• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.8
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• pp.665-672
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• 2013

One of the major causes of stiffness and strength degradations in laminated composite structures is the delamination between composite layers. In most engineering applications, laminated composite structures have certain curvatures. If the curved composite structure is subjected to bending that tends to flatten the composite structures, through the thickness stresses can be generated in the thickness direction of the composites. Under normal operation open mode delamination could occur at the sites of peak interlaminar stress. This paper describes a technique to determine radial direction stress of a laminated composite structure using a curved beam. Stacking sequence effects of interlaminar stress were studied. The radial location and intensity of the open mode delamination stress were calculated and compared with the results obtained from the analytical solution and finite element method.

• Computers and Concrete
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• v.22 no.3
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• pp.279-289
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• 2018

Shear walls are one of the important structural elements for bearing loads imposed on buildings due to winds and earthquakes. Composite shear walls with high lateral resistance, and high energy dissipation capacity are considered as a lateral load system in such buildings. In this paper, a composite shear wall consisting of steel faceplates, infill concrete and tie bars which tied steel faceplates together, and concrete filled steel tubular (CFST) as boundary columns, was modeled numerically. Test results were compared with the existing experimental results in order to validate the proposed numerical model. Then, the effects of some parameters on the behavior of the composite shear wall were studied; so, the diameter and spacing of tie bars, thickness and compressive strength of infill concrete, thickness of steel faceplates, and the effect of strengthening the bottom region of the wall were considered. The seismic behavior of the modeled composite shear wall was evaluated in terms of stiffness, ductility, lateral strength, and energy dissipation capacity. The results of the study showed that the diameter of tie bars had a trivial effect on the performance of the composite shear wall, but increasing the tie bars spacing decreased ductility. Studying the effect of infill concrete thickness, concrete compressive strength, and thickness of steel faceplates also showed that the main role of infill concrete was to prevent buckling of steel faceplates. Also, by strengthening the bottom region of the wall, as long as the strengthened part did not provide a support performance for the upper part, the behavior of the composite shear wall was improved; otherwise, ductility of the wall could be reduced severely.

• Journal of Technologic Dentistry
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• v.30 no.2
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• pp.23-29
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• 2008

The purpose of this study is to evaluate possibility of using indirect composite resin instead of porcelain through the measurement of shear bond strength between zirconia core and indirect composite resin under treatment of $Rocatec^{TM}$ system for improving the adhesion of indirect composite resin. 20 cylindrical zirconia core specimens were divided into 2 groups, according to zirconia surface treatment and attached materials: 1) treated with sandblast and attached with indirect composite resin, 2) treated with sandblast + $Rocatec^{TM}$ system and attached with indirect composite resin. The shear bond strength of each experimental group was measured by MTS and the changes of zirconia core surface according to surface treatments were obtained by SEM observation and measurements of surface roughness. The mean shear bond strength values are $0.55\;{\pm}\;0.11MPa$(Group SC) and $1.16\;{\pm}\;0.46MPa$(Group SRC). The mean Ra values for the surface treatments were follows: $0.39\;{\pm}\;0.13$($100{\beta}_{{\mu}m}$ sandblast) and $0.50\;{\pm}\;0.03$($100{\beta}_{{\mu}m}$ sandblast + $Rocatec^{TM}$ system). In the analysis of EDS, Si element was detected in the Group SC. The shear bond strength between zirconia core and indirect composite resin was improved significantly by using $Rocatec^{TM}$ system.

• Composites Research
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• v.30 no.1
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• pp.52-58
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• 2017

This paper presents the optimum design methodology for composite wing structure which automatically calculates the safety margin using optimization framework integrating failure modes. Particularly, its framework is possible to optimize sizing procedure to prevent failure mode which has the greatest effect on reducing the sizing time of composite structure. The main failure mode was set as the first ply failure, buckling failure mode, and bolted joint stress field, and the margin was calculated to minimize the weight. The design variable is a laminate sequence database and the responses are strain, buckling, bolted joint stress field. The objective function is the mass of the wing structure. The results of buckling analysis were compared using the finite element model to verify the robustness and reliability of Composite Optimizer.

• Journal of Korean Association for Spatial Structures
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• v.18 no.3
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• pp.57-66
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• 2018

Recently various composite beams in which concrete is filled in the U-shaped steel plate have been developed for saving story height and reducing construction period. Due to the high flexural stiffness and strength, they are widely being used for the building with large loads and long spans. The semi-slim AU composite beam has proven to take highly improved stability compared to the existing composite beams, because it consists of the closed steel section by attaching cap-type shear connectors to the upper side of U-shaped steel plate. In this study the finite element analyses were performed to evaluate the safety of the AU composite beam with unconsolidated concrete which were sustained through the closed steel section during the construction phase. The analyses were performed on the two types of cross section applied to the fabrication of AU composite beams, and the results were compared to the those of 2-point bending tests. In addition, the flexural performance according to the space of intermittent cap-type shear connectors and the location of reinforcing steel bars for compression was comparatively investigated. Through the results of analytical studies, it is preferable to adopt the yield moment of AU composite beam for evaluating the safety in the construction phase, and to limit the space of intermittent shear connectors to 400 mm or less for the construction load.

