• Title/Summary/Keyword: Thermal Cracking

Search Result 370, Processing Time 0.025 seconds

In-Site Measurement and Analysis of Heat of Hydration for Kumdang Bridge (금당교 교대기초 수화열 계측 및 해석)

  • 안상구;이필구;차수원
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • 2001.11a
    • /
    • pp.363-368
    • /
    • 2001
  • Abutments in Kumdang bridge are massive concrete structures of which total height is l0m, length is 30m, and width is 7m. Therefore, there is every probability that early age thermal cracking such as hydration heat occur. We measure heat of hydration, strains of rebar, and stresses of concrete abutment during construction. Using analysis of measuring data, we examine thermal stresses, and make use of results as method which control thermal cracking. Finally, we develope thermal stress analysis program which have pre/post processor to be easy of accessing and the usefulness of that is estimated through comparison of results.

  • PDF

Sensitivity Study of Thermal Stresses in Mass Concrete Structures (매스 콘크리트 구조물의 수화열 및 응력 해석의 민감도 분석)

  • 차수원;김광수
    • Journal of the Korean Society of Safety
    • /
    • v.16 no.4
    • /
    • pp.160-167
    • /
    • 2001
  • Cracking in connote structures is one of the main issues of structural design next to ensuring the load-bearing capacity. Thermal analysis is used to prevent thermal mucking, but concrete properties are uncertain variable, and analysis results have uncertainty, too. In this study, sensitivity analysis is performed to investigate the effect of conductivity, specific heal and pouring temperature. The results show that lower conductivity and higher specific heat increase the maximum temperature and maximum tensile stress. The structure with internal restraint is mostly influenced by the change of conductivity and specific heat.

  • PDF

Risk Evaluation of Longitudinal Cracking in Concrete Deck of Box Girder Bridge (콘크리트 박스거더 교량 바닥판의 종방향 균열 위험성 정가)

  • Kim, Eui-Sung
    • Journal of the Korean Society of Safety
    • /
    • v.23 no.5
    • /
    • pp.84-90
    • /
    • 2008
  • The occurrence of longitudinal cracking in concrete deck of box girder bridge is affected by many factors, but the most important factors are the shrinkage and thermal gradient of deck slabs. In this study, therefore, the tensile stresses at the bottom of deck were calculated from the experimental data(autogeneous shrinkage, drying shrinkage, and thermal gradient of deck slab). Also, the possibility of longitudinal cracks at bottom of deck was estimated. For this purpose, full-scale box girder segments have been fabricated and tested. The thermal gradients and shrinkage strains of deck slabs were measured after placement of concrete. Also, analytic program was conducted for the evaluation of longitudinal cracking in bridge deck considering differential shrinkage induced from non-uniform moisture distributions in concrete.

THE CHARACTERISTICS OF HEAT TRANSFER AND CHEMICAL REACTION FOR THERMAL CRACKING OF ETHANE IN TUBULAR REACTOR (에탄 열분해 반응이 동반된 관형 반응기에서의 열전달 및 화학반응 특성 연구)

  • Shin, C.Y.;Ahn, J.
    • Journal of computational fluids engineering
    • /
    • v.21 no.1
    • /
    • pp.43-49
    • /
    • 2016
  • Thermal cracking is commonly modeled as plug flow reaction, neglecting the lateral gradients present. In this paper, 2-dimensional computational fluid dynamics including turbulence model and molecular reaction scheme are carried out. This simulation is solved by means of coupled implicit scheme for stable convergence of solution. The reactor is modeled as an isothermal tube, whose length is 1.2 m and radius is 0.01 m, respectively. At first, The radial profile of velocity and temperature at each point are predicted in its condition. Then the bulk temperature and conversion curve along the axial direction are compared with other published data to identify the reason why discussed variations of properties are important to product yield. Finally, defining a new non-dimensional number, Effect of interaction with turbulence, heat transfer and chemical reaction are discussed for design of thermal cracking furnace.

Thermal Cracking Control of Mass Concrete by Vertical Pipe Cooling Method (연직파이프쿨링 공법에 의한 매스콘크리트 온도균열 제어)

  • Seo, Tae-Seok;Lim, Chang-Keun;Cho, Yun-Gu
    • Journal of the Korean Recycled Construction Resources Institute
    • /
    • v.2 no.3
    • /
    • pp.233-238
    • /
    • 2014
  • In case of the slender mass concrete like attached wall, retaining wall and bridge tower, the low heat cement and the control joint are mainly used for thermal cracking control. However, even if these cracking control methods are considered, it is impossible to control thermal cracks perfectly, because the external restraint is largely in these mass concrete. Because these cracks occurring in slender mass concrete members almost penetrate concrete member, the special cracking control is demanded in these mass concretes. The vertical pipe cooling method improving existing pipe cooling method was developed for the active thermal cracking control of slender mass concrete, and applied at the field attached wall. In results, the maximum temperature dropped more than $10^{\circ}C$ by vertical pipe cooling method, and the cracks decreased about more than 50%.

