• Structural Engineering and Mechanics
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• v.14 no.6
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• pp.679-698
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• 2002

In this paper some techniques for the dynamic analysis of non-classically damped linear systems are reviewed and compared. All these methods are based on a transformation of the governing equations using a basis of complex or real vectors. Complex and real vector bases are presented and compared. The complex vector basis is represented by the eigenvectors of the complex eigenproblem obtained considering the non-classical damping matrix of the system. The real vector basis is a set of Ritz vectors derived either as the undamped normal modes of vibration of the system, or by the load dependent vector algorithm (Lanczos vectors). In this latter case the vector basis includes the static correction concept. The rate of convergence of these bases, with reference to a parametric structural system subjected to a fixed spatial distribution of forces, is evaluated. To this aim two error norms are considered, the first based on the spatial distribution of the load and the second on the shear force at the base due to impulsive loading. It is shown that both error norms point out that the rate of convergence is strongly influenced by the spatial distribution of the applied forces.

• Structural Monitoring and Maintenance
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• v.1 no.1
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• pp.131-157
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• 2014

Special track systems used to divert a train to other directions or other tracks are generally called 'railway turnout'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material, 'fibre-reinforced foamed urethane (FFU)' bearers, has been carried out at a complex turnout junction under heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle 'AK Car'), track settlement (based on survey data), track dynamics, and acoustic characteristics have been measured. Operational train pass-by measurements have been analysed to evaluate the effectiveness of the replacement methodology. Comparative studies show that the use of FFU bearers generates higher rail and sleeper accelerations but the damping capacity of the FFU help suppress vibration transferring onto other track components. The survey data analysis suggests a small vertical settlement and negligible lateral movement of the turnout system. The static and dynamic behaviours of FFU bearers appear to equate that of natural timber but its service life is superior.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.6
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• pp.529-538
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• 2016

The simplified plate theory is presented for static and free vibration analysis of power-law(P) and sigmoid(S) Functionally Graded Materials(FGM) plates. This theory considers the parabolic distribution of the transverse shear stress, and satisfies the condition that requires the transverse shear stress to be zero on the upper and lower surfaces of the plate, without the shear correction factor. The simplified plate theory uses only four unknown variables and shares strong similarities with classical plate theory(CPT) in many aspects such as stress-resultant expressions, equation of motion and boundary conditions. The material properties of the plate are assumed to vary according to the power-law and sigmoid distributions of the volume fractions of the constituents. The Hamilton's principle is used to derive the equations of motion and Winkler-Pasternak elastic foundation model is employed. The results of static and dynamic responses for a simply supported FGM plate are calculated and a comparative analysis is carried out. The results of the comparative analysis with the solutions of references show relevant and accurate results for static and free vibration problems of FGM plates. Analytical solutions for the static and free vibration problems are presented so as to reveal the effects of the power law index, elastic foundation parameter, and side-to-thickness ratio.

• Structural Engineering and Mechanics
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• v.89 no.5
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• pp.491-505
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• 2024

This study evaluates the seismic performance of a premodern six story reinforced concrete building typology designed during the communism period of Albania and build throughout the country. During the November 26, 2019 Earthquake in Albania, the most affected reinforced concrete buildings were among the old templates, lacking shear walls and inadequate reinforcement details which suffer from concrete aging. The mathematical model of the selected building is done in the environments of ZeusNL software, developed especially for earthquake engineering applications. The capacity curve of the structure is gained using the conventional static nonlinear analysis. On the other hand, the demand estimation is utilized using one of the recent methods known as Incremental Dynamic Analysis with a set of 18 ground motion records. The limit states in both curves are defined based on the modern guidelines. For the pushover, immediate occupancy (IO), life safety (LS) and collapse prevention (CP) are plotted in the same graph with capacity curve. Furthermore, on each IDA derived, the IO, CP and global instability (GI) are determined. Moreover, the IDA fractiles are generated as suggested by the literature, 16%, 50% (median) and 84%. In addition, the comparative assessment of the IDA median with capacity curve shows good correlation points. Lastly, this study shows the approach of determination of LS in IDA fractiles for further vulnerability assessment based on the local seismic hazard map with 95 and 475 return period.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.3
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• pp.222-235
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• 2015

The purpose of this study is to suggest guidelines for riser fatigue analysis in terms of selection of reasonable analysis method. Three analysis methods (spectral, regular wave, rain-flow counting) are introduced and compared. As the riser systems give non-linear response, the time-domain analysis method is more preferred than frequency-domain analysis method. The spectral fatigue analysis method, however, is still useful for identifying fatigue prone areas. Once stress RAO is established, fatigue damage can be calculated very quickly. The regular wave method and the rain-flow counting method are more time consuming but give more exact results compare to spectral method. In case of regular wave method, a set of regular waves which represent random sea states is considered for dynamic analysis. The rain-flow counting method is the most intuitive and exact method because it refers time history stresses containing most of non-linear effects of the riser system. However, it is not common for early design stage to use rain-flow counting method because of its high cost. In this study, it was confirmed that the regular wave method is the most cost effective way in specific cases. However, if the system is highly non-linear, it seems that the regular wave method gives less accurate results than rain-flow counting method. Therefore, it is imperative that the engineers select appropriate analysis method based on design stage and given engineering period. This paper also discusses the theoretical background of each calculation method and hydrodynamic aspects of marine riser systems. A steel catenary riser (SCR) line on FPSO was considered and marine dynamic program (OrcaFlex) was used for static and dynamic analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.3
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• pp.203-209
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• 2012

