• Steel and Composite Structures
• /
• v.45 no.1
• /
• pp.23-38
• /
• 2022

This paper presents experimental and analytical studies of eccentrically loaded concrete-filled double steel (CFDST) and concrete-filled double skin tube (DCFST) columns having outer stainless steel tube. Eighteen CFDST and DCFST column specimens were manufactured and tested to examine the strength and load-deflection responses. In the study, the main parameters were concrete strength, load eccentricity, cross section and slenderness. The strengths, load-deflection diagrams and failure patterns of the columns were observed. In addition, the tested CFDST and DCFST columns were analyzed to attain the capacity and load versus lateral deflection responses. The obtained theoretical results were compared with the test results. A parametric study was also performed to research the effects of the ratio of eccentricity (e/H_o) slenderness ratio (L/r), H_o/t_o ratio, H_i/t_i ratio and the concrete compressive strength on the behavior of columns. In this work, the obtained results indicated that the ductility and capacity of columns were affected by cross section, concrete strength, steel strength, loading eccentricity and slenderness.

• Computers and Concrete
• /
• v.33 no.2
• /
• pp.121-136
• /
• 2024

In recent times, there has been a growing need to retrofit and strengthen reinforced concrete (RC) structures that have been damaged. Numerous studies have explored various methods for strengthening RC beams. However, there is a significant dearth of research investigating the utilization of ultra-high-performance concrete (UHPC) for retrofitting damaged RC beams within a concrete frame. This study aims to develop a finite element (FE) model capable of accurately simulating the nonlinear behavior of RC beams and subsequently implementing it in an RC concrete frame. The RC frame is subjected to loading until failure at two distinct degrees, followed by retrofitting and strengthening using Ultra high performance shotcrete (UHPS) through two different methods. The results indicate the successful simulation of the load-displacement curve and crack patterns by the FE model, aligning well with experimental observations. Novel techniques for reinforcing deteriorated concrete frame structures through ABAQUS are introduced. The second strengthening method notably improves both the load-carrying capacity and initial stiffness of the load-displacement curve. By incorporating embedded rebars in the frame's columns, the beam's load-carrying capacity is enhanced by up to 31% compared to cases without embedding. These findings indicate the potential for improving the design of strengthening methods for damaged RC beams and utilizing the FE model to predict the strengthening capacity of UHPS for damaged concrete structures.

• Steel and Composite Structures
• /
• v.51 no.5
• /
• pp.529-543
• /
• 2024

The bonding efficacy of steel I-section embedded in metakaolin-fly ash-based geopolymer concrete (MK-FA-GC) was investigated in this study. Push-out tests were conducted on nine column specimens to evaluate the influence of compressive strength of concrete, embedded length of steel I-section, thickness of concrete cover, and stirrup ratio on the bond performance. Failure patterns, load-slip relationships, bond strength, and distribution of bond stress among the specimens were analyzed. The characteristic bond strength of geopolymer concrete (GC) increased with higher compressive strength, longer embedded steel section length, thicker concrete cover, and larger stirrup ratio. Empirical formulas for bond strength at the loading end were derived based on experimental data and a bond-slip constructive model for steel-reinforced MK-FA-GC was proposed. The calculated bond-slip curves showed good agreement with experimental results. Furthermore, numerical simulations using ABAQUS software were performed on column specimens by incorporating the suggested bond-slip relationship into connector elements to simulate the interface behavior between MK-FA-GC and the steel section. The simulation results showed a good correlation with the experimental findings.

