• Elastomers and Composites
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• v.56 no.3
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• pp.152-163
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• 2021

Liquid butadiene rubber (LqBR) is used as a processing aid and plays a vital role in the manufacture of high-performance tire tread compounds. In this study, center-functionalized LqBR (C-LqBR) was polymerized with different vinyl content via anionic polymerization. The effects of the vinyl content on the properties of the compounds were investigated by partially replacing the treated distillate aromatic extract (TDAE) oil with C-LqBR in silica-filled rubber compounds. C-LqBR compounds showed a low Payne effect and Mooney viscosity regardless of the vinyl content, because of improved silica dispersion due to the ethoxysilyl group. As the vinyl content of C-LqBR increased, the optimum cure time (t₉₀) increased owing to a decrease in the number of allylic hydrogen. Moreover, the glass transition temperature (T_g) of the compound increased, and snow traction and abrasion resistance performance decreased, whereas wet grip improved. The energy loss characteristics revealed that the hysteresis attributed to the free chain ends of C-LqBR was dominant.

• Elastomers and Composites
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• v.56 no.4
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• pp.223-233
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• 2021

In this study, epoxidized liquid isoprene rubber (E-LqIR) was used as a processing aid in a silica-filled natural rubber compound to improve the fuel efficiency, abrasion resistance, and oil migration problems of truck and bus radial tire tread. The wear resistance, fuel efficiency, and extraction resistance of the compound were evaluated according to the molecular weight of E-LqIR. Results of the evaluation showed that the E-LqIR compound had a lower chemical crosslink density than that of a treated distillate aromatic extract (TDAE) oil compound because of the sulfur consumption of E-LqIR. However, the filler-rubber interaction improved because of the reaction of E-LqIR with silica and crosslink with the base rubber by sulfur. As the molecular weight of E-LqIR increased, crosslink with sulfur was facilitated, and the filler-rubber interaction improved, resulting in improved abrasion resistance. The fuel efficiency performance of the E-LqIR compound was poorer than that of the TDAE oil compound because of the low chemical crosslink density and hysteresis loss at the free chain end of E-LqIR. However, the fuel efficiency performance improved as the molecular weight of E-LqIR increased.

• Smart Structures and Systems
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• v.24 no.1
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• pp.111-125
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• 2019

Metallic shape memory alloys present fascinating physical properties such as their super-elastic behavior in austenite phase, which can be exploited for providing a structure with both a self-centering capability and an increased ductility. More or less accurate numerical models have been introduced to model their behavior along the last 25 years. This is the reason for which the literature is rich of suggestions/proposals on how to implement this material in devices for passive and semi-active control. Nevertheless, the thermo-mechanical coupling characterizing the first-order martensite phase transformation process results in several macroscopic features affecting the alloy performance. In particular, the effects of day-night and winter-summer temperature excursions require special attention. This aspect might imply that the deployment of some devices should be restricted to indoor solutions. A further aspect is the dependence of the behavior from the geometry one adopts. Two fundamental lacks of symmetry should also be carefully considered when implementing a SMA-based application: the behavior in tension is different from that in compression, and the heating is easy and fast whereas the cooling is not. This manuscript focuses on the passive devices recently proposed in the literature for civil engineering applications. Based on the challenges above identified, their actual feasibility is investigated in detail and their long term performance is discussed with reference to their fatigue life. A few available semi-active solutions are also considered.

• Electronic Materials Letters
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• v.14 no.6
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• pp.749-754
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• 2018

Previous studies have reported on the mechanical robustness and chemical stability of flexible amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) on plastic substrates both in flat and curved states. In this study, we investigate how the polyimide (PI) substrate affects hydrogen concentration in the a-IGZO layer, which subsequently influences the device performance and stability under bias-temperature-stress. Hydrogen increases the carrier concentration in the active layer, but it also electrically deactivates intrinsic defects depending on its concentration. The influence of hydrogen varies between the TFTs fabricated on a glass substrate to those on a PI substrate. Hydrogen concentration is 5% lower in devices on a PI substrate after annealing, which increases the hysteresis characteristics from 0.22 to 0.55 V and also the threshold voltage shift under positive bias temperature stress by 2 ${\times}$ compared to the devices on a glass substrate. Hence, the analysis and control of hydrogen flux is crucial to maintaining good device performance and stability of a-IGZO TFTs.

• Steel and Composite Structures
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• v.31 no.3
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• pp.217-232
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• 2019

Modular steel buildings consist of prefabricated room-sized structural units that are manufactured offsite and installed onsite. The inter-module connections must fulfill the assembly construction requirements and soundly transfer the external loads. This work proposes an innovative assembled connection suitable for modular buildings with concrete-filled steel tube columns. The connection uses pretensioned strands and plugin bars to vertically connect the adjacent modular columns. The moment-transferring performance of this inter-module connection was studied through monotonic and cyclic loading tests. The results showed that because of the assembly construction, the connected sections were separated under lateral bending, and the prestressed inter-module connection performed as a weak semirigid connection. The moment strength at the early loading stage originated primarily from the contact bonding mechanism with the infilled concrete, and the postyield strength depended mainly on the tensioned strands. The connection displayed a self-centering-like behavior that the induced deformation was reversed during unloading. The energy dissipation originated primarily from frictional slipping of the plugin bars and steel strands. The moment transferring ability was closely related to the section dimension and the arrangements of the plugin bars and steel strands. A simplified strength calculation and evaluation method was also proposed, and the effectiveness was validated with the test data.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.1
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• pp.33-39
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• 2018

