• International Journal of Highway Engineering
• /
• v.1 no.1
• /
• pp.107-119
• /
• 1999

The joints in the jointed concrete pavement provide a control against transverse or longitudinal cracking at slab, which may be caused by temperature or moisture variation during or after hydration. Without control of cracking, random cracks cause more serious distresses and result in structural or functional failure of pavement system. However, joints nay cause distresses due to its inherent weakness in structural integrity. Thus, the evaluation at joint is very important. and the joint-related distresses should be evaluated reasonably for economic rehabilitation. The purpose of this paper was to develop an evaluation system at joints of jointed concrete pavement using finite element analysis program, ILLI-SLAB, and nondestructive testing device. FWD. To develop an evaluation system for JCP, a sensitivity analysis was performed using ILLI-SLAB program with a selected variables which might affect fairly to on the performance of transverse joints. The most significant variables were selected from precise analysis. An evaluation charts were made for jointed concrete pavement by adopting the field FWD data. It was concluded that the variables which most significantly affect to pavement deflections are the modulus of subgrade reaction(K) and the modulus of dowel/concrete interaction(G), and limiting criteria on the performance of joints at JCP are 300pci. 500,000 lb/in. respectively. Using these variables and FWD test, a charts of load transfer ratio versus surface deflection at joints were made in order to evaluate the performance of JCP. Practically, Chungbu highway was evaluated by these evaluation charts and FWD field data for jointed concrete pavement. For Chungbu highway, only one joint showed smaller value than limiting criterion of the modulus of dowel/concrete interaction(G). The rest joints showed larger values than limiting criteria of the modulus of subgrade reaction(K) and the modulus of dowel/concrete interaction(G).

• Journal of the Korea Concrete Institute
• /
• v.27 no.4
• /
• pp.451-458
• /
• 2015

The infill-wall strengthening method has been widely used for the seismic performance enhancement of the conventional reinforced concrete (RC) frame structures with non-seismic detail, which is one of the promising techniques to secure the high resisting capacity against lateral forces induced by earthquake. During the application of the infill-wall strengthening method, however, it often restricts the use of the structure. In addition, it is difficult to cast the connection part between the wall and the frame, and also difficult to ensure the shear resistance performances along the connection. In this study, an advanced strengthening method using the externally-anchored precast wall-panel (EPCW) was proposed to overcome the disadvantages of the conventional infill-wall strengthening method. The one-third scaled four RC frame specimens were fabricated, and the cyclic loading tests were conducted to verify the EPCW strengthening method. The test results showed that the strength, lateral stiffness, energy dissipation capacity of the RC frame structures strengthened by the proposed EPCW method were significantly improved compared to the control test specimen.

• Journal of the Korea Concrete Institute
• /
• v.27 no.4
• /
• pp.399-409
• /
• 2015

Recently, the use of composite construction method using precast (PC) and cast-in-place (CIP) concrete is increased in modular construction. For PC members, pre-tensioning is used to improve efficiency of the structural performance. However, current design codes do not clearly define shear strength of prestressed PC-CIP composite members. In this study, 22 specimens were tested to evaluate shear strength of prestressed composite members with vertical shear reinforcement. The test variables were the area ratio of high-strength (60 MPa) to low-strength concrete (24 MPa), prestressing force of strands, shear span-to-depth ratio(a/d), and vertical shear reinforcement ratio. The test results showed the prestressing force did not completely restrain diagonal cracking of non-prestressed concrete in the web. Thus, the effect of prestress force was not insignificant in the effect for monolithic beams. The vertical shear strength and horizontal shear strength of the composite beams were compared with the strength predictions of KCI design method.

