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This study examines the use of steel fibers in enhancing the ductility of an economical ultra‐high strength concrete (UHSC). The addition of fibrous material with very small geometry in this mixture is an effective solution to improve its ductility and prevent its brittle failure which is a common characteristic of UHSC. Different mechanical properties of reinforced and unreinforced concrete (e.g., slump flow, compressive, splitting tensile strength tests, and failure modes) were taken into account to find out the efficiency of micro steel fibers. The test results showed that concrete containing 25 mm length and 0.20 mm diameter steel fibers at a volume fraction of 0.5% not only presented a reasonable improvement in ductility performance but also ensured cost‐effectiveness. The cost evaluation conducted on several existing mix designs is also introduced in this study to investigate the influence of various steel fiber contents on the total cost of concrete so that figure out the lowest budget solution. The evaluation shows the high price of fiber reinforcement in which an addition of steel fibers by 5% volume could increase 7% of the total concrete cost. [ABSTRACT FROM AUTHOR]

Contrary to conventional buildings, the structural robustness of modular high-rise buildings has not been studied due to the lack of the numerical and experimental studies and design guides. To gain a better understanding of their structural robustness against progressive collapse, this paper investigates the robustness of modular high-rise buildings using the alternative load path method with nonlinear time-history analysis. A numerical model of a typical modular tall building subjected to a corner module removal scenario was developed to explore its typical response, resistance mechanism and progressive collapse. A comprehensive parametric study was then performed to examine the effects of a wide range of parameters (e.g. column cross-section, inter-module connection and bracing system) and configurations on the progressive collapse and structural robustness of modular buildings. The result showed that bracing systems can enhance the structural robustness effectively by sharing redistributed loads and restraining structural members. The removal of corner members is more critical because there are limited adjacent members for sharing the redistributed loads. Inter-module connections should provide adequate strength to develop more alternative load paths when extreme events occur. Finally, design recommendations for improving the robustness of modular buildings were also proposed based on the findings from the parametric study. [ABSTRACT FROM AUTHOR]

This paper proposes a new general framework of higher-order shear deformation theory (HSDT) and solves the structural responses of the functionally graded (FG) plates using novel exponential shape functions for the Ritz method. Based on the fundamental equations of the elasticity theory, the displacement field is expanded in a unified form which can recover to many different shear deformation plate theories such as zeroth-order shear deformation plate theory, third-order shear deformation plate theory, various HSDTs and refined four-unknown HSDTs. The characteristic equations of motion are derived from Lagrange's equations. Ritz-type solutions are developed for bending, free vibration and thermal buckling analysis of the FG plates with various boundary conditions. Three types of temperature variation through the thickness are considered. Numerical results are compared with those from previous studies to verify the accuracy and validity of the present theory. In addition, a parametric study is also performed to investigate the effects of the material parameters, side-to-thickness ratio, temperature rise and boundary conditions on the structural responses of the FG plates. [ABSTRACT FROM AUTHOR]

Loss functions, which govern a deep learning-based optimization process, have been widely investigated to handle the class imbalanced data issue in crack segmentation. However, their performance varies according to models and datasets, making it challenging to choose the most appropriate ones. To address this issue, the paper conducts a large-scale performance comparison of twelve commonly used loss functions on four benchmark datasets. Various aspects are considered using a statistical test-based ranking scheme, which integrates accuracy, sensitivity to threshold change, and varying degrees of imbalance severity for a comprehensive comparison. The results show that most loss functions achieve relatively similar accuracy on mildly imbalanced datasets, while weighted binary cross-entropy loss, Focal loss, Dice-based loss, and compound loss functions significantly outperform others as imbalance severity increases. In general, Focal Tversky loss function exhibits excellent performance in handling the imbalanced data issue. • The effects of imbalanced data and loss functions are comprehensively investigated. • Four benchmark datasets and 12 loss functions are considered. • A loss ranking scheme is proposed to examine the performance of loss functions. • Binary cross-entropy, Dice and Jaccard losses are proposed for mildly imbalanced data. • Focal Tversky is the most robust loss function for severely imbalanced data. [ABSTRACT FROM AUTHOR]

