• International journal of steel structures
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• v.18 no.4
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• pp.1153-1166
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• 2018

This paper was concerned with the nonlinear analysis on the overall stability of H-type honeycombed composite column with rectangular concrete-filled steel tube flanges (STHCC). The nonlinear analysis was performed using ABAQUS, a commercially available finite element (FE) program. Nonlinear buckling analysis was carried out by inducing the first buckling mode shape of the hinged column to the model as the initial imperfection with imperfection amplitude value of L/1000 and importing the simplified constitutive model of steel and nonlinear constitutive model of concrete considering hoop effect. Close agreement was shown between the experimental results of 17 concrete-filled steel tube (CFST) specimens and 4 I-beams with top flanges of rectangular concrete-filled steel tube (CFSFB) specimens conducted by former researchers and the predicted results, verifying the correctness of the method of FE analysis. Then, the FE models of 30 STHCC columns were established to investigate the influences of the concrete strength grade, the nominal slenderness ratio, the hoop coefficient and the flange width on the nonlinear stability capacity of SHTCC column. It was found that the hoop coefficient and the nominal slenderness ratio affected the nonlinear stability capacity more significantly. Based on the results of parameter analysis, a formula was proposed to predict the nonlinear stability capacity of STHCC column which laid the foundation of the application of STHCC column in practical engineering.

• Earthquakes and Structures
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• v.26 no.5
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• pp.383-400
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• 2024

For a conventionally repaired frame-supported-transfer-slab (FSTS) reinforced concrete (RC) structure, both the transfer slab and the beam-to-column and transfer slab-to-column joints remain vulnerable to secondary earthquakes. Aimed at improving the seismic performance of a damaged FSTS RC structure, an innovative retrofitting scheme is proposed, which adopts the sector lead rubber dampers (SLRDs) at joints after the damaged FSTS RC structure is repaired by conventional approaches. In this paper, a series of quasi-static cyclic tests was conducted on a large-scale retrofitted FSTS RC structure. The seismic performance was evaluated and the key test results, including deformation characteristics, damage pattern, hysteretic behaviour, bearing capacity and strains on key components, were reported in detail. The test results indicated that the SLRDs started to dissipate energy under the service level earthquake, and thus prevented damages on the beam-to-column and transfer slab-to-column joints during the secondary earthquakes and shifted the plastic hinges away from the beam ends. The retrofitting scheme of using SLRDs also achieved the seismic design concept of 'strong joint, weak component'. The FSTS RC structure retrofitted by the SLRDs could recover more than 85% bearing capacity of its undamaged counterpart. The hysteresis curves were featured by the inverse "S" shape, indicating good bearing capacity and hysteresis performance. The deformation capacity of the damaged FSTS RC structure retrofitted by the SLRDs met the corresponding codified requirements for the case of the maximum considered earthquake, as set out in the Chinese seismic design code. The stability of the FSTS RC structure retrofitted by the SLRDs, which was revealed by the developed stains of the RC frame and transfer slab, was improved compared with the undamaged FSTS RC structure.

• Journal of the Korean Geotechnical Society
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• v.37 no.6
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• pp.5-20
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• 2021

In this study, a modified empirical formula for estimating the bearing capacity of the steel pipe prebored and precast pile was proposed by performing 20 cases of real-scale field pile loading tests. The proposed formula will be based on expanded SPT N-value in order to consider the realistic condition of the surrounding soil. The formula is proposed based on a statistic approach of the data points from the field pile loading test, in order to ensure safe engineering practice while finding a reliable formula. The statistical analysis of the data points from the loading test indicated that the existing formula has been underestimated the bearing capacity of the prebored and precast pile. The proposed formula estimates 15% and 20% higher pile End bearing capacity (q_t=230P_driven(kN/m²)) and the shaft resistance (f_max=3.0N_s^E(kN/m²)) compared to the existing formula. The accuracy and the stability of the proposed formula was verified by comparing the estimated results with additional field test data. The verification process showed that the proposed formula was estimated to be more accurate than the existing formula.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.35 no.6
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• pp.138-145
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• 2023

A study using numerical analysis techniques was conducted to examine the scour effect of pier-type dolphin structures installed in the domestic marine environment, and the effect of scour on horizontal bearing capacity was examined. In this study, we designed the berthing structures, taking into account the environmental and ground conditions of the target maritime area, and after calculating the predicted scour area, stability evaluation was performed by removing the ground elements of the area. The increase in scour depth was found to induce a direct decrease in horizontal bearing capacity due to soil loss in contact with the foundation, establishing a relationship that increases horizontal displacement. However, in the foundation designed to withstand the design load by reflecting the safety rate, the increase in horizontal displacement formed by possible scour is not large, which did not have a dominant effect on the horizontal bearing capacity of the foundation. In the future, research is required to analyze the impact of each factor and formalize evaluation and design techniques to evaluate the scour safety of marine foundations and pier-type structures installed in various ground conditions and structural formats.