This study performed experimental validation of the hysteretic steel slit damper's basic and dependent characteristics, which should be considered for the design. The basic characteristic of the steel slit damper is used for determining design properties of non-linear analysis, such as yielding strength, yielding displacement, elastic stiffness and post-yielding stiffness. In order to evaluate dependent characteristics of the hysteretic steel slit damper, repeated deformation capacity with respect to the displacement, velocity and aspect ratio of the damper was evaluated. In this study, steel slit damper, which is widely used in Korea, was considered. The slit dampers with 55kN and 240kN of yielding strength were produced and tested. It was concluded that the slit damper's hysteresis behavior was affected by the dependent characteristics: displacement, velocity and aspect ratio. In other words, the steel slit damper's behavior was stable within limit displacement, and aspect ratio of the strut affected repeated deformation capacity of the damper subjected to large deformation. In addition, it was observed that the repeated deformation capacity abruptly decreased at the high speed range (${\geq}60mm/sec$). Furthermore, the experimental results were evaluated with the criterion of the damping device specified in ASCE7-10.

• Steel and Composite Structures
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• v.43 no.5
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• pp.565-579
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• 2022

This study investigated the yielding capacity and performance of seismic dampers constructed with steel ring plates using numerical and analytical approaches. This study aims to provide an analytical relationship for estimating the yielding capacity and initial stiffness of steel ring dampers. Using plastic analysis and considering the mechanism of plastic hinge formation, a relation has been obtained for estimating the yielding capacity of steel ring dampers. Extensive parametric studies have been carried out using a nonlinear finite element method to examine the accuracy of the obtained analytical relationships. The parametric studies include investigating the influence of the length, thickness, and diameter of the ring of steel ring dampers. To this end, comprehensive verification studies are performed by comparing the numerical predictions with several reported experimental results to demonstrate the numerical method's reliability and accuracy. Comparison is made between the hysteresis curves, and failure modes predicted numerically or obtained/observed experimentally. Good agreement is observed between the numerical simulations and the analytical predictions for the yielding force and initial stiffness. The difference between the numerical models' ultimate tensile and compressive capacities was observed that average of about 22%, which stems from the performance of the ring-dampers in the tensile and compression zones. The results show that the steel ring-dampers are exhibited high energy dissipation capacity and ductility. The ductility parameters for steel ring-damper between values were 7.5 to 4.1.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.4
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• pp.143-148
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• 2023

Among the characteristics of SRM, due to nonlinearity, it is difficult to properly operate to form maximum torque and minimum torque pulsation. In addition, in the case of fixed switching angle control, torque formation according to speed variation is unstable, thereby reducing efficiency. Therefore, active switching angle control according to speed variation is required. Therefore, active switching angle control according to speed variation is required. In this paper, a method for improving driving performance by reducing torque ripple by automatic control of the advance angle and increasing output torque was sought from the problem caused by the nonlinearity of the SRM. In addition, the optimal operation of SRM due to the switching variable according to the performance of the hysteretic current controller was examined.

• Steel and Composite Structures
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• v.47 no.3
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• pp.375-382
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• 2023

The H-shaped steel beam is popular due to its ease of manufacturing and connection to the column. This profile, which is used as a shallow beam, needs the high weak-axis bending stiffness and torsional stiffness to meet the overall stability. Achieving the local beam flange stability, bearing capacity, bending stiffness, and torsional requirements need a great thickness and width of the beam flange, which causes, which will cause more uneconomical structural design. So, the box-section beam is the ideal alternative. However, the current design specifications do not have design rules for the bolt-and-welded connection of the box-section beam and box-section column. The paper proposes a novel bolt-and-welded connection of the box-section beams and box-section columns based on a high-rise structural design scheme. Three connection models, BASE, WBF, and RBS, are analyzed under cyclic loading in ABAQUS software. The failure modes, hysteresis response, bearing capacity, ductility, plastic rotation angle, energy dissipation, and stiffness degradation of all models are determined and compared. Compared with the other two models, the model WBF exhibited excellent seismic performance, ductility, and plastic rotation ability. Finally, model WBF was chosen as the connection scheme used in the project design.

• Structural Engineering and Mechanics
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• v.89 no.3
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• pp.239-252
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• 2024

Steel plate shear walls (SPSWs) are classified as lateral load-resisting systems. The feasibility of openings in the steel plate is a characteristic of SPSWs. The use of openings in SPSWs can lower the load capacity, stiffness, and energy dissipation. This study proposes a novel form of SPSWs that provides convenient access through openings by combining steel plates and eccentrically braced frames (EBFs). The proposed system also avoids a substantial reduction in the strength and stiffness. Hence, various geometric forms were analyzed through two different structural approaches. Groups 1, 2, and 3 included a steel EBF with a steel plate between the column and EBF in order to improve system performance. In Group 4, the proposed system was evaluated within an SPSW with openings and an EBF on the opening edge. To evaluate the performance of the proposed systems, the nonlinear finite element method (NL-FEM) was employed under cyclic loading. The hysteresis (load-drift) curve, stress contour, stiffness, and damping were evaluated as the structural outputs. The numerical models indicated that local buckling within the middle plate-EBF connection prevented a diagonal tension field. Moreover, in group 4, the EBF and stiffeners on the opening edge enhanced the structural response by approximately 7.5% in comparison with the base SPSW system.