• Computers and Concrete
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• v.1 no.2
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• pp.211-226
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• 2004

A relatively simple multiple-vertical-line-element macro model has been incorporated into a standard computer code DRAIN-2D. It was used in blind predictions of seismic response of cantilever RC walls subjected to a series of consequent earthquakes on a shaking table. The model was able to predict predominantly flexural response with relative success. It was able to predict the stiffness and the strength of the pre-cracked specimen and time-history response of the highly nonlinear wall as well as to simulate the shift of the neutral axis and corresponding varying axial force in the cantilever wall. However, failing to identify the rupture of some brittle reinforcement in the third test, the model was not able to predict post-critical, near collapse behaviour during the subsequent response to two stronger earthquakes. The analysed macro model seems to be appropriate for global analyses of complex building structures with RC structural walls subjected to moderate/strong earthquakes. However, it cannot, by definition, be used in refined research analyses monitoring local behaviour in the post critical region.

• Computational Structural Engineering : An International Journal
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• v.3 no.1
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• pp.1-7
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• 2003

For system identification of large structures, it is not practical to identify the entire structure due to the prohibitive computational time and difficulty in numerical convergence. This paper explores the possibility of performing system identification at substructure level, taking advantage of reduction in both the number of unknowns and the number of degrees of freedom involved. Another advantage is that different portions (substructures) of a structural system can be identified independently and even concurrently with parallel computing. Two substructural identification methods are formulated on the basis whether substructural approach is used to obtain first-order or second-order model. For substructural first-order model, identification at the substructure level will be performed by means of the Observer/Kalman filter Identification (OKID) and the Eigensystem Realization Algorithm (ERA) whereas identification at the global level will be performed to obtain second-order model in order to evaluate the system's stiffness and mass parameters. In the case of substructural second-order model, identification will be performed at the substructure level throughout the identification process. The efficiency of the proposed technique is shown by numerical examples for multi-storey shear buildings subjected to random forces, taking into consideration the effects of noisy measurement data. The results indicate that both the proposed methods are effective and efficient for damage identification of large structures.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.5
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• pp.702-710
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• 1999

U-shaped bellows are usually used to piping system pressure sensor and controller for refriger-ator. Bellows subjected to internal pressure are designed for the purpose of absorbing deformation. Internal pressure on the convolution sidewall and end collar will be applied to an axial load tend-ing to push the collar away from the convolutions. To find out deformation behavior of bellow sub-jected to internal pressure the axisymmetric shell theory using the finite element method is adopted in this paper. U-shaped bellows can be idealized by series of conical frustum-shaped ele-ments because it is axisymmetric shell structure. The displacements of nodal points due to small increment of force are calculated by the finite element method and the calculated nodal displace-ments are added to r-z cylindrical coordinates of nodal points. The new stiffness matrix of the sys-tem using the new coordinates of nodal points is adopted to calculate the another increments of nodal displacement that is the step by step method is used in this paper. The force required to deflect bellows axially is a function of the dimensions of the bellows and the materials from which they are made. Spring constant is analyzed according to the changing geometric factors of U-shaped bellows. The FEM results were agreed with experiment. Using developed FORTRAN PROGRAM the internal pressure vs. deflection characteristics of a particu-lar bellows can be predicted by input of a few factors.

• Composites Research
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• v.28 no.4
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• pp.204-211
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• 2015

This paper presents a theory related to a two-dimensional linear cross-sectional analysis, recovery relationship and a one-dimensional nonlinear beam analysis for composite wing structure with initial twist. Using VABS including a related theory, the design process of the composite rotor blade has been described. Cross-sectional analysis was performed at cutting point including all the details of geometry and material. Stiffness matrix and mass matrix were linked to each section to make 1D beam model. The 3D strain distributions within the structure were recovered based on the global behavior of the 1D beam analysis and visualize numerical results.

• Structural Engineering and Mechanics
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• v.12 no.4
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• pp.347-362
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• 2001

The paper deals with preventing the collapse of by the means of supporting the bridges by rubber bearings and pedeck structures of skew and curved bridges during earthquakes, rmitting pounding between the decks and the abutments. Seismic response during pounding is characterized by various phenomena, such as the caging of bridge decks between abutments during an earthquake or decks popping out. These behaviors depend on only a small difference in seismic intensity. Regarding the global characteristics of a seismic response, smaller clearance between a deck and its abutments results in smaller impact damage of the abutments as well as lesser deformation of the rubber bearings. Similarly, smaller clearance between a deck and the side blocks results in smaller damage. The stiffnesses of the bearings and the stiffness ratio between them control the deck displacement. In short to medium length bridges, zero clearance between a deck and the abutments or the deck and the side blocks is the most effective way in preventing the deck from falling and limits the damage to the abutments or the side blocks.

