• Steel and Composite Structures
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• v.29 no.6
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• pp.689-701
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• 2018

Corrosion of steel reinforcement is a principal cause of deterioration of RC columns. Making these corrosion-damaged columns conform to new safety regulations and functions is a tremendous technological challenge. This study presented an experimental investigation on steel-concrete jacketed corrosion-damaged RC columns. The influences of steel jacket thickness and concrete strength on the enhancement performance of the strengthened specimens were investigated. The results showed that the use of steel-concrete jacketing is efficient since the stub strengthened columns behaved in a more ductile manner. Moreover, the ultimate strength of the corrosion-damaged RC columns is increased by an average of 5.3 times, and the ductility is also significantly improved by the strengthening method. The bearing capacity of the strengthening columns increases with the steel tube thickness increasing, and the strengthening concrete strength has a positive impact on both bearing capacity, whereas a negative influence on the ductility. Subsequently, a numerical model was developed to predict the behavior of the retrofitted columns. The model takes into account corrosion-damage of steel rebar and confining enhancement supplied by the steel tube. Comparative results with the experimental results indicated that the developed numerical model is an effective simulation. Based on extensive verified numerical studies, a design equation was proposed and found to predict well the ultimate eccentric strength of the strengthened columns.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.3
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• pp.263-272
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• 2019

The aim of this study is to develop a rapid calculation technique of the residual strength in order to prevent sequential events under grounding accidents. Very Large Crude-Oil Carrier (VLCC), Suezmax, and Aframax double hull oil tankers carrying large quantities of crude oil were selected for target structures. The rock geometries are chosen from the published regulation by Marine Pollution Treaty (MARPOL) of the International Maritime Organization (IMO). Oceanic rocks as the most frequently encountered obstruction with ships are applied in this work. Damage condition was predicted using ALPS/HULL program based on grounding scenario with selected parameters, i.e. depth of penetration, damage location and tanker type. The results of the scenarios are quantified to form an empirical formula which can evaluate the residual strength. The proposed formula is validated by applying a series of random grounding scenarios.

• Structural Engineering and Mechanics
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• v.86 no.5
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• pp.663-671
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• 2023

Freeze-thaw cycles induce strength loss at the frozen soil-concrete interface and deterioration of bonding, which causes construction engineering problems. To clarify the deterioration characteristics of the interface under the freeze-thaw cycle, a frozen soil-concrete sample was used as the research object, an interface scanning electron microscope test under the freeze-thaw cycle was carried out to identify the micro index information, and an interface shear test was carried out to explore the loss law of interface shear strength under the freeze-thaw cycle. The results showed that the integrity of the interface was destroyed, and the pore number and pore size of the interface increased significantly with the number of freeze-thaw cycles. The connection form gradually deteriorates from surface-to-surface contact to point-to-surface contact and point-to-point contact, and the interfacial shear strength decreases the most at 0-3 freeze-thaw cycles, with small decreases from to 3-8 cycles. After 12 freeze-thaw cycles, the interfacial shear strength tends to be stable, and shear the failure occurs internally in the soil.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.655-664
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• 2007

The inherent characteristic of concrete tensile cracks, directional nonlocal crack damage, causes so-called rotating tensile crack damage and softening of compressive strength. In the present study, a plasticity model was developed to describe the behavior of reinforced concrete planar members In tension-compression. To describe the effect of directional nonlocal crack damage, the concept of microplane model was combined with the plasticity model. Unlike existing models, in the proposed model, softening of compressive strength as well as the tensile crack damage were defined by the directional nonlocal crack damage. Once a tensile cracking occurs, the microplanes of concrete are affected by the nonlocal crack damage. In the microplanes, microscopic tension and compression failure surfaces are calculated. By integrating the microscopic failure surfaces, the macroscopic failure surface is calculated. The proposed model was implemented to finite element analysis, and it was verified by comparisons with the results of existing shear panel tests.

• Journal of the Korean Institute of Gas
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• v.3 no.3 s.8
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• pp.45-50
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• 1999

The LPG refueling station's explosion at Bucheon city was a major accident which with rare frequency of occurrence and large damage effect. Therefore, to prevent similar accident in the future from LPG charging stations which located in urban area. It needs to identify the damage effects of such facilities by comparing theoretically quantities risk and actual damage. The BLEVE effects from the accident showed similar damage effect in case of heat flux, however, the overpressure level reflected at the reduced distance by $15\%$. The structure damage to the near by area showed comparatively large heat radiation damage to the concrete structure strength and shape changes through heat flux while the overpressure effect was small.