• Journal of the Korea Concrete Institute
• /
• v.28 no.5
• /
• pp.611-620
• /
• 2016

In the construction of nuclear power plants, only 420 MPa reinforcing bars are allowed and, therefore, so many large-diameter bars are placed, which results in steel congestion. Consequently, re-bar works are difficult and the quality of RC structures may be deteriorated. To solve the steel congestion, 550 MPa bars are necessary. Among many items for verifying structural performance of reinforced concrete with 550 MPa bars, the 43 mm hooked bars are examined in this study. All specimens failed by side-face blowout and the side cover explosively spalled at maximum loads. The bar force was initially transferred to the concrete primarily by bond along a straight portion. At the one third of maximum load, the bond reached a peak capacity and began to decline, while the hook bearing component rose rapidly. At failure, most load was resisted by the hook bearing. For confined specimens with hoops, the average value of test-to-prediction ratios by KCI code is 1.45. The modification factor of confining reinforcement which was not allowed for larger than 35 mm bars can be applied to 43 mm hooked bars. For specimens with 70 MPa concrete, the average value of test-to-prediction ratios by KCI code is 1.0 which is less than the values of the other specimens. The effects of concrete compressive strength should be reduced. An equation to predict anchorage capacity of hooked bars was developed from regression analysis including the effects of compressive strength of concrete, embedment length, side cover thickness, and transverse reinforcement index.

• Korean Journal of Biological Psychiatry
• /
• v.23 no.2
• /
• pp.63-68
• /
• 2016

Objectives Haenyeo are Korean professional women breath-hold divers in Jeju island. The aim of this study was to investigate the clinical characteristics of depressed Haenyeo group, compared to non-Haenyeo depressed group. Methods This study included 75 Haenyeo and 340 non-Haenyeo with depressive disorders recruited from the Dementia Early Detection Program in Jeju island. Structural diagnostic interviews were performed using the Korean version of Mini International Neuropsychiatric Interview. All patients completed the questionnaires, including the Subjective Memory Complaints Questionnaire (SMCQ), the Patient Health Questionnaire-15 (PHQ-15), and the Blessed dementia scale. Depression was evaluated by the Korean version of short form the Geriatric Depression Scale (K-SGDS) and cognition was assessed by the Korean version of the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) assessment packet. Results Although the mean scores of the K-SGDS were similar between Haenyeo and non-Haenyeo depressed groups, the Haenyeo group showed a higher mean score on the PSQ-15 (p < 0.001, ANCOVA adjusting for age, the K-SGDS and education). The Haenyeo group showed poorer performance on the Korean Version of Frontal Assessment Batter (p < 0.001), the Mini-Mental State Examination in the Korean version of the CERAD Assessment Packet (p < 0.018), the word fluency test (p < 0.001), and the word list memory test (p = 0.012) in ANCOVA adjusting for age and education. The mean SMCQ score was higher in the Haenyeo depressed group than in the non-Haenyeo depressed group. Conclusions The Haenyeo depressed group shows cognitive dysfunction, especially frontal lobe dysfunction, compared to the non-Haenyeo depressed group, indicating the Haenyeo depressed group may have more severe frontolimbic dysfunction due to chronic exposure to hypoxia. The Haenyeo depressed group suffers more somatic symptoms than the non-Haenyeo depressed group.

• Journal of the Korea Concrete Institute
• /
• v.18 no.5 s.95
• /
• pp.595-602
• /
• 2006

An experimental study was conducted to investigate seismic behaviour of post-tensioned(PT) exterior slab-column connections used for the purpose to resist gravity loads only. For these, 2/3-scale, two PT post-tensioned exterior connections with two different tendon arrangement patterns and one conventional reinforced concrete(RC) exterior connection was tested under quasi-static, uni-directional reversed cyclic loading. During the lateral testing, gravity forces transferred to the column were kept constant to closely simulate a moment to shear ratio of a real building. One of the objectives of this study was to assess the necessity and/or the quantity of bottom bonded reinforcement needed to resist moment reversal which would occur under significant inelastic deformations of the adjacent lateral force resisting systems. The ACI 318 and 352 provisions for structural integrity were applied to provide the bottom reinforcement passing through the column for the specimens. Prior test results were also collected to conduct comparative studies for some design parameters such as the tendon arrangement pattern, the effect of post-tensioning forces and the use of bottom bonded reinforcement. Consequently, the impact of tendon arrangement on the seismic performance of the PT connection, that is lateral drift capacity and ductility, dissipated energy and failure mechanism, was considerable. Moreover, test results showed that the amount of bottom reinforcement specified by ACI 352. 1R-89 was sufficient for resisting positive moments arising from moment reversal under reversed cyclic loads. Shear strength of the tested specimens was more accurately predicted by the shear strength equation(ACI 318) considering the average compressive stress over the concrete($f_{pc}$) due to post-tensioning forces than that without considering $f_{pc}$.

