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Four different composite coupling beam-to-composite plate shear wall (CPSW/CF) connection details were developed and proposed. Six large-scale specimens representing the four connections were designed, fabricated, and tested. The connections were subassemblies of coupled composite plate shear walls/concrete filled (CC-PSW/CF) subjected to cyclic lateral loading. The coupling beams were designed to be flexure-critical with clear span-to-depth (Lb/d) ratios of 3.5 or 5.1. This paper presents the experimental program, capacities, and detailed behavioral observations of all six specimens. The effects of connection type and Lb/d ratio on the ultimate strength, stiffness, ductility, and failure modes are evaluated. Major limit states and events included yielding of the steel plates comprising the coupling beam, followed by local inelastic buckling, fracture initiation in the base metal (near the weld toes), and fracture propagation through the beam flange and web plates, leading to loss of flexural strength and failure. All the connections were able to develop and transfer the flexural capacity of the composite beam section. The composite coupling beams developed flexural capacities (10%–50%) greater than those calculated using the plastic stress distribution method. The underlying reasons for this overstrength are evaluated. The AISC flexural stiffness equation for filled composite sections could reasonably estimate the stiffness of the composite coupling beam sections. A fiber-based model of the cross-section was used to calculate the section moment–curvature response of the filled composite beam sections. The calculated flexural capacities were consistent with those calculated by the plastic stress distribution method but lower than the experimentally observed values. The flexural stiffness values were slightly higher than the experimental results. For more accurate comparisons with experimental results, a numerical model is needed to estimate the cyclic lateral load-deformation response while accounting for the effects of local buckling, low cycle fatigue, and fracture. [ABSTRACT FROM AUTHOR]

To operate small and medium-sized helicopters even under critical icing conditions, new deicing technologies are necessary because the existing heating solutions cannot be economically downscaled without drastically reducing the helicopters' payload. Therefore, this paper investigates the potential of a low-frequency electromechanical deicing (EMDI) system for an actual fiber composite helicopter structure and its combination with an ice detection system that uses the EMDI components for ice detection. The primary objective of this study is the design of the deicing system for a given helicopter structure and its evaluation under realistic icing conditions. Experimental and numerical modal analyses are used to analyze the vibration behavior of the structure and to select favorable positions and phase relations for the actuators. To determine the performance of the EMDI system, experimental deicing tests were performed in a deicing test facility that is able to generate realistic icing conditions. The EMDI system can cause delaminations and cracks in glaze ice layers and partially remove the ice on the test object. The results show that there is an upper and lower limit for ice thickness at which the system is effective. Therefore, the system needs to be combined with an ice detection system that is capable of measuring the ice thickness on the surface of the structure. Using the piezoelectric actuators of the EMDI, this can be achieved by monitoring their impedance changes, which is experimentally proven for different ice thicknesses and different temperatures on a carbon fiber composite plate. The findings of this study support the idea of a combined ice detection and deicing system using the same hardware components. Integrating an autonomous control system, local icing phenomena on a rotorcraft structure can be detected and consequently, ice accretion can be removed with low energy consumption. [ABSTRACT FROM AUTHOR]

Steel-plate composite walls comprise a steel plate encased in the middle of a reinforced concrete shear wall [referred to as "composite plate shear walls-concrete encased (C-PSW/CE)"], or a concrete infill sandwiched between two steel faceplates [referred to as "double-skin composite (DSC) walls"]. In this study, two I-shaped C-PSW/CE specimens with a shear-to-span-ratio of 1.2 were experimentally tested to investigate the cyclic in-plane shear behavior of C-PSW/CE used for high-rise buildings. Both wall specimens were identical in geometric dimensions and reinforcement details, with the exception of axial force ratio. The results indicated that shear failure occurred in the two wall specimens due to serious spalling of web concrete, followed by buckling of the embedded steel plate and vertically distributed reinforcements. The increase in axial force ratio from 0.16 to 0.29 resulted in an 11.8% rise in peak strength and a decrease in ultimate shear strain of 27% for C-PSW/CE. A comparison between C-PSW/CE and DSC walls indicated that the latter had a similar peak strength to the former, but clearly improved the ultimate drift. This is because the double faceplates of DSC walls provided a more effective restraint to the infilled concrete and prevented spalling of concrete. Then, this paper developed a refined numerical model to simulate C-PSW/CE and compared the analytical results with the experimental data. Finally, shear strength design formulas specified in Chinese and US codes were verified against a large volume of test data and numerical simulation results. The shear strength of C-PSW/CE was reasonably estimated by the JGJ 3-2010 design formulas (Chinese code), while significantly underestimated by the AISC 341-16 formula (US code) which neglects the shear contribution of reinforced concrete encasement. [ABSTRACT FROM AUTHOR]