Structural steel frames exhibit significantly geometric and material nonlinearities which can be captured using the second-order inelastic analysis, also known as advanced analysis. Current specifications of most modern steel design codes, e.g. American code AISC360, European code EC3, Chinese code GB50017 and Australian code AS4100 permit the use of advanced analysis methods for the direct design of steel structures to avoid tedious member capacity checks. In the past three decades, a huge number of advanced analysis and modeling methods have been developed to predict the behavior of steel and composite frames. This paper presents a comprehensive review of their developments, which focus on beam-column elements with close attention to the way to capture geometric and material nonlinearity effects. A brief outline of analysis methods and analysis tools for frames was presented in the initial part of the paper. This was followed by a discussion on the development of displacement-based, force-based and mixed beam elements with distributed plasticity and concentrated plasticity models. The modeling of frames subjected to fire and explosion was also discussed. Finally, a review of the beam-column models for composite structures including concrete-filled steel tubular (CFST) columns, composite beams and composite frames was presented. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubular (CFST) columns are adopted in many structural applications, especially for tall buildings, bridges and large infrastructure due to their substantial structural and economic benefits. However, the design guidelines for CFST columns with high strength materials and slender sections are still limited. In acknowledging these limitations, a large number of tests on high strength CFST columns have been conducted. In this paper, the most recent experimental data on CFST columns with high strength materials and slender sections are collected and merged with existing databases to establish a comprehensive database with over 3100 tests. The test results are then compared with those predicted from existing design codes, including Eurocode 4, Australian/New Zealand code AS/NZS 2327 and American code AISC 360-16 to calibrate their accuracy in strength prediction of CFST columns. In general, all codes give conservative predictions for CFST columns. Eurocode 4 and AS/NZS 2327 give the best predictions, whilst AISC 360-16 gives conservative predictions. The effects of material strengths and section slenderness on the code predictions are also investigated to evaluate the applicability of the codes beyond their material strength and section slenderness limits. • A comprehensive database of 3103 tests on CFST columns was collected. • Test results were compared with the predictions from three modern design codes. • The effects of material strengths and section slenderness on the code predictions were examined. • The applicability of the design codes beyond their material strength and section slenderness limits was evaluated. [ABSTRACT FROM AUTHOR]

This study aims to investigate the postbuckling response of functionally graded (FG) nanoplates by using the nonlocal elasticity theory of Eringen to capture the size effect. In addition, Reddy’s third-order shear deformation theory is adopted to describe the kinematic relations, while von Kámán’s assumptions are used to account for the geometrical nonlinearity. In order to calculate the effective material properties, the Mori-Tanaka scheme is adopted. Governing equations are derived based on the principle of virtual work. Isogeometric analysis (IGA) is employed as a discretization tool, which is able to satisfy the C 1 -continuity demand efficiently. The Newton-Raphson iterative technique with imperfections is employed to trace the postbuckling paths. Various numerical studies are carried out to examine the influences of gradient index, nonlocal effect, ratio of compressive loads, boundary condition, thickness ratio and aspect ratio on the postbuckling behaviour of FG nanoplates. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the elastic properties of fibre-reinforced polymer (FRP) structures printed by three-dimensional (3D) printing technology. Both experimental and theoretical approaches are adopted to investigate the performance of FRP 3D-printed structures and predict their elastic properties. Three types of FRP materials were considered in this study including Carbon, Kevlar and Glass printed in selected arrangements of fibre filaments and Nylon matrix. An analytical model was developed based on the Volume Average Stiffness (VAS) method to predict elastic properties of 3D printed coupons, while the numerical model was developed using Abaqus to predict the failure modes and damage in the FRP 3D-printed coupons tested in this study. A parametric study was carried out to develop the mathematical expressions for calculating elastic properties of FRP 3D-printed structures. The parametric study indicates that the level of fibre reinforcements and their orientation arrangement have significant effects on the structural performance of FRP 3D-printed composite sections. [ABSTRACT FROM AUTHOR]

The objective of this study is to develop an effective numerical model within the framework of an isogeometric analysis (IGA) to investigate the geometrically nonlinear responses of functionally graded (FG) microplates subjected to static and dynamic loadings. The size effect is captured based on the modified strain gradient theory with three length scale parameters. The third-order shear deformation plate theory is adopted to represent the kinematics of plates, while the geometric nonlinearity is accounted based on the von Kármán assumption. Moreover, the variations of material phrases through the plate thickness follow the rule of mixture. By using Hamilton’s principle, the governing equation of motion is derived and then discretized based on the IGA technique, which tailors the non-uniform rational B-splines (NURBS) basis functions as interpolation functions to fulfil the C 2 -continuity requirement. The nonlinear equations are solved by the Newmark’s time integration scheme with Newton-Raphson iterative procedure. Various examples are also presented to study the influences of size effect, material variations, boundary conditions and shear deformation on the nonlinear behaviour of FG microplates. [ABSTRACT FROM AUTHOR]