• Steel and Composite Structures
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• v.39 no.5
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• pp.529-542
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• 2021

Shear connectors are required to build composite (concrete and steel) beams. They are placed at the interface of concrete and steel to transfer shear and normal forces between two structural components. Such composite beams are sensitive to provide structural integrity when exposed to fire as they loss strength, stiffness, and ductility at elevated temperature. The present study is designed to investigate the shear resistance and the failure modes of the headed stud shear connectors at fire exposure and post-fire exposure. The study includes ordinary concrete and concrete with carbon nanotubes (CNTs) to build composite (concrete-steel) beams with structural steel. Experimental push tests were conducted on composite beams at ambient and elevated temperatures, such as 200, 400 & 600℃. Moreover, push tests were performed on the composite beams after being exposed to 200, 400 & 600℃. Push test results illustrated the reduction of ultimate shear capacity and stiffness of headed stud shear connectors as the temperature increased. Although similar values of ultimate shear were obtained for the headed stud connectors in both ordinary and CNT concrete, the CNT modified concrete reduced the concrete spalling and cracking compared to ordinary concrete and was observed to be effective at temperatures greater than 400℃. All specimens showed a lower shear resistance at fire exposures compared to the corresponding post-fire exposures. Moreover, numerical simulation by Finite Element (FE) analyses were carried out at ambient temperature and at fire conditions. The FE analysis results show a good agreement with the experimental results. In the experimental studies, failure of all specimens occurred due to shear failure of headed stud, which was later validated by FE analyses using ABAQUS.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.4
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• pp.321-328
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• 2021

This paper derives numerically new buckling Knockdown factors for the lightweight design of the composite propellant tanks for space launch vehicles. A nonlinear finite element analysis code, ABAQUS, is used for the present postbuckling analysis of composite cylinders under compressive loads. Various thickness ratios (R/t) and slenderness ratios (L/R) are considered and Single Perturbation Load Approach is applied to represent the geometric initial imperfection of the composite cylinder. For the composite cylinder with thickness ratio of 500 and slenderness ratio of 2.04, the buckling Knockdown factor derived in this work is higher by 84.38% than NASA's previous buckling design criteria. Therefore, it is investigated that a lightweight design is possible when the present Knockdown factors are used for the design of composite propellant tanks. In addition, it is shown that global buckling loads and buckling Knockdown factors decrease as the thickness ratio or slenderness ratio of composite cylinders increases.

• Steel and Composite Structures
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• v.44 no.1
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• pp.33-47
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• 2022

This paper presents a finite element model for predicting the monotonic behaviour of bolted endplate joints connecting steel-concrete composite walls and steel beams. The demountable Hollo-bolts are utilised to facilitate the quick installation and dismantling for replacement and reuse. In the developed model, material and geometric nonlinearities were included. The accuracy of the developed model was assessed by comparing the numerical results with previous experimental tests on hollow/composite column-to-steel beam joints that incorporated endplates and Hollo-bolts. In particular, the Hollo-bolts were modelled with the expanded sleeves involved, and different material properties of the Hollo-bolt shank and sleeves were considered based on the information provided by the manufacture. The developed models, therefore, can be applied in the present study to simulate the wall-to-beam joints with similar structural components and characteristics. Based on the validated model, the authors herein compared the behaviour of wall-to-beam joints of two commonly utilised composite walling systems (Case 1: flat steel plates with headed studs; Case 2: lipped channel section with partition plates). Considering the ease of manufacturing, onsite erection and the pertinent costs, composite walling system with flat steel plates and conventional headed studs (Case 1) was the focus of present study. Specifically, additional headed studs were pre-welded inside the front wall plates to enhance the joint performance. On this basis, a series of parametric studies were conducted to assess the influences of five design parameters on the behaviour of bolted endplate wall-to-beam joints. The initial stiffness, plastic moment capacity, as well as the rotational capacity of the composite wall-to-beam joints based on the numerical analysis were further compared with the current design provision.

• Steel and Composite Structures
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• v.48 no.6
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• pp.693-708
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• 2023

Composite beams, two materials joined together, have become more common in structural engineering over the past few decades because they have better mechanical and structural properties. The shear connectors between their layers exhibit some deformability with finite stiffness, resulting in interfacial shear slip, a phenomenon known as partial shear interaction. Such a partial shear interaction contributes significantly to the composite beams. To provide precise predictions of the geometric nonlinear behavior shown by two-layered composite beams with interfacial shear slips, a robust analytical model has been developed that incorporates the influence of significant displacements. The application of a higher-order beam theory to the two material layers results in a third-order adjustment of the longitudinal displacement within each layer along the depth of the beam. Deformable shear connectors are employed at the interface to represent the partial shear interaction by means of a sequence of shear connectors that are evenly distributed throughout the beam's length. The Von-Karman theory of large deflection incorporates geometric nonlinearity into the governing equations, which are then solved analytically using the Navier solution technique. Suggested model exhibits a notable level of agreement with published findings, and numerical outputs derived from finite element (FE) model. Large displacement substantially reduces deflection, interfacial shear slip, and stress values. Geometric nonlinearity has a significant impact on beams with larger span-to-depth ratio and a greater degree of shear connector deformability. Potentially, the analytical model can accurately predict the geometric nonlinear responses of composite beams. The model has a high degree of generality, which might aid in the numerical solution of composite beams with varying configurations and shear criteria.

• Composites Research
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• v.19 no.1
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• pp.15-21
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• 2006

It is very difficult to make complex 3 dimensional curved-shape composite laminates using the advanced unidirectional composite prepregs. This study shows development process of subscale composite parabolic antenna reflector using unidirectional AS4/PEEK prepreg tapes. The AS4/PEEK thermoplastic composite materials are known to have good thermal and chemical stabilities in addition to their high specific strength and modulus. Various lamination methods were investigated through finite element analyses to make up the laminate design of the reflector. The automated fiber placement method was used to fabricate the reflector. The thermal expansion test using full-bridge strain gage circuits was done to verity the performance of the composite product.