• Journal of the Korea Institute of Building Construction
• /
• v.18 no.4
• /
• pp.329-335
• /
• 2018

The objective of this study is to develop a mortar mixture with high workability and adhesive strength for section jacketing in seismic strengthening technology of existing concrete structures. To achieve targeted requirements of the mortars (initial flow exceeding 200 mm, compressive strength of 30MPa, and adhesive strength exceeding 1MPa), step-by-step tests were conducted under the variation of the following mixture parameters: water-to-binder ratio, sand-to-binder ratio, polymer-to-binder ratio, dosage of viscosity agent, and content of ultra-rapid-hardening cement. The adhesive strength of the mortars was also estimated with respect to the various surface treatment states of existing concrete. Based on the test results, the mortar mixture with the polymer-to-binder ratio of 10% and the content of ultra-rapid-hardening cement of 5% can be recommended for the section jacketing materials. The recommended mortar mixture satisfied the targeted requirements as follows: initial flow of 220 mm, high-early strength gain, 28-day compressive strength of 35MPa, and adhesive strength exceeding 1.2MPa.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.765-768
• /
• 2008

The prevent methods of Alkali-Silica Reaction (ASR) are studying after the failure cases by ASR were reported in Korea. When ASR failure is causing to the step of maintenance, the available repair methods were rarely studied in the World. In this study, premixed fly ash cement was applied to prevent ASR in the concrete pavement. The ratio of fly ash and cement is 20 percent and 80 percent by weight of total cementious material. The construction performance of premixed fly ash cementious concrete pavement was studied that the application is verify to performance collected data during the constructing in the field. The freeze-thaw test was studied to verify durability of the premixed fly ash cementious material made specimen in the laboratory. The results show that construction performance and durability are well condition in this test section and freeze-thaw test.

• Computers and Concrete
• /
• v.19 no.3
• /
• pp.233-241
• /
• 2017

During the last two decades, CFRP have been extensively used for repair and rehabilitation of existing structures as well as in new construction applications. For rehabilitation purposes CFRP are currently used to increase the load and the energy absorption capacities and also the shear strength of concrete columns. Thus, the effect of CFRP confinement on the strength and deformation capacity of concrete columns has been extensively studied. However, the majority of such studies consider empirical relationships based on correlation analysis due to the fact that until today there is no general law describing such a hugely complex phenomenon. Moreover, these studies have been focused on the performance of circular cross section columns and the data available for square or rectangular cross sections are still scarce. Therefore, the existing relationships may not be sufficiently accurate to provide satisfactory results. That is why intelligent models with the ability to learn from examples can and must be tested, trying to evaluate their accuracy for composite compressive strength prediction. In this study the forecasting of wrapped CFRP confined concrete strength was carried out using different Data Mining techniques to predict CFRP confined concrete compressive strength taking into account the specimens' cross section: circular or rectangular. Based on the results obtained, CFRP confined concrete compressive strength can be accurately predicted for circular cross sections using SVM with five and six input parameters without spending too much time. The results for rectangular sections were not as good as those obtained for circular sections. It seems that the prediction can only be obtained with reasonable accuracy for certain values of the lateral confinement coefficient due to less efficiency of lateral confinement for rectangular cross sections.

• Steel and Composite Structures
• /
• v.8 no.1
• /
• pp.1-18
• /
• 2008

Observations from experiments and real fire indicate that restrained steel beams have better fire-resistant capability than isolated beams. Due to the effects of restraints, a steel beam in fire condition can undergo very large deflections and the run away damage may be avoided. In addition, axial forces will be induced with temperature increasing and play an important role on the behaviour of the restrained beam. The factors influencing the behavior of a restrained beam subjected to fire include the stiffness of axial and rotational restraints, the load type on the beam and the distribution of temperature in the cross-section of the beam, etc. In this paper, a simplified model is proposed to analyze the performance of restrained steel beams in fire condition. Based on an assumption of the deflection curve of the beam, the axial force, together with the strain and stress distributions in the beam, can be determined. By integrating the stress, the combined moment and force in the cross-section of the beam can be obtained. Then, through substituting the moment and axial force into the equilibrium equation, the behavior of the restrained beam in fire condition can be worked out. Furthermore, for the safety evaluation and repair after a fire, the behaviour of restrained beams during cooling should be understood. For a restrained beam experiencing very high temperatures, the strength of the steel will recover when temperature decreases, but the contraction force, which is produced by thermal contraction, will aggravate the tensile stresses in the beam. In this paper, the behaviour of the restrained beam in cooling phase is analyzed, and the effect of the contraction force is discussed.