The present study uses the isogeometric analysis (IGA) to investigate the post-buckling behavior of functionally graded (FG) microplates subjected to mechanical and thermal loads. The modified a strain gradient theory with three length scale parameters is used to capture the size effect. The Reddy third-order shear deformation plate theory with the von Kámán nonlinearity (i.e., small strains and moderate rotations) is employed to describe the kinematics of the microplates. Material variations in the thickness direction of the plate are described using a rule of mixtures. In addition, material properties are assumed to be either temperature-dependent or temperature-independent. The governing equations are derived using the principle of virtual work, which are then discretized using the IGA approach, whereby a C 2 -continuity requirement is fulfilled naturally and efficiently. To trace the post-buckling paths, Newton’s iterative technique is utilized. Various parametric studies are conducted to examine the influences of material variations, size effects, thickness ratios, and boundary conditions on the post-buckling behavior of microplates. [ABSTRACT FROM AUTHOR]

This paper presents free vibration of composite beams under axial load using a four-unknown shear and normal deformation theory. The constitutive equation is reduced from the 3D stress-strain relations of orthotropic lamina. The governing differential equations of motion are derived using the Hamilton’s principle. A two-node C 1 beam element is developed by using a mixed interpolation with linear and Hermite-cubic polynomials for unknown variables. Numerical results are computed and compared with those available in the literature and commercial finite element software (ANSYS and ABAQUS). The comparison study illustrates the effects of normal strain, lay-ups and Poisson’s ratio on the natural frequencies and load-frequency curves of composite beams. [ABSTRACT FROM AUTHOR]

This paper presents a robust numerical model, which takes into account both size-dependent and shear deformation effects, for the bending, buckling and free vibration analyses of functionally graded microplates. The size-dependent effect is captured by using the modified strain gradient elasticity theory with three length scale parameters, whilst the shear deformation effect is accounted by using the third-order shear deformation theory. The rule of mixture is employed to describe the distributions of material phrases through the plate thickness. By using Hamilton’s principle, the governing equations are derived and then discretized by employing an Isogeometric Analysis (IGA) approach, where the Non-Uniform Rational B-Splines (NURBS) basis functions are adopted to meet the C 2 -continuity requirement. Physical mesh convergence and verification studies are performed to prove the accuracy and reliability of the present model. In addition, parametric studies are also carried out to investigate the size effect in conjunction with the influences of gradient index, shear deformation effect and boundary conditions on the responses of microplates. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive review on the development of higher-order continuum models for capturing size effects in small-scale structures. The review mainly focus on the size-dependent beam, plate and shell models developed based on the nonlocal elasticity theory, modified couple stress theory and strain gradient theory due to their common use in predicting the global behaviour of small-scale structures. In each higher-order continuum theory, various size-dependent models based on the classical theory, first-order shear deformation theory and higher-order shear deformation theory were reviewed and discussed. In addition, the development of finite element solutions for size-dependent analysis of beams and plates was also highlighted. Finally a summary and recommendations for future research are presented. It is hoped that this review paper will provide current knowledge on the development of higher-order continuum models and inspire further applications of these models in predicting the behaviour of micro- and nano-structures. [ABSTRACT FROM AUTHOR]

This paper explores the use of an explicit solver available in ABAQUS/Explicit to simulate the behaviour of blind bolted endplate connections between composite beams and concrete-filled steel tubular (CFST) columns. Main aspects of the explicit analysis such as solution technique, blind bolt modelling, choice of element type and contact modelling are discussed and illustrated through the simulation of a large-scale test on the considered joint. The mass scaling option and smooth step amplitude are very effective tools to speed up the explicit simulation. Shell elements can be used in modelling the I-beam due to their computational efficiency and accuracy in capturing local buckling effects. With a proper control of the loading rate, the explicit analysis can provide accurate and efficient predictions of the quasi-static behaviour of the bolted endplate composite connections. [ABSTRACT FROM AUTHOR]