• Structural Engineering and Mechanics
• /
• v.90 no.5
• /
• pp.447-458
• /
• 2024

This study investigated the influence of scale ratio and vertical load on the seismic performance of Puzuo joints in traditional Chinese timber structures. Three low-cyclic reversed loading tests were conducted on three scaled specimens of Bujian Puzuo in Yingxian Wooden Pagoda. This study focused on the deformation patterns and analyzed seismic performance under varying scale ratios and vertical loads. The results indicated that the slip and rotational deformations of Bujian Puzuo were the primary deformations. The scale of the specimen did not affect the layer where the maximum interlayer slip occurred, but it did decrease the proportion of slip deformation. Conversely, the reducing vertical load caused the layer with the maximum slippage and the position of the damaged Dou components to shift upward, and the proportion of slip deformation increased. When the vertical load was decreased by 3.7 times, the maximum horizontal bearing capacity under positive and negative loadings, initial stiffness, and energy dissipation of the specimen decreased by approximately 60%, 58.79%, 69.62%, and 57.93%, respectively. The horizontal bearing capacity under positive loading and energy dissipation of the specimen increased by 35.63% and 131.54%, when the specimen scale was doubled and the vertical load was increased by 15 times.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.5 s.57
• /
• pp.142-148
• /
• 2009

This paper is to investigate the fracture behavior characteristics of box culvert and incremental crack width of upper slab for the incremental loading by the 3-axis loading system. In the 3-axes loading system, loading directions are upper side, left and right side which simulate earth pressure and static traffic load. With the incremental load, crack patterns is investigated on the upper slab, left and right wall. Especially, on the upper slab, crack width is measured by crack gage. Based on the experimental results, structural internal force indices of box culvert are estimated quantitatively.

• The Journal of Korean Academy of Prosthodontics
• /
• v.41 no.6
• /
• pp.732-746
• /
• 2003

Statement of problem. Soft lining materials, also referred to as tissue conditioning materials, tissue heating materials, relining materials, soft liners or tissue conditioners, were first introduced to dentistry by a plastic manufacturer in 1959. Since the introduction of the materials to the dental field, their material properties have been continually improved through the effort of many researchers. Soft lining materials have become widely accepted, particularly by prosthodontists, because of their numerous clinical advantages and ease of manipulation. Unfortunately, few reports have been issued upon the topic of increasing the bond strength between the base metal alloy used in cast denture bases and PMMA soft liner modified with 4-META, nor upon the pattern of debonding and material change in wet environment like a intra oral situation. Purpose. The purposes of this study were comparing the bond strength between base metal alloy used for the cast denture bases and PMMA soft liner modified with 4-META, and describing the pattern of debonding and material property change in wet environment like the intraoral situation. Material and Methods. This study consisted of four experiments: 1. The in vitro measurement of shear bond strength of the adhesive soft liner. 2. The in vitro measurement of shear bond strength of the adhesive soft liner after 2 weeks of aging. 3. A comparison of debonding patterns. 4. An evaluation the Relation time of modified soft liner. The soft liner used in this study was commercially available as Coe-soft (GC America.IL.,USA), which is provided in forms of powder and liquid. This is a PMMA soft liner commonly used in dental clinics. The metal primer used in this study was 4-META containing primer packed in Meta fast denture base resin (Sun Medical Co., Osaka, Japan). The specimens were formed in a single lap joint desist which is useful for evaluating the apparent shear bond strength of adhesively bonded metal plate by tensile loading. Using the $20{\times}20mm$ transparent grid, percent area of adhesive soft liner remaining on the shear area was calculated to classify the debonding patterns. To evaluate the change of the initial flow of the modified adhesive soft liner, the gelation time was measured with an oscillating rheometer (Haake RS150W/ TC50, Haake Co., Germany). It was a stress control and parallel plate type with the diameter of 35mm. Conclusion. Within the conditions and limitations of this study, the following conclusions were drawn as follows. 1. There was significant increase of bond strength in the 5% 4-META, 10% 4-META containing groups and in the primer coated groups versus the control group(P<0.05). 2. After 2 weeks of aging, no significant increase in bond strength was found except for the group containing 10% 4-META (P<0.05). 3. The gelation times of the modified soft liner were 9.3 minutes for the 5% 4-META containing liner and 11.5 minutes for the 10% 4-META liner. 4. The debonding patterns of the 4-META containing group after 2 weeks of aging were similar to those of immediaely after preparation, but the debonding pattern of the primer group showed more adhesive failure after 2 weeks of aging.

