• Journal of the Korea Concrete Institute
• /
• v.23 no.2
• /
• pp.169-176
• /
• 2011

In this study, the flexural test for reinforced high performance fiber reinforced cementitious composites (R/HPFRCC) members has been conducted in order to investigate the flexural behavior including the effect of an ordinary tensile reinforcing bar. Through the test, it was observed that the flexural strength increased due to the stable tensile stress transfer of HPFRCC, even up to the ultimate state. In addition, no localized crack appeared until the yielding of the reinforcement. From the layered section analysis of the tested members, it was found that the analysis with the tensile model obtained from the tension stiffening test showed better agreement with the flexural test results, whereas the analysis with direct tension test results overestimated the flexural capacity. Through the experimental and analytical studies, two flexural failure modes have been defined in this paper; concrete crushing at the top compression layer or tensile failure at the bottom tensile layer of the beam section. Based on these two flexural failure modes, a simple formula that estimates the ultimate flexural strength of the member has been proposed in this paper. The proposed equations can be useful in a design and an analysis of R/HPFRCC members.

• Journal of Korean Society of Steel Construction
• /
• v.28 no.5
• /
• pp.345-354
• /
• 2016

In the present study, hybrid moment connections of welding and bar reinforcement for composite beam-column connections were proposed. Concrete-filled octagonal tube and U-section were used for the column and beam, respectively. In the beam-column connection, the top flange and web of the beam U-section were connected to the column plate by welding. However, to reduce stress concentration at the weld joints, the bottom flange of the beam was not welded to the column plate. Instead, to transfer the tension force of the beam flange, reinforcing bars passing through the column plate were used. Four exterior connections with conventional welded and hybrid moment connections were tested under cyclic loading and their cyclic behaviors were investigated. The test results showed that the hybrid moment connections successfully transferred the beam moment to the column. The strength and ductility of the hybrid moment connections were comparable to the conventional welded moment connection with exterior diaphragm; however, the connection performance was significantly affected by the details of the hybrid moment connection.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.3
• /
• pp.21-31
• /
• 2018

This paper presents an experimental investigation on the structural performance of precast ribbed panel specimens and bridge deck specimens fabricated from the panels. The panel specimens are developed for permanent deck forms of railway bridges (PSC girder). The decks of railway bridges have short lengths compared with highway bridges. Therefore, precast panels for railway bridges are different from those of highway bridges. The precast panels have ribs designed for crack control at the bottom of the sections. Two kinds of specimens were examined: one with 400-mm width and one with 1200-mm width. Three specimens of each type were fabricated, and a total of 12 specimens were tested. In this test, the ultimate load, strain of the reinforcement and concrete, crack width, deformation, and slip were measured. The structural performance of the specimens was assessed using the Korea railway bridge design code and Eurocode. All specimens met the current design criteria for structural strength and serviceability.

• International Journal of Highway Engineering
• /
• v.12 no.1
• /
• pp.1-8
• /
• 2010

Construction of road closed to mountains is inevitable in Korea because the mountainous region in Korea is more than 70% in area. Recently, due to global warming, typhoons or heavy rainfalls frequently occur, and accordingly, mountain roads are seriously damaged by landslides, debris flows, and uplift pressure below pavement. in this study, damage on pavement by uplift pressure was investigated. Various influencing factors such as slope angle, reinforcement of slope surface, thickness of soil cover underlain by rock, and types of drainage system were considered to evaluate uplift pressure acting on the bottom of pavement. Raising of water table up to the surface of slope may depend on the duration and intensity of rainfall. It shows that the installation of subdrain can reduce the uplift water pressure. Therefore, It is concluded that the use of subdrain system is effective to decrease uplift pressure and cement treated base is more endurable than typical crushed-stone base.

• Journal of Navigation and Port Research
• /
• v.30 no.6 s.112
• /
• pp.439-446
• /
• 2006

In ship structures many of the structural plates have cutouts, for example, at inner bottom structure, girder, upper deck hatch, floor and dia-frame etc. In the case where a plate has a cutout it experiences reduced buckling and ultimate strength and at the same time the in-plane stress under compressive load produced by hull girder bending will be redistributed In general, actual ship structure adopted reinforcement of stiffener around the cutout in order to preventing from buckling so it need to examine a buckling and ultimate strength behaviour considering a cutout because In many ship yards used class rule for calculating buckling strength but it is difficult to evaluate perforate stiffened plate with random size. In the present paper, we investigated several kinds of perforated stiffened model from actual ship and then was performed finite element series analysis varying the cutout ratio, web height, thickness and type of cross-section using commercial FEA program(ANSYS) under compressive load.

