• Journal of the Korea institute for structural maintenance and inspection
• /
• v.12 no.2
• /
• pp.49-58
• /
• 2008

Generally, steel corrosion occurs in concrete structures due to carbonation in down-town area and underground site and it propagates to degradation of structural performance. In general diagnosis and inspection, only carbonation depth in sound concrete is evaluated but unsound concrete such as joint and cracked area may occur easily in a concrete member due to construction process. In this study, field survey of carbonation for RC columns in down-town area is performed and carbonation depth in joint and cracked concrete including sound area is measured. Probability of durable failure with time is calculated through probability variables such as concrete cover depth and carbonation depth which are obtained from field survey. In addition, service life of the structures is predicted based on the intended probability of durable failure in domestic concrete specification. It is evaluated that in a RC column, various service life is predicted due to local condition and it is rapidly decreased with insufficient cover depth and growth of crack width. It is also evaluated that obtaining cover depth and quality of concrete is very important because the probability of durable failure is closely related with C.O.V. of cover depth.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.14 no.4
• /
• pp.126-132
• /
• 2010

Carbonation is the results of the interaction of carbon dioxide gas in the atmosphere with the alkaline hydroxides in the concrete. Reinforced steel corrosion due to concrete carbonation is one of main factors on the decrease in durability of RC structure. This study investigates the influence of carbonation on the bridges under various environment condition and quantifies the effect of carbonation various domestic field data. The failure probability of durability is evaluated on the basis of reliability concept. In addition, service life of the structures is predicted based on the intended probability of durable failure in domestic concrete specification. According to experimental results of the carbonation depth, the carbonation depth increased with structural age. It is analyzed that carbonation velocity of the structures under urban area and sea condition is 1.6-1.9 times faster than the river condition. Service life of the bridges under urban area and sea condition is decreased about 2.4-3.3 times than river condition.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.5
• /
• pp.67-74
• /
• 2015

RC (Reinforced Concrete) structures are considered as cost-benefit and durable however performances of structural safety and durability are degraded due to steel corrosion. Service life in RC structure is differently evaluated due to different local environmental conditions even if it is exposed to the same chloride attack. In the paper, 25 concrete cores from field investigation are obtained from 4 RC columns with duration of 3.5~4.5 years exposed to sea water. Through total chloride content measurement, surface chloride contents and apparent diffusion coefficients are evaluated. Service life of the target structure is estimated through deterministic method based on Fick's $2^{nd}$ Law and probabilistic method based on durability failure probability, respectively. Probability method is evaluated to be more conservative and relatively decreased service life is evaluated in tidal zone and splash zone over 40.0 m. Chloride penetration behavior with coring location from sea level and the present limitations of durability design method are investigated in the paper.

• Journal of Chest Surgery
• /
• v.19 no.1
• /
• pp.83-91
• /
• 1986

The Carpentier-Edwards porcine xenograft valve was used in 21 patients at Seoul National University Hospital during the period between 1977 and 1979. Twenty-four Carpentier-Edwards valves were implanted along with 2 others. Three patients died within 30 days of operation, an operative mortality rate of 14.3%. Eighteen early survivors were followed up for a total 67.5 patient-years [mean, 45.0$\pm$32.0 months]. There were 2 late deaths with a linealized late mortality rate of 2.96%/patient-year; one died from cerebral bleeding [1.48% bleeding/patient-year] and the other from prosthetic valve endocarditis [1, 48% endocarditis/patient-year]. There was no case of thromboembolism. Two patients developed mitral regurgitation [2.96% failure/patient-year]. Symptomatic improvement was excellent. The actuarial survival rate and the probability of freedom from overall valve failure were 75.3$\pm$9.6% and 80.7$\pm$12.9% at 9 years after surgery respectively. During the period from October, 1968, through June, 1985, 1, 190 substitute heart valves were used in a total of 967 patients at Seoul National University Hospital; of which, 90.9% were either porcine aortic or bovine pericardial xenograft valves. For the evaluation of the xenograft tissue valves, the consecutive patients with lonescu-Shiley valve in the mitral, aortic and both positions, Angell-Shiley valve and Carpentier-Edwards valve were recently studied on the clinical ground. They were 531 patients, and 643 xenograft valves were used. The operative mortality rate was 6.97% and a linealized late mortality rate 2.94%/patient-year. A total of 490 early survivors were followed up for 917.6 patient-years [mean, 22.5 months], and 70% of patients completed the follow-up. The linealized incidences of complications were: 2.29% emboli/patient-year, 1.98% bleeding/patient-year, 1.20% endocarditis/patient-year, and 3.49% failure/patient-year. These clinical resutls are fully comparable with those in the major reports. The durability of the glutaraldehydepreserved xenograft heart valves remains as a great concern and a continuing debate, expecially for the group of patients in the pediatric age. The need of more durable material for the improved tissue valves was also discussed.

• Journal of Chest Surgery
• /
• v.19 no.1
• /
• pp.75-82
• /
• 1986

The use of the Angell-Shiley porcine xenograft cardiac valve was limited in number at Seoul National University Hospital chiefly because of the cessation of supply from the manufacturer, Forty-eight Angell-Shiley valves along with the 5 other mechanical or tissue valves were used in 46 patients during the period from 1977 to 1980, and a total of consecutive cases was studied for their early and long-term clinical results. The operative mortality rate was 4.3%; no death after single and 2 deaths after double valve replacement within 30 days of surgery. The 44 early survivors were followed up for a total of 171.6 patient-years and a mean of 46.8$\pm$31.1 months. Four died during the follow-up period with a linealized late mortality rate of 2.33%/patient-year. Four patients had experienced 5 episodes of thromboembolism and one died; a linealized incidence of 2.91% emboli/patient-year. A single case each had a bleeding complication related to the anticoagulants, 0.58% bleeding/patient-year, and prosthetic valve endocarditis, 0.58% endocarditis/patient-year. The clinical improvement was excellent by 70% of the survivors having no cardiac symptoms at the end of the follow-up. The actuarial survival rates were 89.9$\pm$4.9% at 5 years and 69.2$\pm$15.0% at 9 years after surgery. The probabilities of freedom from thromboembolic complication were 92.3$\pm$5.5% and 80.9$\pm$9.0% at 5 and 9 years after surgery. And, the probability of freedom from overall valve failure was 83.4$\pm$6.3% at 5 years and it declined sharply down to 55.9$\pm$22.2% at 9th year of the follow-up. These results are comparable with those in the major reports, except a more accelerated and time-related increases in valve failure after 5 or 6 years after operation with the Angell-Shiley valve. The durability of the xenograft tissue valve remains as the most important debate and the need of more durable tissue valves was also discussed.