• Steel and Composite Structures
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• v.22 no.5
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• pp.1073-1084
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• 2016

Rectangular concrete-filled steel tubular columns with unequal wall thickness were investigated in the paper. The physical centroid, the centroidal principal axes of inertia, and the section core were given. The generalized bending formula and the generalized eccentric compression formula were deduced, and the equation of the neutral axis was also provided. The two rectangular concrete-filled steel tubular stub specimens subjected to the compression load on the physical centroid and the geometric centroid respectively were tested to verify the theoretical formulas.

• Structural Engineering and Mechanics
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• v.6 no.1
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• pp.31-40
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• 1998

The research and applications of numerical methods of design optimization on structural dynamic behaviors are presented in this paper. The emphasis is focused on the dynamic design optimization of aerospace structures, particularly those composed of composite laminate and sandwich plates. The methods of design modeling, sensitivity analysis on structural dynamic responses, and the optimization solution approaches are presented. The numerical examples of sensitivity analysis and dynamic structural design optimization are given to demonstrate the effectiveness of the numerical methods.

• Steel and Composite Structures
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• v.42 no.4
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• pp.459-475
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• 2022

In this paper a model for the prediction of the ultimate axial compressive capacity of square and rectangular Concrete Filled Steel Tubes, based on an Artificial Neural Network modeling procedure is presented. The model is trained and tested using an experimental database, compiled for this reason from the literature that amounts to 1193 specimens, including long, thin-walled and high-strength ones. The proposed model was selected as the optimum from a plethora of alternatives, employing different activation functions in the context of Artificial Neural Network technique. The performance of the developed model was compared against existing methodologies from design codes and from proposals in the literature, employing several performance indices. It was found that the proposed model achieves remarkably improved predictions of the ultimate axial load.

• Smart Structures and Systems
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• v.19 no.3
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• pp.309-322
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• 2017

In this paper, the buckling, and free vibration analysis of tapered functionally graded carbon nanotube reinforced composite (FG-CNTRC) micro Reddy beam under longitudinal magnetic field using finite element method (FEM) is investigated. It is noted that the material properties of matrix is considered as Poly methyl methacrylate (PMMA). Using Hamilton's principle, the governing equations of motion are derived by applying a modified strain gradient theory and the rule of mixture approach for micro-composite beam. Micro-composite beam are subjected to longitudinal magnetic field. Then, using the FEM, the critical buckling load, and natural frequency of micro-composite Reddy beam is solved. Also, the influences of various parameters including ${\alpha}$ and ${\beta}$ (the constant coefficients to control the thickness), three material length scale parameters, aspect ratio, different boundary conditions, and various distributions of CNT such as uniform distribution (UD), unsymmetrical functionally graded distribution of CNT (USFG) and symmetrically linear distribution of CNT (SFG) on the critical buckling load and non-dimensional natural frequency are obtained. It can be seen that the non-dimensional natural frequency and critical buckling load decreases with increasing of ${\beta}$ for UD, USFG and SFG micro-composite beam and vice versa for ${\alpha}$. Also, it is shown that at the specified value of ${\alpha}$ and ${\beta}$, the dimensionless natural frequency and critical buckling load for SGT beam is more than for the other state. Moreover, it can be observed from the results that employing magnetic field in longitudinal direction of the micro-composite beam increases the natural frequency and critical buckling load. On the other hands, by increasing the imposed magnetic field significantly increases the stability of the system that can behave as an actuator.

• Tribology and Lubricants
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• v.30 no.5
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• pp.278-283
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• 2014

Carbon nanotubes (CNTs) are used in various composite materials to enhance electrical, thermal and mechanical properties of composite materials. In this study, we investigate the wear characteristics of polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) blends containing multi-walled carbon nanotubes (MWCNTs). PC/ABS blends are commonly used in many industrial applications such as cellular phones and display cases and MWCNTs have been added to the PC/ABS blends to improve their electromagnetic interference shielding (EMS). We performed wear tests on PC/ABS blends containing MWCNTs under reciprocating linear sliding conditions with chrome steel balls as a counterpart material. The normal loads were 10, 30, 50, 70, 100 N, the sliding speed was 10 mm/s, the stroke length was 15 mm, and the tests lasted 900 s. The MWCNTs included in the PC/ABS blends lower the wear volume and friction coefficient of the composites. We analyzed the wear debris collected from the composites during the tests in terms of the MWCNT concentration using inductively coupled plasma optical emission spectroscopy. The results show that the quantity of MWCNTs in the debris is proportional to the concentration of MWCNTs in the composite, indicating that the exposure of the MWCNTs to environments by wear could be increased with their concentration in the composite.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.249-252
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• 2005