• Structural Monitoring and Maintenance
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• v.2 no.3
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• pp.269-282
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• 2015

Civil structures should be designed with the lowest cost and longest lifetime possible and without service failure. The efficient and sustainable use of materials in building design and construction has always been at the forefront for civil engineers and environmentalists. Timber is one of the best contenders for these purposes particularly in terms of aesthetics; fire protection; strength-to-weight ratio; acoustic properties and seismic resistance. In recent years, timber has been used in commercial and taller buildings due to these significant advantages. It should be noted that, since the launch of the modern building standards and codes, a number of different structural systems have been developed to stabilise steel or concrete multistorey buildings, however, structural analysis of high-rise and multi-storey timber frame buildings subjected to lateral loads has not yet been fully understood. Additionally, timber degradation can occur as a result of biological decay of the elements and overloading that can result in structural damage. In such structures, the deficient members and joints require strengthening in order to satisfy new code requirements; determine acceptable level of safety; and avoid brittle failure following earthquake actions. This paper investigates performance assessment and damage assessment of older multi-storey timber buildings. One approach is to retrofit the beams in order to increase the ductility of the frame. Experimental studies indicate that Sprayed Fibre Reinforced Polymer (SFRP) repairing/retrofitting not only updates the integrity of the joint, but also increases its strength; stiffness; and ductility in such a way that the joint remains elastic. Non-linear finite element analysis ('pushover') is carried out to study the behaviour of the structure subjected to simulated gravity and lateral loads. A new global index is re-assessed for damage assessment of the plain and SFRP-retrofitted frames using capacity curves obtained from pushover analysis. This study shows that the proposed method is suitable for structural damage assessment of aged timber buildings. Also SFRP retrofitting can potentially improve the performance and load carrying capacity of the structure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.4
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• pp.769-777
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• 2015

In this study, the rheological models were introduced and developed to reflect rate dependent tensile behaviour of concrete. In general, mechanical properties(e.g. strength, elasticity, and fracture energy) of concrete are increased under high loading rates. The strength of concrete shows high rate dependency among its mechanical properties, and the tensile strength has higher rate dependency than the compressional strength. To simulate the rate dependency of concrete, original spring set of RBSN(Rigid-Body- Spring-Network) model was adjusted with viscous and friction units(e.g. dashpot and Coulomb friction component). Three types of models( 1) visco-elastic, 2) visco-plastic, and 3) visco-elasto- plastic damage models) are considered, and the constitutive relationships for the models are derived. For validation purpose, direct tensile test were simulated, and characteristics of the three different rheological models were compared with experimental stress-strain responses. Simulation result of the developed visco-elasto-plastic damage(VEPD) model demonstrated well describing and fitting with experimental results.

• Geomechanics and Engineering
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• v.14 no.4
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• pp.307-314
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• 2018

Strength of loess that experienced cyclic freeze and thaw is of great significance for evaluating stability of slopes and foundations in loess regions. This paper takes the frequently encountered loess in the Northwestern China as the study object and carried out three kinds of laboratory tests including freeze-thaw test, direct shear test and SEM test to investigate the strength behaviors of loess after cyclic freeze and thaw, and the correlation with meso-level changes in soil structure. Results show that for loess specimens at four dry densities, the cohesion decreases with freeze-thaw cycles until a residual value is reached and thus an exponential equation is proposed. Besides, little change in the angle of internal friction was observed as freeze-thaw proceeds. This may depend on the varying of soil structure, based on which a clue can be found from the surface morphology and mesoscopic scanning of loess specimens. Clearly we observed significant changes in surface morphology of loess and it tends to aggravate at higher water contents or more cycles of freeze and thaw. Moreover, freeze-thaw cycling leads to obvious changes in the meso-structure of loess including lowering the particle aggregates and increasing both the proportion of fine particles and porosity area ratio. A damage variable dependent on the ratio of porosity area is introduced based on the continuum damage mechanics and its correlation with cohesion is discussed.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.4
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• pp.182-190
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• 2020

This study reports a series of drop impact tests performed to generate denting damages on stiffened plates and their residual ultimate strength tests under axial compression. The models were fabricated of general structural steel, and each model has six longitudinal stiffeners and two transverse frames. Among six fabricated models, four were damaged, and two were left intact for reference. To investigate the effects of collision velocity and impact location on the extent of damage, the drop height and the impact location were changed in each impact test. After performing the collision tests, the ultimate axial compression tests were conducted to investigate the residual strengths of the damaged stiffened plates. Finite element analyses were also carried out using a commercial package Abaqus/Explicit. The material properties obtained from a quasi-static tensile tests were used, and the strain-rate sensitivity was considered. After importing the collision simulation results, the ultimate strength calculations were carried out and their results were compared with the test data for the validation of the finite element analysis method.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.109-115
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• 2012

In order to evaluate the effect of structural degradation of a GFRP composite bogie frame due to ballast-flying phenomena, the impact test and residual compression test after impact was conducted for glass fiber/epoxy 4-harness satin woven laminate composites applied to skin part of a bogie frame. The impact test was performed using a instrumented impact testing system with energy levels of 5J, 10J, and 20J, and the impactor was designed to have various ballast shapes such as sphere, cube, and cone to consider the ballasted track environments. The residual compression strength was tested to evaluate the degradation of mechanical properties of impact-damaged laminate composites. The results showed that the damage area and the degradation of residual compressive strength after impact for laminate composites was increased with increase of impact energy for all ballast shapes, and was particularly most influenced by ballast shape of cone.