• Steel and Composite Structures
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• v.17 no.1
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• pp.105-121
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• 2014

A fundamental limitation of steel structures is the decrease in their load-bearing capacity at high temperatures in fire situations such that structural members may require some additional treatment for fire resistance. In this regard, this paper evaluates the structural stability of fire-resistant steel, introduced in the late 1999s, through tensile coupon tests and proposes some experimental equations for the yield stress, the elastic modulus, and specific heat. The surface temperature, deflection, and maximum stress of fire-resistant steel H-section columns were calculated using their own mechanical and thermal properties. According to a comparison of mechanical properties between fire-resistant steel and Eurocode 3, the former outperformed the latter, and based on a comparison of structural performance between fire-resistant steel and ordinary structural steel of equivalent mechanical properties at room temperature, the former had greater structural stability than the latter through $900^{\circ}C$.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.7-21
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• 2008

Foundation failure due to bridge scour during floods is the leading cause of bridge failure. Performed were the evaluation of bridge scour vulnerability and prioritization on real bridges registered in the National Highway Bridge Inventory of the capital region. The case studies for 30 national highway bridges consist of site investigation including boring test, bridge scour analysis fur the design flood, bearing capacity evaluation of the bridge foundation before and after scour, comprehensive evaluation of bridge scour vulnerability, and prioritization. Nine of 26 spread (feting bridges showed the potential future vulnerability to scour with significant decrease in the bearing capacity of foundations due to scour and the remaining 17 spread footing bridges were expected to maintain their stability to resist the effects of scour. Three of 4 pile foundation bridges exhibited considerable decrease in the bearing capacity of foundation after scour.

• Journal of the Korean GEO-environmental Society
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• v.20 no.8
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• pp.5-12
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• 2019

A pile group, that consists of several piles connected by a pile cap, is used as the superstructure. The pile supports vertical and horizontal load to design the pile group, but the effect of bearing capacity of the pile cap has not considered. Various researches have been conducted to reflect the effect of bearing capacity of the pile cap in order to reduce the amount of piles in the range of the stability under the vertical load of the superstructure. However, the effect of bearing capacity under the horizontal seismic load has not been studied adequately. Therefore, a shaking table test was carried out with different-sized pile caps that support the superstructure in this study. This test was to verify the influence of the size of the pile cap in the group pile under the horizontal load. The result shows that the size of the pile cap affects to the dynamic behavior of the superstructure and the pile group. Also, the bigger size of the pile group makes the larger constraint effect of ground, and it results that both the ground and the pile moves as a whole.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.121-129
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• 2008

Numerical analysis for the in-situ top base foundation (In-situ TBF) was carried out in order to investigate the effect of bearing capacity and the load delivering mechanisms in granular soil. The input data for the numerical model was prepared from the result obtained from the plate load test and full size in-situ TBF field tests. According to the result of numerical analysis, the behavior of in-situ TBF showed that bearing capacity of the foundation increased by $50{\sim}100%$ and settlement was reduced up to $1/2{\sim}1/3$ comparing to other types foundation. The effect of cone-shaped part of the in-situ TBF was as important as pile part for the improvement of foundation stability. The variation of the length of pile part indicated that the present length was proved satisfactory in terms of effectiveness.

• Computers and Concrete
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• v.24 no.5
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• pp.459-468
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• 2019

The stability and safety of concrete plug structure of diversion tunnel is crucial for the impoundment of upstream reservoir in hydropower projects. The ongoing Wudongde hydropower plant in China plans to adopt straight column plugs and curved column plugs to replace the traditional expanded wedge-shaped plugs. The performance of the proposed new plug structures under high water head is then a critical issue and attracts the attentions of engineers. This paper firstly studied the joint bearing mechanism of plug and surrounding rock mass and found that the quality and mechanical properties of the interfaces among plug concrete, shotcrete, and surrounding rock mass play a key role in the performance of plug structures. By performing geophysical and mechanical experiments, the contact state and the mechanical parameters of the interfaces were analyzed in detail and provide numerical analysis with rational input parameters. The safety evaluation is carried out through numerical calculation of plug stability under both construction and operation period. The results indicate that the allowable water head acting on columnar plugs is 3.1 to 7.4 times of the designed water head. So the stability of the new plug structure meets the design code requirement. Based on above findings, it is concluded that for the studied project, it is feasible to adopt columnar plugs to replace the traditional expanded wedge-shaped plugs. It is hoped that this study can provide reference for other projects with similar engineering background and problems.

• Journal of the Korean GEO-environmental Society
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• v.11 no.4
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• pp.51-59
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• 2010

This article is a case study for the example of the foundation design, in the project area of the silty sand layer that is spread shallowly with loose status, to make the site for a structure and build it up. The site is located on the dredged and reclaimed land in Gun-San and In-Cheon that is formed the silty sand layer with loose status range around 10 meters underground level, the solid ground for the lower pile is shown around 20 meters underground level. Therefore, this area has to be done by ground improvement when applying for the shallow method of foundation. Dynamic compaction method considering the conditions of the design loads in each zone has to be decided through comparative review on the method of foundations and pilot field test was conducted, and drilling investigation and plate bearing test were achieved as well. The analysis results of the tests prove that stability against bearing capacity was acquired by ground improvement effect.