• Computers and Concrete
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• v.14 no.2
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• pp.109-125
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• 2014

The force transfer mechanism in positive moment continuity details for prestressed concrete girder bridges is investigated in this paper using a three-dimensional detailed finite element model. Positive moment reinforcement in the form of hairpin bars as recommended by the National Cooperative Highway Research Program Report No 519 is incorporated in the model. The cold construction joint that develops at the interface between girder ends and continuity diaphragms is also simulated via contact elements. The model is then subjected to the positive moment and corresponding shear forces that would develop over the service life of the bridge. The stress distribution in the continuity diaphragm and the axial force distribution in the hairpin bars are presented. It was found that due to the asymmetric configuration of the hairpin bars, asymmetric stress distribution develops at the continuity diaphragm, which can be exacerbated by other asymmetric factors such as skewed bridge configurations. It was also observed that when the joint is subjected to a positive moment, the tensile force is transferred from the girder end to the continuity diaphragm only through the hairpin bars due to the lack of contact between the both members at the construction joint. As a result, the stress distribution at girder ends was found to be concentrated around the hairpin bars influence area, rather than be resisted by the entire girder composite section. Finally, the results are used to develop an approach for estimating the cracking moment capacity at girder ends based on a proposed effective moment of inertia.

• Korean Journal of Materials Research
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• v.5 no.2
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• pp.157-168
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• 1995

The effects of Mo additions on the microstructure and the room temperature deformation behavior of polysynthetically twinned (PST) crystals of TiAl were studied in order to get a basic conception for alloying additions on the two-phase TiAl compounds with the lamellar structure. It was found that the Mo additions in TiAl PST crystals increase both the yield stress and tensile elongation to fracture but the increase in yield stress deppend on the angle $\Phi$at which the lamellar boundaries lie from the loading axis. The large difference in yield stress between specimens deformed parallel($\Phi = 0^\circ$)or perpendicular($\Phi = 90^\circ$) to the loading axis and those deformed in intermediate orientations could be plained by the difference in Mo content between the TiAl and the $$Ti_{3}Al$ phases. It was also found that the Mo-doped specimens with intermediate orientation fail by cracking zigzag across to the lamellar boundaris, which is the same fracture mode as that of binary specimens with intermediate orientations tested in vacuum This suggests that Mo atoms are thought to play a role to reduce the environmental embrittlement of binary PST crystals, resulting in increasing the tensile ductility.

• Journal of the Society of Disaster Information
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• v.13 no.2
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• pp.147-154
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• 2017

Duplex stainless steel finds increasing use as an alternative to austenitic stainless steel, particularly where chloride or sulphide stress corrosion cracking is of primary concern, due to the excellent combination of strength and corrosion resistance. During welding, duplex stainless steel does not create the same magnitude or distribution of weld-induced residual stresses as those in welded austenitic stainless steel due to the different physical and mechanical properties between them. In this work, an experimental study on the residual stresses in butt-welded duplex stainless steel is performed utilizing the layering technique to investigate the characteristics of residual stresses in the weldment.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.39-49
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• 2007

The objective of this study was to investigate features of transverse crack occurrence and propagation in continuously reinforced concrete pavement(CRCP) when subjected to environmental loading. The finite element model of CRCP was developed and the element removal method was implemented to predict the crack propagation process. To investigate the effect of the type of environmental loading on the CRCP behavior and cracking aspects, the following three different cases were considered: (1) the temperature gradient between top and bottom of the slab does not vary and the constant temperature drop throughout the depth occurs; (2) the temperature at the slab bottom does not vary and the temperature gradient increases; and (3) the temperature between the mid-depth and the bottom of the slab is the same and does not vary and the temperature at the top decreases. The analysis results showed that the crack occurrence and propagation through the depth of the slab in CRCP were significantly affected by the type of environmental loading. The changes in stress distribution and displacements during the crack occurrence and propagation process could also be investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.269-276
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• 2017

In order to study ultimate flexure behavior of FRP-concrete composite structures which can replace reinforced concrete structures, ABAQUS, a general purpose analysis program, was utilized for numerical nonlinear analysis of structural performance and behavior characteristics of FRP-concrete composite beams. Explicit nonlinear finite element analysis was conducted and the numerical results were compared with previous experiments. Concrete damaged plasticity model was adopted as material properties of concrete and Euro code was used as compressive stress state. Nonlinear analysis was performed for four different types of FRP-concrete composite beams, and ultimate load and cracking pattern was compared and analyzed. The model suggested in this research was able to simulate ultimate load and cracking pattern properly, it is expected to be utilized in study of precise structural and behavioral characteristics of various FRP-concrete composite structures.

