• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.2
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• pp.15-26
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• 1991

The lateral forces such as the earthquake and wind my cause the torsion to be coupled with the lateral bending in the gider, the cross-section of wich has only one axis of symmetry. This induces additional stresses especially in cables arranged in double-planes. Since this effect cannot be considered by using the conventional frame elements, the stiffness and the mass matrices of the geometrically nonlinear thin-walled frame element are developed in this study to model the girder. The equivalent modulus of elasticity proposed by Ernst is used for the cable elements. Verification of the present theory is made through a numerical example. Then, the free vibration of a three dimensional cable-stayed bridge is analyzed to study the coupled flexural-torsional behavior.

• Earthquakes and Structures
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• v.20 no.4
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• pp.389-403
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• 2021

Skewed bridges, being irregular structures with complicated dynamic behavior, are more susceptible to earthquake damage. Reliable seismic-resistant design of skewed bridges can be achieved by accurate determination of nonlinear seismic demands. However, the effect of geometric characteristics on the response modification factor (R-factor) is not accounted for in bridge design practices. This study attempts to investigate the effects of changes in the number of spans, skew angle and bearing stiffness on R-factor values and to assess the seismic fragility of skewed bridges. Results indicated that changes in the skew angle had no significant effect on R-factor values which were in consonance with code-prescribed R values. Also, unlike the increase in the number of spans that resulted in a decrease in the R-factor, the increase in bearing stiffness led to higher R-factor values. Findings of the fragility analysis implied that although the increase in the number of spans, as well as the increase in the skew angle, led to a higher failure probability, greater values of bearing stiffness reduced the collapse probability. For practicing design engineers, it is recommended that maximum demands on substructure elements to be calculated when the excitation angle is applied along the principal axes of skewed bridges.

• Smart Structures and Systems
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• v.23 no.2
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• pp.155-171
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• 2019

In this study, Semi-active Tuned Mass Dampers (STMDs) are employed in order to cover the prevailing uncertainties and promote the efficiency of the Tuned Mass Dampers (TMDs) to mitigate undesirable structural vibrations. The damping ratio is determined using type-1 and type-2 Fuzzy Logic Controllers (T1 and T2 FLC) based on the response of the structure. In order to increase the efficiency of the FLC, the output membership functions are optimized using genetic algorithm. The results show that the proposed FLC can reduce the sensitivity of STMD to excitation records. The obtained results indicate the best operation for T1 FLC among the other control systems when the uncertainties are neglected. According to the irrefutable uncertainties, three supplies for these uncertainties such as time delay, sensors measurement noises and the differences between real and software model, are investigated. Considering these uncertainties, the efficiencies of T1 FLC, ground-hook velocity-based, displacement-based and TMD reduce significantly. The reduction rates for these algorithms are 12.66%, 26.43%, 20.98% and 21.77%, respectively. However, due to nonlinear behavior and considering a range of uncertainties in membership functions, T2 FLC with 7.2% reduction has robust performance against uncertainties compared to other controlling systems. Therefore, it can be used in actual applications more confidently.

• Steel and Composite Structures
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• v.32 no.2
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• pp.265-279
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• 2019

The self-centering capacity and energy dissipation performance have been recognized critically for increasing the seismic performance of structures. This paper presents an innovative steel moment frame with self-centering steel reinforced concrete (SRC) wall panel incorporating replaceable energy dissipation devices (SF-SCWD). The self-centering mechanism and energy dissipation mechanism of the structure were validated by cyclic tests. The earthquake resilience of wall panel has the ability to limit structural damage and residual drift, while the energy dissipation devices located at wall toes are used to dissipate energy and reduce the seismic response. The oriented post-tensioned strands provide additional overturning force resistance and help to reduce residual drift. The main parameters were studied by numerical analysis to understand the complex structural behavior of this new system, such as initial stress of post-tensioning strands, yield strength of damper plates and height-width ratio of the wall panel. The static push-over analysis was conducted to investigate the failure process of the SF-SCWD. Moreover, nonlinear time history analysis of the 6-story frame was carried out, which confirmed the availability of the proposed structures in permanent drift mitigation.

• Earthquakes and Structures
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• v.16 no.1
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• pp.41-54
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• 2019

Reinforced Concrete (RC) shear walls are widely used in Nuclear power plants as effective lateral force resisting elements of the structure and these may experience nonlinear behavior for higher earthquake demand. Short shear walls of aspect ratio less than 1.5 generally experience combined shear flexure interaction. This paper presents the results of the displacement-controlled experiments performed on six RC short shear walls with varying aspect ratios (1, 1.25 and 1.5) for monotonic and reversed quasi-static cyclic loading. Simulation of the shear walls is then carried out by Finite element modeling and also by macro modeling considering the coupled shear and flexure behaviour. The shear response is estimated by softened truss theory using the concrete model given by Vecchio and Collins (1994) with a modification in softening part of the model and flexure response is estimated using moment curvature relationship. The accuracy of modeling is validated by comparing the simulated response with experimental one. Moreover, based on the experimental work a multi-linear hysteretic model is proposed for short shear walls. Finally ultimate load, drift, ductility, stiffness reduction and failure pattern of the shear walls are studied in details and hysteretic energy dissipation along with damage index are evaluated.

