• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.679-688
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• 2003

For box girders in which the longitudinal tendon is profiled in the inclined webs, longitudinal prestressing force will induce transverse effects as well as longitudinal ones. In this paper, the method to estimate transverse effects induced by longitudinal prestressing is proposed. The concept of transverse equivalent loading which is calculated through longitudinal prestressing analysis is developed. The transverse stress in slabs of box girders due to longitudinal prestressing are investigated. The comparison of numerical results of the proposed method and those of folded plate method represents that the method is reasonable. Numerical analyses are carried out depending on the parameters such as web inclination and ratio of girder length to tendon eccentricity. Analysis results show that when only prestressing are considered the magnitude of transverse stress in slabs of box girder is not so large. However, if the other stresses due to dead and live load et al. are superposed on these stresses, it may be that the longitudinal prestressing effects are significant.

• Magazine of the Korea Concrete Institute
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• v.6 no.5
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• pp.171-182
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• 1994

Recently, several prestressed concrete box girder bridges have experienced severe cracking along the tendon path when prestress force has been transferred to the anchorage zone. The purpose of the present study is therefore to explore characteristics of the local stress distribution, to study the effects of section geometry of anchorage zones, i.e., tendon inclination, tendon eccentricity and concrett. cover thickness anti to develop recornrncnd;itions for specific design criteria for post~tensioned a:lchorage zones. 7'0 accomplish these objectives, a cc~mprehen sive nonlinar finite element study has been conducted. From this study, realistic forrnulas for crackinq and ultimate load capacities are proposed. 'These equations reasonably well predict the crackinq and ultimate loads of prestressed concrete anchorage zones.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.725-734
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• 2012

A new modular pier system using concrete filled circular steel tubes was suggested to realize modular bridge substructures for accelerated bridge construction. Structural details and connection details were proposed by connection multiple concrete filled tubes (CFT) for standardized products of fabrication, delivery and erection. Static tests were performed for the modular pier with suggested details under lateral load conditions for weak and strong axes. Due to the eccentricity by the bracing system, the modular pier showed 5.23 times higher flexural stiffness and 6 times greater flexural strength from the test. It is proper for the rational design to evaluate stress and deformation by frame modeling of the modular CFT pier. Structural capacity of the pier can be obtained by adjusting the spacing of the CFT columns. Design recommendations were derived from the test.

• Earthquakes and Structures
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• v.9 no.1
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• pp.49-71
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• 2015

The present paper aims at evaluating damage and collapse behavior of low-rise buildings with unidirectional mass irregularities in plan (torsional buildings). In previous earthquake events, such buildings have been exposed to extensive damages and even total collapse in some cases. To investigate the performance and collapse behavior of such buildings from probabilistic points of view, three-dimensional three and six-story reinforced concrete models with unidirectional mass eccentricities ranging from 0% to 30% and designed with modern seismic design code provisions specific to intermediate ductility class were subjected to nonlinear static as well as extensive nonlinear incremental dynamic analysis (IDA) under a set of far-field real ground motions containing 21 two-component records. Performance of each model was then examined by means of calculating conventional seismic design parameters including the response reduction (R), structural overstrength (${\Omega}$) and structural ductility (${\mu}$) factors, calculation of probability distribution of maximum inter-story drift responses in two orthogonal directions and calculation collapse margin ratio (CMR) as an indicator of performance. Results demonstrate that substantial differences exist between the behavior of regular and irregular buildings in terms of lateral load capacity and collapse margin ratio. Also, results indicate that current seismic design parameters could be non-conservative for buildings with high levels of plan eccentricity and such structures do not meet the target "life safety" performance level based on safety margin against collapse. The adverse effects of plan irregularity on collapse safety of structures are more pronounced as the number of stories increases.

• Journal of Korean Society of Steel Construction
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• v.14 no.4
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• pp.471-479
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• 2002

In this paper, 18 square CFT columns filled with high-strength concrete were tested under concentric or eccentric axial loading. Two parameters of the experimental program included the buckling length-section depth ratio ($L_K$/D) and the eccentricity of the appled compressive load (e). In additon, mechanical properties such as the compressive concrete strength and compressive and tensile steel strength were measured and incorporated into the material models for the stress-strain relationships of concrete and steel. This model was used in an elasto-plastic analysis in order to predict the behavior of the slender CFT columns. Observtions of the failure mode during the tests under axial loadig were also presented. The strengths obtained from the analysis. Recommendations for Design, and Constructions of CFT structures were presented, as verified by the experimental results.

• Tribology and Lubricants
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• v.34 no.1
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• pp.16-22
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• 2018

Cylindrical turbine guide bearings (TGBs) with simple plain pads have conventionally been used in vertical hydro-power turbine-generator applications in order to provide turbine runner shafts with smooth rotation guides and supports. To overcome low-load/low-eccentricity performance drawbacks, such as very low film stiffness and lack of design credibility in the stiffness values themselves, of conventional cylindrical TGBs, the introduction of a rotational-directional leading-edge taper to each partitioned pad, simply pad leading-edge taper, has been found to be very effective in enhancing their design-application availability and usefulness. In this study, we investigate the effects of taper angle and length for given taper heights in detail in order to systematically establish the effectiveness of design on the performance improvement of vertical hydro-power application cylindrical TGBs with pad leading-edge tapers. The analysis results with $4-Pad{\times}1-Row$ cylindrical TGBs show that the lubrication performance of the cylindrical TGBs is optimized with an approximate taper angle ratio of 0.8 and taper length ratio of 0.9. We conclude that the introduction of pad leading-edge tapers along with the optimization of taper designs can be very effective in improving the overall operation reliability of cylindrical TGBs and the rotordynamic characteristics of vertical hydro-power turbine-generator rotor-bearing systems as well, to which the TGBs are applied.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.1
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• pp.117-124
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• 1991