• CORROSION AND PROTECTION
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• v.12 no.1
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• pp.30-38
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• 2013

Austenitic stainless steels and Ni-base alloys are widely used as structural materials for major components and piping system in pressurized water reactors (PWRs). These austenitic alloys are known to be susceptible to environmental assisted cracking (EAC), such as environmentally-assisted fatigue (EAF) and primary water stress corrosion cracking (PWSCC) during long-term exposure to PWR primary water environment. In this paper, the current understanding on the phenomena and mechanisms of these EAC are briefly introduced using experimental results and literature review. The mechanisms for EAF and PWSCC for austenitic stainless steels and Ni-base alloys are discussed. Currently, austenitic stainless steels are known to be more susceptible to EAF, while less susceptible to PWSCC than Ni-base alloys. The possible explanations to such behaviors are proposed and discussed in view of the role of hydrogen and internal oxidation.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.581-586
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• 2005

High-performance concrete (HPC), which is particularly sensitive to self-desiccation, is required to be durable even in severe environmental conditions, i.e. costal area, cold district, etc. However, in recent years, some attention was particularly given to cracking sensitivity of high performance concrete at early age. It has been argued and demonstrated experimentally that such concrete undergoes autogenous shrinkage due to self-desiccation at early age under restrained condition, nd, as a result, internal tensile stress may develop, leading to micro cracking and macro cracking. This shrinkage-introduced crack produces a major serviceability problem for concrete structures. One possible method to reduce cracking due to autogenous shrinkage is the addition of expansive additive. Tests conducted by many researches have shown the beneficial effects of addition of expansive additive for reducing the risk of autogenous shrinkage-introduced cracking. However, the research on hydration model of expansion additive has been hardly researched up to now. This paper presents a study of the hydration model of Ettringite-Gypsum type expansive additive. As a result of comparing forecast values with experiment value, proposed model is shown to expressible of hydration of expansive additive.

• Smart Structures and Systems
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• v.1 no.4
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• pp.385-404
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• 2005

The paper presents a model to calculate reinforcement strain using measured crack width in members under applied tension, flexure, and/or shear stress. Crack mapping using a new type of distributed coaxial cable sensors for health monitoring of large-scale civil engineering infrastructure was recently proposed and developed by the authors. This paper shows the results and performance of such sensors mounted on near surface of two flexural beams and a large scale reinforced concrete box girder that was subjected to cyclic combined shear and torsion. The main objectives of this health monitoring study was to correlate the sensor's response to strain in the member, and show that magnitude of the signal's reflection coefficient is related to increases in applied load, repeated cycles, cracking, and reinforcement yielding. The effect of multiple adjacent cracks, and signal loss was also investigated. The results shown in this paper are an important step in using the sensors for crack mapping and determining reinforcement strain for in-situ structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.219-225
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• 2019

Computing low temperature performance of asphalt mixture is one of the important tasks especially for cold regions. It is well known that experimental creep testing work is needed for computation of thermal stress and critical cracking temperature of given asphalt mixture. Thermal stress is conventionally computed through two steps of computation. First, the relaxation modulus is generated thorough the inter-conversion of the experimental creep stiffness data through the application of Hopkins and Hamming's algorithm. Secondly, thermal stress is numerically estimated solving the convolution integral. In this paper, one-step thermal stress computation methodology based on the Laplace transformation is introduced. After the extensive experimental works and comparisons of two different computation approaches, it is found that Laplace transformation application provides reliable computation results compared to the conventional approach: using two step computation with Hopkins and Hamming's algorithm.

• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.29-35
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• 2015

Recent studies to develop Very Large Floating Structure(VLFS) has shown that the construction procedure of the structure needs to acquire precast concrete module connection system using prestressing. However, the loads occurring on water are complex combinations of various condition, so the safe and stable performance of the module joints and bonding materials are key to the success of the construction. Therefore, micro-silica mixed aqua-epoxy development was introduced in Part 1 using a bonding material developed in this study. The performance of the micro-silica mixed aqua-epoxy(MSAE) applied joint of concrete module specimens connected by prestressing tendon was evaluated to verify the usability and safety of the material. RC beam, spliced beam connected by prestressing tendon and MSAE, and continuous prestressed concrete beam were tested for their initial cracking and maximum loads as well as cracking procedure and pattern. The results showed that the MSAE can control the stress concentration effect of the shear key and the crack propagation, and the maximum load capacity of MSAE joint specimens are only 5% less than that of continuous RC specimen. The details of the study are discussed in detail in the paper.