• Composites Research
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• v.20 no.4
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• pp.1-8
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• 2007

In this study, carbon fiber reinforced polymeric (CFRP) composites with different resin composition were manufactured and resin formulation in composite materials were presented through tensile tests for cryogenic use. Thermo-mechanical cyclic loading (up to 6 cycles) was applied to CFRP unidirectional laminate specimens from room temperature to $-150^{\circ}C$. Tensile tests were then performed at $-150^{\circ}C$ using an environmental test chamber. In addition, matrix-dominant properties such as the transverse and in-plane shear characteristics of each composite model were measured at $-150^{\circ}C$ to examine the effects of resin formulation on their interfacial properties. The tensile tests showed that the composite models with large amounts of bisphenol-A epoxy and CTBN modified rubber in their resin composition had good mechanical performance at cryogenic temperature (CT).

• Earthquakes and Structures
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• v.25 no.2
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• pp.125-134
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• 2023

In the present work, a new global damage index is proposed for the seismic performance and failure analysis of concrete gravity dams. Unlike the existing indices of concrete structures, this index doesn't need scaling with an ultimate or an upper value. For this purpose, the Beni-Haroun dam in north-eastern Algeria, is considered as a case study, for which an average seismic capacity curve is first evaluated by performing several incremental dynamic analyses. The seismic performance point of the dam is then determined using the N2 method, considering multiple modes and taking into account the stiffness degradation. The seismic demand is obtained from the design spectrum of the Algerian seismic regulations. A series of recorded and artificial accelerograms are used as dynamic loads to evaluate the nonlinear responses of the dam. The nonlinear behaviour of the concrete mass is modelled by using continuum damage mechanics, where material damage is represented by a scalar field damage variable. This modelling, which is suitable for cyclic loading, uses only a single damage parameter to describe the stiffness degradation of the concrete. The hydrodynamic and the sediment pressures are included in the analyses. The obtained results show that the proposed damage index faithfully describes the successive brittle failures of the dam which increase with increasing applied ground accelerations. It is found that minor damage can occur for ground accelerations less than 0.3 g, and complete failure can be caused by accelerations greater than 0.45 g.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.233-242
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• 2008

This study presents a non-prismatic beam element for modeling the elastic and inelastic behavior of steel beams, which have the post-Northridge(cover plate) connections in steel moment frames that are subjected to earthquake ground motions. The elastic stiffness matrix for non-prismatric members with increased beam section (IBS) connection is in the closed-form. The plasticity model is of a discrete type and is composed of a series of nonlinear hinges connected by rigid links. The hardening rules can model the inelastic behavior for monotonic and random cyclic loading, and the effects of local buckling. Moreover the determination of yield surfaces, stiffness parameters, and hardening (or softening) rule parameters for IBS beam element were described. Analytical results of the IBS beam element show good correlation with test data and FEM results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4C
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• pp.221-230
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• 2008

The George Massey immersed tunnel passes the Fraser River near Vancouver, Western Canada. The tunnel was founded on sandy soils and its behavior during earthquake was analyzed by an effective stress constitutive model called UBCSAND. This model is able to calculate pore pressure rise and resulting tunnel movements due to cyclic loading. Centrifuge tests conducted at Rensselaer Polytechnic Institute (RPI) were used to verify the model performance. The centrifuge tests consisted of 2 models: Model 1 was designed for an original ground condition, Model 2 for a ground improvement by densification. In Model 1, large deformation of the tunnel was observed due to liquefaction of surrounding soil. Because of the densified zones around the tunnel the vertical and horizontal displacements of the tunnel in Model 2 was 50% less than Model 1. Measured excess pore pressures, accelerations, and displacements from centrifuge tests were in close agreement with the predictions of UBCSAND model. Therefore, the model can be used to predict seismic behavior of immersed tunnels on sandy soils and optimize liquefaction remediation methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.1C
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• pp.21-31
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• 2009

Based on the proven feasibility of bottom ash and tire shred-soil mixtures as lightweight fill materials, tire shred-bottom ash mixtures were suggested as a new lightweight fill material to replace the conventional construction material (soil) with bottom ash. Therefore, we carried out the field compaction test and performance test of large scale embankment in order to evaluate their suitability for the use of lightweight fill materials. In these tests, we could assess the settlement, earth pressure, stress-strain relation, vibration of large scale embankment which were made with tire shred-bottom ash mixture and the conventional fill material(weathered soil) respectively. The earthpressure and vibration transmission was decreased and the settlement behaviour of the 2 materials (tire shred mixture and weathered soil) was measured similarly under static/cyclic loading condition.

• Earthquakes and Structures
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• v.26 no.1
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• pp.49-58
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• 2024

The purpose of this study was to develop a system capable of restoring the seismic performance of a precast concrete (PC) connection damaged by an earthquake. The developed PC connection consists of a top-and-seat angle, post-tensioning (PT) tendons, and U-shaped steel. The PC beam can be replaced by cutting the PT tendons in the event of damage. In addition, the seismic performance of the developed PC beam-column connection was evaluated experimentally. A PC beam-column connection specimen was fabricated, and a quasistatic cyclic loading test was conducted to a maximum drift ratio of 2.3%. Subsequently, the PC beam was replaced by a new PC beam, and the repaired PC connection was loaded to a maximum drift ratio of 5.1%. The structural performance of the repaired PC connection was then compared with that of the original PC connection. The difference in the load at the drift ratio of 2.3% between the original and the repaired PC specimens was only 0.2%. The residual drift ratio in the repaired PC specimen did not exceed 1.0% at the 2.0 % drift ratio cycles, which satisfies the life safety performance level specified in ACI 374.2R-13. When the developed PC connection system is used, structural performance can be restored by rapidly replacing the damaged elements.