Prediction of damage caused by low-velocity impact in laminated composite plate is an important problem faced by designers using composites. Not only the inplane stresses but also the interlaminar normal and shear stresses playa role in estimating the damage caused. The work reported here is an effort in getting better predictions of damage in composite plate using DNS approach. In the DNS model, we discretize the composite plates through separate modeling of fiber and matrix for the local microscopic analysis. Through comparison with the homogenized model. In the view of microscopic mechanics with DNS model, interlaminar stress behaviors in the inside of composite materials is investigated and compared with the results of the homogenized model which has been used in the conventional approach of impact analysis.

• Steel and Composite Structures
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• v.9 no.1
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• pp.39-58
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• 2009

Composite joints, considering the composite action of steel and concrete, exhibit, in general, high strength and high ductility. As a consequence, the use of this type of joint has been increasing in many countries, especially in those that are located in earthquake-prone regions. In this paper, a hysteretic model with pinching is presented that is able to reproduce the cyclic response of steel and composite joints. Secondly, the computer implementation and adaptation of the model in a spring element within the computer code Seismosoft is described. The model is subsequently calibrated using a series of experimental test results for composite joints subjected to cyclic loading. Finally, typical parameters for the various joint configurations are proposed.

• Structural Engineering and Mechanics
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• v.60 no.5
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• pp.829-849
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• 2016

In this paper, experimental as well as numerical analysis of Glass Fiber Reinforced Polymer (GFRP) laminated composite has been presented under ballistic impact with varying projectile nose shapes (conical, ogival and spherical) and incidence velocities. The experimental impact tests on GFRP composite plate reinforced with woven glass fiber ($0^{\circ}/90^{\circ}$)s are performed by using pneumatic gun. A three dimensional finite element model is developed in AUTODYN hydro code to validate the experimental results and to study the ballistic perforation characteristic of the target with different parametric variations. The influence of projectile nose shapes, plate thickness and incidence velocity on the variation of residual velocity, ballistic limit, contact force-time histories, energy absorption, damage pattern and damage area in the composite target have been studied. The material characterization of GFRP composite is carried out as required for the progressive damage analysis of composite. The numerical results from the present FE model in terms of residual velocity, absorbed energy, damage pattern and damage area are having close agreement with the results from the experimental impact tests.

• Structural Engineering and Mechanics
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• v.88 no.3
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• pp.201-208
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• 2023

In this work, the effect of the correction fibers direction on the efficiency of repairing damaged composite plates was highlighted. The composite plates studied in this work consist of eight layers of graphite/epoxy, while the patch used in this repair consists of four layers of the same type. The results obtained in this work, whether with regard to the experimental or analytical side, showed that the fibers orientation affects the repair efficiency, so the closer the angle of fibers inclination is to the tensile strength direction, the performance of the composite material is ideal. Hence, we conclude that the composite materials with longitudinal fibers (Parallel to tensile strength) is the most powerful and efficient material in performance.

• Structural Engineering and Mechanics
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• v.31 no.5
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• pp.605-619
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• 2009

A comparative experimental study of prestressed continuous steel-concrete composite beams was carried out. Two continuous composite beams were tested, one of which was plain continuous steel-concrete composite beam, while the other was a composite beam prestressed with external tendons. Cracking behavior and the load carrying capacity of the beams were investigated experimentally. Full plasticity was developed in the mid-span section each beam, the maximum moments attained at the internal support sections however were governed by local buckling which was related to the slenderness of composite section. It was found that in hogging moment regions, the ultimate resistance of an externally prestressed composite beam would be governed by either distortional lateral buckling or local buckling, or interactive mode of these two buckling patterns. The results show that exerting prestressing on a continuous composite beam with external tendons will increase the extent of internal force and moment redistribution in the beam. The influences of local and distortional buckling on the behaviors of the composite continuous beams are discussed. The Moment redistribution and the load carrying capacity of the prestressed continuous composite beams are evaluated, and it is found that at the ultimate state, the moment redistribution in the prestrssed continuous composite beams is greater than that in non-prestressed composite beams.