• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.77-83
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• 1993

A modified Lanczos method combined with a substructure analysis technique was used for calculating natural frequencies and mode shapes of large structural systems. The method does not require generation and storage of stiffness and mass matrices of the entire structure. It only uses the stiffness and mass matrices of each substucture. No approximating assumptions are required other than the usual assumption of linear elastic system modelled by finite elements. Thus, natural frequencies and mode shapes for the finite element model employed are the same as those with or without the suhstructuring algorithm. To check the efficiency of the proposed method, first ten natural frequencies and the corresponding mode shapes of an open truss helicopter tail-boom structure are calculated by using it.

• Smart Structures and Systems
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• v.20 no.2
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• pp.127-137
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• 2017

Identification of damping characteristics is of significant importance for dynamic response analysis and condition assessment of structural systems. Damping is associated with the behavior of the energy dissipation mechanism. Identification of damping ratios based on the sensitivity of dynamic responses and the model updating technique is investigated with numerical and experimental investigations. The effectiveness and performance of using the sensitivity-based model updating method and vibration monitoring data for damping ratios identification are investigated. Numerical studies on a three-dimensional truss bridge model are conducted to verify the effectiveness of the proposed approach. Measurement noise effect and the initial finite element modelling errors are considered. The results demonstrate that the damping ratio identification with the proposed approach is not sensitive to the noise effect but could be affected significantly by the modelling errors. Experimental studies on a steel planar frame structure are conducted. The robustness and performance of the proposed damping identification approach are investigated with real measured vibration data. The results demonstrate that the proposed approach has a decent and reliable performance to identify the damping ratios.

• Structural Engineering and Mechanics
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• v.64 no.5
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• pp.671-681
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• 2017

This study investigates the structural performance of 3D steel pipe rack suspended scaffolding systems. For the purpose, a standard full scale 3D steel pipe rack suspended scaffolding system considering two frames, two plane trusses, purlins and wooden floor is constructed in the laboratory. A developed load transmission system was placed in these experimental systems to distribute single loads to the center of a specific area in a step-by-step manner using a load jack. After each load increment, the displacements are measured by means of linear variable differential transducers placed in several critical points of the system. The tests are repeated for five different system conditions to determine the structural performance. The means of system conditions is the numbers of the tie bars which are used to connect plane trusses under level. Finite elements models of the 3D steel pipe rack suspended scaffolding systems considering different systems conditions are constituted using SAP2000 software to support the experimental tests and to use the models in future studies. Each of models including load transmission platform is analyzed under a single loading and the displacements are obtained. In addition, to calibrate the numerical models some uncertain parameters such as elasticity modulus of wooden floor and connection rigidity of purlins to plane trusses are assessed experimentally. The results of this work demonstrate that when increasing numbers of tie bars the displacement values are decreased. Also the results obtained from developed numerical models have harmony with those of experimental. In addition, the scaffolding system with two tie bars at the beginning and at the end of the plane truss has the optimum structural performance compared the results obtained for other scaffolding system conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.11
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• pp.1415-1421
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• 2013

Recently, to resolve problems regarding legal liability for accidents and disasters, various simulation techniques such as F.E.M. and F.V.M. have been used in the field of forensic engineering. In this study, we performed mechanical structure analysis using ADINA to investigate the cause of bridge collapse accidents. Such accidents occurred owing to modified and missing processes in comparison with the original design while filling with concrete. Modified and missing processes cause buckling of the upper plate and twisting of the main girder. Through this study, we determine the exact cause of bridge collapse by comparing the evaluation of the structure stability of the original design with the evaluation of the structure stability of the modified and missing process using ADINA structure analysis. Hence, this result indicates that buckling prediction through FEA is the most effective method.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.159-165
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• 2006

In this study, structural analysis is executed about cone structure of KSL V-1 2nd stage KMS(kick motor support structure) which is designed for support the load developed from 2nd stage kick motor. KMS is consisted of cone structure and truss structure which is designed for supporting load developed from 2nd stage payload. Applied loads to cone structure are tension load by inertia developed from kick motor and compression load developed from kick motor. Also, shear and bending load are developed according to flight condition. In this study, structural analysis of cone structure is executed under several load condition which may be applied to cone structure. Also, structural analysis with two finite element model is performed according to pressure vent scheme. In result of structural analysis, critical load condition is equivalent tension load with cut-out.

