• Structural Engineering and Mechanics
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• v.60 no.6
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• pp.1063-1077
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• 2016

Components manufactured from composite materials are frequently subjected to superimposed mechanical and thermal loadings during their operating service. Both types of loadings may cause fracture and failure of composite structures. When composite cross-ply laminates of type [$0_m/90_n]_s$ are subjected to uni-axial tensile loading, different types of damage are set-up and developed such as matrix cracking: transverse and longitudinal cracks, delamination between disoriented layers and broken fibers. The development of these modes of damage can be detrimental for the stiffness of the laminates. From the experimental point of view, transverse cracking is known as the first mode of damage. In this regard, the objective of the present paper is to investigate the effect of transverse cracking in cross-ply laminate under thermo-mechanical degradation. A Finite Element (FE) simulation of damage evolution in composite crossply laminates of type [$0_m/90_n]_s$ subjected to uni-axial tensile loading is carried out. The effect of transverse cracking on the cross-ply laminate strength under thermo-mechanical degradation is investigated numerically. The results obtained by prediction of the numerical model developed in this investigation demonstrate the influence of the transverse cracking on the bearing capacity and resistance to damage as well as its effects on the variation of the mechanical properties such as Young's modulus, Poisson's ratio and coefficient of thermal expansion. The results obtained are in good agreement with those predicted by the Shear-lag analytical model as well as with the obtained experimental results available in the literature.

• Steel and Composite Structures
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• v.30 no.4
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• pp.365-382
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• 2019

In steel frame-tube structures (SFTSs) the application of flexural beam is not suitable for the beam with span-to-depth ratio lower than five because the plastic hinges at beam-ends can not be developed properly. This can lead to lower ductility and energy dissipation capacity of the SFTS. To address this problem, a replaceable shear link, acting as a ductile fuse at the mid length of deep beams, is proposed. SFTS with replaceable shear links (SFTS-RSLs) dissipate seismic energy through shear deformation of the link. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings and finite element models (FEMs) were established to study their hysteretic behavior. Static pushover and dynamic analyses were undertaken in comparing seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial lateral stiffness. Compared with SFTS, SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. During earthquakes, SFTS-RSL had lower interstory drift, maximum base shear force and story shear force compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrates plasticity on the shear link. Other structural components remain elastic during seismic loading. It is expected that the SFTS-RSL will be a reliable dual resistant system. It offers the benefit of being able to repair the structure by replacing damaged shear links after earthquakes.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.04b
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• pp.215-221
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• 2000

A simple numerical modeling technique is proposed for the analysis of framed tube structures with multiple internal tubes. The structures are analysed using a continuum approach in which each tube is individually modelled by a tube beam that accounts for the flexural and shear deformations, as well as the shear lag effects. By simplifying assumptions regarding the form of strain distributions in external and internal tubes, the structural behaviours is reduced to the solution of a single second order linear differential equation. The numerical analysis uses the variational approach on the basis of the minimum potential energy priniciple. Three framed-tube sructures with single, two and three internal tubes are analysed to verify the applicability and reliability of the proposed method.

• Steel and Composite Structures
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• v.10 no.3
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• pp.223-243
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• 2010

This paper reports recent developments concerning the application of Generalised Beam Theory (GBT) to the structural analysis of steel-concrete composite bridges. The potential of GBT-based semi-analytical or finite element-based analyses in this field is illustrated/demonstrated by showing that both accurate and computationally efficient solutions may be achieved for a wide range of structural problems, namely those associated with the bridge (i) linear (first-order) static, (ii) vibration and (iii) lateral-torsional-distortional buckling behaviours. Several illustrative examples are presented, which concern bridges with two distinct cross-sections: (i) twin box girder and (ii) twin I-girder. Allowance is also made for the presence of discrete box diaphragms and both shear lag and shear connection flexibility effects.

• Coupled systems mechanics
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• v.12 no.3
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• pp.241-260
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• 2023

The objective of this study is to evaluate the effects of adding fibers to concrete and the distribution rate of the porosity on the interfacial stresses of the beams strengthened with various types of functionally graded porous (FGP) plate. Toward this goal, the beams strengthened with FGP plate were considered and subjected to uniform loading. Three types of beams are considered namely RC beam, RC beam reinforced with metal fibers (RCFM) and RC beam reinforced with Alfa fibers (RCFA). From an analytical development, shear and normal interfacial stresses along the length of the FGP plates were obtained. The accuracy and validity of the proposed theoretical formula are confirmed by the others theoretical results. The results showed clearly that adding fibers to concrete and the distribution rate of the porosity have significant influence on the interfacial stresses of the beams strengthened with FGP plates. Finally, parametric studies are carried out to demonstrate the effect of the mechanical properties and thickness variations of FGP plate, concrete and adhesive on interface debonding, we can conclude that, This research is helpful for the understanding on mechanical behavior of the interface and design of the FRP-RC hybrid structures.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.26-36
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• 2001

