• Steel and Composite Structures
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• v.51 no.6
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• pp.647-659
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• 2024

Given the increased interest in enhancing structural sustainability, the current study sought to apply multiobjective optimization to a footbridge with a steel-concrete composite I-girder structure. It was considered as objectives minimizing the cost for building the structure, the environmental impact assessed by CO2 emissions, and the vertical accelerations created by human-induced vibrations, with the goal of ensuring pedestrian comfort. Spans ranging from 15 to 25 meters were investigated. The resistance of the slab's concrete, the thickness of the slab, the dimensions of the welded steel I-profile, and the composite beam interaction degree were all evaluated as design variables. The optimization problem was handled using the Multiobjective Harmony Search (MOHS) metaheuristic algorithm. The optimization results were used to generate a Pareto front for each span, allowing us to assess the correlations between different objectives. By evaluating the values of design variables in relation to different levels of pedestrian comfort, it was identified optimal values that can be employed as a starting point in predimensioning of the type of structure analyzed. Based on the findings analysis, it is possible to highlight the relationship between the structure's cost and CO2 emission objectives, indicating that cost-effective solutions are also environmentally efficient. Pedestrian comfort improvement is especially feasible in smaller spans and from a medium to a maximum level of comfort, but it becomes expensive for larger spans or for increasing comfort from minimum to medium level.

• Wind and Structures
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• v.18 no.2
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• pp.103-116
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• 2014

Aeroelasticity is the main source of instability in structures which are subjected to aerodynamic forces. One of the major reasons of instability is the coupling of bending and torsional vibration of the flexible bodies, which is known as flutter. The presented investigation aims to study the aeroelastic stability of composite blades of wind turbine. Geometry, layup, and loading of the turbine blades made of laminated composites were calculated and evaluated. To study the flutter phenomenon of the blades, two numerical and analytical methods were selected. The finite element method (FEM), and JAR-23 standard were used to perform the numerical studies. In the analytical method, two degree freedom flutter and Lagrange's equations were employed to study the flutter phenomena analytically and estimate the flutter speed.

• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.927-933
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• 1994

Alumina composite membranes were prepared by chemical vapor deposition (CVD) using aluminum-tri-isopropoxide as a precursor. Porous alumina supports were used in deposition, which were in disk shape with mean pore diameter of 0.1 ${\mu}{\textrm}{m}$ and prepared by slip-coasting process. film deposition morphology on porous support was simulated through depositing alumina film on polycrystalline silicon pattern, and its step coverage observed by SEM showed one deviated from uniform step coverage. N2 permeability through composite membranes and the pressure dependence decreased as the deposition time increased. Initially, the N2 permeability of the top layer was tend to decrease rapidly, and then the degree of decrease in N2 permeability was tend to diminish with deposition time. The N2 permeability increased with heat treatment temperature and the crack was generated in top layer at 100$0^{\circ}C$.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.4
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• pp.308-312
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• 2002

To determine the natural frequencies and damping ratios of composite laminated plates, we present an officient modal parameter estimation technique by developing residual spectrum based structural system reconstruction. The modal parameters can be estimated from poles and residues of the system transfer functions, derived from the state space system matrices. From vibration tests on cross-ply and angle-ply composite laminates, the natural frequencies and damping ratios can be estimated using the modal coordinates of the structural dynamic system reconstructed from the experimental frequency response functions. These results are compared with those of finite element analysis and single-degree-of-freedom curve fitting.

• Structural Engineering and Mechanics
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• v.5 no.5
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• pp.553-563
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• 1997

A procedure is being developed for bolting plates to the sides of existing reinforced concrete beams to strengthen and stiffen them. Unlike standard composite steel and concrete beams in which there is longitudinal-partial-interaction at the steel/concrete interface (that is slip along the length of the beam), composite bolted side-plated reinforced-concrete beams are unique in that they also exhibit transverse-partial-interaction, that is slip transverse to the length of the beam. In this work, the fundamental mathematical models for transverse-partial-interaction and its interaction with longitudinal-partial-interaction are developed. The fundamental models are then further developed to determine the number of connectors required to resist the transverse forces and to limit the degree of transverse-partial-interaction in bolted side-plated reinforced concrete beams.