• The Journal of the Korea Contents Association
• /
• v.21 no.10
• /
• pp.594-602
• /
• 2021

This study aims to identify the learning behavior patterns recognized by students to find effective tutoring operational methods, and further analyze the impact of learning behavior patterns on academic performance and learning satisfaction. To this end, 105 participants in the tutoring program at D University based in Busan Metropolitan City collected data and conducted descriptive statistics, correlation analysis and regression analysis according to research problems. First, the study found that students who participated in tutoring had the most environment-dependent and self-taught learning behavioral styles and environment-independent and self-taught learning behavioral style. Second, the correlation between learning behavioral styles and academic achievement and learning satisfaction shows that there is a high correlation between positive and cooperative learning behavioral styles and environment-independent and self-taught learning behavioral styles. Third, regression analysis on academic achievement and learning satisfaction showed that positive and cooperative learning behavioral styles significantly affects learning satisfaction, but environment-independent and self-taught learning behavioral style, environment-dependent and self-taught learning behavioral style, and passive learning behavioral style were not significant. These results suggest that from the school perspective, learning behavior can be recognized as an important factor in students' academic success and failure, so instructors need to check learners' learning behavior patterns and provide appropriate tutoring teaching and learning design plans.

• The Journal of Korean Academy of Prosthodontics
• /
• v.47 no.4
• /
• pp.424-434
• /
• 2009

Statement of problem: Problems such as loosening and fractures of retained screws and fracture of implant fixture have been frequently reported in implant prosthesis. Purpose: Implant has weak mechanical properties against lateral loading compared to vertical occlusal loading, and therefore, stress analysis of implant fixture depending on its material and geometric features is needed. Material and methods: Total 28 of external hexed implants were divided into 7 of 4 groups; Group A (3i, FULL $OSSEOTITE^{(R)}$Implant), Group B (Nobelbiocare, $Br{\aa}nemark$ $System^{(R)}$Mk III Groovy RP), Group C (Neobiotec, $SinusQuick^{TM}$ EB), Group D (Osstem, US-II). The type III gold alloy prostheses were fabricated using adequate UCLA gold abutments. Fixture, abutment screw, and abutment were connected and cross-sectioned vertically. Hardness test was conducted using MXT-$\alpha$. For fatigue fracture test, with MTS 810, the specimens were loaded to the extent of 60-600 N until fracture occurred. The fracture pattern of abutment screw and fixture was observed under scanning electron microscope. A comparative study of stress distribution and fracture area of abutment screw and fixture was carried out through finite element analysis Results: 1. In Vicker's hardness test of abutment screw, the highest value was measured in group A and lowest value was measured in group D. 2. In all implant groups, implant fixture fractures occurred mainly at the 3-4th fixture thread valley where tensile stress was concentrated. When the fatigue life was compared, significant difference was found between the group A, B, C and D (P<.05). 3. The fracture patterns of group B and group D showed complex failure type, a fracture behavior including transverse and longitudinal failure patterns in both fixture and abutment screw. In Group A and C, however, the transverse failure of fixture was only observed. 4. The finite element analysis infers that a fatigue crack started at the fixture surface. Conclusion: The maximum tensile stress was found in the implant fixture at the level of cortical bone. The fatigue fracture occurred when the dead space of implant fixture coincides with jig surface where the maximum tensile stress was generated. To increase implant durability, prevention of surrounding bone resorption is important. However, if the bone resorption progresses to the level of dead space, the frequency of implant fracture would increase. Thus, proper management is needed.

