. The presents results from a series of pilot model test on vertically loaded piles foundation of bolted bonding method and hook type bonding method, pile foundation is identified to safety due to pile foundation exceed 8.5~21% which more than yield stress of steel pipe pile. As the results of horizontal loading tests, peak load of piles foundation of hook type bonding method has estimated in 41.1tonf and it was exceed about 33% which more than pile foundation of bolted bonding method.

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A Study on the Improvement of Durability Design of Underground RC Structures (RC 지하구조물의 내구성설계 개선에 관한 연구)

  • Im, Jung-Soon;Bahng, Yun-Suk
    • Journal of the Korean Society of Hazard Mitigation
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    • v.7 no.4
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    • pp.13-18
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    • 2007
  • The research was performed to review the design factors which affect the durability of structures. For the study, domestic and foreign literature review were performed on various design criteria. Based on Korean standard specifications, the results showed that the durability of structure as the diameter of reinforcing steel bar becomes smaller and the distance between reinforcing bar is closer than the normal gap. The results were also presented that the minimum required bar cover is 6.6cm to obtain the durability index value. In addition, the maximum limited bar cover was 12cm considering the durability index and the change of increasing value of durability index. In case that there is no specified regulation for the bar cover thickness change, the durability life by neutralization is proportional to the thickness of bar cover.

Effect of Passing Aged Years and Coating Thickness on Corrosion Properties of Reinforcing Steel in Mortar (W/C:0.5) (모르타르(W/C:0.5)내의 철근의 부식 특성에 미치는 재령 년수와 피복두께의 영향)

  • Moon, Kyung-Man;Lee, Sung-Yul;Jeong, Jin-A;Lee, Myeong-Hoon;Baek, Tae-Sil
    • Corrosion Science and Technology
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    • v.14 no.2
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    • pp.99-105
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    • 2015
  • The structures of reinforced concrete have been extensively increased with rapid development of industrial society. Futhermore, these reinforced concretes are easy to expose to severe corrosive environments such as seawater, contaminated water, acid rain and seashore etc.. Thus, corrosion problem of steel bar embedded in concrete is very important in terms of safety and economical point of view. In this study, specimens having six different coating thickness (W/C:0.5) were prepared and immersed in flowing seawater for five years to evaluate the effect of coating thickness and immersion time on corrosion property. The polarization characteristics of these embedded steel bars were investigated using electrochemical methods such as corrosion potential, anodic polarization curve, and impedance. At the 20-day immersion, the corrosion potentials exhibited increasingly nobler values with coating thickness. However, after 5-yr. immersion their values were shifted in the negative direction, and the relationship between corrosion potential and coating thickness was not shown. Although 5-yr. immersion lowered corrosion potential, 5-yr. immersion did not increase corrosion rate. In addition, after 5-yr. immersion, the thinner cover thickness, corrosion current density was decreased with thinning coating thickness. It is due to the fact that ease incorporation of water, dissolved oxygen and chloride ion into a steel surface caused corrosion and hence, leaded to the formation of corrosion product. The corrosion product plays the role as a corrosion barrier and increases polarization resistance. The corrosion probability evaluated depending on corrosion potential may not be a good method for predicting corrosion probability. Hence, the parameters including cover thickness and passed aged years as well as corrosion potential is suggested to be considered for better assessment of corrosion probability of reinforced steel exposed to partially or fully in marine environment for long years.

Relationship Analysis between Half Cell Potential and Open Circuit Potential Considering Temperature Condition (온도 영향을 고려한 RC 구조의 반 전위 및 OCP의 상관성 분석)

  • Yoon, Yong-Sik;Kwon, Seung-Jun
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.10 no.1
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    • pp.124-132
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    • 2022
  • The corrosion potential in concrete varies greatly with exposure and concrete mix conditions. In this study, RC (Reinforcement Concrete) samples were prepared considering cover depth, chloride concentration, and W/C(water to cement) ratio as variables, and HCP(Half Cell Potential) was measured, which evaluated comparative potential between embedded steel and concrete surface. In addition, OCP(Open Circuit Potential) was measured using buried steel and CE(Counter Electrode). Agar and NaOH solution were used as ion exchange materials and Hg/HgO was used for RE(Reference Electrode), which was more sensitive to temperature than HCP. Among the influencing factors, the exposure period and chloride concentration had a relatively greater effect than cover depth and w/c ratio. Additionally, the entire measured HCP and OCP showed a clearly linear relationship with increasing cover depth and w/c ratio. Through multiple regression analysis, the relationship between HCP and OCP was quantified, and an improved correlation was obtained with temperature effect.