In this paper, a method to overcome inefficiency of the finite element method in the calculation of compressive strength of one-sided stiffened plates, is proposed. In this method the collapse modes of stiffened plates are assumed as follows. a) Overall buckling $\rightarrow$ Overall collapse b) Local buckling $\rightarrow$ Overall collapse c) Local buckling $\rightarrow$ Local collapse In each collapse mode, shape of deflection is assumed, and then elastic large deformation analysis based on the Rayleigh-Ritz method is carried out. One-sided stiffening effect is considered by taking into account of the moment due to eccentricity. Plastic analysis by assuming hinge lines is also carried out. The ultimate strength of a stiffened plate is obtained as the point of intersection of the elastic analysis curve and the plastic one. From this study, it is concluded that the angles between the plastic hinge lines in plastic collapse mode are determined as the ones which give the minimum collapse load, and these angles are different from the ones assumed in the previous studies. Minimum stiffness ratios can also be calculated. Calculated results according to this method show good agreements with the results by the finite element method.

• Advances in concrete construction
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• v.13 no.2
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• pp.163-181
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• 2022

To study the mechanical properties of steel reinforced recycled concrete (SRRC) filled circular steel tube columns under eccentric compression loads, this study presents a finite element model which can simulate the eccentrically compressed columns using ABAQUS software. The analytical model was established by selecting the reasonable nonlinear analysis theory and the constitutive relationship of materials in the columns. The influences of design parameters on the eccentric compressive performance of columns were also considered in detail, such as the diameter-thickness ratio of circular steel tube, replacement percentage of recycled coarse aggregate (RCA), slenderness ratio, eccentricity, recycled aggregate concrete (RAC) strength and steel strength and so on. The deformation diagram, stress nephogram and load-displacement curves of the eccentrically compressed columns were obtained and compared with the test results of specimens. The results show that although there is a certain error between the calculation results and the test results, the error is small, which shows the rationality on the numerical model of eccentrically compressed columns. The failure of the columns is mainly due to the symmetrical bending of the columns towards the middle compression zone, which is a typical compression bending failure. The eccentric bearing capacity and deformation capacity of columns increase with the increase of the strength of steel tube and profile steel respectively. Compared with profile steel, the strength of steel tube has a greater influence on the eccentric compressive performance of columns. Improving the strength of RAC is beneficial to the eccentric bearing capacity of columns. In addition, the eccentric bearing capacity and deformation capacity of columns decrease with the increase of replacement percentage of RCA. The section form of profile steel has little influence on the eccentric compression performance of columns. On this basis, the calculation formulas on the nominal eccentric bearing capacity of columns were also put forward and the results calculated by the proposed formulas are in good agreement with the test values.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.201-210
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• 2023

This study is to evaluate the ductility strengthening effect of aramid fiber sheets on piloti-type structures. Two piloti-type structure specimens were prepared and tested under statical cyclic lateral loads. The ductility strengthening effect was validated from the analysis of lateral load-displacement relationship, displacement ductility ratio, work damage index and torsion behavior. Test results showed that the post-peak behavior of piloti-type structures with columns strengthened with aramid fiber sheets tended to be ductile resulting from preventing shear failure and minimizing torsion due to the effective lateral confinement of column concrete by aramid fiber sheet. Consequently, the displacement ductility ratio and work damage index of piloti-type structures with columns with strengthened with aramid fiber sheets were 4.63 and 42.81 times higher than those of non strengthened piloti-type structures.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.1125-1146
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• 2018

Segment lining applied to the TBM tunnel is mainly made of concrete, and it requires sufficient structural capacity to resist loads received during the construction and also after the completion. When segment lining is design to the Limit State Design, both Ultimate Limit State (ULS) and Service Limit State (SLS) should be met for the possible load cases that covers both permanent and temporary load cases - such as load applied by TBM. When design segment lining, it is important to check structural capacity at the joints as both temporary and permanent loads are always transferred through the segment joints, and sometimes the load applied to the joint is high enough to damage the segment - so called bursting failure. According to the various design guides from UK (PAS 8810, 2016), compression stress at the joint surface can generate bursting failure of the segment. This is normally from the TBM's jacking force applied at the circumferential joint, and the lining's hoop thrust generated from the permanent loads applied at the radial joint. Therefore, precast concrete segment lining's joints shall be designed to have sufficient structural capacity to resist bursting stresses generated by the TBM's jacking force and by the hoop thrust. In this study, bursting stress at the segment joints are calculated, and the joint's structural capacity was assessed using Leonhardt (1964) and FEM analysis for three different design cases. For those three analysis cases, hoop thrust at the radial joint was calculated with the application of the most widely used limit state design codes Eurocode and AASHTO LRFD (2017). For the circumferential joints bursting design, an assumed TBM jack force was used with considering of the construction tolerance of the segments and the eccentricity of the jack's position. The analysis results show reinforcement is needed as joint bursting stresses exceeds the allowable tensile strength of concrete. This highlights that joint bursting check shall be considered as a mandatory design item in the limit state design of the segment lining.