• Journal of Korean Society of Steel Construction
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• v.23 no.5
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• pp.535-546
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• 2011

In this paper, semi-rigid elasto-plastic post-buckling analysis of a space frame was performed using various explicit arc-length methods. Various explicit arc-length methodsand a large-deformation and small-strain elasto-plastic 3D space frame element with semi-rigid connections and plastic hinges were developed. This element can be appliedto both explicit and implicit numerical algorithms. In this study, the Dynamic Relaxation method was adopted in the predictor and corrector processesto formulate an explicit arc-length algorithm. The developed "explicit-predictor" or "explicit-corrector" were used in the elasto-plastic post-buckling analysis. The Eulerian equations for a beam-column with finite rotation, which considers the bowing effects, were adopted for the elastic system and extended to theinelastic system with a plastic hinge concept. The derived tangent stiffness matrix was asymmetrical due to the finite rotation. The joint connection elements were introduced for semi-rigidity using a static condensation technique. Semi-rigid elasto-plastic post-buckling analyses were carried out to demonstrate the potential of the developed explicit arc-length method and advanced space frame element in terms of accuracy and efficiency.

• 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.

• Land and Housing Review
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• v.7 no.1
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• pp.31-41
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• 2016

In this paper, we propose experimental results, which target the major variables that influence the structural performance of a wall, as well as the resulting seismic and hysteretic behavior. Results also provide the basis for the application of performance based design by identifying the nonlinear hysteretic behavior of the wall with boundary element details recently proposed in previous study by Chun et al(2011). From the experimental results, the crack and fracture patterns of a specimen, which adopt the proposed boundary element details, showed similar tendencies regardless of whether axial force or high performance steel bars is applied. Furthermore, results show that the maximum strength of the specimen can be predicted accurately based on the design equation proposed by the standard. In addition, with a higher axial force, there is a tendency that both the initial load and maximum strength increase as deformation capacity reduces, requiring consideration of the reduced deformation capacity due to a high axial force. For walls under such high axial forces, using high performance steel bars is a very effective manner of enhancing deformation capacity. Therefore, reinforcing the plastic hinge region with boundary elements using high performance steel bars is preferable.

• Journal of Korean Society of Steel Construction
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• v.29 no.5
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• pp.361-368
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• 2017

ASCE 7-10 defines the torsional irregular structure as the one that has large torsional responses caused by the eccentricity. The code requires that these structures should be designed abide by the torsional provisions. This study evaluates the influence of torsional provisions on the performance of the designed multiple steel moment frames with different eccentricity. In this study, 3D response history analyses are performed. The results show that the moment frame design according to the standard with torsional irregularity provisions showed larger performance as the eccentricity increased and the distribution of plastic hinges similarly to orthopedic structures.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.6 s.40
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• pp.31-43
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• 2004

Seismic risk assessment of bridge is presented using fragility curves which represent the probability of damage of a structure virsus the peak ground acceleration. In theseismic fragility analysis, the structural damage is defined using the rotational ductility at the base of the bridge pier, which is obtained through nonlinear dynamic analysis for various input earthquakes. For the assessment of seismic risk of bridge, peak ground accelerations are obatined for various return periods from the seismic hazard map of Korea, which enables to calculate the probability density function of peak ground acceleration. Combining the probability density function of peak ground acceleration and the seismic fragility analysis, seismic risk assessment is performed. In this study, seismic fragility analysis is developed as a function of not the surface motion which the bridge actually suffers, but the rock outcrop motion which the aseismic design code is defined on, so that further analysis for the seismic hazard assessment may become available. Besides, the effects of the friction pot bearings and the friction pendulum bearings on the seismic fragility and risk analysis are examined. Lastly, three regions in Korea are considered and compared in the seismic risk assessment.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.2
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• pp.93-106
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• 2021

In general, segment lining tunnel refers to a tunnel formed by connecting precast concrete segments as a ring and connecting such rings to each other in the longitudinal direction of the tunnel. As the structural properties of the segment lining is highly dependent on the behavior of the segment joints, thus correct modelling of joint behavior is crucial to understand and design the segment tunnel lining. When the tunnel is subjected to ground loads, the segment joint behaves like a hinge that resists rotation, and when the induced moment exceeds a certain limit of the rotation then it may enter into non-linear field. In understanding the effect of the segment joint on the lining behavior, a moment-rotation relationship of the segment joint was explored based on the Japanese practice and Janssen's approach commonly used in the actual design. This study also presents a method to determine the rotational stiffness of joint refer to the bearing strength. The rotation of the segment joint was estimated in virtual design conditions based on the existing models and the proposed method. And the sectional force of the segment lining and joint were calculated along with the estimated rotation. As the rotation at the segment joint increases, the joint contact area decreases, so the designer have to verify the segment joint for bearing strength as well. This paper suggests a consistent method to determine the rotational stiffness and bearing strength of joints.