Smart sensors and actuators have recently been developed. In this study, first, small-diameter fiber Bragg grating (FBG) sensors developed by the author, whose cladding and polyimide coating diameters were 40 and $52{\mu}m$, respectively, were embedded inside a laminate without resin-rich regions around sensors and the deterioration of mechanical properties of the composite laminate. The small-diameter FBG sensor was embedded in $0^{\circ}$ ply of a CFRP laminate for the detection of transverse cracks in $90^{\circ}$ ply of the laminate. The reflection spectra from the FBG sensor were measured at various tensile stresses. The spectrum became broad and had some peaks with an increase of the transverse crack density. Furthermore, the theoretical calculation reproduced the change in the spectrum very well. These results show that the small-diameter FBG sensors have a potential to detect the occurrence of transverse cracks through the change in the form of the spectrum, and to evaluate the transverse crack density quantitatively by the spectrum width. On the other hand, shape memory alloy (SMA) films were used to suppress the initiation and growth of transverse cracks in CFRP laminates. Pre-strained SMA films were embedded between laminas in CFRP laminates and then heated to introduce the recovery stress in SMA films and compressive stresses in the weakest plies ($90^{\circ}$ ply). The effects of recovery stresses are demonstrated in the experiments and well predicted using the shear-lag analysis and the nonlinear constitutive equation of SMA films.

• Structural Engineering and Mechanics
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• v.48 no.3
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• pp.395-414
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• 2013

The present study fundamentally investigated the mechanical performance of the rib-stiffened super-wide bridge deck with twin box girders in concrete, which is a very popular application to efficiently widen the bridges with normal span. The shear lag effects of the specific cross-sections were firstly studied. The spatial stress distribution and local stiffness of the bridge deck with twin box girders were then investigated under several typical wheel load conditions. Meanwhile, a comparative study for the bridge deck with and without stiffening ribs was also carried out during the investigation; thereby, a design optimization for the stiffening ribs was further suggested. Finally, aiming at the preliminary design, an approximate methodology to manually calculate the bending moments of the rib-stiffened bridge deck was analytically proposed for engineers to quickly assess its performance. This rib-stiffened bridge deck with twin box girders can be widely applied for concrete (especially concrete cable-stayed) bridges with normal span, however, requiring a super-wide bridge width due to the traffic flow.

• Computers and Concrete
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• v.27 no.5
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• pp.407-416
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• 2021

The checking stresses in the Chinese codes for reinforced concrete (RC) or prestressed concrete (PC) bridges are aimed for the thin-web beam, which cannot reflect the actual behavior of the modern structures. The incompleteness of the checking stresses could give rise to the deficiency in the design and calculation, and unable to reveal the reason of some common cracks in the structure. In this paper, the complete stress checklist for RC or PC girder bridges are listed, as well as the corresponding crack shapes. The expression of the complete checking stresses is proposed in details. Spatial Grid Model can reflect all the concerned stresses in the structure. Through the comparison of the calculation results from the spatial grid model and the solid model, it is seen that the spatial grid model can reflect load effects such as shear lag effect, thin-wall effect and local effect. The stresses obtained from the spatial grid model could help engineers to have a good understanding of the structural behavior. Meanwhile, the stress checklist provides the information for analyzing and solving the deficiency in the structure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.29-36
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• 2004

In this work, the effect of composite couplings on hub loads of a hingeless rotor in forward flight is investigated. The hingeless composite rotor blade is idealized as a laminated thin-walled box-beam. The nonclassical effects such as transverse shear, torsional warping are considered in the structural formulation. The nonlinear differential equations of motion are obtained by applying Hamilton's principle. The blade response and hub loads are calculated using a finite element formulation in space and time. The aerodynamic forces acting on the blade are calculated by quasi-steady strip theory. The theory includes the effects of reversed flow and compressibility. The magnitude of elastic couplings obtained by MSC/NASTRAN is compared with the classical pitch-flap $({\delta}3)$ or $pitch-lag({\alpha}1)$ coupling. It is found that the elastic couplings have a substantial effect on the behavior of $N_b/rev$ hub loads. Nearly 10 to 40% of hub loads is reduced by appropriately tailoring the fiber orientation angles in the laminae of the composite blade.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.9 no.1
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• pp.59-69
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• 2001

The rotor blade is modeled using a composite box beam with arbitrary wall. The active constrained damping layers are bonded to the upper and lower surfaces of the box beam to provide active and passive damping. A finite element model, based on a hybrid displacement theory, is used in the structural analysis. The theory is capable of accurately capturing the transverse shear effects in the composite primary structure, the viscoelastic and the piezoelectric layers within the ACLs. A reduced order model is derived based on the Hankel singular value. A linear quadratic Gaussian (LQG) controller is designed based on the reduced order model and the available measurement output. However, the LQG control system fails to stabilize the perturbed system although it shows good control performance at the nominal operating condition. To improve the robust stability of LQG controller, the loop transfer recovery (LTR) method is applied. Numerical results show that the proposed controller significantly improves rotor aeromechanical stability and suppresses rotor response over large variations in rotating speed by increasing lead-lag modal damping in the coupled rotor-body system.