• Magazine of the Korea Concrete Institute
• /
• v.8 no.3
• /
• pp.187-195
• /
• 1996

A finite element formulation based on the CFT(Compression Field Theory), considering the effect of compression softening in cracked concrete, and macro-scopic and rotating crack models etc., was presented for the nonlinear behaviour of structural concrete. Considering the computational efficency and the ability of modelling the post-ultimate behaviour as major concerns, the Incremental displacement solution algorithm involving initial material stiffnesses and the relaxation procedure for fast convergence was adopted and formulated in a type of 8-noded quadrilateral isoparametric elements. The analysis program NASCOM(Non1inear Analysis of Structural Concrete by FEM : Monotonic Loading) developed in this way enables the predictions of strength and deformation capacities in a full range, crack patterns and their corresponding widths, and yield extents of reinforcement. As the verification purpose of NASCOM, the predictions were made for Bhide's Panel(PB21) and Leonhardt's deep beam tests. The predicted results shows somewhat stiff behaviour for the panel test, and vice versa for deep beam tests. More refining process would be necessary hereafter in terms of more accurately simulating the effects of tension-stiffening and compression softening in concrete.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.1
• /
• pp.55-61
• /
• 2016

This paper presents the geotechnical characteristics of the soil mixed with various waste(waste soil) in the landfill. The physical and mechanical tests were conducted to find out the waste soil. The tests include the gradation, consistency tests, shear and compression and the consolidation tests using both the Rowe cell and the constant ration stress. The analyses of the test results show the waste soil belongs to the well graded sand(SW) in the laboratory and sand-gravel(SG) to fine sand(SF) in the field monitoring based on the unified classification soil system. The shear strength is increasing with increasing the shear displacement, however, the peak of the shear strength does not appear through the test and there is no distinct peak value of the strength obtained. The compression index(Cc) results in as increasing the amount of the sludge included and the compression index is proportional to the sludge included, which means more settlement is expected. The hydraulic conductivity of the waste soil ranges between $1.6{\times}10^{-5}cm/sec$ and $1.8{\times}10^{-7}cm/sec$.

• Geomechanics and Engineering
• /
• v.12 no.3
• /
• pp.541-560
• /
• 2017

In this research, experimental and numerical simulations were adopted to investigate the effects of ligament angle on compressive strength and failure mode of rock-like material specimens containing two non-coplanar filled fissures under uniaxial compression. The experimental results show that with the increase of ligament angle, the compressive strength decreases to a nadir at the ligament angle of $60^{\circ}$, before increasing to the maximum at the ligament angle of $120^{\circ}$, while the elastic modulus is not obviously related to the ligament angle. The shear coalescence type easily occurred when ${\alpha}$ < ${\beta}$, although having the same degree difference between the angle of ligament and fissure. Numerical simulations using $PFC^{2D}$ were performed for flawed specimens under uniaxial compression, and the results are in good consistency with the experimental results. By analyzing the crack evolution process and parallel bond force field of rock-like material specimen containing two non-coplanar filled fissures, we can conclude that the coalescence and propagation of crack are mainly derived from parallel bond force, and the crack initiation and propagation also affect the distribution of parallel bond force. Finally, the displacement vectors in ligament region were used to identify the type of coalescence, and the results coincided with that obtained by analyzing parallel bond force field. These experimental and numerical results are expected to improve the understanding of the mechanism of flawed rock engineering structures.

• Transactions of Materials Processing
• /
• v.29 no.5
• /
• pp.257-264
• /
• 2020

This paper is concerned with the influence of the plastic property of the rivet on the numerical prediction of the Self-Piercing Rivet (SPR) Joining. In order to predict the plastic property of the rivet, a ring compression specimen was directly fabricated from the rivet used for the mechanical joining of dissimilar materials, and the FE analysis together with the ring compression test was iteratively carried out by changing the plastic property of the rivet. For reliable FE analysis, a friction coefficient was estimated based on a friction calibration curve, measuring the reductions in inner diameter and height of the ring specimen after the compression test. From each simulation result, the force-displacement curves were then compared from each other so as to obtain the rivet plastic property that shows good agreement with the experimental result. The SPR joining between GA590 1.0t and Al5052 2.0t was conducted, and the numerical prediction was performed with the use of the plastic property evaluated based on the inverse analysis and the one referred from Mori et al. [11]. Comparison of the experiment and the numerical predictions in terms of the interlock and bottom thickness revealed that the reliable evaluation of the plastic property of the rivet is necessary for the trustworthy numerical prediction of the SPR joining.

