• Coupled systems mechanics
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• v.9 no.2
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• pp.163-182
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• 2020

Coupled thermo-mechanical analysis of reinforced concrete slab at elevated temperatures from a fire accounting for nonlinear thermal parameters is carried out. The main focus of the paper is put on a one-way continuous reinforced concrete slab exposed to fire from the single (bottom) side as the most typical working condition under fire loading. Although contemporary techniques alongside the fire protection measures are in constant development, in most cases it is not possible to avoid the material deterioration particularly nearby the exposed surface from a fire. Thereby the structural fire resistance of reinforced concrete slabs is mostly influenced by a relative distance between reinforcement and the exposed surface. A parametric study with variable concrete cover ranging from 15 mm to 35 mm is performed. As the first part of a one-way coupled thermo-mechanical analysis, transient nonlinear heat transfer analysis is performed by applying the net heat flux on the exposed surface. The solution of proposed heat analysis is obtained at certain time steps of interest by α-method using the explicit Euler time-integration scheme. Spatial discretization is done by the finite element method using a 1D 2-noded truss element with the temperature nodal values as unknowns. The obtained results in terms of temperature field inside the element are compared with available numerical and experimental results. A high level of agreement can be observed, implying the proposed model capable of describing the temperature field during a fire. Accompanying thermal analysis, mechanical analysis is performed in two ways. Firstly, using the guidelines given in Eurocode 2 - Part 1-2 resulting in the fire resistance rating for the aforementioned concrete cover values. The second way is a fully numerical coupled analysis carried out in general-purpose finite element software DIANA FEA. Both approaches indicate structural fire behavior similar to those observed in large-scale fire tests.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.2
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• pp.149-158
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• 2011

Utilization of the fiber reinforced polymer (FRP) material has been increased as an alternative in a bid to supplement the problems with general construction materials such as long-term problems corrosion, etc. However, there are still many problems in using a linear-shaped FRP material for a tunnel lining structure which has arch-shape in general. In this study, the loading tests for the FRP-concrete composite member was carried out to evaluate their applicability as a tunnel reinforcement material, which are based on the results from preliminary numerical studies for identifying the behavioral characteristics of FRP-concrete composite member. Moreover, numerical analysis under the same condition as applied in the loading tests was again conducted for analysis of mechanical behavior of the composite member. As a result of the load test and numerical analysis, it appears that the FRP-concrete composite member is greatly subject to shear movement caused by bending tension acting on the interface between two constituent members.

• Advances in nano research
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• v.8 no.2
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• pp.135-148
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• 2020

The incorporation of carbon nanotubes in a polymer matrix makes it possible to obtain nanocomposite materials with exceptional properties. It's in this scientific background that this work was based. There are several theories that deal with the behavior of plates, in this research based on the Mindlin-Reissner theory that takes into account the transversal shear effect, for analysis of the critical buckling load of a reinforced polymer plate with parabolic distribution of carbon nanotubes. The equations of the model are derived and the critical loads of linear and parabolic distribution of carbon nanotubes are obtained. With different disposition of nanotubes of carbon in the polymer matrix, the effects of different parameters such as the volume fractions, the plate geometric ratios and the number of modes on the critical load buckling are analysed and discussed. The results show that the critical buckling load of parabolic distribution is larger than the linear distribution. This variation is attributed to the concentration of reinforcement (CNTs) at the top and bottom faces for the X-CNT type which make the plate more rigid against buckling.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.967-972
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• 2004

The role of transfer films formed during sliding of polymer composites against steel counterfaces was studied in terms of the tribological behaviors of composites. Four kinds of composites were included in this study: (1) unfilled PPS, (2) PPS+2%CuO, (3) PPS+2%CuO+5% carbon fiber (CF), and (4) PPS+2%CuO+15%Kevlar. The filler material CuO was in nanoscale particulate form and the reinforcing material was in the form of short fibers. The composites were prepared by compression molding at $310^{\circ}C$ and sliding tests were run in the pin-on-disk sliding configuration. The counterface was made of tool steel hardened to 55-60 HRC and finished to a surface roughness of 0.09-0.10 ${\mu}m$ Ra. Wear tests were run for 6 hrs at the sliding speed of 1 m/s and contact pressure of 0.65 MPa. Transfer films formed on the counterfaces during sliding were investigated using AFM and SEM. The results showed that as the transfer film became smooth and uniform, wear rate decreased. PPS+2%CuO+15%Kevlar composite showed the lowest steady state wear rate in this study and its transfer film showed the smoothest and the most uniform characteristics. The examination of worn surfaces of PPS+2%CuO composite using X-ray area scanning (dot mapping) showed back-transfer of steel counterface material to the polymer pin surface. This behavior is believed to strengthen the polymer pin surface during sliding thereby contributing to the decrease in wear rate.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.113-123
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• 2006

An experimental investigation on the behavior of reinforced concrete coupling beams is presented. The test variables are the span-to-depth ratio, the ratio of flexural reinforcements and the ratio of shear rebars. The distribution of arch action and truss action which compose the mechanism of shear resistance is discussed. The increase of plastic deformation after yielding transforms the shear transfer by arch action into by truss action. This study proposes the deformation model for reinforced concrete coupling beams considering the bond slip of flexural reinforcement. The strain distribution model of shear reinforcements and flexural reinforcements based on test results is presented. The yielding of flexural reinforcements determines yielding states and the ultimate states of reinforced concrete coupling beam are defined as the ultimate compressive strain of struts and the degradation of compressive strength due to principal tensile strain of struts. The flexural-shear failure mechanism determines the ultimate state of RC coupling beams. It is expected that this model can be applied to displacement-based design methods.

