• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.3
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• pp.147-156
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• 2003

In this paper, a damage detection method using mode shapes of truss structures is presented. The theory is formulated based on the changes in the modal strain energy in a truss type structures due to damage. To examine the feasibility, the theory is applied to an experimental data of a 1:6 scale model of a typical hexagonal truss structure. The experiment consists of 17 damage scenarios subjected to three different types of damage. The damage evaluation results show that the proposed method detects successfully damage in truss elements and also show that the performance of proposed method can be significantly impacted by the noise in the measurement data for small damage.

• Magazine of the Korean Society of Agricultural Engineers
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• v.29 no.4
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• pp.73-92
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• 1987

Formulation of the geometric optimization for truss structures based on the elasticity theory turn out to be the nonlinear programming problem which has to deal with the cross-sectional area of the member and the coordinates of its nodes simultaneously. A few techniques have been proposed and adopted for the analysis of this nonlinear programming problem for the time being. These techniques, however, bear some limitations on truss shapes, loading conditions and design criteria for the practical application to real structures. A generalized algorithm for the geometric optimization of the truss structures, which can eliminate the above mentioned limitations, is developed in this study. The algorithm proposed utilizes the two-levels technique. In the first level which consists of two phases, the cross-sectional area of the truss member is optimized by transforming the nonlinear problem into SUMT, and solving SUMT utilizing the modified Newton Raphson method. In the second level, which also consists of two phases the geometric shape is optimized utillzing the unindirectional search technique of the Powell method which make it possible to minimize only the objective functlon. The algorithm proposed in this study is numerically tested for several truss structures with various shapes, loading conditions and design criteria, and compared with the results of the other algorithms to examine its applicability and stability. The numerical comparisons show that the two- levels algorithm proposed in this study is safely applicable to any design criteria, and the convergency rate is relatively fast and stable compared with other iteration methods for the geometric optimization of truss structures. It was found for the result of the shape optimization in this study to be decreased greatly in the weight of truss structures in comparison with the shape optimization of the truss utilizing the algorithm proposed with the other area optimum method.

• Journal of Navigation and Port Research
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• v.32 no.3
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• pp.215-221
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• 2008

Dynamic characteristics of a structure, i.e., natural frequency and mode shape, have been widely using as an input data in the area of structural integrity or health monitoring which combined with the damage evaluation and structural system identification techniques. It is very difficult, however, to get those information by the conventional modal analysis method from large structures, such as the offshore structure or the long-span bridge, since the source of vibration is not available. In this paper, a method to obtain the frequencies and the mode shapes of a large span truss structure using only acceleration responses is studied. The calculation procedures to obtain acceleration responses and frequency response functions are provided utilizing a numerical model of the truss, and the process to extract natural frequencies and mode shapes from the modal analysis is cleary explained. The extracted mode shapes by proposed method are compared with those from eigenvalue analysis for the estimation of accuracy. The validity of the mode shapes is also demonstrated using an existing damage detection technique for the truss structure by simulated damage cases.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.262-265
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• 2007

Metallic sandwich plates constructed of two face sheets and low relative density cores have lightweight characteristics and various static and dynamic load bearing functions. To predict the formability and performance of these structured materials, a computationally efficient FE-analysis method incorporating virtual equivalent projected model has been newly introduced for analysis of metallic sandwich plates. Two dimensional models using the projected shapes of 3D structures have the same equivalent elastic-plastic properties with original geometries including anisotropic stiffness, yield strength and linear hardening function. The projected shapes and virtual properties of the virtual equivalent projected model have been estimated analytically with the same equivalent properties and face buckling strength of 3D pyramidal truss core.

• Steel and Composite Structures
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• v.30 no.6
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• pp.577-589
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• 2019

In this study, on-site testing was carried out to investigate the vibration performance of a composite steel-bar truss slab with steel girder system. Ambient vibration was performed to capture the primary vibration parameters (natural frequencies, damping ratios, and mode shapes). The composite floor possesses low frequency (< 10 Hz) and damping (< 2%). Based on experimental, theoretical, and numerical analyses on natural frequencies and mode shapes, the boundary condition of SCSC (i.e., two opposite edges simply-supported and the other two edges clamped) is deemed more reasonable for the composite floor. Walking excitations by one person (single excitation), two persons (dual excitation), and three persons (triple excitation) were considered to evaluate the vibration serviceability of the composite floor. The measured acceleration results show a satisfactory vibration perceptibility. For design convenience and safety, a crest factor ${\beta}_{rp}$ describing the ratio of peak acceleration to root-mean-square acceleration induced from the walking excitations is proposed. The comparisons of the modal parameters determined by ambient vibration and walking tests reveal the interaction effect between the human excitation and the composite floor.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.910-921
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• 2002