• Steel and Composite Structures
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• v.27 no.2
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• pp.229-242
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• 2018

High strength steel is widely used in industrial applications to improve the load-bearing capacity and reduce the overall weight and cost. To take advantage of the benefits of this type of steel in construction, an innovative hybrid fabricated member consisting of high strength steel tubes welded to mild steel plates has recently been developed. Component-scale uniaxial and multiaxial cyclic experiments have been conducted with simultaneous constant or varying axial compression loads using a multi-axial substructure testing facility. The structural interaction of high strength steel tubes with mild steel plates is investigated in terms of member capacity, strength and stiffness deterioration and the development of plastic hinges. The deterioration parameters of hybrid specimens are calibrated and compared against those of conventional steel specimens. Effect of varying axial force and loading direction on the hysteretic deterioration model, failure modes and axial shortening is also studied. Plate and tube elements in hybrid members interact such that the high strength steel is kept within its ultimate strain range to prevent sudden fracture due to its low ultimate to yield strain ratio while the ductile performance of plate governs the global failure mechanism. High strength material also significantly reduces the axial shortening in columns which prevents undesirable frame deformations.

• Computers and Concrete
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• v.6 no.4
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• pp.319-341
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• 2009

A new formulation based on lumped plasticity and inelastic hinges is presented in this paper for nonlinear analysis of Reinforced Concrete (RC) frame structures. Inelastic hinge behaviour is described using the principles of Continuum Damage Mechanics (CDM). Member formulation contains provisions to model stiffness degradation due to cracking of concrete and yielding of reinforcing steel. Depending on its nature, cracking is classified as concentrated or distributed. Concentrated cracking is accounted through a damage variable and its growth is defined based on strain energy principles. Presence of distributed flexural cracks in a member is taken care of by modelling it as non-prismatic. Plasticity theory supported by effective stress concept of CDM is applied to describe the post-yield response. Nonlinear quasi-static analysis is carried out on a RC column and a wide two-storey RC frame to verify the formulation. The column is subjected to constant axial load and monotonic lateral load while the frame is subjected to only lateral load. Computed results are compared with those due to experiments or other numerical methods to validate the performance of the formulation and also to highlight the contribution of distributed cracking on global response.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.11-24
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• 1998

The composite sandwich plate is constructed by combining two laminated facings with high strength and a thick core of light weight material. The governing equations for the analysis of bending of simply supported sandwich plates with laminated facings are derived and analysed using the analytical method including the local shear deformations. The accuracy of the approach is ascertained by comparing solutions from the sandwich plate theory with composite facings to the laminate plate theory. Since the present analysis considers the bending stiffness of the core and also the transverse shear deformations of the laminated facings, it is expected that the analysis is capable to analyze the general anisotropic laminated plates with global shear deformations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.394-399
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• 2005

In this paper, a structural damage identification method (SDIM) is developed to identify the line crack-like directional damages generated within a cylindrical shell. First, the equations of motion fur a damaged cylindrical shell are derived. Based on a theory of continuum damage mechanics, a small material volume containing a directional damage is represented by the effective orthotropic elastic stiffness, which is dependent of the size and the orientation of the damage with respect to the global coordinates. The present SDIM is then derived from the frequency response function (FRF) directly solved from the dynamic equations of the damaged cylindrical shell. In contrast with most existing SDIMs which require the modal parameters measured in both intact and damaged states, the present SDIM requires only the FRF-data measured in damaged state. By virtue of utilizing FRF-data, one may choose as many sets of excitation frequency and FRF measurement point as needed to acquire a sufficient number of equations fer damage identification analysis. The numerically simulated damage identification tests are conducted to study the feasibility of the present SDIM.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1993.10a
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• pp.77-83
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• 1993

In this paper, the dynamics of a 2-DOF not 1:1 resonant Hamiltonian system are studied. In the first part of the work, the behaviors of special periodic orbits called normal modes are examined by means of the harmonic balance method and their approximate stability ar analyzed by using the Synge's concept named stability in the kinematico-statical sense. Secondly, the global dynamics of the system for low and high energy are studied in terms of a perturbation analysis and Poincare' maps. In this part, one can see that the unstable normal mode generates chaotic motions resulting from the transverse intersections of the stable and unstable manifolds. Although there exist analytic methods for proving the existence of infinitely many periodic orbits, chaos, they cannot be applied in our case and thus, the Poincare' maps constructed by direct numerical integrations are utilized fot detecting chaotic motions. In the last part of the work, the existence of arbitrarily many periodic orbits of the system are proved by using a subharmonic Melnikov's method. We also study the possibility of the breakdown of invariant KAM tori only when h>h$_{0}$ (h$_{0}$:bifurcating energy) and investigate the generality of the destruction phenomena of the rational tori in the systems perturbed by stiffness and inertial coupling.