Evaluation of Half Cell Potential Measurement in Cracked Concrete Exposed to Salt Spraying Test (염해에 노출된 균열부 콘크리트의 반전위 평가)

  • Kim, Ki-Bum;Park, Ki-Tae;Kwon, Seung-Jun
    • Journal of the Korea Concrete Institute
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    • v.25 no.6
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    • pp.621-630
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    • 2013
  • Several techniques for steel corrosion detection are proposed and HCP (half cell potential) technique is widely adopted for field investigation. If concrete has cracks on surface, steel corrosion is rapidly accelerated due to additional intrusion of chloride and carbon dioxide ions. This study is for an evaluation of HCP in cracked concrete exposed chloride attack. For this work, RC (reinforced concrete) beams are prepared considering 3 w/c ratios (0.35, 0.55, and 0.70) and several cover depths (10~60 mm) and various crack widths of 0.0~1.0 mm are induced. For 35 days, SST (salt spraying test) is performed for corrosion acceleration, and HCP and corrosion length of rebar are evaluated. With increasing crack width, w/c ratios, and decreasing cover depth, HCP measurements increase. HCP evaluation technique is proposed considering the effects of w/c ratios, crack width, and cover depth. Furthermore anti-corrosive cover depths are obtained through Life365 program and the results are compared with those from this study. The results shows relatively big difference in cracked concrete, however provide similar anti-corrosive conditions in sound concrete.

Numerical evaluation of deformation capacity of laced steel-concrete composite beams under monotonic loading

  • Thirumalaiselvi, A.;Anandavalli, N.;Rajasankar, J.;Iyer, Nagesh R.
    • Steel and Composite Structures
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    • v.20 no.1
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    • pp.167-184
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    • 2016
  • This paper presents the details of Finite Element (FE) analysis carried out to determine the limiting deformation capacity and failure mode of Laced Steel-Concrete Composite (LSCC) beam, which was proposed and experimentally studied by the authors earlier (Anandavalli et al. 2012). The present study attains significance due to the fact that LSCC beam is found to possess very high deformation capacity at which range, the conventional laboratory experiments are not capable to perform. FE model combining solid, shell and link elements is adopted for modeling the beam geometry and compatible nonlinear material models are employed in the analysis. Besides these, an interface model is also included to appropriately account for the interaction between concrete and steel elements. As the study aims to quantify the limiting deformation capacity and failure mode of the beam, a suitable damage model is made use of in the analysis. The FE model and results of nonlinear static analysis are validated by comparing with the load-deformation response available from experiment. After validation, the analysis is continued to establish the limiting deformation capacity of the beam, which is assumed to synchronise with tensile strain in bottom cover plate reaching the corresponding ultimate value. The results so found indicate about $20^{\circ}$ support rotation for LSCC beam with $45^{\circ}$ lacing. Results of parametric study indicate that the limiting capacity of the LSCC beam is more influenced by the lacing angle and thickness of the cover plate.

Non Destructive Technique for Steel Corrosion Detection Using Heat Induction and IR Thermography (열유도 장치와 적외선 열화상을 이용한 철근부식탐지 비파괴 평가기법)

  • Kwon, Seung Jun;Park, Sang Soon
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.16 no.2
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    • pp.40-48
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    • 2012
  • Steel corrosion in concrete is a main cause of deterioration and early failure of concrete structures. A novel integration of electromagnetic heat induction and infrared (IR) thermography is proposed for nondestructive detection of steel corrosion in concrete, by taking advantage of the difference in thermal characteristics of corroded and non-corroded steel. This paper focuses on experimental investigation of the concept. An inductive heater is developed to remotely heat the embedded steel from concrete surface, which is integrated with an IR camera. Concrete samples with different cover depths are prepared. Each sample is embedded with a single rebar in the middle, resulting an identical cover depth from the front and the back surfaces, which enable heat induction from one surface and IR imaging from the other simultaneously. The impressed current (IC) method is adopted to induce accelerated corrosion on the rebar. IR video images are recorded during the entire heating and cooling periods. The test results demonstrate a clear difference in thermal characteristics between corroded and non-corroded samples. The corroded sample shows higher rates of heating and cooling than those of the non-corroded sample. This study demonstrates a potential for nondestructive detection of rebar corrosion in concrete.

Confinement Effects of High-Strength Reinforced Concrete Tied Columns

  • Han, Byum-Seok;Shin, Sung-Woo
    • International Journal of Concrete Structures and Materials
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    • v.18 no.2E
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    • pp.133-142
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    • 2006
  • An experimental study was conducted to investigate the effectiveness of transverse steel in reinforced concrete tied columns subjected to monotonically increasing axial compression. Eighteen large-scale columns($260{\times}260{\times}1,200mm$) were tested. Effects of such main variables as concrete compressive strength, configurations of transverse steel, transverse reinforcement ratio, spacing of transverse steel, and spalling of concrete cover were investigated. High-strength concrete columns under concentric axial loads show extremely brittle behavior unless the columns are confined with transverse steel that can provide sufficiently high lateral confinement pressure. A consistent decrease in the deformability of the column test specimens was observed with increasing concrete strength. Test results of this study were compared with existing confinement models of modified Kent-Park, Sheikh-Uzumeri, Mander, and Saatcioglu-Razvi. The comparison indicates many existing models to predict the behavior of confined concrete overestimate or underestimate the ductility of confined concrete.