This paper presents flexural analysis of composite and sandwich beams using a quasi-3D theory, which considers simultaneously three effects such as normal and shear deformation as well as anisotropy coupling. The axial and transverse displacements are assumed to be cubic and parabolic variation through the beam depth. In order to solve problem, two-node C 1 beam elements with six degrees of freedom per node are developed. Numerical examples are carried out and the results are compared with those available in literature to validate the accuracy of the present theory. The effects of fibre angle, lay-up and span-to-height ratio on displacements and stresses are studied. Some new results, which can be useful for future references, are also given. [ABSTRACT FROM AUTHOR]

This paper proposes a new simple shear deformation theory for isotropic plates. The present theory involves one unknown and one governing equation as in the classical plate theory, but it is capable of accurately capturing shear deformation effects. The displacement field of the present theory was based on a two variable refined plate theory in which the transverse displacement is partitioned into the bending and shear parts. Based on the equilibrium equations of three-dimensional (3D) elasticity theory, the relationship between the bending and shear parts was established. Therefore, the number of unknowns of the present theory was reduced from two to one. Closed-form solutions were presented for both Navier- and Levy-type plates. Numerical results indicate that the obtained predictions are comparable with those generated by ABAQUS and available results predicted by 3D elasticity theory, first-order and third-order shear deformation theories. [ABSTRACT FROM AUTHOR]

By leveraging the merits of structural steel and concrete materials, concrete-filled steel tubular (CFST) structures have been increasingly used in the composite construction of bridges and high-rise buildings. However, their design equations are more complicated than those of steel and reinforced concrete (RC) structures, especially for circular columns under eccentric loading. Therefore, the use of emerging data-driven approaches will help structural engineers ease the design process. This paper explores the use of data-driven design methods as alternatives to conventional mechanics-based design models. Five boosting algorithms, including adaptive boosting (AdaBoost), gradient boosting machine (GBR), extreme gradient boosting (XGBoost), light gradient boosting machine (LightGBM), and categorical gradient boosting (CatBoost), are employed to develop predictive models for four different types of CFST columns (i.e., circular columns, rectangular columns, circular beam–columns, and rectangular beam–columns). These predictive models are trained using the most up-to-date and comprehensive database collected from over 3,200 test specimens. Reliability analysis is conducted to calibrate the resistance reduction factors for three different design frameworks (i.e., the US, Eurocode, and Australian frameworks) to ensure that the newly developed predictive models meet the target reliability indices required by different design frameworks. A web-based design tool is also developed to promote the practical use of data-driven methods for the design of CFST columns. • ML models for predicting the resistance of CFST columns and beam–columns were created. • The models were based on five boosting algorithms and a 3,208-test database. • The models outperformed the design provisions of AISC 360, EC 4, and AS/NZS 2327. • Resistance factors were determined from reliability analyses for three design frameworks. • A web application based on the ML models was created and deployed to the cloud. [ABSTRACT FROM AUTHOR]

Abstract This study presents a free vibration analysis of spherical shell segments using simple first-order shear deformation shell theory (S-FSDT) for the first time. The shell structure is made of functionally graded porous graphene platelet reinforced composite (FGP-GPLRC) – one kind of porous material strengthened by graphene platelets (GPLs). Effective material properties of the FGP-GPLRC are determined by the modified Halpin-Tsai micromechanical model and the mixture rule. Four types of porosity distributions and GPL dispersions are considered fully in this study. The governing equations of the shell are derived based on the S-FSDT and classical shell theory, then solved by the well-known Rayleigh-Ritz method and the artificial spring technique. The results show that the S-FSDT can capture well the behaviors of the spherical shell segments. Besides, the best profile of novel FGP-GPLRC is not fixed; the physical parameters, geometric parameters, and material characteristics of the shells need to be investigated fully. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study on the structural performance of blind bolted endplate composite connections to concrete filled steel tubular (CFST) columns under static loading. Four full-scale sub-assemblages of cruciform composite joints representing the internal region of a composite frame were tested. The parameters varied were the shape of column sections and the type of endplates. The performance of the joints in terms of rotational stiffness, moment resistance and rotation capacity was evaluated to explore the effects of the shape of column sections and endplate types. An analytical model was also developed to predict the moment-rotation behaviour of composite joints. The experimental results indicated that both moment resistance and initial stiffness of the tested connections are considerably enhanced if the flush endplate and square column were replaced by the extended endplate and circular column, respectively. [ABSTRACT FROM AUTHOR]