• Journal of the Korea Concrete Institute
• /
• v.27 no.3
• /
• pp.215-227
• /
• 2015

In this study, twenty four steel-fiber reinforced concrete (SFRC) beams using recycled coarse aggregates (RCA) were manufactured to examine the shear behavior of SFRC and to determine the beams' ultimate shear strengths. The RCA replacement ratio was fixed at 30%. The variables studied in this investigation are: (1) shear span-to-depth ratios (a/d) of 2, 3 and 4; (2) longitudinal reinforcement ratio (${\rho}$) of 0.008 and 0.0127; and (3) steel fiber volume fractions ($V_f$) of 0, 0.5, 0.75 and 1%. Test results were analyzed and then compared with the findings and proposals of various other researchers. Based on the test results, the more steel fiber volume fraction is increased, the large crack resistance and shear strength are exhibited. Most of the experimental data is higher than the theoretical value. Therefore, steel-fiber reinforced concrete beams using recycled coarse aggregates are suggested to be applied for building structures.

• Journal of the Korea Concrete Institute
• /
• v.29 no.1
• /
• pp.23-32
• /
• 2017

The joints between precast PSC slabs of the intermediate road slab in double deck tunnel are inevitably generated in the road traffic vehicle traveling direction. Therefore, it is important to make the behavior of parts on the joint in one piece. The imtermediate road slab system of double deck tunnel in great depth proposed in this study will be constructed with precast PSC slab in order to minimize the construction period. And the joint connection between the precast slab has been developed in two methods: the 'Transverse tendon reinforcement method' and 'High strength bolts connection method'. Also, the experiments were performed for the full scale model in order to evaluate the performance of the intermediate road deck slab with two type joints systems, the structural stability was verified through the F.E.M analsysis. The results of static loading test and F.E.M analysis investigated a very stable behavior of intermediate road deck slab in double deck tunnel applying the joint methods developed in this study, in the cracks and deflections to satisfy the design standards of Highway Roads Bridges (2011), it was determined that there is no problem even servicebility.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.19 no.2
• /
• pp.283-299
• /
• 2017

The leakage of tunnel causes the long-term durability of the structures such as concrete lining to deteriorate. The cause of durability degradation can be various substances contained in groundwater such as chloride, sulphate, water, and gas. In this study, a series of test were carried out to determine the watertightness performance and the resistance to salt water of the spray-applied membrane used as non-structural rock support or as a waterproof material for tunnels. As a result, it was found that the penetration of water could occur in a specimen, and the reason was that the internal pores generated by the mixing of the liquid polymer and the powder material and the internal pores were connected by the water pressure. The tensile strength of the test specimens immersed in distilled water and saline water was found to be reduced to less than half of the tensile strength in normal condition. In addition, The elongation was measured to be higher in distilled water than in salt water. However, this result will require further investigation.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.4A
• /
• pp.315-327
• /
• 2009

In this study, the static test of CFT truss girders for different f/L ratios was conducted to determine how the ultimate strength of the CFT truss girder was affected by different f/L ratios. A total of two CFT truss girders were constructed and tested under bending condition. The length of all specimens is 20,000 mm. The CFT truss girder is a tubular truss composed of chord members made of concrete-filled circular tubes. The main parameter analyzed in the experimental study was the f/L ratio. This factor was experimentally investigated to assess their influence on ultimate strength and stiffness. The test results show that CFT truss girder has good elastic-plastic property and ductility. The presence of the f/L ratios in CFT truss girders alters its ultimate strength because of the global stiffness of the CFT truss girders. The ultimate strength of CFT truss girders increases as the f/L ratio increases. If the f/L ratio of the CFT truss girders increases twofold, the ultimate strengths increase by 80%. The CFT truss girders showed that they retained large deformation capacity, even after reaching the ultimate strength. Results of this investigation demonstrated the potential for efficiently using a CFT truss as a bridge girder.