• Structural Engineering and Mechanics
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• v.39 no.1
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• pp.125-145
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• 2011

Pushover analysis has gained significant popularity as an analytical tool for realistic determination of the inelastic behaviour of RC structures. Though significant work has been done to evaluate the demands realistically, the evaluation of capacity and realistic failure modes has taken a back seat. In order to throw light on the inelastic behaviour and capacity evaluation for the RC framed structures, a 3D Reinforced concrete frame structure was tested under monotonically increasing lateral pushover loads, in a parabolic pattern, till failure. The structure consisted of three storeys and had 2 bays along the two orthogonal directions. The structure was gradually pushed in small increments of load and the corresponding displacements were monitored continuously, leading to a pushover curve for the structure as a result of the test along with other relevant information such as strains on reinforcement bars at critical locations, failure modes etc. The major failure modes were observed as flexural failure of beams and columns, torsional failure of transverse beams and joint shear failure. The analysis of the structure was by considering all these failure modes. In order to have a comparison, the analysis was performed as three different cases. In one case, only the flexural hinges were modelled for critical locations in beams and columns; in second the torsional hinges for transverse beams were included in the analysis and in the third case, joint shear hinges were also included in the analysis. It is shown that modelling and capturing all the failure modes is practically possible and such an analysis can provide the realistic insight into the behaviour of the structure.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.279-289
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• 2003

Geosynthetic reinforced earth wall was introduced about 20 years ago and many structures have been constructed. Especially, segmental concrete panel facing and friction tie system are the most popular system in Korea, and this friction tie was composed of high tenacity PET filament and LDPE(Low Density Polyethylene) sheath. Due to the lack of direct-test results, design coefficients of friction tie (creep reduction factor) had been determined by quoting the previous and the foreign reference data. This is an unreasonable fact for the use of friction ties. In this study, the creep tests were performed to evaluate the creep behavior of friction tie, and the reduction factor of creep was calculated for the correct design of geosynthetic reinforced earth retaining walls. From the test results, finally it was found that the allowable creep strength of friction tie is 60% of Tult during service life, and creep reduction factor is 1.67 for each grade of friction ties.

• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.153-160
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• 1994

Ten Half precast concrete slabs reinforced with welded deformed wire fabric were tested under two concentrated loads to investigate the flexural moment and ductile capacity. The test variables were the compressive strength of topping concrete, quantitative roughness, and reinforcernent ratio. The effects of each test variables were studied separately. Test results were as followings. The ultimate strength design method is applicable to predict flexural strength for Half P.C. concrete slab with welded deformed wire fabric and quantitative roughness. It is proper to consider 0.0035 strain ;is yielding stress of the welded deformed wire fabric. The ductility index of Half precast concrete slab with welded deformed wire fabric showed lower value. Therefore to enhance the ductility capacity the normal defomed bar should be used with the welded deformed wire fabric for the longitudinal reinforcement.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.257-267
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• 2008

Results of seventy-seven specimens tested by this study and previous research were collected and evaluated to propose the flexural strength and shear strength for flexural members with steel fiber concrete. For strength evaluation, structural parameters such as compressive strength, steel fiber content, tensile reinforcement ratio, and shear span to effective depth ratio are involved. The proposed equations for flexural and shear strength are regarded to give a good prediction for the strength of steel fiber reinforced composite and/or RC beams to compare with equations by previous researchers. Especially, the proposed shear strength equation in this study shows the lowest the mean value, the coefficient of variation and the error ratio among predictions by several equations. Therefore, equations for shear strength and flexure strength, which are proposed in this study are to be useful measure to predict the actual behavior and failure mode of steel fiber reinforced composite beams.

• Journal of the Korean GEO-environmental Society
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• v.6 no.2
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• pp.39-49
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• 2005

In this study, the fifteen month behavior of two geosynthetic reinforced walls which was constructed on the shallow weak ground was measured and analyzed. The walls were backfilled with clayey soil obtained from the construction site nearby, and the safety factors obtained from general limit equilibrium analysis were less than 1.3 in both wall. The measured and analyzed data were horizontal earth pressures, strain of reinforcements, and excess pore water pressures. The used reinforcements were nonwoven geotextile, woven geotextile and geogrid. Although the length of reinforcement was only 30% of wall height and the safety factors of the walls were less than 1.3, the walls were constructed without any problems on the such weak ground. The analysis results showed that the maximum strain of reinforcements were negligible and the strain was between 2.3 and 6.0% according to tensile characteristic of the reinforcements. The excess pore water pressure was not changed due to the rainfall and the horizontal earth pressures in upper and lower part of the walls were larger than the active and the rest pressure.