• Steel and Composite Structures
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• v.33 no.4
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• pp.615-627
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• 2019

This paper aims to study the compressive behavior of circular hollow and concrete-filled steel tubular stub columns under simulated marine atmospheric corrosion. The specimens after salt spray corrosion were tested under axial compressive load. Steel grade and corrosion level were mainly considered in the study. The mechanical behavior of circular CFST specimens is compared with that of the corresponding hollow ones. Design methods for circular hollow and concrete-filled steel tubular stub columns are modified to consider the effect of marine atmospheric corrosion. The results show that linear fitting curves could be used to present the relationship between corrosion rate and the mechanical properties of steel after simulated marine atmospheric corrosion. The ultimate strength of hollow steel tubular and CFST columns decrease with the increase of corrosion rate while the ultimate displacement of those are hardly affected by corrosion rate. Increasing corrosion rate would change the failure of CFST stub column from ductile failure to brittle failure. Corrosion rate would decrease the ductility indexes of CFST columns, rather than those of hollow steel tubular columns. The confinement factor ${\xi}$ of CFST columns decreases with the increase of corrosion rate while the ratio between test value and nominal value shows an opposite trend. With considering marine atmospheric corrosion, the predicted axial strength of hollow steel tubular and CFST columns by Chinese standard agree well with the tested values while the predictions by Japanese standard seem conservative.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.2
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• pp.85-91
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• 2016

The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.

• Steel and Composite Structures
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• v.30 no.4
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• pp.365-382
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• 2019

In steel frame-tube structures (SFTSs) the application of flexural beam is not suitable for the beam with span-to-depth ratio lower than five because the plastic hinges at beam-ends can not be developed properly. This can lead to lower ductility and energy dissipation capacity of the SFTS. To address this problem, a replaceable shear link, acting as a ductile fuse at the mid length of deep beams, is proposed. SFTS with replaceable shear links (SFTS-RSLs) dissipate seismic energy through shear deformation of the link. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings and finite element models (FEMs) were established to study their hysteretic behavior. Static pushover and dynamic analyses were undertaken in comparing seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial lateral stiffness. Compared with SFTS, SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. During earthquakes, SFTS-RSL had lower interstory drift, maximum base shear force and story shear force compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrates plasticity on the shear link. Other structural components remain elastic during seismic loading. It is expected that the SFTS-RSL will be a reliable dual resistant system. It offers the benefit of being able to repair the structure by replacing damaged shear links after earthquakes.

• Earthquakes and Structures
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• v.16 no.4
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• pp.469-485
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• 2019

A numerical investigation regarding local (${\mu}_L$) and story (${\mu}_S$) ductility demand evaluation of steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (IGF), is conducted in this study. The interior connections are modeled, firstly as perfectly pinned (PP), and then as semi-rigid (SR). Three models used in the SAC steel project, representing steel buildings of low-, mid-, and high-rise, are considered. The story ductility reduction factor ($R_{{\mu}S}$) as well as the ratio ($Q_{GL}$) of $R_{{\mu}S}$ to ${\mu}_L$ are calculated. ${\mu}_L$ and ${\mu}_S$, and consequently structural damage, at the PMRF are significant reduced when the usually neglected effect of SR connections is considered; average reductions larger than 40% are observed implying that the behavior of the models with SR connections is superior and that the ductility detailing of the PMRF doesn't need to be so stringent when SR connections are considered. $R_{{\mu}S}$ is approximately constant through height for low-rise buildings, but for the others it tends to increase with the story number contradicting the same proportion reduction assumed in the Equivalent Static Lateral Method (ESLM). It is implicitly assumed in IBC Code that the overall ductility reduction factor for ductile moment resisting frames is about 4; the results of this study show that this value is non-conservative for low-rise buildings but conservative for mid- and high-rise buildings implying that the ESLM fails evaluating the inelastic interstory demands. If local ductility capacity is stated as the basis for design, a value of 0.4 for $Q_{GL}$ seems to be reasonable for low- and medium-rise buildings.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.1
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• pp.37-47
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• 2023

A new clamped mechanical splice system was proposed to develop structural performance and constructability for precast concrete connections. The proposed mechanical splice resists external loading immediately after the engagement. The mechanical splices applicable for both large-scale rebars for plants and small-scale rebars for buildings were developed with the same design concept. Quasi-static lateral cyclic loading tests were conducted with reinforced and precast concrete members to verify the seismic performance. Also, shaking table tests with three types of seismic wave excitation, 1) random wave with white noise, 2) the 2016 Gyeongju earthquake, and 3) the 1999 Chi-Chi earthquake, were conducted to confirm the dynamic performance. All tests were performed with real-scale concrete specimens. Sensors measured the lateral load, acceleration, displacement, crack pattern, and secant system stiffness, and energy dissipation was determined by lateral load-displacement relation. As a result, the precast specimen provided the emulative performance with RC. In the shaking table tests, PC frames' maximum acceleration and displacement response were amplified 1.57 - 2.85 and 2.20 - 2.92 times compared to the ground motions. The precast specimens utilizing clamped mechanical splice showed ductile behavior with energy dissipation capacity against strong motion earthquakes.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.2_2
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• pp.333-340
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• 2023