• The Journal of Korean Academy of Prosthodontics
• /
• v.47 no.1
• /
• pp.46-52
• /
• 2009

Statement of problem: Recently, titanium has become popular as superstructure material in implant dentistry because titanium superstructure can be easily milled by means of computer-aided design and manufacture (CAD/CAM) technique. But retention form such as nail head or bead cannot be cut as a result of technical limitation of CAD/CAM milling and bond strength between titanium and porcelain is not as strong as that of conventional gold or metal alloy. Purpose: The objective of this study was to evaluate the shear bond strength of three different materials: heat curing resin, composite resin, porcelain which were bonded to grade II commercially pure Titanium (CP-Ti). Material and methods: Thirty seven CP-Ti discs with 9 mm diameter, 10 mm height were divided into three groups and were bonded with heat curing resin (Lucitone 199), indirect composite resin (Sinfony), and porcelain (Triceram) which were mounted in a former with 7 mm diameter and 1 mm height. Samples were thermocycled for 1000 cycles at between $5-55^{\circ}C$. Shear bond strength (MPa) was measured with Instron Universal Testing Machine with cross head speed of 1 mm/min. The failure pattern was observed at the fractured surface and divided into adhesive, cohesive, and combination failure. The data were analyzed by one-way ANOVA and Scheffe's multiple range test (${\alpha}=0.05$). Results: Lucitone 199 ($17.82{\pm}5.13\;MPa$) showed the highest shear bond strength, followed by Triceram ($12.97{\pm}2.11\;MPa$), and Sinfony ($6.00{\pm}1.31\;MPa$). Most of the failure patterns in Lucitone 199 and Sinfony group were adhesive failure, whereas those in Triceram group were combination failure. Conclusion: Heat curing resin formed the strongest bond to titanium which is used as a CAD/CAM milling block. But the bond strength is still low compared with the bond utilizing mechanical interlocking and there are many adhesive failures which suggest that more studies to enhance bond strength are needed.

• Radiation Oncology Journal
• /
• v.24 no.4
• /
• pp.230-236
• /
• 2006

$\underline{Purpose}$: To analyze the response, toxicity, patterns of failure and survival rate of patients with locally advanced non-small cell lung cancer who were treated with concurrent chemoradiotherapy with weekly paclitaxel. $\underline{Materials\;and\;Methods}$: Twenty-three patients with locally advanced non-small cell lung cancer patients who received radical chemoradiotherapy from October 1999 to September 2004 were included in this retrospective study. Patients received total $55.4{\sim}64.8$ (median 64.8) Gy (daily 1.8 Gy per fraction, 5 days per weeks) over $7{\sim}8$ weeks. 50 or $60\;mg/m^2$ of paclitaxel was administered on day 1, 8, 15, 22, 29 and 36 of radiotherapy. Four weeks after the concurrent chemoradiotherapy, three cycles of consolidation chemotherapy consisted of paclitaxel $135\;mg/m^2$ and cisplatin $75\;mg/m^2$ was administered every 3 weeks. $\underline{Results}$: Of the 23 patients, 3 patients refused to receive the treatment during the concurrent chemoradiotherapy. One patient died of bacterial pneumonia during the concurrent chemoradiotherapy. Grade 2 radiation esophagitis was observed in 4 patients (17%). Sixteen patients received consolidation chemotherapy. During the consolidation chemotherapy, 8 patients (50%) experienced grade 3 or 4 neutropenia and one of those patients died of neutropenic sepsis. Overall response rate for 20 evaluable patients was 90% including 4 complete responses (20%) and 14 partial responses (70%). Among 18 responders, 9 had local failure, 3 had local and distant failure and 2 had distant failure only. Median progression-free survival time was 9.5 months and 2-year progression-free survival rate was 19%. Eleven patients received second-line or third-line chemotherapy after the treatment failure. The median overall survival time was 21 months. 2-year and 5-year survival rate were 43% and 33%, respectively. Age, performance status, tumor size were significant prognostic factors for progression-free survival. $\underline{Conclusion}$: Concurrent chemoradiotherapy with weekly paclitaxel revealed high response rate and low toxicity rate. But local failure occurred frequently after the remission and large tumor size was a poor prognostic factor. Further investigations are needed to improve the local control.