Composite plate shear walls/concrete-filled (C-PSW/CFs), also known as SpeedCore systems, are a relatively new structural member in American codes and standards. Prior research has focused primarily on C-PSW/CF walls with either flange/closure plates or filled composite members as boundary elements. Walls without boundary elements have also been studied, but they are no longer permitted by the American Institute of Steel Construction (AISC 341-22). The reason is that composite walls without boundary elements do not provide adequate ductility for seismic design. This paper presents the results of experimental and numerical studies conducted to evaluate the cyclic lateral load behavior of C-PSW/CFs using hot-rolled structural steel members as boundary elements. The steel web plates of the C-PSW/CF specimens were connected to each other using threaded tie bars with double nut connections. Composite interaction between the steel and concrete infill was achieved using the tie bars and additional shear studs welded to the boundary elements. The composite walls were embedded and anchored to reinforced concrete foundation blocks using welded deformed bar anchors. The experimental investigations focused on the cyclic lateral load-drift responses including test observations and limit states, moment-rotation response of the plastic hinge and the section moment-curvature relationship, overall lateral stiffness, strength, and displacement ductility. The experimental results show that the specimens exceeded their nominal flexural capacities calculated using the plastic stress distribution method or fiber-based section modeling using measured material properties. The specimens had plastic hinge rotation capacity greater than 0.028 rad. and displacement ductility ratio greater than 5.2. Detailed 3D nonlinear inelastic finite element models and simpler fiber-based macro models of the tested specimens were developed and benchmarked using experimental results. The detailed 3D finite element models can reasonably simulate the global and local behavior of the specimens, and are recommended for conducting further parametric studies of composite wall design details. Simpler fiber-based macro models can efficiently simulate the cyclic lateral load behavior of the specimens, and are recommended for modeling C-PSW/CFs while simulating the behavior of multi-story building structures. [ABSTRACT FROM AUTHOR]

This paper presents findings from experiments conducted on four large-scale T-shaped concrete filled composite plate shear walls (C-PSW/CF) specimens subjected to axial force and flexure. A C-PSW/CF is a sandwich type of construction by which concrete (without rebars) is enclosed between steel plates connected by tie bars. One of the walls was subjected to a cyclic wind loading protocol and the other walls were cycled with a seismic loading protocol. Their dimensions were identical, but different axial loads (up to 30% of the crushing load of the infill concrete, Acfc′) were applied. The plastic hinge development was investigated along with the composite behavior and compared with the calculated plastic moment of the corresponding cross section. These tests along with the results on C-shaped wall tests were conducted to establish the development of design guidelines for high-rise core-wall steel buildings having C-PSW/CF as the primary lateral force resisting system. [ABSTRACT FROM AUTHOR]

Composite plate shear walls–concrete-filled (C-PSW/CF) are a new and innovative lateral force–resisting system intended for high-rise buildings. High-rise building applications of this system are particularly efficient in the coupled wall configuration, in which the walls are C-PSW/CF and the coupling beams are concrete filled steel box sections. This paper presents a capacity design principle for the seismic design of coupled composite plate shear wall–concrete filled (CC-PSW/CF) systems. The capacity design principle implements a strong wall–weak coupling beam approach, in which flexural yielding occurs in the coupling beams before flexural yielding at the base of walls. The coupling beams are sized to resist the calculated seismic lateral force level. The composite walls are sized to resist an amplified seismic lateral force corresponding to the overall plastic mechanism for the structure, while accounting for the capacity-limited forces from the coupling beams and the coupling action between the walls. The paper summarizes the recommendations and requirements for appropriate sizing of the composite coupling beams and walls. These recommendations were used along with the capacity design principle to design four example (8–22-story) structures and evaluate their seismic behavior. The structures were modeled using benchmarked finite-element models and fiber-based models that accounted for the various limit states, including steel yielding, local buckling, fracture, concrete crushing, confinement, and tension cracking. The numerical models were analyzed for monotonic pushover loading and scaled seismic ground motions. The structural responses from the nonlinear pushover analysis and the nonlinear time history analyses were in accordance with the capacity limited design philosophy, thus confirming its efficacy. [ABSTRACT FROM AUTHOR]