In this paper, cross-sectional stiffnesses, static stresses, and dynamic natural frequencies are analyzed to examine the structural performance of wind turbine composite blades. The material properties of composite materials are based on room-temperature and radiation curing processes. The cross-sectional stiffnesses of composite blades are calculated by applying a beam theory with solid-profile cross sections. The wind turbine blades are modeled with a finite element program, and static analyses are carried out to check the maximum displacement and stress of the blades. In addition, dynamic analyses are performed to predict the rotating natural frequencies of the composite blades including the effects of centrifugal force. By comparing these analysis results, mainly owing to the material properties of composite materials, an improvement in the structural performance of the blades according to the curing process is investigated.

• Journal of the Korean Society of Safety
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• v.35 no.3
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• pp.49-57
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• 2020

In comparison with the existing static reliability analysis methods, the dynamic reliability analysis(DyRA) method is more suitable for estimating the failure probability of a structure subjected to earthquake excitations because it can take into account the frequency characteristics and damping capacity of the structure. However, the DyRA is known to have an issue of numerical stability due to the uncertainty in random sampling of the earthquake excitations. In order to solve this numerical stability issue in the DyRA approach, this study proposed two earthquake-scale factors. The first factor is defined as the ratio of the first earthquake excitation over the maximum value of the remaining excitations, and the second factor is defined as the condition number of the matrix consisting of the earthquake excitations. Then, we have performed parametric studies of two factors on numerical stability of the DyRA method. In illustrative example, it was clearly confirmed that the two factors can be used to verify the numerical stability of the proposed DyRA method. However, there exists a difference between the two factors. The first factor showed some overlapping region between the stable results and the unstable results so that it requires some additional reliability analysis to guarantee the stability of the DyRA method. On the contrary, the second factor clearly distinguished the stable and unstable results of the DyRA method without any overlapping region. Therefore, the second factor can be said to be better than the first factor as the criterion to determine whether or not the proposed DyRA method guarantees its numerical stability. In addition, the accuracy of the numerical analysis results of the proposed DyRA has been verified in comparison with those of the existing first-order reliability method(FORM), Monte Carlo simulation(MCS) method and subset simulation method(SSM). The comparative results confirmed that the proposed DyRA method can provide accurate and reliable estimation of the structural failure probability while maintaining the superior numerical efficiency over the existing methods.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.294-301
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• 2005

Ground response analysis is one of the most important and most commonly encountered problems in geotechnical earthquake engineering. It is a prerequisite step for liquefaction assessment of saturated soil or the pseudo-static and dynamic analysis of geotechnical structures. A number of techniques have been developed for ground response analysis. In this study, ground response analyses were performed using the computer programs that are currently being used domestically. From these analyses, the analysis techniques applied to the programs were compared and analyzed. The results of ground response analyses were compared as follows: 1) 1-dimensional analysis vs. 2-dimensional analysis; 2) equivalent linear analysis vs. nonlinear analysis.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.3
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• pp.42-51
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• 1999

An experimental modeling of cutting and structural dynamics and the on-line detection of malfunction process is substantial not only for the investigation of the static and dynamic characteristics of cutting process but also for the analytic realization of diagnostic systems. In this regard, We have discussed on the comparative assessment of two recursive time series modeling algorithms that can represent the machining process and detect the abnormal machining behaviors in precision round shape machining such as turning, drilling and boring in mold and die making. In this study, simulation and experimental work were performed to show the malfunctioned behaviors. For this purpose, two new recursive approach (REIVM, RLSM) were adopted fur the on-line system identification and monitoring of a machining process, we can apply these new algorithm in real process for the detection of abnormal machining behaviors such as chipping, chatter, wear and round shape lobe waviness.

• Steel and Composite Structures
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• v.50 no.3
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• pp.249-263
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• 2024

This article presents a comparative analysis of seismic behavior in steel-beam reinforced concrete column (RCS) frames versus steel and reinforced concrete frames. The study evaluates the seismic response and collapse behavior of RCS frames of varying heights through nonlinear modeling. RCS, steel, and reinforced concrete special moment frames are considered in three height categories: 5, 10, and 20 stories. Two-dimensional frames are extracted from the three-dimensional structures, and nonlinear static analyses are conducted in the OpenSEES software to evaluate seismic response in post-yield regions. Incremental dynamic analysis is then performed on models, and collapse conditions are compared using fragility curves. Research findings indicate that the seismic intensity index in steel frames is 1.35 times greater than in RCS frames and 1.14 times greater than in reinforced concrete frames. As the number of stories increases, RCS frames exhibit more favorable collapse behavior compared to reinforced concrete frames. RCS frames demonstrate stable behavior and maintain capacity at high displacement levels, with uniform drift curves and lower damage levels compared to steel and reinforced concrete frames. Steel frames show superior strength and ductility, particularly in taller structures. RCS frames outperform reinforced concrete frames, displaying improved collapse behavior and higher capacity. Incremental Dynamic Analysis results confirm satisfactory collapse capacity for RCS frames. Steel frames collapse at higher intensity levels but perform better overall. RCS frames have a higher collapse capacity than reinforced concrete frames. Fragility curves show a lower likelihood of collapse for steel structures, while RCS frames perform better with an increase in the number of stories.