• Earthquakes and Structures
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• v.20 no.2
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• pp.201-213
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• 2021

Contrast to the conventional jointed bridge design, integral abutment bridges (IABs) offer some marked advantages like reduced maintenance and enhanced service life of the structure due to elimination of joints in the deck and monolithic construction practices. However, the force transfer mechanism during seismic and thermal movements is a topic of interest owing to rigid connection between superstructure and substructure (piers and abutments). This study attempts to model an existing IAB by including the abutment backfill interaction and soil-foundation interaction effects using Winkler foundation assumption to determine its seismic response. Keeping in view the significance of abutment behavior in an IAB, the probability of damage to the abutment is evaluated using fragility function. Incremental Dynamic Analysis (IDA) approach is used in this regard, wherein, nonlinear time history analyses are conducted on the numerical model using a selected suite of ground motions with increasing intensities until damage to abutment. It is concluded from the fragility analysis results that for a MCE level earthquake in the location of integral bridge, the probability of complete damage to the abutment is minimal.

• Steel and Composite Structures
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• v.43 no.3
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• pp.375-388
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• 2022

Nibellen structural system is a novel resilient bracing system based on the application of Bellville disks and Nitinol rods. The cyclic behavior of Nibellen assembly was obtained, and the design equations were developed based on the available literature. Seismic performance of the system was then studied analytically. Two groups of buildings with different lateral force resisting systems were designed and studied: one group with the Nibellen system, and the other with the special concentrically braced frame system. Each building group consisted of 5-, 10-, and 15-story buildings. The Design-Base-Event (DBE) and Maximum Considered Event (MCE) were considered as the seismic hazard, and a suite of seven ground motions were scaled accordingly for response history analyses. Finally, the resiliency of the buildings was studied by obtaining the functionality curve of the buildings before and after the seismic event. The construction cost of the 5-story building with Nibellen bracing system increased but the post-earthquake cost decreased significantly. The application of Nibellen system in the 10- and 15-story buildings reduced both the construction and repair costs, considerably. Resiliency of all the buildings was improved when Nibellen system was used as the lateral force resisting system.

• Structural Monitoring and Maintenance
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• v.9 no.1
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• pp.81-105
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• 2022

The use of concrete filled steel tube (CFST) column is widely accepted due to its property of high axial load carrying capacity, more ductility and more resistant to earthquake specially using in bridges and high-rise buildings. The initial imperfection (δ) that produces during casting or fixing causes the reduction in load carrying capacity, this is the reason, experimental capacity is always less then theoretical one. In this research, the effect of δ on load carrying capacity and behavior of concrete filled steel tube (CFST) column have been investigated by numerically simulation of large number of models with different δ and other geometric parameters that include length (L), width (B), steel tube thickness (t), f'_c and f_y. Finite element analysis software ANSYS v18 is used to develop model of SCFST column to evaluate strength capacity, buckling and failure pattern of member which is applied during experimental study under cyclic axial loading. After validation of results, 42 models with different parameters are evaluated to develop empirical equation predicting axial load carrying capacity for different value of δ. Results indicate that empirical equation shows the 0 to 9% error for finite element analysis Forty-two models in comparison with ANSYS results, respectively. Empirical equation can be used for predicting the axial capacity of early estimating the axial capacity of SCFT column including 𝛿.

• Steel and Composite Structures
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• v.49 no.3
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• pp.257-270
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• 2023

In this study, the feasibility and applicability of a friction damper with a vertical installation scheme are investigated. This device is composed of a steel section and two friction hinges at both ends which dissipate seismic energy. Due to its small width and vertical installation scheme, the proposed damper can minimize the interference with architectural functions. To evaluate the performance of the proposed damper, its mechanical behavior is theoretically evaluated and the required formulas for the yield strength and elastic stiffness are derived. The theoretical formulas are verified by establishing the analytical model of the damper in the SAP2000 software and comparing their results. To further investigate the performance of the developed damper, the provided analytical model is applied to a 4-story reinforced concrete (RC) structure and its performance is evaluated before and after retrofit under the Maximum Considered Earthquake (MCE) hazard level. The seismic performance is thoroughly evaluated in terms of maximum interstory drift ratio, displacement time history, residual displacement, and energy dissipation. The results show that the proposed damper can be efficiently used to protect the structure against seismic loads.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.1
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• pp.171-180
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• 2005

In this study the seismic performance of a three-story knee-braced moment-resisting frame (KBMRF), which is typically employed to support pipelines for oil or gas, was investigated. Nonlinear static pushover analyses were performed first to observe the force-displacement relationship of KBMRF under increasing seismic load. The results show that, when the maximum inter-story drift reached 1.5% of the story height, the main structural members, such as beams and columns, still remained elastic. Then nonlinear dynamic time-history analyses were carried out using eight earthquake ground motion time-histories scaled to at the design spectrum of UBC-97. It turned out that the maximum inter-story drift was smaller than the drift limit of 1.5 % of the structure height, and that the columns remained elastic. Based on these analytical results, it can be concluded that the seismic performance of the structure satisfies all the requirements regulated in the seismic code.