• Journal of the Korea Concrete Institute
• /
• v.14 no.2
• /
• pp.216-222
• /
• 2002

With deterioration of the nation's infrastructure comes the growing, need for effective means of rehabilitating structures. Possibly one for the most challenging tasks is to upgrade the overall capacity of concrete structure. Therefore, considerable efforts are still being made to develop new construction materials. Rehabilitation of damaged RC structures occasionally requires the removal and replacement of concrete in the tension zone of the structural members. Typical situation where the tension zone repair is necessary is when the concrete in the tension zone in beams or slabs has spalled off as a result of corrosion in the bottom reinforcing bars or due to extensive fire. The rehabilitation of such conditions normally involves the removal of the concrete beyond the reinforcement bars, cleaning or replacing the tensile bars and reinstatement of concrete to cover the steel bars the original shape and size. This study focused on the flexural behavior of reinforced concrete beams strengthened by steel strand and carbon fiber sheet in the tension zone. The properties of beams are 15$\times$25 cm rectangular and over a 200cm span. Test parameters in this experimental study were strengthening methods, jacking volume, the number of sheet. We investigated the flexural behavior of simply supported RC beams which are strengthened with the carbon fiber sheet, monotonic loads. Attention is concentrated upon overall bending capacity, deflection, ductility index, failure mode and crack development of repaired and rehabilitated beams.

• Journal of Conservation Science
• /
• v.28 no.2
• /
• pp.153-164
• /
• 2012

The major petroglyphs of Bangudae site were composed mainly of hornfelsed shale. Surface of the rock was formed weathering layer (average porosity 25%) that discriminated mineral and chemical composition against fresh rock (average porosity 0.4%). The lost area of major petroglyphs in the past up images carved to the present was calculated about 23.8%. And occurrence area of exfoliation indicated 1.2% of the whole petroglyphs. As a result of the chromaticity analysis, color of the major petroglyphs was changed brighter and yellower than fresh rock by chemical and biological weathering factors. Average ultrasonic velocity of petroglyphs was measured 2,865m/s. This result indicated that ultrasonic velocity decreased especially bottom of petroglyphs than measured result in 2003 year. The results of the evaluation for slope stability, it identified the possibility of toppling, planar and wedge failure in host rock. The 3D image analysis and modeling data of the cavern obtained for structural reinforcement.

• The Journal of Engineering Geology
• /
• v.17 no.4
• /
• pp.525-534
• /
• 2007

The peculiarity of end-expanded soil nailing method(EESNM) is in fixing the wedge-type steel body spreaded by collars and grouting its surroundings by cement milk within soils, after extending hole bottom over drilling hole diameter with top drill bit. The present study was done to establish the effect of this method. Laboratory model test were carried out to investigate the behavior characteristics with the performance of the pull-out test and failure experiment, after preparing soil test box having 1,300mm length, width 1,000mm, and height 1,100mm, and the same experimental condition was set up to compare with the general soil nailing method(GSNM). The pull-out force of about 23 percentage was increased, and the horizontal displacements 1.2 from 9.1 percentage in soil-nailed wall decreased in EESNM compare with GSNM. The axial force acting on nail increased considerably at load level over 7 ton in EESNM and 5 ton in GSNM. The predicted failure line from the maxima analyzed by axial tensile strain located at long distance from soil-nailed wall in EESNM. The EESNM demonstrated the superiority of reinforcement effect in comparison with GSNM from the results above mentioned.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.6A
• /
• pp.457-464
• /
• 2011

An experimental study was performed to evaluate the possibility of using stiff type PolyUrea(PU) on RC slab as a strengthening material. Stiff type PU(STPU) was sprayed on the bottom surface of the slab specimens, which were then attached with CFRP or GFRP sheets. Also the evaluation of the bond capacity, the single most influential parameter on strengthening of RC structures, was carried out the flexural capacity evaluation test results showed that the load carrying capacity of the PU specimen was greater and less than the unstrengthened and FRP sheet attached specimens, respectively. The STPU specimens showed a ductile flexural behavior in the plastic displacement range. With respect to bond capacity, the bond strength of all of the specimen exceeded the code required bond strength of 1.5 MPa. Also, the STPU sprayed specimen without using epoxy resin did not peel off when the tensile grip was applied for testing. The stability of the PU bond failure indicate a good bond strength of PU when applied to concrete.

• Journal of the Society of Disaster Information
• /
• v.15 no.4
• /
• pp.479-492
• /
• 2019

Purpose: The purpose of this study is to accurately analyze the damage of bridges in order to determine whether fire bridges can be used continuously or to provide information on maintenance augmentation data. Method: XRD, SEM and EDS analyzes of concrete were carried out to estimate the fire temperature transferred to the structure, and analyzed by depth and area from PSCI beam and bottom plate concrete surface. Results: Test results G_12,11 for the fire zone concrete were confirmed to be affected by heat up to depth of 60mm and the temperature of the hydrothermal heat was above 1000℃. Also, the girder G_10,9,8 was relatively weakly damaged compared to G_12,11, and the degree of damage was confirmed to be affected by heat up to a depth of 40 mm. Conclusion: Based on the analyzed data, it is considered that if the repair / reinforcement and periodic inspection are carried out, the bridge can secure sufficient safety even considering the damage caused by the fire.