In this paper, thermal buckling and free vibration of a rectangular plate reinforced with carbon nanotubes (CNT) are investigated within the framework of third-order shear deformation theory (TSDT). CNT distribution along the thickness direction of the plate is uniformly or functionally graded. The equivalent properties of the reinforced composite plate are calculated based on the extended rule of mixture. Governing equations of motion are derived using the Hamilton principle. Obtained governing differential equations are analyzed by utilizing Fourier series expansion along the longitudinal and latitudinal direction for simply supported edges boundary conditions whereas for other edges boundary conditions we used the differential quadrature method (DQM) to solve numerically. Validation of the present formulation is assessed by comparing the results with those reported in the open literature. The effect of CNT volume fraction, the different patterns of CNT distribution, temperature difference, aspect ratio, and thickness-to-length ratio on buckling and vibration behavior of carbon nanotube-reinforced composite (CNTRC) plate is studied. The numerical illustration reveals that in the FG-X pattern of CNT distribution natural frequency and thermal buckling load is more significant compared with the other patterns of CNT distribution. [ABSTRACT FROM AUTHOR]

In this paper, the seismic design factors for uncoupled composite plate shear walls/concrete filled (C-PSW/CF), a.k.a. SpeedCore, are verified by conducting a study using FEMA methodology. These are the seismic response modification factor, R, the deflection amplification factor, Cd, and the overstrength factor, Ωo; and their values for C-PSW/CF are specified as 6.5, 5.5, and 2.5, respectively. A study was needed, as these factors for uncoupled C-PSW/CFs, included in ASCE 7 since as far back as its 2000 edition, were chosen solely based on the seismic performance of similar structural systems and engineering judgment of the committee members. For this study, four archetypes with planar walls and three archetypes with C-shaped C-PSW/CF walls were chosen. Two different damage measures (DM) were chosen for this study; namely, 3% and 5% maximum interstory drifts. Based on FEMA methodology, all archetypes satisfied the specified performance requirement considering a "good" rating for total system collapse uncertainty (βTOT). [ABSTRACT FROM AUTHOR]

Long-term exposure to a harsh environment leads to irreversible degradation of mechanical properties of fiber-reinforced polymer (FRP) profiles. Understanding the aging effects on pultruded FRP composites due to long-term exposure is essential. The moisture diffusion process plays a significant role in understanding material degradation of E-glass/polyester-reinforced polymer composite laminates exposed to hygrothermal environments. In this paper, the moisture diffusion process in pultruded (GFRP) composite bridge members is numerically simulated using the finite-element method. The moisture diffusion parameters were calibrated by gravimetric tests of pultruded composite thin plates. Gravimetric tests of three different rectangular specimens were conducted to investigate three-dimensional moisture diffusion at different temperatures and environments. The calibrated mass diffusion parameters were validated by comparing the average time-dependent moisture concentration obtained from non-Fick finite-element (FE) simulation with experimental results. [ABSTRACT FROM AUTHOR]

Discrete response of structures often is a key probabilistic quantity of interest. For example, one may need to identify the probability of a binary event, such as whether a structure has buckled. This study used an adaptive domain-based decomposition and classification method, combined with sparse grid sampling, to develop an efficient classification surrogate modeling algorithm for such discrete outputs. An assumption of monotonic behavior of the output with respect to all model parameters, based on the physics of the problem, helps to reduce the number of model evaluations and makes the algorithm more efficient. As an application problem, this paper developed a computational framework for generation of a probabilistic penetration response of S- 2 glass/SC -15 epoxy composite plates under ballistic impact. This enables the computationally feasible generation of the probabilistic velocity response (PVR) curve, or the V0−V100 curve, as a function of the impact velocity, and prediction of the ballistic limit velocity as a function of the model parameters. The PVR curve incorporates the variability of the model input parameters and describes the probability of penetration of the plate as a function of impact velocity. [ABSTRACT FROM AUTHOR]

Nonlinear progressive failure analysis (PFA) of piezolaminated composite shell panel under mechanical out-of-plane loading in the hygro-thermal environment is performed. The higher-order shear deformation theory (HSDT) with von-Karman nonlinear kinematics are used for basic formulation. Using variational principle governing equation for panel structure obtained by Newton's Raphson approach through finite element method is employed to compute the necessary PFA. The second-order perturbation technique (SOPT) is utilized to obtain statistics in terms of mean and corresponding coefficient of variance (COV) of first ply and last ply failure load (FPFL and LPFL) through ply-by-ply failure counting by assuming random input system parameters. Convergence and validation analysis is performed to check the exactness of MATLAB version 2013a code. Shell panels are subjected to environmental conditions with uniform temperature and moisture distribution over entire shell panels. Initially, the paper presents the response of the composite plate and shell with the application of uniformly distributed flexural loading in the form of transverse central deflection (TCD) and mean FPFL and LPFL using a deterministic approach. Then, statistics in terms of mean and corresponding COV of FPFL and LPFL are obtained using a probabilistic approach through PFA. The effect of thickness and aspect ratio, types of loading, lamination sequences, curvatures, temperature increment, moisture content, the position of piezoelectric layers, and voltage variation on statistics of PFA has been examined. [ABSTRACT FROM AUTHOR]