This paper deals with the prediction of the initial rotational stiffness and moment resistance of bolted endplate joints between I-beams and hollow or concrete filled steel tubular (CFST) columns. An extensive numerical analysis was carried out on a wide range of configurations of hollow and CFST columns subjected to transverse forces. Based on numerical simulation results, the stiffness models for the ‘column side walls in tension and compression’ and ‘column face in bending’ which is the most deformable component within a joint were proposed. The proposed models were then incorporated into the component method adopted in EC3 and EC4 to predict the initial rotational stiffness and moment resistance of bolted endplate joints. The obtained predictions were compared with the experimental results of 44 available tests to verify the validity of the proposed models. The comparison of results indicated that the proposed models are more reliable than the existing ones and thus could be incorporated into EC3 and EC4 guidelines for the design of bolted endplate joints with hollow or CFST sections. [ABSTRACT FROM AUTHOR]

This paper presents an effective reliability analysis procedure and proposes the system resistance factors for the system design of steel-concrete composite frames that comprise of concrete-filled steel tubular (CFST) columns and composite beams. Advanced analysis is employed to predict the ultimate resistance of frames using fibre beam-column elements in OpenSees. The obtained predictions of the load-carrying capacity of frames compare well with experimental results with the mean value of the test-to-prediction ratio around 1.027 and the coefficient of variation (CoV) of 8.4%. Both Monte Carlo (MC) and subset simulations are used in the reliability analysis. The uncertainties of model error, geometric and material properties, and external loads are included to predict the system reliability index. Five different frame configurations are considered. The results of the reliability analysis show that the system resistance factors for both US and AS codes are quite similar. In the case of gravity load, the system resistance factor is from 0.78 to 0.90, whilst this value for the case of combined wind and gravity load is from 0.8 to 0.95. The resistance factors suggested herein become valuable reference information for the system design of composite frames. • Monte Carlo and subset simulations are integrated with OpenSees for reliability analysis of steel-concrete composite frames. • All uncertainties in model error, geometry, material, and loading are considered. • The predicted load-carrying capacities are compared well with experimental results of 38 tests on composite frames. • A comprehensive parametric study is conducted to propose system resistance factors of steel-concrete composite frames. [ABSTRACT FROM AUTHOR]

This paper presents an accurate and efficient numerical procedure for evaluating the system reliability of steel frames with semi-rigid connections. The ultimate strength and behaviour of the frame were predicted using a refined plastic hinge model due to its computational efficiency, whilst the nonlinear behaviour of semi-rigid connections was captured using a three-parameter power model. The statistical properties for the three parameter power model were obtained based on available experimental results. The sensitivity of reliability to the model error was also studied. Monte Carlo simulation was used to estimate the probability of failure and the reliability index of a system. Two example frames subjected to combined gravity and wind loads were examined and their system reliability indices for both strength and serviceability limit states were evaluated based on the randomness in loadings, material and geometric properties and semi-rigid connections. The results indicate that the frame reliability is strongly affected by semi-rigid connections. [ABSTRACT FROM AUTHOR]

In this paper, a comprehensive review of various theories for the modeling and analysis of functionally graded plates and shells is presented. The review is devoted to theoretical models which were developed to predict the global responses of functionally graded plates and shells under mechanical and thermal loadings. This review mainly focuses on the equivalent single layer theories including the classical plate theory, first-order shear deformation theory, higher-order shear deformation theories, simplified theories and mixed theories since they were widely used in the modeling of functionally graded plates and shells. In addition, a thorough review of the literature related to the development of three-dimensional elasticity solutions and a unified formulation is also presented. [ABSTRACT FROM AUTHOR]

This paper proposes an accurately and efficiently numerical procedure for distributed plasticity analysis of semi-rigid steel frames. Both geometric and material nonlinearities are included in the proposed analysis. Geometric nonlinearities due to the large and small P-Delta effects are respectively captured using the corotational formulation and curvature-based displacement procedure. Material nonlinearities due to residual stresses and inelastic behaviour of materials are taken into account using a fibre model. The nonlinear semi-rigid behaviour of beam-to-column connections is simulated using a zero-length connection element. The validity of the present analysis is verified by comparing the obtained predictions with existing solutions. A case study of a very large-scale steel frame indicates that the present analysis is very reliable and computationally efficient and thus would be a valuable tool for daily use in office engineering design. [ABSTRACT FROM AUTHOR]

