• Steel and Composite Structures
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• v.41 no.5
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• pp.731-746
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• 2021

The purpose of this paper is to investigate the axial bearing capacity and residual properties of steel reinforced recycled aggregate concrete (SRC) column after elevated temperature. A total of 48 SRC columns were designed for the static loading test after elevated temperature. The variables include replacement ratios, designed temperature, target duration, thicknesses of cover concrete, steel ratios and stirrup spacing. From this test, the mass loss ratio and stress load-deformation curve were obtained, and the influence of various parameters on residual bearing capacity were analyzed. ABAQUS was used to calculate the temperature field of specimens, and then got temperature damage distribution on the cross-section concrete. It was shown that increasing of the elevated temperatures leaded to the change of concrete color from smoky-gray to grayish brown and results in reducing the bearing capacity of SRC columns. The axial damage and mechanism of SRC columns were similar to those of reinforced natural aggregate concrete columns at the same temperatures. Finally, the calculation method of axial compressive residual bearing capacity of SRC columns recycled concrete columns after high temperature was reported based on the test results and finite element analysis.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1996.04a
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• pp.202-211
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• 1996

A number of typical type of steel-box pedestrian bridges are constructed in the metropolitan highway or heavy traffic urban area. Although it has the advantage of speedy construction because of its simple structural form and prefabricated erection method, it has been reported that many of these bridges are deteriorated or damaged and thus are in the state such that it would give unsafe and uncomfortable feeling to pedestrians. In the paper, for the realistic assessment of safety and residual earring-capacity of deteriorated and/or damaged steel box pedestrian bridges, an interactive non-linear limit state model are formulated based on the von Mises' combined stress yield criterion. It is demonstrated that the proposal model is effective for the reliability-based safety assessment and residual carrying-capacity evaluation of steel-box pedestrian bridges. In addition, this study suggests an effective and practical field load test method for pedestrian bridges.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.893-902
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• 2005

Reasonable prediction of residual capacity of fire-damaged reinforced columns is important for both the safety measurement and the rehabilitation of the reinforced concrete structures suffered from exposure to extensive fire. In order to predict the residual behavior of fire-damaged reinforced concrete columns, its predictive model must be able to take into account the amount of heat transferred into the column, the level of deterioration of constituent materials and various column geometries. The numerical model presented in this research includes all these factors. The model has been shown to reasonably predict the residual behavior of fire-damaged columns. Parametric studies were performed using this model for the effects of cover thickness, exposure time to fire and column geometries on the residual behavior of reinforced concrete columns. It was found that serious damage on the residual capacity of column resulted from a longer exposure time to fire but only marginal differences from other factors.

• Structural Engineering and Mechanics
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• v.85 no.4
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• pp.531-543
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• 2023

The existing concrete bridges are time-varying working systems, where the maintenance strategy should be planned according to the time-varying performance of the bridge. This work proposes a time-dependent residual capacity assessment procedure, which considers the non-stationary bridge load effects under growing traffic and non-stationary structural deterioration owing to material degradations. Lifetime bridge load effects under traffic growth are predicated by the non-stationary peaks-over-threshold (POT) method using time-dependent generalized Pareto distribution (GPD) models. The non-stationary structural resistance owing to material degradation is modeled by incorporating the Gamma deterioration process and field inspection data. A three-span continuous box-girder bridge is illustrated as an example to demonstrate the application of the proposed procedure, and the time-varying reliability indexes of the bridge girder are calculated. The accuracy of the proposed non-stationary POT method is verified through numerical examples, where the shape parameter of the time-varying GPD model is constant but the threshold and scale parameters are polynomial functions increasing with time. The case study illustrates that the residual flexural capacities show a degradation trend from a slow decrease to an accelerated decrease under traffic growth and material degradation. The reliability index for the mid-span cross-section reduces from 4.91 to 4.55 after being in service for 100 years, and the value is from 4.96 to 4.75 for the mid-support cross-section. The studied bridge shows no safety risk under traffic growth and structural deterioration owing to its high design safety reserve. However, applying the proposed numerical approach to analyze the degradation of residual bearing capacity for bridge structures with low safety reserves is of great significance for management and maintenance.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.2
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• pp.94-101
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• 2010

Composite materials have a higher specific strength and modulus than traditional metallic materials. Additionally, these materials offer new design flexibilities, corrosion and wear resistance, low thermal conductivity and increased fatigue life. These, however, are susceptible to impact damage due to their lack of through-thickness reinforcement and it causes large drops in the load-carrying capacity of a structure. Therefore, the impact damage behavior and subsequently load-carrying capacity of impacted composite materials deserve careful investigation. In this study, the residual strength and impact characteristics of plain-woven CFRP composites with impact damage are investigated under axial tensile test. Impact test was performed using drop weight impact tester. And residual strength behavior by impact was evaluated using the caprino model. Also we evaluated behavior of residual strength by change of mass and size of impactor. Examined change of residual strength by impact energy change through this research and consider impactor diameter in caprino model.