Planar composite plate shear walls/concrete filled (C-PSW/CF) consist of two steel web plates and two flange (or closure) plates making up a long hollow box section that is filled with concrete. The web plates are connected to each other using regularly spaced steel tie bars. Steel headed stud anchors (shear studs) may be added to reduce the steel plate slenderness for local buckling considerations in the composite phase. This paper presents the results of experimental investigations conducted to evaluate the behavior of five planar C-PSW/CF specimens subjected to constant axial compression and cyclic lateral loading. Parameters included are the axial load level, steel plate slenderness ratio, and tie reinforcement ratio. The cyclic lateral load-deflection responses of the composite wall specimens are discussed along with their lateral stiffness, strength, and deformation capacity. Experimental results indicate that the lateral load capacity of composite walls is governed by flexural yielding of the steel plates followed by plate inelastic local buckling and concrete crushing. All the wall specimens developed and exceeded the flexural capacity calculated using the plastic stress distribution method (while including the effects of axial compression). The post-peak strength degradation of wall specimens is governed by the initiation and propagation of fracture through the steel flange plates and web plates. A fiber-based model was developed and used to calculate the section moment-curvature response of the specimens. Comparing the experimental and numerical moment-curvature responses indicates that the section flexural stiffness and flexural capacity can be estimated using the fiber-based analysis method. [ABSTRACT FROM AUTHOR]

This paper presents the results of a comparative study conducted to assess the applicability and effectiveness of constitutive material model laws specific to composite materials contained in the LS-DYNA FE code. The LS-DYNA constitutive material model laws evaluated were MAT22, MAT54, MAT55, MAT58, and MAT59, where the selected material law is based on either progressive failure or continuum damage mechanics. The experimental data obtained from unidirectional (UD) carbon fiber–reinforced polymer (CFRP) laminates subjected to transverse impact at different energy levels were used to validate both two- and three-dimensional (2D and 3D) LS-DYNA FE models using the aforementioned constitutive material model laws. The outcome of the comparative study revealed that all the material models and their associated failure criteria displayed poor correlation to experimental test results at the low impact energy test condition (5 J) where damage is dominated by matrix cracking. Of all the material model laws, the continuum damage–based model law (CDM) MAT58 with 2D shell elements predicted damage zone shape and size satisfactorily compared with experimental data. [ABSTRACT FROM AUTHOR]

This paper deals with the investigations of supersonic flutter characteristics of laminated composite plates. The composite plates are modelled using a recently developed nonpolynomial shear deformation theory, which considers the required shear deformation effects in terms of an inverse hyperbolic function of thickness coordinate. The aerodynamic load is calculated by implementing linear piston theory including the influence of yaw angle. An isoparametric generalized finite-element formulation is developed for the aeroelastic analysis taking into account of required structural equations such as constitutive relations, kinematics relations, displacement field, and the principle of minimum potential energy together with the supersonic aerodynamics based on linear piston theory. The results are obtained by solving the developed system of governing equations for the flutter boundary, and the obtained results are validated against the existing analytical and numerical solutions. It is concluded that the developed formulation is accurate and efficient for the investigation of flutter behavior of laminated composite plates. Moreover, the strength and stiffness properties of composite plates are greatly influenced by fiber orientation, stacking sequence and material orthotropic ratio, flow characteristics are dependent on the flow angle, and geometric conditions mainly depend upon the boundary conditions. The influences of these stiffness characteristics (fiber orientation, stacking sequence, and material orthotropic ratio), geometric characteristics, and flow characteristics on the flutter boundary are examined and various benchmark conclusions are made. It is concluded that stiffness, flow, and geometric parameters must be considered as essential design parameters for enhanced flutter speed of supersonic vehicles fabricated of composite materials. [ABSTRACT FROM AUTHOR]