• Steel and Composite Structures
• /
• v.32 no.3
• /
• pp.361-372
• /
• 2019

Tubular joints are used in the construction of offshore structures and other land-based structures because of its ease of fabrication. These joints are subjected to different environmental loadings in their lifetime. At the time of fabrication or modification of an existing offshore platform, tubular joints are usually strengthened to withstand the environmental loads. Currently, various strengthening techniques such as ring stiffeners, gusset plates are employed to strengthen new and existing tubular joints. Due to some limitations with the present practices, some new techniques need to be addressed. Many researchers used Fibre Reinforced Polymer (FRP) to strengthen tubular joints. Some of the studies were focused on axial compression of Glass Fibre Reinforced Polymer (GFRP) strengthened tubular joints and found that it was an efficient technique. Earlier, the authors had performed studies on Carbon Fibre Reinforced Polymer (CFRP) strengthened tubular joint subjected to axial compression. The study steered to the conclusion that FRP composites is an alternative strengthening technique for tubular joints. In this work, the study was focused on axial compression of Y-joint and in plane and out of plane bending of T-joints. Experimental investigations were performed on these joints, fabricated from ASTM A106 Gr. B steel. Two sets of joints were fabricated for testing, one is a reference joint and the other is a joint strengthened with CFRP. After performing the set of experiments, test results were then compared with the numerical solution in ANSYS Parametric Design Language (APDL). It was observed that the joints strengthened with CFRP were having improved strength, lesser surface displacement and ovalization when compared to the reference joint.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.12
• /
• pp.41-46
• /
• 2018

In this research, numerical analysis was performed to determine the effects of hydrogen on biogas combustion for homogeneous charged compression ignition (HCCI) engines. The target engine specifications were a 2300cc displacement volume, 13:1 compression ratio, 15kW of electricity, and 1.2 bar boost pressure. The engine speed was fixed to 1800rpm. By varying the excess air ratio and hydrogen contents, the cylinder pressure, nitric oxide, and carbon dioxide were measured as a function of the hydrogen contents. According to preliminary studies related to the reaction mechanism for methane combustion and oxidation, a GRI 3.0 mechanism as the base mechanism was selected for HCCI combustion calculations describing the detailed reaction mechanism. By adding hydrogen, NO was increased while $CO_2$ was decreased. The cylinder pressure was also increased, having advanced timing for the maximum cylinder pressure and pressure rise region. Furthermore, lean operation limits were extended by adding hydrogen to the HCCI engine.

• Journal of the Korean Geotechnical Society
• /
• v.38 no.8
• /
• pp.75-84
• /
• 2022

Currently, tension ground anchors are divided into temporary and permanent based on their purpose and period of use, and their performance evaluations are presented separately. Therefore, applying the current performance evaluation's upper and lower limits to practice seems reasonable. However, because compression ground anchors have been mainly used as permanent, performance evaluation corresponding to permanent is conducted without distinction between temporary and permanent. This evaluation is a strict standard for ground anchors used as temporary, including the removal type. Because of examining the existing performance evaluation for the compression ground anchor, the lower limit can be applied without distinguishing between the temporary and permanent. However, the upper limit should be presented separately for the temporary and permanent. In applying the upper limit, it is necessary to adjust the upper limit of the anchor considering the anchored ground condition (rock or soil), the period of use, and particularly whether the load-displacement curve maintains the elastic state.

