• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.4
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• pp.119-126
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• 2006

This paper presents the results of a test program for flexural strengthening characteristics of continuous unidirectional carbon-fiber sheets bonded or/and developed to reinforced concrete (RC) beams. A total of six $150mm{\times}250mm{\times}2000mm$ concrete beams were tested. Various sheet development locations were studied to determine their effects on the ultimate flexural strength of the beams. From the test, it was found that the strength increases remarkably with the development of sheets at shear bar. Among the various location, multi-developed sheet provided the most effective strengthening for concrete beam. Beam strengthened using this scheme showed 53% increase in flexural capacity as compared to the control beam without any strengthening.

• Journal of Korean Society of Steel Construction
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• v.17 no.5 s.78
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• pp.561-568
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• 2005

The object of this paper is to determine appropriateness for use of high-strength tensile bar as a tension web member. The gap K-joint of tensile bar types were compared with gap K-joint of square hollow section (SHS) types. For the same width-to-thickness ratio ($2{\gamma}=33.3$ ), tests were performed on four specimens of the SHS type and eight specimens of the tensile bar type. The comparison of capacity with the experimental results showed a capacity of the SHS type joint to be higher than that of the tensile bartype joint for the same brace-to-chord width ratio. Moreover, the capacity of the SHS type joints increased proportionally to the width ratio ${\beta}$), while tensile bar type joints increased as the tension width ratio (${\beta}2$). In failure mode, SHS-type specimens showed local buckling of the compression brace and plastic failure was observed between the tension brace and chord face, and with the tensile bar type specimens there appeared punching shear failure of the chord face at the toe of the connection plate. It is, therefore, concluded that width-to-thickness ratio should be lower than that of the hollow-section type and the relation between tension and compression width ratio should be considered.

• Journal of Korean Society of Steel Construction
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• v.17 no.3 s.76
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• pp.325-335
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• 2005

This study tackles the development of an improved detail of partially restrained CFT square column-to-beam connection and the evaluation of its mechanical behavior under monotonic loading. The connection is designed to strengthen shearing capacity at the bottom of the connection due to the ultimate behavior of PR-CC by its detail of the bottom connection and simplify the fabrication process. The suggested connection is the welded bottom beam flange connection(M-2) and is compared with the existing PR-CC of bolted seat angle connection(M-1). Two specimens were fabricated in actual size and tested under monotonic loading. Based on the test results, the welded bottom beam flange connection exhibited about 85% of the stiffness of steel beam. It was similar to the bolted seat angle connection and behaved as PR-CC. The specimen of the supposed connection type failed at the shear connection of web but was similar to the bolted seat angle connection until the failure. It obtained sufficient stiffness and capacity through the reinforcingsteel and the capacity and deformational ability equivalent to the full-plastic moment through the anchor inside the steel tube at the web connection. So, it can be said that the suggested connection exhibits sufficient ductile behavior.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.3-14
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• 2012

This paper describes experimental results on the seismic performance of SHCC (strain-hardening cement composite) infill wall for improving damage tolerance capacity of non-ductile frame. To investigate the effect of tensile strain capacity and cracking behavior of SHCC materials on the shear behavior of SHCC infill wall, three infill walls were fabricated and tested under cyclic loading. The test parameter in this study is a type of cement composites; concrete and SHCCs. The two types of SHCC materials were prepared for infill walls. In order to induce crack damages into the mid-span of the infill wall, each infill wall had two 100-mm-deep-notches on both sides. Test results indicated that SHCC infill walls showed superior crack control capacities and much larger drift ratios at the peak loads than RC (reinforced concrete) infill wall, as expected. In particular, due to the bridging actions of the reinforcing fibers, SHCC matrix used in this study would delay the stiffness degradation of infill wall after the first inclined cracking. Moreover, from the damage classes based on the cracks' maximum width in the infill walls, it was observed that PIW-SHD specimen possessed nearly threefold seismic capacities compared to PIW-SLD specimen. Also, from the results on the strain of diagonal reinforcements, it can be concluded that the SHCC matrix would resist a part of tensile stresses transferred along steel rebar in the infill wall.

• Geotechnical Engineering
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• v.12 no.2
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• pp.71-84
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• 1996

In order to investigate the influence of slanting angle of reticulated root piles(RRP) on their bearing capacities, model tests of compressive and uplift loads on RRP with different slanting angles, which were installed in sandy soils with a relative density of 47%, were carried out. Each pile which is made of a steel bar of 5mm in diameter and 300mm in length, is coated with sand to be 6.5mm in diameter. One set of RRP consists of 8 piles which are installed in circular patterns forming two concentric circles, each of which has 4 piles. Slanting angles of RRP for load tests are 0$^{\circ}$, 5$^{\circ}$, 10$^{\circ}$, 15$^{\circ}$, 20$^{\circ}$, and 25$^{\circ}$. In addition, compressive load tests on circular footing whose diameter is the same as the outer circle of RRP were carried out. Test results show that maximum load bearing capacities of RRP by regression analysis are obtained at about 12$^{\circ}$ and 13$^{\circ}$ of slanting angles for compressive and uplift load tests, respectively. Maximum compressive bearing capacity is estimated to be 13oA bigger than that of the vertical RRP and 95% bigger than that of surface footing. Maximum uplift capacity is estimated to be 21% bigger than that of the vertical RRP. And it can be appreciated that increasing the slanting angle makes the load -Settlement behavior more ductile.