Composite shear walls are widely used to resist the lateral load in high rise-buildings nowadays; however, prior experimental tests have shown high damages and residual drifts at the plastic zone region. At present time, designing resilient buildings with low or no damage is one of main goal in performance-based seismic design of structures. In current research, a new design of an innovative low damage self-centering composite steel plate shear wall (SC-C-SPSW) equipped with unbonded posttension tendons (UPTs) is proposed to control the damage and the residual drift under seismic loading. To this end, five specimens including two composite steel plate shear walls (C-SPSW) and three SC-C-SPSWs were tested under gravity and reverse cyclic loading. The SC-C-SPSWs were detached using a pair of steel plates placed symmetrically under the wall boundary elements in order to form the bottom gaps with the foundation. The gap length, steel plate dimensions, and the initial prestressing on UPTs were considered as experimental parameters in this study. The construction details and the seismic performance including failure modes, damage progression, hysteretic response, and energy dissipation are presented in detail. The experimental results indicated that SC-C-SPSWs have excellent behavior in term of lateral strength and ductility and experienced low damage levels in comparison with C-SPSWs. The SC-C-SPSW walls experienced a large lateral displacement before initiation of the strength degradation, and the residual drifts were much smaller in comparison with C-SPSWs. [ABSTRACT FROM AUTHOR]

Recently, the construction of composite steel plate girder bridges that uses precast concrete deck planks has significantly increased due to their ease of construction, rapid installment, relatively low cost, and lightweight. Recent structural failures have been reported for this type of bridge system, which include the total collapse of one section of the Mexico City Metro Overpass in May 2021. The bridge collapse killed 23 people, and dozens were injured. This study provides an overview of the causes of the failure of the Mexico City Metro Overpass. It highlights important structural deficiencies that are currently overlooked in design codes and could cause future catastrophic collapses in existing bridges that utilize the same type of bridge. Therefore, a detailed finite-element model of a composite steel girder bridge that uses precast deck planks was established. The bridge dimensions, properties, and loading conditions that were used in this study were obtained from the Mexico City Metro Overpass parameters with some modifications. The performance of the bridge structure was investigated under different conditions with consideration of joint deterioration between the precast concrete planks. The results indicated that the deterioration in the transverse joints due to long-term exposure to moisture, environmental conditions, and vibrations affected the amount of force that was transferred between the concrete deck and the bare steel girder and, therefore, hindered the composite action. The gradual loss of composite action could cause a significant increase in the demands that are imposed on the bare steel section and result in high deflections in the bridge deck. Further deterioration in the transverse joints could be ongoing due to the repetitive vehicle loading on the compromised composite girder. Vibrations and exposure of the cracked joints to moisture and weather could worsen these conditions. Catastrophic failure of the bridge could occur if the deterioration issues were not observed and addressed in a timely manner. This study concludes by providing recommendations for design considerations to improve bridge performance, extend service life, and prevent such failures. The collapse of the Mexico City Metro Overpass killed 23 people and injured many others and inspired this study. The system used in this bridge is a composite plate girder with full-depth precast concrete (FDPC) deck, a recent system that allows rapid construction. The best way for engineers to prevent repeating these accidents is to understand the factors that lead bridges to fail. This study starts by exploring the causes of failure in bridges when focusing on the expected deterioration effects in the long run. Simulation techniques are employed to build a model for a bridge that is similar to the system that collapsed in the Mexico City Metro Overpass. It was used to understand the factors that led to the collapse under the moving train load. The results showed that adhering to current design codes and guidelines is not sufficient to prevent the failure of a bridge. This is a serious issue, because the codes are expected to provide the minimum requirements that guarantee the safety of structures during their service life. Therefore, this study concludes by providing recommendations for design considerations to improve bridge performance, extend service life, and prevent such failures. [ABSTRACT FROM AUTHOR]

Industry interest in mass timber hybrid construction is driving research into new connections, lateral load-resistance systems, seismic design, and fire safety design for low-carbon structures. However, only limited attention has hitherto been paid to the vibration serviceability of mass timber floor systems, which often controls their allowable maximum floor spans. This study investigated the vibration characteristics and serviceability performance of a promising modular prefabricated cross-laminated timber (CLT)–steel composite flooring solution under normal walking actions through both experimental testing and subjective evaluations. The study demonstrates that the flooring solution is a high-frequency floor system. The floor exhibits transient vibration response and can achieve acceptable vibration performance in residential and office settings. Its vibration performance can be reasonably assessed through the measured vibration dose value (VDV) over peak and root-mean-squared acceleration values when its modules are connected using self-tapping screws. The research outcomes will contribute to the vibration serviceability assessment of CLT-steel hybrid floor systems. [ABSTRACT FROM AUTHOR]