• Journal of Korean Association for Spatial Structures
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• v.9 no.3
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• pp.75-82
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• 2009

This paper investigates the variation of post-buckling behaviours of spatial structures after sizing optimization with linear assumptions. The mathematical programming technique is used to produce the optimum member size of spatial structures against external load. Total weight of structure is considered as the objective function to be minimized and the displacement occurred at loading point and member stresses of structures are used as the constraint functions. The finite difference method is used to calculate the design sensitivity of objective function with respect to design variables. The post-buckling analysis carried out by using the geometrically nonlinear finite element analysis code ISADO-GN. It is found to be that there is a huge difference between the post buckling behaviours of the initial and optimized structures. Therefore, the stability of optimized spatial structures with linear assumption should be throughly checked by appropriate nonlinear analysis techniques. Finally, the present numerical results are provided as benchmark test suite for future study of large spatial structures.

• Smart Structures and Systems
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• v.15 no.3
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• pp.683-698
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• 2015

Railroad bridges form an integral part of railway infrastructure throughout the world. To accommodate increased axel loads, train speeds, and greater volumes of freight traffic, in the presence of changing structural conditions, the load carrying capacity and serviceability of existing bridges must be assessed. One way is through system identification of in-service railroad bridges. To dates, numerous researchers have reported system identification studies with a large portion of their applications being highway bridges. Moreover, most of those models are calibrated at global level, while only a few studies applications have used globally and locally calibrated model. To reach the global and local calibration, both ambient vibration tests and controlled tests need to be performed. Thus, an approach for system identification of a railroad bridge that can be used to assess the bridge in global and local sense is needed. This study presents system identification of a railroad bridge using free vibration data. Wireless smart sensors are employed and provided a portable way to collect data that is then used to determine bridge frequencies and mode shapes. Subsequently, a calibrated finite element model of the bridge provides global and local information of the bridge. The ability of the model to simulate local responses is validated by comparing predicted and measured strain in one of the diagonal members of the truss. This research demonstrates the potential of using measured field data to perform model calibration in a simple and practical manner that will lead to better understanding the state of railroad bridges.

• Computers and Concrete
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• v.7 no.3
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• pp.203-220
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• 2010

In the present study, exterior beam-column sub-assemblage from a regular reinforced concrete (RC) building has been considered. Two different types of beam-column sub-assemblages from existing RC building have been considered, i.e., gravity load designed ('GLD'), and seismically designed but without any ductile detailing ('NonDuctile'). Hence, both the cases represent the under-designed structure at different time frame span before the introduction of ductile detailing. For designing 'NonDuctile' structure, Eurocode and Indian Standard were considered. Non-linear finite element (FE) program has been employed for analysing the sub-assemblages under cyclic loading. FE models were developed using quadratic concrete brick elements with embedded truss elements to represent reinforcements. It has been found that the results obtained from the numerical analysis are well corroborated with that of experimental results. Using the validated numerical models, it was proposed to correlate the energy dissipation from numerical analysis to that from experimental analysis. Numerical models would be helpful in practice to evaluate the seismic performance of the critical sub-assemblages prior to design decisions. Further, using the numerical studies, performance of the sub-assemblages with variation of axial load ratios (ratio is defined by applied axial load divided by axial strength) has been studied since many researchers have brought out inconsistent observations on role of axial load in changing strength and energy dissipation under cyclic load.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.1
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• pp.113-124
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• 2008

Distributed operation of overall structural design process, by which product optimization and process parallelization are simultaneously implemented, is presented in this paper. The database-interacted hybrid method, which selectively takes the accustomed procedure of the conventional method in the framework of the optimal design, is utilized here. The staged application of design constraints reduces the computational burden for large complex optimization problems. Two kinds of numeric and graphic processes are simultaneously implemented by concurrent engineering approach in the distributed environment of PC networks. The former is based on finite element optimization method and the latter is represented by AutoCAD using AutoLISP programming language. Numerical computation and database interaction on servers and graphic works on independent clients are communicated through message passing. The numerical experiments for some steel truss models show the validity and usability of the method. This study has sufficient adaptability and expandability, in that it is based on general methodologies and industry standard platforms.

• Journal of Korean Society of Steel Construction
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• v.23 no.1
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• pp.99-111
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• 2011

This paper presents an investigation of the structural stability of cable-stayed bridges in the construction stage, using geometric nonlinear finite-element analysis and considering various geometric nonlinearities, such as the sag effect of the cables, the P-${\Delta}$ effects of the girder and mast, and the large displacement effect. Initial shape analysis and construction-stage analysis were performed to determine the equilibrium of the structure in the construction stage. After that, geometric nonlinear analysis was performed to study structural stability. In this study, the weight of the derrick crane and the key segment were considered the main external loads, which were applied to the tip of the center span. The cable arrangement type and the stiffness ratios of the girder and mast were considered the main parameters of the analytic research. Based on the results of the analysis, the change in the buckling mode and critical load factors with respect to the cable arrangement type and the stiffness ratios of the girder and mast was investigated. The buckling modes of the steel cable-stayed bridges in the construction stage were classified, and the ranges of the stiffness ratios of the girder and mast, which show these classified buckling modes, were suggested.