• Journal of Electrochemical Science and Technology
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• v.15 no.1
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• pp.67-95
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• 2024

Direct alcohol fuel cells (DAFCs) have gained much attention as promising energy conversion devices due to their ability to utilize alcohol as a fuel source. In this regard, Molybdenum-based electrocatalysts (Mo-ECs) have emerged as a substitution for expensive Pt and Ru-based co-catalyst electrode materials in DAFCs, owing to their unique electrochemical properties useful for alcohol oxidation. The catalytic activity of Mo-ECs displays an increase in alcohol oxidation current density by several folds to 1000-2000 mA mg_Pt^-1, compared to commercial Pt and PtRu catalysts of 10-100 mA mg_Pt^-1. In addition, the methanol oxidation peak and onset potential have been significantly reduced by 100-200 mV and 0.5-0.6 V, respectively. The performance of Mo-ECs in both acidic and alkaline media has shown the potential to significantly reduce the Pt loading. This review aims to provide a comprehensive overview of the bifunctional mechanism involved in the oxidation of alcohols and factors affecting the electrocatalytic oxidation of alcohol, such as synthesis method, structural properties, and catalytic support materials. Furthermore, the challenges and prospects of Mo-ECs for DAFCs anode materials are discussed. This in-depth review serves as valuable insight toward enhancing the performance and efficiency of DAFC by employing Mo-ECs.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.145-159
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• 2004

The conventional method for assessment of liquefaction potential proposed by Seed and Idriss has been widely used in most countries because of simplicity of tests. Even though various data such as stress, strain, stress path, and excess pore water pressure can be obtained from the dynamic test, especially, two simple experimental data such as the maximum deviatoric stress and the number of cycles at liquefaction have been used in the conventional assessment. In this study, a new detailed assessment for liquefaction potential to reflect both characteristics of real earthquake motion and dynamic soil resistance is proposed and verified. In the assessment, the safety factor of the liquefaction potential at a given depth of a site can be obtained by the ratio of a resistible cumulative plastic shear strain determined through the performance of the conventional cyclic test and a driving cumulative plastic shear strain calculated from the shear strain time history through the ground response analysis. The last point to cumulate the driving plastic shear strain to initiate soil liquefaction is important for this assessment. From the result of cyclic triaxial test using real earthquake motions, it was concluded that liquefaction under the impact-type earthquake loads would initiate as soon as a peak loading signal was reached. The driving cumulative plastic shear strain, therefore, can be determined by adding all plastic shear strains obtained from the ground response analysis up to the peak point. Through the verification of the proposed assessment, it can be concluded that the proposed assessment for liquefaction potential can be a progressive method to reflect both characteristics of the unique soil resistance and earthquake parameters such as peak earthquake signal, significant duration time, earthquake loading type, and magnitude.

• Clinics in Shoulder and Elbow
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• v.12 no.2
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• pp.207-214
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• 2009

Purpose: In arthroscopic rotator cuff repairs there are generally weak link in tendon suture interface, arthroscopic rotator cuff repairs can have higher retear rates than open repairs. The purpose of this study was to compare the strength of UU (Ulsan University) suture than open modified MA (Mason-Allen) suture when suture anchored into bone. Materials and Methods: The human supraspinatus tendons were harvested from the shoulder of the cadaver and split in 2 times, producing four tendons per one shoulder, for a total of 24 specimens. Two suture configurations (UU, MA) were randomized and checked on each set of tendons. Specimens were cyclically loaded under force control between 5 and 30 N at 0.25 Hz for fifty cycles. Each specimen was loaded to failure under displacement control at 1 mm/sec. Cyclic elongation, peak to peak displacement, stiffness, ultimate tensile load, mode of failure were checked. Results: No significant difference was found between two suture configuration with respect to peak to peak displacement, cyclic elongation, and stiffness. With regard to ultimate failure load, there were no significant difference statistically between the UU suture and modified MA suture (109.4 N, 110.6 N). The most common mode of failure between both sutures was suture pull-out through the tendon. Conclusion: The UU suture and modified MA suture produced similar biomechanical properties.

• Journal of Korean Society of Steel Construction
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• v.18 no.1
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• pp.11-22
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• 2006

Message Signs (VMS) structures offer an increase in traffic safety through their ability to relay massages to motorists for warnings of hazards ahead, traffic congestion, accidents, and lane closings. The geometry of these signs sometimes results in the significant cyclic loading of the supports structure due to wind gusts, which can result from passing trucks or from natural wind. This study presents the results of analytical and experimental investigations of VMS structures. The commercially available softwareGTSTRUDL (2003) was used to perform space-frame structural analyses of these welded tubular structures. Fatigue evaluations were performed using stress ranges from field measurements and from structural analyses. Based on the results of the structural analyses that were conducted, where fatigue design loadings that had been derived from AASHTO Specifications for Structural Supports for Highway Signs, Luminaries, and Traffic Signals (2001) were used, the structures that had been studied were found not to have infinite fatigue life. According to the limited measurements that were made in this study, the fatigue design loadings derived from AASHTO Specifications (2001) appear to be conservative, but they are not overly conservative. The results of this study should be used to make a reasonable design of VMS structures, and to maintain their standards.