For the prediction of shear behavior of reinforced concrete beams, this paper proposed Transformation Angle Truss Model (TATM) considered bending moment effect. Shear stress-strain relationship obtained from the TATM was agreed well with test results conducted by this study Further, shear strength obtained from the TATM was compared to the experimentally observed results of 170 reinforced concrete beams which had various shear span ratios shapes of support and shapes of cross section. The shear strength of reinforced concrete beams obtained from test was better predicted by the TATM with 0.96 in average and 11.9％ in coefficient of variation than by other truss models. And the ratio of experimental results to theoretical results obtained from the TATM was almost constant regardless of the η and a/d.

• Earthquakes and Structures
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• v.2 no.1
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• pp.89-107
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• 2011

In this paper a simple mathematical model is presented for estimating the natural frequencies and corresponding mode shapes of a tall building with outrigger-belt truss system. For this purposes an equivalent continuum system is analyzed in which a tall building structure is replaced by an idealized cantilever continuum beam representing the structural characteristics. The equivalent system is comprised of a cantilever shear beam in parallel to a cantilever flexural beam that is constrained by a rotational spring at outrigger-belt truss location. The mathematical modeling and the derivation of the equation of motion are given for the cantilevers with identically paralleled and rotational spring. The equation of motion and the associated boundary conditions are analytically obtained by using Hamilton's variational principle. After obtaining non-trivial solution of the eigensystem, the resulting is used to determine the natural frequencies and associated mode shapes of free vibration analysis. A numerical example for a 40 story tall building has been solved with proposed method and finite element method. The results of the proposed mathematical model have good adaptation with those obtained from finite element analysis. Proposed model is practically suitable for quick evaluations during the preliminary design stages.

• Steel and Composite Structures
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• v.19 no.2
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• pp.263-275
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• 2015

This study presents conceptual information of newly optimized shapes and connectivity of the so-called outrigger truss system for modern tall buildings that resists lateral loads induced by wind and earthquake forces. In practice, the outrigger truss consists of triangular or Vierendeel types to stiffen tall buildings, and the decision of outrigger design has been qualitatively achieved by only engineers' experience and intuition, including information of structural behaviors, although outrigger shapes and the member's connectivity absolutely affect building stiffness, the input of material, construction ability and so on. Therefore the design of outrigger trusses needs to be measured and determined according to scientific proofs like reliable optimal design tools. In this study, at first the shape and connectivity of an outrigger truss system are visually evaluated by using a conceptual design tool of the classical topology optimization method, and then are quantitatively investigated with respect to a structural safety as stiffness, an economical aspect as material quantity, and construction characteristics as the number of member connection. Numerical applications are studied to verify the effectiveness of the proposed design process to generate a new shape and connectivity of the outrigger for both static and dynamic responses.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.167-176
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• 1999

This paper is concerned with the damage detection of existing 2 and 3-dimensional truss structures based on free vibration equation and extended Kalman filter. The local damage is characterized in terms of the stiffness degradation of damaged members. As the observed data, the natural frequencies and mode shapes of damaged truss structure model are adopted. Both location and stiffness of damaged parts of members in truss structures can be estimated by the proposed inverse solution procedure. The applicability and effectiveness of proposed inverse solution procedure are demonstrated through the numerical examples.

• Smart Structures and Systems
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• v.18 no.5
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• pp.983-1004
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• 2016

Nowadays, there are two classes of methods for damage detection in structures consisting of static and dynamic. The dynamic methods are based on studying the changes in structure's dynamic characteristics. The theoretical basis of this method is that damage causes changes in dynamic characteristics of structures. The dynamic methods are divided into two categories: signal based and modal based. The modal based methods utilize the modal properties consisting of natural frequencies, modal damping and mode shapes. As the modal properties are sensitive to changes in the structure, these can be used for detecting the damages. In this study, using dynamic method and modal based approach (natural frequencies and mode shapes), the objective function is formulated. Then, detection of damages of truss structures is addressed by using Simplified Dolphin Echolocation algorithm and solving inverse optimization problem. Many scenarios are used to simulate the damages. To demonstrate the ability of the algorithm, different truss structures with several multiple elements scenarios are tested using a few runs. The influence of the two different levels of noise in the modal data for these scenarios is also considered. The last example of this article is investigated using a different mutation. This mutation obtains the exact answer with fewer loops and population by limited computational effort.