This paper is devoted to the mechanical buckling analysis of thick composite plates under straight single-walled carbon nanotubes reinforcement with uniform distribution and random orientations resting on an elastic foundation. To develop the fundamental equations, the finite strip method, along with third-order shear deformation theory, is employed, and the total potential energy is minimized, which leads to an eigenvalue problem. The elastic foundation is modeled by classical and two-parameter simulations. For deriving the effective modulus of composite plates reinforced with carbon nanotubes, a method is used in which each straight carbon nanotube is modeled as a fiber with transversely isotropic elastic properties. The results of the numerical experiments, including the critical buckling loads for thick rectangular composite plates reinforced by carbon nanotubes with various boundary conditions and different volume fractions of nanotubes, are provided, and the positive effect of using carbon nanotubes reinforcement in mechanical buckling of plates is illustrated. [ABSTRACT FROM AUTHOR]

This paper examines a technique for flexurally strengthening reinforced concrete (RC) beams using newly developed steel-wire continuous basalt fiber composite plates (SBFCPs) that comprise steel wires and continuous basalt-fiber-reinforced polymer (BFRP) composites. The test parameters consist of the volumetric ratio of steel wires in the SBFCPs, the composite plate type, and anchoring measures. The test results demonstrate that the SBFCP-strengthened specimens performed better than the unstrengthened specimen with respect to load capacity and member stiffness. Further, the flexural cracks are distributed more closely and uniformly than in the unstrengthened specimen. The SBFCP-strengthened beams have competitive advantages, particularly with respect to their ductility and performance-cost ratio, in comparison with specimens strengthened with carbon-fiber-reinforced polymer (CFRP) materials. A parametric study demonstrates that the volumetric ratio of steel wires in the SBFCPs affects the load capacity and stiffness of specimens strengthened with SBFCPs. The results also indicate that anchorage by steel plates and bolts improves the load capacity and ductility of strengthened specimens. [ABSTRACT FROM AUTHOR]

Graphene is recognized as one of the most alluring reinforcements for composite materials due to its exceptional mechanical capabilities. However, the existing models disregarding the compatible requirements of interlaminar stresses in the literature may meet severe challenges for the dynamic analysis of functionally graded graphene-reinforced composite (FG-GRC) laminated thick plates. If transverse shear deformations cannot be described accurately, the prediction of natural frequencies for FG-GRC laminated plates will be seriously and directly affected. Accordingly, an attractive plate theory in conjunction with the analytical approach and finite-element formulation is proposed for free vibration analysis of FG-GRC plates. An improved transverse shear stress field is acquired in terms of the three-dimensional (3D) elasticity equations and the Reissner mixed variational theorem (RMVT). The performance of the suggested model was evaluated using 3D elasticity solutions and the results obtained from other models. Numerical results showed that the suggested model can produce promising results for the thick laminated and sandwich plates. Additionally, a thorough investigation was conducted to study the effects of several graphene parameters, including volume fractions, distribution patterns, span-to-thickness ratios, aspect ratios, boundary conditions, and stacking sequences, on the dynamic responses of FG-GRC laminated plates. [ABSTRACT FROM AUTHOR]

Superior mechanical properties such as ultrahigh stiffness and strength along with amazing physical properties have led to the use of nano graphene platelets (GPLs) as a reinforcement in polymer composite structures such as sandwich plates. In this research, free vibration analysis of rectangular sandwich plates with functionally graded (FG) GPL-reinforced face sheets and a soft core is investigated. A high-order three-layer accurate sandwich plate theory is employed to model the soft-core sandwich structure. Third order shear deformable plate theory is applied for functionally graded graphene nano-composite face sheets while second and third order polynomials are used for displacements of the soft core. In this theory, the transverse flexibility of the core as well as the continuity conditions of transverse shear stresses are assumed. Hamilton's principle is applied to extract the motion equations and the corresponding analytical solutions are presented. The effects of materials properties and geometrical parameters on the natural frequencies of the sandwich plates are studied. A comparison of the present results in particular cases with those of published studies confirms the accuracy of the present analysis. Results show that the natural frequencies of the sandwich plates are enhanced by reinforcing the face sheets with GPLs. [ABSTRACT FROM AUTHOR]

The influence of the initial stretching of a simply supported plate containing two neighboring circular inclusions on the forced vibration analysis of the plate caused by the time-harmonic bending forces on the upper face plane is studied in the plane-strain state. The corresponding boundary-value problem is formulated using the three-dimensional linearized theory of elastic waves in initially stressed bodies and is solved numerically by the FEM. The materials of each component of the plate (i.e., the circular inclusions and the matrix) are selected to be isotropic. Numerical results on the dynamic stress concentrations around the inclusions and the influence of the initial stretching on those concentrations are presented and compared with the corresponding numerical values of plates with two neighboring circular holes and a plate without holes. [ABSTRACT FROM AUTHOR]