• 연구논문집
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• s.29
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• pp.151-162
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• 1999

In general, manufacturing processes of thermosetting composites consist of mold filling and resin cure. The important parameters used in modeling and designing mold filling are the permeability of the fibrous preform and the viscosity of the resin. To consolidate a composite, resin cure or chemical reaction plays an essential role. Cure kinetics. Therefore, is necessary to quantify the extent of chemical reaction or degree of cure. It is also important to predict resin viscosity which can change due to chemical reaction during mold filling. There exists a heat transfer between the mold and the composite during mold filling and resin cure. Cure kinetics is also used to predict a temperature profile inside composite. In this study, a new scheme which can determine cure kinetics from dynamic temperature scaning was proposed. The method was applied to epoxy resin system and was verified by comparing measurements and predictions.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.38-42
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• 2002

An apparatus was developed to repetitively apply a $-196^{\circ}C$ thermal load to coupon-sized mechanical test specimens. Using this device, IM7/5250-4 (carbon / bismaleimide) cross-ply and quasi-isotropic laminates were submerged in liquid nitrogen ($LN_2$) 400 times. Ply-by-ply micro-crack density, laminate modulus, and laminate strength were measured as a function of thermal cycles. Quasi-isotropic samples of IM7/977-3 (carbon / epoxy) composite were also manually cycled between liquid nitrogen and an oven set at $120^{\circ}C$ for 130 cycles to determine whether including elevated temperature in the thermal cycle significantly altered the degree or location of micro-cracking. In response to thermal cycling, both materials micro-cracked extensively in the surface plies fellowed by sparse cracking of the inner plies. The tensile modulus of the IM7/5250-4 specimens was unaffected by thermal cycling, but the tensile strength of two of the lay-ups decreased by as much as 8.5%.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.107-110
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• 2003

The electromagnetic intereference(EMI) shielding is very essential for commercial and military purposes. We fabricated multi-walled carbon nanoube(MWNT)/epoxy composites and studied the electromagnetic characteristics of the composites before we study the characteristics of MWNT-filled glass fiber-reinforced composites. After setting up the fabrication process, we measured the permittivities of MWNT/epoxy composites with process variables and MWNT concentrations in X-band(8.2GHz- 12.4GHz). Process variables changed the degree of dispersion, which influenced permittivities and permittivities increased rapidly from 0.5wt% to 1.0wt%.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.33-37
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• 2002

Recently, composites have been widely applied in the sporting goods, automobile, aerospace industry. As the use of advanced composites increase, specific techniques have been developed to repair damaged composite structures. In order to repair the damaged part, it is required that the material in the damaged area be removed first by utilizing the proper method, and prepreg be laid up in the area and cured under vacuum using the vacuum bagging materials. In curing process, either in an oven or autoclave is to be delamination can be occurred in the sound areas during and/or after the exposure to the elevated curing temperature in case that the repair process is repeated. Therefore, this study was conducted to evaluate the degree of degradation of properties of the cured parts and how it affects to the delamination phenomenon between laminated skin and honeycomb core.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.87-90
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• 2005

This paper presents an evaluation of the effect of titanium dioxide nanoparticles in sulfonated poly(ether ether ketone) (SPEEK) with sulfonation degree of 57%. A series of inorganic-organic hybrid membranes were prepared with a systematic variation of titanium dioxide nanoparticles content. Their water uptake, methanol permeability and proton conductivity as a function of temperature were investigated. The results obtained show that the inorganic oxide network decreases the proton conductivity and water swelling. It is also found that increase in inorganic oxide content leads to decrease of methanol permeability. In terms of morphology, membranes are homogeneous and exhibit a good adhesion between inorganic domains and the polymer matrix. The properties of the composite membranes are compared with standard nafion membrane.