Environmental regulations are being strengthened worldwide to solve global warming. For this reason, interest in eco-friendly gas fuels such as LNG and hydrogen is continuously increasing. However, when adopting eco-friendly gas fuel, liquefying at a cryogenic temperature is essential to ensure economic feasibility in storage and transportation. Although austenitic stainless steel is typically applied to store cryogenic liquefied gas, structural steel can experience sudden heat shrinkage in the case of leakage in the loading and unloading process of LNG. In severe cases, the phase of the steel may change, so care is required. This study conducted Charpy impact tests on steel material in nine different temperature ranges, from room to cryogenic temperatures, to analyze the effects of cryogenic liquefied gas leaks. As a result of the study, it was not easy to find variations in ductile to brittle transition temperature (DBTT) due to the leakage of cryogenic liquefied gas. Still, the overall impact toughness tended to decrease, and these results were verified through fracture surface analysis. In summary, brittle fracture of the steel plate may occur when a secondary load is applied to steel for hull structural use exposed to a cryogenic environment of -40 ℃ or lower. Therefore, it needs to be considered in the ship design and operating conditions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.283-293
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• 2023

With the steady increase in the annual number of earthquakes in South Korea, the need to apply seismic reinforcement on public facilities has recently increased. To reinforce seismic capacity, spaced full-column-height steel bars are attached to column faces. In this study, nonlinear finite element analysis was conducted to analyze the effect of external reinforcement steel bars on the seismic capacity of RC columns with a square or rectangular cross-section. For verification, the analysis results were compared with test results. Results showed that the finite element analysis reasonably predicted the actual structural behavior of RC columns with steel bars. In addition, both the analysis and the test results showed that the failure mode was converted from brittle failure to ductile fracture, owing to the external reinforcement steel bars. Both loading capacity and ductility were increased as well. Therefore, the external reinforcement steel bar can effectively enhance the seismic capacity of existing RC columns. This study is expected to contribute to relevant research areas such as the development of design methods.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.180-192
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• 2008

The purpose of this research is to evaluate the structural performance of mortar-filled ductile cast iron sleeve splice developed for SD500 high-strength reinforcing bar under cyclic loading. The test variables adopted in this study are the development length of bar, compressive strength of mortar, bar size, sleeve types and others. In this research, it is showed that the mortar-filled sleeve splice for SD500 high-strength bar satisfied the structural performance required in ACI, AIJ code as well as domestic code. Also the results of experimental research presented in this paper provided basic engineering data for developing a reasonable design method of mortar-filled sleeve splice for SD500 high-strength reinforcing bar.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.687-696
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• 2004

It has been known that practically unavoidable lap splices of longitudinal reinforcement in the plastic hinge region have a bad effect on the seismic performance of reinforced concrete bridge columns. Lap splices were usually located in the plastic hinge region of most bridge columns designed before the implementation of the new seismic design provisions of 1992 Korea Bridge Design specification. The objective of this research is to evaluate the seismic performance of full-sized reinforced concrete bridge piers with lap splice of longitudinal reinforcement in the plastic hinge region, and to develop an appropriate lateral confinement concept of RC bridge columns with lap-spliced longitudinal steels in low or moderate seismicity region. Eight test specimens in the aspect ratio of 4.0 were made with three types of lap splicing, two levels of confinement steel ratios and two types of tie configurations. It was confirmed from the Quasi-Static test that displacement ductility ratios were significantly reduced for nonseismic test columns with lap spliced longitudinal steels but were satisfied the seismic requirement for limited ductile design specimens. As a conclusion, pertinent lateral confinement content was proposed for the seismic. performance of RC bridge piers with $50\%$ lap-spliced longitudinal reinforcing steels in low or moderate seismicity region.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.27-34
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• 2005

The purpose of this study is to investigate the structural behavior of RC Piers using high strength concrete and high strength rebars. The high strength concrete offers many advantages such as enhanced mechanical performance and durability, in addition to member size reduction. The high strength rebars are used here to reduce the amount of rebars, which facilitates the placement of concrete and labor works. Five RC piers were tested under a constant axial load and a cyclically reversed horizontal load. The seismic design of piers were implemented, according to the current Korean Bridge Design Code. The test variables include concrete compressive strength, steel strength, and steel ratio. The test results indicate that RC piers using the high strength concrete and high strength rebars exhibit ductile behavior and appropriate seismic performance, in compliance with the design code. The present study allows more realistic application of high strength rebars and concrete to RC piers, which will provide enhanced durability as well as more economy.