• Journal of Chest Surgery
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• v.13 no.4
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• pp.364-374
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• 1980

Twenty-two patients were selected for evaluation of pre-and postoperative pulmonary function. These patients were performed open cardiac surgery with the extracorporeal circulation from March 1979 to July 1980 at the Department of Thoracic and Cardiovascular Surgery, Kyungbook National University Hospital. Patients were classified with ventricular septal defect 5 cases, atrial septal defect 5 cases, tetralogy of Fallot 5 cases, mitral stenosis 4 cases, rupture of aneurysm of sinus Valsalva 1 case, left atrial myxoma I case, and aortic insufficiency 1 case. The pulmonary function tests were performed and listed: [1] respiratory rate, tidal volume [TV], and minute volume[MV], [2] forced vital capacity [FVC] and forced expiratory volume[FEV 0.5 & FEV 1.0], [3] forced expiratory flow [FEF 200-1200 ml & FEF 25-75%]. [4] Maximal voluntary ventilation [MVV], [5] residual volume [RV] and functional residual capacity[FRC], measured by a helium dilution technique. Respiratory rate increased during the early postoperative days and tidal volume decreased significantly. These values returned to the preoperative levels after postoperative 5-6 days. Minute volume decreased slightly, but essentially unchanged. Preoperative mean values of the forced vital capacity, functional residual capacity and total lung capacity decreased [63.2%, 87.2% & 77.3% predicted, respectively], and early postoperatively these values decreased further [19.6%, 76.0% & 38.0% predicted], but later progressively increased to the preoperative levels. In residual volume, there was no decline in the preoperative mean values [100.9% predicted] and postoperatively the value rather increased [106.3-161.7% predicted]. Forced expiratory volume [FEV 0.5 & FEV 1.0] and forced expiratory flow [FEF 200-1200 ml & FEF 25-75%] also revealed significant declines in the early postoperative period. There was no significant difference in values of the spirometric pulmonary function tests, such as FEF 1.O and FEF 25-75% between successful weaning group [17 cases] extubated within 24 hrs post-operatively and unsuccessful weaning group [5 cases] extubated beyond 24 hrs. Static compliance and airway resistance measured for the two cases during assisted ventilation, however, any information was not obtained. Long term follow-up pulmonary function studies were carried out for 8 cases in 9 months post-operatively. All of the results returned to the pre-operative or to normal predicted levels except FVC, FEV 1.0, and FEF 25-75% those showed minimal declines compared to the pre-operative figures.

• Journal of Korean Society of Steel Construction
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• v.22 no.5
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• pp.399-409
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• 2010

Steel structures are threatened to reduce load-carrying capacity as the cross section is decreased by corrosion. However, there has been no method in definitely evaluating residual load-carrying capacity and the effect of corrosion to the load-carrying capacity of steel. This study evaluated tensile residual load-carrying capacity of corroded steel plates by using tensile tests of specimens, which were selected from the web of temporary structure's main beam. After the surface shapes were measured and tensile tests were examined, the rust of 21 corroded specimens was, first of all, removed using a chemical method. From the tensile test result, which of reference specimens that was picked off at the flange of the same main 13-mm-thick beam and corroded specimens were based, surface geometry and correlation with the reduction of corroded thickness and strain, yield strength or tensile strength was established as constant numbers. Effective thickness of corroded steel with irregular cross sections could be calculated using average residual thickness and standard deviation. The irregular cross sections could be the evaluated tensile strength that is equalized to non-corroded uniform steel's regardless of corrosion. Also, reasonable measuring intervals of residual thickness could be proposed by using this result to apply for executive work.

• Advances in concrete construction
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• v.10 no.4
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• pp.289-299
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• 2020

A reliability analysis of the axial compressive load bearing capacity of postfire reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) sheets was presented. A 3D finite element (FE) model was built for heat transfer analysis using software ABAQUS. Based on the temperature distribution obtained from the FE analysis, the residual axial compressive load bearing capacity of RC columns was worked out using the section method. Formulas for calculating the residual axial compressive load bearing capacity of the columns after fire exposure and the axial compressive load bearing capacity of postfire columns retrofitted with CFRP sheets were developed. Then the Monte Carlo method was used to analyze the reliability of the axial compressive load bearing capacity of the RC columns retrofitted with CFRP sheets using a code developed in MATLAB. The effects of fire exposure time, load ratio, number of CFRP layers, concrete cover thickness, and longitudinal reinforcement ratio on the reliability of the axial compressive load bearing capacity of the columns after fire were investigated. The results show that within 60 minutes of fire exposure time, the reliability index of the RC columns after retrofitting with two layers of CFRPs can meet the requirements of Chinese code GB 50068 (GB 2001) for safety level II. This method is effective and accurate for the reliability analysis of the axial load bearing capacity of postfire reinforced concrete columns retrofitted with CFRP.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.99-106
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• 2018

This study presents experimental investigation on the residual capacity of fire-damaged voided slabs according to loading conditions. In this study, two voided slab specimens were fabricated, and heated by ISO standard fire during 120 minutes with different loading conditions of presence of loading. These specimens were cooled down to room temperature, and the residual capacity of fire-damaged voided slabs was investigated. Based on test results, thermal distribution of voided slab through the depth of concrete sections is different by the loading conditions. The temperature of loaded specimen is rapidly elevated through the whole depth of concrete sections compared to the unloaded specimen. The residual strength of fire-damaged voided slab specimens are 60% and 66% of that of voided slab specimen without fire damage, and the residual stiffness of fire-damaged voided slab specimens decreases by 15%~23% of that of voided slab specimen without fire damage. In case of voided slab specimens subjected ISO standard fire, the loaded specimen shows the decrease of 10% in the residual strength and the decrease of 15% in the residual stiffness compared to the unloaded specimen. It seems to result from higher temperature of bottom reinforcements in the loaded specimen due to the cracks, and more extensive damage on concrete cover of reinforcements by spalling process according to load level.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.385-390
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• 2005

A specimen with residual stress due to welding was analyzed by three-dimensional cohesive zone model. The residual stress distribution was calculated by simulating welding process, and cohesive elements were located along crack propagation planes. Crack growth is possible since two planes of the cohesive element are separated beyond a maximum load carrying capacity. Stress fields around a crack tip are compared for specimens with and without residual stresses. Load-displacement curves and crack growth behaviors are also examined.