• Fashion & Textile Research Journal
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• v.24 no.6
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• pp.667-685
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• 2022

This paper aims to investigate 4D printing materials for soft robots. 4D printing is a targeted evolution of the 3D printed structure in shape, property, and functionality. It is capable of self-assembly, multi-functionality, and self-repair. In addition, it is time-dependent, printer-independent, and predictable. The shape-shifting behaviors considered in 4D printing include folding, bending, twisting, linear or nonlinear expansion/contraction, surface curling, and generating surface topographical features. The shapes can shift from 1D to 1D, 1D to 2D, 2D to 2D, 1D to 3D, 2D to 3D, and 3D to 3D. In the 4D printing auxetic structure, the kinetiX is a cellular-based material design composed of rigid plates and elastic hinges. In pneumatic auxetics based on the kirigami structure, an inverse optimization method for designing and fabricating morphs three-dimensional shapes out of patterns laid out flat. When 4D printing material is molded into a deformable 3D structure, it can be applied to the exoskeleton material of soft robots such as upper and lower limbs, fingers, hands, toes, and feet. Research on 4D printing materials for soft robots is essential in developing smart clothing for healthcare in the textile and fashion industry.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.65-73
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• 2012

In this study, we tested structural performance of Half-Decked PSC girder which was developed for applying to long span bridge. We operated 4 point bending test with 60 m span full scale girder designed as simple bridge with hinge-roller boundary condition. Actuators were set on the both sides of girder, 5.5 m away from the center, and 4 stages of cyclic loading was applied at rate of 1 kN/sec. Through stages 1 to 4, loading and unloading 1,000 kN, 1,200 kN, 1,500 kN, and 2,000 kN were repeated and displacement, strain of concrete and steel, crack of girder were checked. From these results, the strength of girder was assessed and resilience and ductility were observed after removing the load. Since initial flexural crack occurred in the vicinity of 1,400 kN, non-linearity of load-displacement curve appeared and definite residual strain was measured at that point. The test result showed that initial cracking load was over twice the DB-24 load which means the developed girder had sufficient strength. To verify the experimental results, we numerically analyze the test and confirmed that the data were similar with results from the test above. Half-Decked PSC type of 60 m-girder developed in this study showed its adequate structural capacity through static loading test, which proved that possibility of applying the girder to actual bridges practically.

• Journal of Korean Society of Steel Construction
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• v.29 no.1
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• pp.81-88
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• 2017

Residual stress is defined as stress that already exists on a structural member from the effects of welding and plastic deformation before the application of loading. Due to such residual stress, welded H-section compression members under centroidal compression load can undergo buckling and failure for strength values smaller than the predicted buckling load and specified compressive strength. Therefore, this study was carried out to evaluate the effect of residual stress from welding on the determination of the buckling load and specified compressive strength of the H-section compression member according to the column length variation. A three-dimensional nonlinear finite element analysis was performed for the H-section compression member where the welded joint was fillet welded by applying heat inputs of 3.1kJ/mm and 3.6kJ/mm using the SAW welding method.

• Journal of Korean Society of Steel Construction
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• v.28 no.6
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• pp.439-448
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• 2016

Extended end-plate connections(EEPC) are a type of connection applied in Pre-Engineered Building structures comprising beam-column connections of steel structures or tapered members. Extended end-plate connections(EEPC) show different behavioral characteristics owing to the influence of plate thickness, gauge distance of high strength bolt, diameter of high strength bolt frame, and the number of high strength bolts. In the USA and Europe, extended end-plate connections(EEPC) are applied in beam-column connections of steel structures in various forms; however, these are not widely applied in structures in Korea.This can be attributed to the fact that the proposal of design strength types for extended end-plate connections(EEPC), proposal of connection specifications, evaluation of seismic performance, and are not being performed appropriately. Therefore, the purpose of this study is to provide basic data for the domestic application of Unstiffened extended endplate connections. To realize this, nonlinear finite element analysis was conducted on a 12-mm thick Unstiffened extended endplate connections.