• Archives of Plastic Surgery
• /
• v.40 no.1
• /
• pp.44-50
• /
• 2013

Background The aim of this investigation was to systematically review the current literature to provide the best data for indications, outcomes, survival, and complication rates of pedicled propeller perforator flaps for upper body defects. Methods A comprehensive literature review for articles published from January 1991 to December 2011 was performed using the PubMed, Medline, and Cochrane Databases. Articles without available full-text, single case reports or papers with excessive missing data were excluded. Papers reporting pedicle-perforator (propeller) flaps used for lower extremity reconstruction were excluded from meta-analysis. Results From the initial 1,736 studies our search yielded, 343 studies qualified for the second stage of selection. Of 117 full-text reports screened, 41 studies, met the definitive inclusion and exclusion criteria. Of the selected 41 articles, 26 were case series, original papers or retrospective reviews and were included, whereas 15 were case report papers and therefore were excluded. Two hundred ninety-five propeller flaps were reported to have been used in a total of 283 patients. Indications include repair of trauma-induced injuries, post-trauma revision surgery, cancer resection, chronic infection, pressure sores, and chronic ulcers with a major complication rate (3.3%) comparable to that of free flaps. No specific exclusion criteria for the procedure were presented in the studies reviewed. Conclusions Pedicled propeller flaps are a versatile and safe reconstructive option that are easy and quick to raise and that provide unlimited clinical solutions because of the theoretical possibility of harvesting them based on any perforator chosen among those classified in the body.

• International Journal of Highway Engineering
• /
• v.14 no.2
• /
• pp.1-10
• /
• 2012

As old concrete pavements of over 20years in age are increasing in expressways, the repair and rehabilitation of concrete pavement have become an important issue. Although asphalt overlay is widely used as an alternative to rehabilitate the old concrete pavement, problems due to infiltrated water such as reflection crack and pothole are imposing a very serious threat to its performance. This study proposes waterproof membrane as a solution to minimize the damage due to reflection crack and infiltrated water, and accelerated pavement testing was carried out for the performance comparison of composite pavement with waterproof membrane and ordinary tack coating. The experiment used water spraying to simulate rainfall, and the behavior and moisture resistance characteristics of overlay pavement were analyzed. The experimental result indicated that the strain pattern of waterproof membrane section differed from ordinary tack coating section because waterproof membrane caused the asphalt pavement and concrete pavement to move together. Additionally, since waterproof membrane minimized the infiltration of water and delayed the occurrence of reflection crack by about 70% in comparison to ordinary tack coating method. Moreover, the damage due to infiltrated water also decreased.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.3
• /
• pp.73-82
• /
• 2015

In evaluating lateral behavior on the seismic and wind load, the purpose of sensitivity analysis is to find critical variables and to identify characteristic response with variability of variables. The sensitivity analysis is very important in structural diagnosis, repair and reinforcement field. This study investigates the sensitivity by linear static analysis applying the TDA method in changing angles of diagrid braces on the same height structures. In case of mid rise model, under the seismic load, the brace member is determined as a major variable at $58^{\circ}$ but a high rise model, under the wind load, has the brace member as a major variable at $67.4^{\circ}$. In addition, location of critical sensitivity on the mid rise model is distributed over middle section, while it is distributed lower section on the high rise model.

• International journal of steel structures
• /
• v.18 no.4
• /
• pp.1336-1349
• /
• 2018

Generally, a precast prestressed concrete (PSC) beam is used as girders for short-to-medium span (less than 30 m) bridges due to the advantages of simple design and construction, reduction of construction budget, maintenance convenience. In order to increase the span length beyond 50 m of precast PSC girder, PSC hollow box girder with unbonded prestressed H-type steel beam placed at the compressive region is proposed. The unbonded compressive prestressing in the H-type steel beams in the girder is made to recover plastic deflection of PSC girder when the pre-stressing is released. Also, the H-steel beams allow minimization of depth-to-length ratio of the girder by reducing the compressive region of the cross-section, thereby reducing the weight of the girder. A quasi-static 3-point bending test with 4 different loading steps is performed to verify safety and plastic deflection recovery of the girder. The experimental results showed that the maximum applied load exceeded the maximum design load and most of the plastic deflection was recovered when the compressive prestressing of H-type steel beams is released. Also using prestressed H-type steel as compression reinforcements in the upper part of cross section, repair and restoration difficulty and cost of PSC girders should be significantly reduced. The study result and analysis are discussed in detail in the paper.

• Journal of the Korean Geotechnical Society
• /
• v.25 no.4
• /
• pp.69-75
• /
• 2009

The load distribution and deformation of pile-bent structures are investigated using a numerical study. A numerical analysis that takes into account the effects of varying cross-sectional area was performed for different pier diameters, loading steps, and soil conditions. Through the comparison study, it is shown that the location of maximum bending moment is almost the same per each loading step, regardless of varying cross-sections. However, the member force (i.e., stress of pile material) has the largest value at the ground surface when the cross-section is changed. Based on the results obtained, it is found that the location of maximum member force influences highly the behavior of pile-bent structure with varying cross-sections for repair works.

• Journal of Gastric Cancer
• /
• v.13 no.1
• /
• pp.65-68
• /
• 2013

Gastric carcinoma rarely presents as a perforation, but when it does, is perceived as advanced disease. The majority of such perforations are Stage III/IV disease. A T1 gastric carcinoma has never been reported to perforate spontaneously in English literature. We present a 56 year-old Chinese male who presented with a perforated gastric ulcer. Intra-operatively, there was no suspicion of malignancy. At operation, an open omental patch repair was performed. Post-operative endoscopy revealed a macroscopic Type 0~III tumour and from the ulcer edge biopsy was reported as adenocarcinoma. Subsequently, the patient underwent open subtotal gastrectomy and formal D2 lymphadenectomy. The final histopathology report confirms T1b N0 disease. The occurrence of a perforated early gastric cancer reemphasises the need for vigilance, including intra-operative frozen section and/or biopsy, as well as routine post-operative endoscopy for all patients.