• Journal of the Korean Geosynthetics Society
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• v.8 no.2
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• pp.47-54
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• 2009

The ballast track, the most common type of conventional railroad track in Korea, is deteriorated by abrasion of ballast, it's penetration into roadbed, and rugged surface of roadbed caused by cyclic loading of train. Persistent occurrence of those phenomena lead to insufficient drain capacity, one of major factors in track design, and it increases pore water pressure and decreases of shear strength under rainfall condition leading to unstable roadbed. In this study, cylindrical model tests are executed for 3 types of geotextile applying cyclic loading in order to observe the characteristics of displacement and bearing capacity of geotextile, and undrained condition has been applied for 0 day, 3 days and 7 days to each geotextiles. The results showed that there was about 1% difference at the final displacement rates between reinforced soils and nature soils and the displacement of the ground surface increases along with the degrees of the saturation. And in case that water contents exceeds the threshold, it is also apparent that weight and tensile strength of geotextile influences displacement of the ground surface. And the larger weight of geotextile is, the smaller plastic displacement. It is evaluated that non-woven fabric comes into effect on reducing the bearing capacity but, the weight of geotextile has little influence on it.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.2
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• pp.9-20
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• 2014

Steel intermediate moment frames (IMFs) have been generally used as seismic load resisting systems (SLRSs) of a building to provide resistances against strong ground shaking. However, most of low and mid-rise steel buildings in Korea were constructed during pre-seismic code era or before the introduction of well-organized current seismic codes. It has been recognized that the seismic performance of these steel IMFs is still questionable. In order to respond to such a question, this study quantitatively investigates the seismic capacities of steel IMFs. Prototype models are built according to the number of stories, the levels of elastic seismic design base shear and the ductilities of structural components. Also, the other prototype models employing hysteretic energy dissipating devices (HEDDs) are considered. The collapse mechanism and the seismic performance of the prototype models are then described based on the results obtained from nonlinear-static and incremental-dynamic analyses. The seismic performance of the prototype models is assessed from collapse margin ratio (CMR) and collapse probability. From the assessment, the prototype model representing new steel IMFs has enough seismic capacities while, the prototype models representing existing steel IMFs provide higher collapse probabilities. From the analytic results of the prototype models retrofitted with HEDDs, the HEDDs enhance the seismic performance and collapse capacity of the existing steel IMFs. This is due to the energy dissipating capacity of the HEDDs and the redistribution of plastic hinges.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.99-106
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• 2001

The main objective of this study is to develop a continuity of double tee slab with two modified dap-ends to solve the problems of excessive moment, slab depth, deflection, and joint cracking in the original simply supported double tee slab systems. The modified joint is produced in a combination with two slabs with modified dap and one rectangular beam. The modified joint can be justified as following different merits. The span capacity for a design load is increased, while the deflection of the slab is decreased due to the decrease of positive moment at the center span of the slab. The joint cracking between slab and beam, which occur frequently in the original slab systems of double tee will be reduced. No more additional form work is needed to cast topping concrete for continuity. Three point loading tests are performed on the specimens with a variable of an amount of main longitudinal reinforcement to evaluate flexural and shear behavior. Following conclusions are obtained from the experimental investigation. The continuity of double tee slab effectively is provided by placing longitudinal steel reinforcement in the topping concrete over the connection, and generally leads to an increase in span capacity of double tee slabs with reduced deflection. It is more effective to control the initial cracking at the connection than that of some simply supported double tee slab systems.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.83-91
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• 2021

In this study, to improve the connection performance between the existing reinforced concrete (R/C) frame and the strengthening member, we proposed a new H-section steel frame with elastic pad (HSFEP) system for seismic rehabilitation of existing medium-to-low-rise reinforced concrete (R/C) buildings. This HSFEP strengthening system exhibits an excellent connection performance because an elastic pad is installed between the existing structure and reinforcing frame. The method shows a strength design approach implemented via retrofitting, to easily increase the ultimate lateral load capacity of R/C buildings lacking seismic data, which exhibit shear failure mechanism. Two full-size two-story R/C frame specimens were designed based on an existing R/C building in Korea lacking seismic data, and then strengthened using the HSFEP system; thus, one control specimen and one specimen strengthened with the HSFEP system were used. Pseudodynamic tests were conducted to verify the effects of seismic retrofitting, and the earthquake response behavior with use of the proposed method, in terms of the maximum response strength, response displacement, and degree of earthquake damage compared with the control R/C frame. Test results revealed that the proposed HSFEP strengthening method, internally applied to the R/C frame, effectively increased the lateral ultimate strength, resulting in reduced response displacement of R/C structures under large scale earthquake conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.2
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• pp.335-344
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• 2019

Micropiles are widely used for foundation underpinning to enhance bearing capacity and reduce settlement of existing foundation. In this study, the main objective is to evaluate underpinning performance of a newly developed micropile called waveform micropile for foundation underpinning during vertical extension. Finite element method (FEM) was used to evaluate the underpinning performance of waveform micropile in terms of load-settlement response of underpinned foundation and load sharing behavior. For comparison, underpinning effects of three conventional micropiles with different lengths were also discussed in this study. Numerical results of load-settlement response for single pile demonstrated that bearing capacity and axial stiffness of waveform micropiles were higher than those of conventional micropiles because of the effect of shear keys of waveform micropiles. When additional loads 20 %, which is according to design loads of the vertical extension, were applied to the underpinned foundation, load sharing capacity of waveform micropile was 40 % higher than conventional micropile at the same size. The waveform micropile also showed better underpinning performance than the conventional micropile of length 1~1.5 times of waveform micropile.