Mechanism of Hot Cracking in High Strength Al Welds (고강도 알루미늄합금 용접부의 고온균열 Mechanism)

  • 이창희;조성석
    • Journal of Welding and Joining
    • /
    • v.14 no.3
    • /
    • pp.93-104
    • /
    • 1996
  • This study evaluated relative hot cracking susceptibility of commercial aluminum alloy welds, and then suggested possible mechanisms operated in the weld fusion zone and in the heat affected zone based on the observed cracking morphologies, fractography and microstructural features. The fusion zone solidification cracking was found to be mainly due to a microsegregation of Cu, Si, and Mg in grain boundaries, while liquation cracking in the HAZ was by the incipient melting of the segregated grain boundaries and the consitutional liquation of large aging precipitates and intermetallic compounds in the partially melted zone adjacent to the fusion line which experienced a rapid thermal excursion during welding.

  • PDF

Analysis of Heat of Hydration for Hyungsan Bridge (형산큰다리 교각기초 콘크리트의 수화열 해석 및 적용)

  • 안동근;김명모
    • Proceedings of the Korea Concrete Institute Conference
    • /
    • 2001.05a
    • /
    • pp.715-722
    • /
    • 2001
  • The main purpose of this study is to evaluate early age thermal stresses and to estimate the risk of thermal cracking in the footings of Hyungsan bridge. In this study, stress analyses are performed for several construction stages using the computation of temperature distributions. The stress analysis results show that, not using the embedded pipe cooling, placing the concrete at once for each footings may cause sever thermal cracking. So, the structures should be constructed with one horizontal construction joint. Then the height of each lifts were determined to be 1.50 meters. Using various time intervals between lifts, temperature and stress.

  • PDF

Effects of a Lift Height on the Thermal Cracking in Wall Structures

  • Kim, Sang-Chel
    • KCI Concrete Journal
    • /
    • v.12 no.1
    • /
    • pp.47-56
    • /
    • 2000
  • Once a structure fabricated with mass concrete is in a form of wall such as retaining wall, side walls of a concrete caisson and so on, cracks induced by hydration heat have been known to be governed by exterior restraints which are mainly related to the boundary conditions of the structure. However, it is thought that the degree of restraints can be alleviated considerably only if a lift height of concrete placement or a panel size of the wall is selected properly before construction. As a way of minimizing thermal cracking commonly observed in massive wall-typed structure, this study aimed at evaluating effects of geometrical configuration on the temperature rise and thermal stress through parametric study. Evaluation of the effect was also performed for cement types using anti-sulphate cement, blast furnace slag cement and cement blended with two mineral admixture and one ordinary Portland Cement. so called ternary blended cement. As a result of analytical study, it was found that a lift height of concrete placement is the most important factor in controlling thermal cracking in massive wall, and the increase of a lift height is not always positive to the crack occurrence as not expected.

  • PDF

Finite element analysis of concrete cracking at early age

  • Aurich, Mauren;Filho, Americo Campos;Bittencourt, Tulio Nogueira;Shah, Surendra P.
    • Structural Engineering and Mechanics
    • /
    • v.37 no.5
    • /
    • pp.459-473
    • /
    • 2011
  • The study of the early age concrete properties is becoming more important, as the thermal effects and the shrinkage, even in the first hours, could generate cracks, increasing the permeability of the structure and being able to induce problems of durability and functionality in the same ones. The detailed study of the stresses development during the construction process can be decisive to keep low the cracking levels. In this work a computational model, based on the finite element method, was implemented to simulate the early age concrete behavior and, specially, the evaluation of the cracking risk. The finite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, moisture diffusion and mechanical which occur at the first days after the concrete cast. The developed software results were compared with experimental values found in the literature, demonstrating an excellent approach for all the implemented analysis.

Diagnosis of Crack Occurrence of Very-Early Strength Latex-Modified Concretes through Field Tests (현장실험을 통한 VES-LMC 균열발생 원인분석)

  • Choi, Pan-Gil;Lee, Bong-Hak
    • Journal of Industrial Technology
    • /
    • v.26 no.A
    • /
    • pp.139-146
    • /
    • 2006
  • Many concrete bridge decks develop transverse cracking shortly after construction. These cracks accelerate corrosion of reinforcing steel and lead to concrete deterioration, damage to components beneath the deck, unsightly appearance. These cracks shorten the service life and increase maintenance costs of bridge structures. In this study, VES-LMC overlay, which provides the same benefits as a conventional overlay, is designed to cure very quickly. Although the materials for VES overlays are more expensive, the cost is more than offset by the savings on traffic control and work zone safety measures. Otherwise, reaction of hydration occurs very rapidly in beginning step(concrete placing). As a results, thermal cracking can be occur by thermal stress in accordance with hydration-heat The purpose of this study was to estimate diagnosis of crack occurrence of VES-LMC through field tests at early-age.

  • PDF