The aerodynamic performance of aircraft can be improved via shape morphing of wings actuated by piezoelectric material. An integrated design approach of piezo-actuated wings was developed while simultaneously considering aeroelastic tailoring of the base wing and actuator optimization. The main purpose was to investigate how the anisotropic composite substrate and the anisotropic piezocomposite actuators affect each other in both passive and active aspects. To this end, an aeroelastic model was established using the finite element method combined with unsteady aerodynamic loads. A structural/actuator integrated design scheme was developed by taking the incremental lift change and the wing thickness as objective functions. The general genetic algorithm (GA) and improved nondominated sorting genetic algorithm II (NSGA-II) were used to solve the single-objective and multiobjective problems, respectively. The results indicate that, with a fixed thickness, control ability on lift change can be improved with lower flutter speed constraint, increased number of layers, smaller incremental angle, and increased number of actuators. The Pareto frontier for the multiobjective case, presenting better control ability, will be available with relatively larger wing thickness. The distribution of the ±45° layers plays a key role in balancing the tradeoff between shape control ability and flutter stability. The designs of the substrate and actuators interact in both passive (mass and stiffness properties) and active (shape morphing and lift enhancement) aspects. The best solution must be obtained by considering the aeroelastic tailoring and actuator optimization in an integrated way. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have attracted many researchers during the last three decades due to their versatile nature and exceptional mechanical properties. In this study, a functionally graded CNT-reinforced laminated composite (FG-CNTRLC) plate subjected to different types of localized in-plane loadings was analyzed semianalytically to determine its dynamic instability and nonlinear vibration characteristics. The effective mechanical properties of the FG-CNTRLC plate were estimated using the extended rule-of-mixture technique. The FG-CNTRLC plate was modeled based on higher-order shear deformation theory (HSDT) in conjunction with von Kármán nonlinearity. The distribution of prebuckling stresses within the plate due to localized in-plane loading was estimated by solving the in-plane elasticity problem using Airy's stress approach. The nonlinear governing partial differential equations (PDEs) of the FG-CNTRLC plate were derived using Hamilton's principle. The Galerkin method was used to convert these nonlinear PDEs to the nonlinear ordinary differential equations (ODEs). The nonlinear ODEs were solved using the incremental harmonic balance (IHB) method to obtain the nonlinear vibration response of the FG-CNTRLC plate. After dropping the nonlinear terms, the linear ODEs were solved by the Bolotin method to trace the dynamic instability regions. The effect of different parameters such as volume fraction of CNTs, different types of localized in-plane loadings, types of CNTs distribution, the static and dynamic load factor on the dynamic instability regions, and the nonlinear vibration characteristics of the FG-CNTRLC plate, were examined. [ABSTRACT FROM AUTHOR]

A coupled analysis of impact damage and compression-after-impact (CAI) strength of laminated composite plates was conducted using efficient analytical and semianalytical models with the goal of demonstrating and validating the overall coupled impact/CAI strength model. Within this coupled framework, the impact model determines the transient response of the plate subjected to low-velocity impact, followed by an estimation of impact damage using a combination of strength and energy-based criteria. The predicted impact damage is idealized and used in conjunction with analytical buckling and postbuckling or kink-band analysis to predict the residual compressive strength. The coupled analysis approach was validated by applying it to impact and compression-after-impact experiments conducted on AS4/8552 laminates. It was shown that the coupled analysis model is able to predict accurately the compression-after-impact strength for a range of impact scenarios and material layups in a fraction of the time required by detailed finite-element models. [ABSTRACT FROM AUTHOR]

Collapse evaluation of composite plate shear walls (C-PSWs) under seismic loading requires a reliable analytical model that can accurately capture deterioration in the strength and stiffness of the system. In this study, research was carried out to develop a macromodeling approach for C-PSWs. Nonlinear time history analyses of six multistory (7-, 10-, and 13-story) C-PSWs (traditional and innovative) located in Western Canada were performed. It was observed that a significant portion of the story shear was resisted by the boundary members, while the RC panel resisted less than 10% of the total story shear. To estimate the seismic response parameters (i.e., ductility-related and overstrength-related force modification factors) for designing C-PSWs, incremental dynamic analysis (IDA) was performed for all archetypes following a standard procedure. It was observed that all archetypes provided significant safety margin against collapse (large collapse margin ratio). In addition, a sensitivity study was conducted and the effects of postyielding parameters (ductility capacity and postcapping stiffness) adopted for the deterioration model for infill plate and postcracking parameters (shear strain corresponding to maximum shear stress, yielding shear strain, and residual stress) adopted for the deterioration model for RC panel on seismic collapse capacities of traditional C-PSWs were investigated. It was observed that postyielding parameters for the steel infill plate can affect the seismic response of C-PSWs. On the other hand, variation of postcracking parameters for the concrete panel had a minor effect on seismic collapse capacity of the C-PSW system. [ABSTRACT FROM AUTHOR]