• Wind and Structures
• /
• v.37 no.4
• /
• pp.289-302
• /
• 2023

Insulating glass units (IGUs) have been widely used in buildings in recent years due to their superior thermal insulation performance. However, because of the panel reciprocating motion and fatigue deterioration of sealants under long-term wind loads, many IGUs have the problem of early failure of watertight properties in real usage. This study aimed to propose a statistical method for wind-induced deflection of IGU panels during the whole life service period, for further precise analysis of the accumulated fatigue damage at the sealed part of the edge bond. By the estimation of the wind occurrence regularity based on wind pressure return period, the events of each wind speed interval during the whole life were obtained for the IGUs at 50m height in Beijing, which are in good agreement with the measured data. Also, the wind-induced deflection analysis method of IGUs based on the formula of airspace coefficient was proposed and verified as an improvement of the original stiffness distribution method with the average relative error compared to the test being about 3% or less. Combining the two methods above, the deformation of the outer and inner panes under wind loads during 30 years was precisely calculated, and the deflection and stress state at selected locations were obtained finally. The results show that the compression displacement at the secondary sealant under the maximum wind pressure is close to 0.3mm (strain 2.5%), and the IGUs are in tens of thousands of times the low amplitude tensile-compression cycle and several times to dozens of times the relatively high amplitude tensile-compression cycle environment. The approach proposed in this paper provides a basis for subsequent studies on the durability of IGUs and the wind-resistant behaviors of curtain wall structures.

• Structural Engineering and Mechanics
• /
• v.14 no.3
• /
• pp.287-306
• /
• 2002

The assessment of structural performance of transfer structures under potential seismic actions is presented. Various seismic assessment methodologies are used, with particular emphasis on the accurate modelling of the higher mode effects and the potential development of a soft storey effect in the mega-columns below the transfer plate (TP) level. Those methods include response spectrum analysis (RSA), manual calculation, pushover analysis (POA) and equivalent static load analysis (ESA). The capabilities and limitations of each method are highlighted. The paper aims, firstly, to determine the appropriate seismic assessment methodology for transfer structures using these different approaches, all of which can be undertaken with the resources generally available in a design office. Secondly, the paper highlights and discusses factors influencing the response behaviour of transfer structures, and finally provides a general indication of their seismic vulnerability. The representative Hong Kong building considered in this paper utilises a structural system with coupled shear walls and moment resisting portal-frames, above and below the TP, respectively. By adopting the wind load profile stipulated in the Code of Practice on Wind Effects: Hong Kong-1983, all the structural members are sized and detailed according to the British Standards BS8110 and the current local practices. The seismic displacement demand for the structure, when built on either rock or deep soil sites, was determined in a companion paper. The lateral load-displacement characteristic of the building, determined herein from manual calculation, has indicated that the poor ductility (brittle nature) of the mega-columns, due mainly to the high level of axial pre-compression as found from the analysis, cannot be effectively alleviated solely by increasing the quantity of confinement stirrups. The interstorey drift demands at lower and upper zones caused by seismic actions are found to be substantially higher than those arising from wind loads. The mega-columns supporting the TP and the coupling beams at higher zones are identified to be the most vulnerable components under seismic actions.

• Earthquakes and Structures
• /
• v.14 no.1
• /
• pp.73-84
• /
• 2018

Low cyclic loading tests are conducted on the steel reinforced recycled concrete (SRRC) column-steel (S) beam composite frame joints. This research aims to evaluate the earthquake damage performance of composite frame joints by performing cyclic loading tests on eight specimens. The experimental failure process and failure modes, load-displacement hysteresis curves, characteristic loads and displacements, and ductility of the composite frame joints are presented and analyzed, which shows that the composite frame joints demonstrate good seismic performance. On the basis of this finding, seismic damage performance is examined by using the maximum displacement, energy absorbed in the hysteresis loops and Park-Ang model. However, the result of this analysis is inconsistent with the test failure process. Therefore, this paper proposes a modified Park-Ang seismic damage model that is based on maximum deformation and cumulative energy dissipation, and corrected by combination coefficient ${\alpha}$. Meanwhile, the effects of recycled coarse aggregate (RCA) replacement percentage and axial compression ratio on the seismic damage performance are analyzed comprehensively. Moreover, lateral displacement angle is used as the quantification index of the seismic performance level of joints. Considering the experimental study, the seismic performance level of composite frame joints is divided into five classes of normal use, temporary use, repair after use, life safety and collapse prevention. On this basis, the corresponding relationships among seismic damage degrees, seismic performance level and quantitative index are also established in this paper. The conclusions can provide a reference for the seismic performance design of composite frame joints.