This research aims to experimentally investigate the flexural behavior of ultra-high-performance concrete (UHPC)–steel composite beams with joints under a negative bending moment in order for the results to be used in the analysis and design of UHPC flange plates in composite beams. Flexural tests were conducted to study three relevant parameters, slab mechanical properties, with/without UHPC joints at the closure strip, and UHPC joint configurations, which might affect the composite beam performance under the negative bending moment. The experimental results showed that steel–UHPC composite beams presented a better mechanical performance in terms of loading carrying capacity and controlling of crack width. Moreover, the existence of joints influences the cracking load and cracking position, leading to different crack distribution. Also, the result demonstrates the contribution of the joint configuration to the cracking development and suggests that sufficient enhancement in the flexural performance under negative moments could be achieved for UHPC–UHPC connections with changing the joint shape. However, the difference in the joint configurations did not significantly influence the yield load and ultimate load. This study may provide an understanding of the mechanical behavior of this emerging UHPC–steel composite beam with and without transverse joints under a negative bending moment. [ABSTRACT FROM AUTHOR]

In the present work, the hygro-thermomechanical response on the static characteristics of symmetric and antisymmetric laminated composite and sandwich plates is obtained using the recently developed inverse hyperbolic zigzag theory (IHZZT). The framework of IHZZT inculcates the shear strain shape function assuming a nonlinear distribution of transverse shear stresses. It satisfies the necessary conditions of interlaminar stress continuity at the layer interfaces as well as the condition of zero transverse shear stresses at the top and bottom surfaces of the plates. The theory has seven unknown field variables, which are layer-independent. The displacement-based finite-element approach is employed, using the eight-noded isoparametric serendipity element, accounting for the C0 continuity. A number of numerical examples are solved considering the effect of temperature, moisture concentration, span-thickness ratio, aspect ratio, boundary conditions, loading conditions, and variations in the number of layers. The results obtained in terms of deflections and stresses are validated with the exact results and results available in the existing literature. A few new results are produced here to establish a benchmark study for future research. [ABSTRACT FROM AUTHOR]

A point-based modeling scheme for the mesostructure of a two-step three-dimensional (3D) braided composite is proposed. The yarn path and the section profile are more realistic than the traditional mesh-based model, and the influence of the braiding process on the yarn path is reflected in the model. Owing to the point feature, the discretization of the matrix is very convenient after the reinforced structure is generated. The deformation and the failure of the braided composites can be directly simulated from the mesostructure model. Several examples, which include calculating the macroscopic elastic modulus and the high-velocity impact on the braided composite plate, show nice accuracies. The failure and fragmentation of the mesostructure can be well simulated with the point model and the mesh-free material point method. [ABSTRACT FROM AUTHOR]

Physically based, multilayered zigzag models have the merit of providing accurate stress predictions with few fixed unknowns, but unfortunately they involve derivatives of functional degrees of freedom (e.g., u,x, w,x, w,xxx, and so on). Here, a variable kinematics zigzag model with up to third-order derivatives always giving accurate predictions is considered in order to apply a technique that enables the conversion of derivatives of the unknowns. Such technique relies on energy updating concepts for finding closed form, modified expressions of displacements constituting the equivalent C0 model. From this model, a simple quadrilateral plate element with standard C0 interpolation functions is developed and tested. The first objective is finding a priori modified displacement fields that make the C0 zigzag model equivalent from the energy standpoint to its initial counterpart containing derivatives. Then a finite element is developed, whose structural model is equivalent from the energy standpoint to its counterpart with derivatives as variables. Comparisons with three-dimensional (3D) elasticity solutions of benchmark test cases and to an experiment show that the present element obtains accurate results. [ABSTRACT FROM AUTHOR]

A failure analysis of composite plates accounting for localized loadings is presented in this work. A unified formulation is adopted to derive classical, higher order, layerwise, and mixed theories. A closed form, Navier-type solution is assumed. Simply supported, cross-ply laminates are investigated. Plates are subjected to a stepwise loading, an off-centric localized one and a localized moment. First-ply failure loading and index are obtained via several failure criteria. The influence of the side-to-thickness ratio is accounted for investigating thin and very thick plates. Symmetric and asymmetric stacking sequences are investigated. The accuracy of the proposed theories is assessed. On the basis of the obtained results, it can be concluded that higher order models are required for a correct failure analysis in which the three-dimensional stress state attributable to the localized loadings is accurately described. [ABSTRACT FROM AUTHOR]