This paper aims to develop a detailed three-dimensional finite element model to study the behaviour of blind bolted endplate composite joints that connect composite beams to a concrete filled steel tubular column. All connection components such as steel beam, profiled sheeting, shear stud, endplate, blind bolt, concrete infill, concrete slab, hollow steel column and reinforcing bars were separately modelled using shell, solid and truss elements. The obtained predictions of the moment–rotation curve and failure mode were compared with experimental results and a very good agreement was established. In addition, an analytical model for predicting the moment–rotation response of composite joints up to failure was also presented based on the component method. Finally, extensive parametric studies were carried out to investigate the influences of shear studs and reinforcement ratio, blind bolt types and diameters, column sections and thickness ratios on the joint performance. [ABSTRACT FROM AUTHOR]

A novel stress–strain model accounting for elastic and inelastic local buckling of thin-walled steel plates was proposed in this paper based on an energy method. The proposed model was then implemented in a fibre force-based beam-column element for the advanced analysis of thin-walled and concrete-filled steel stub columns under axial compression. Both geometric and material nonlinearities are included in the fibre model. The obtained results were compared with independent experimental results and those predicted by ABAQUS using shell and solid elements. As shown in the numerical examples, the proposed stress–strain models can reasonably predict the ultimate strength and local and post-local buckling behaviour of thin-walled and concrete-filled steel stub columns under axial compression. [ABSTRACT FROM AUTHOR]

Static bending, buckling and free vibration behaviors of size-dependent functionally graded (FG) sandwich microbeams are examined in this paper based on the modified couple stress theory and Timoshenko beam theory. To avoid the use of a shear correction factor, equilibrium equations were used to compute the transverse shear force and shear stress. Two types of sandwich beams were considered: (1) homogeneous core and FG skins and (2) FG core and homogeneous skins. Numerical results were presented to illustrate the small scale effects on the behaviors of FG sandwich beams. The results reveals that the inclusion of the size effects results in an increase in the beam stiffness, and consequently, leads to a reduction of deflections and stresses and an increase in natural frequencies and critical buckling loads. Such effects are more pronounced when the beam depth was small, but they become negligible with the increase of the beam depth. [ABSTRACT FROM AUTHOR]

This paper presents static behaviour of functionally graded (FG) sandwich beams by using a quasi-3D theory, which includes both shear deformation and thickness stretching effects. Various symmetric and non-symmetric sandwich beams with FG material in the core or skins under the uniformly distributed load are considered. Finite element model (FEM) and Navier solutions are developed to determine the displacement and stresses of FG sandwich beams for various power-law index, skin-core-skin thickness ratios and boundary conditions. Numerical results are compared with those predicted by other theories to show the effects of shear deformation and thickness stretching on displacement and stresses. [ABSTRACT FROM AUTHOR]

This paper presents a finite element model for free vibration and buckling analyses of functionally graded (FG) sandwich beams by using a quasi-3D theory in which both shear deformation and thickness stretching effects are included. Sandwich beams with FG skins-homogeneous core and homogeneous skins-FG core are considered. By using the Hamilton’s principle, governing equations of motion for coupled axial–shear–flexural–stretching response are derived. The resulting coupling is referred to as fourfold coupled vibration and buckling. Numerical examples are carried out to investigate the thickness stretching effect on natural frequencies and critical buckling loads as well as mode shapes of sandwich beams for various power-law indexes, skin–core–skin thickness ratios and boundary conditions. [ABSTRACT FROM AUTHOR]

A new four-node quadrilateral plate that accounts for shear deformation effect and all couplings from the material anisotropy is developed for laminated composite plates. Lagrangian linear interpolation functions are used to describe the primary variables corresponding to the in-plane displacements, while Hermitian cubic interpolation functions are considered for the transverse displacement. Since the present element is derived based on a refined plate theory that has strong similarity with the classical plate theory, it is capable of modeling both thin and very thick plates without shear locking. The accuracy of the present formulation is verified by comparing the results obtained with those available in the open literature. Numerical results are presented to investigate the effects of thickness ratio, lamination angle and lay-up on the shear deformation and response of laminates. [ABSTRACT FROM PUBLISHER]

In this paper, an accurate finite element model which accounts for the effects of initial local imperfections and residual stresses is developed for the nonlinear analysis of high strength steel box columns infilled with high strength concrete. The inelastic behaviour of the steel box and the concrete core is modelled using an elastic-plastic model with linear hardening and a concrete damaged plasticity model, respectively. In addition, an extensive numerical analysis based on a wide range of width-to-thickness ratios, yield stresses of steel tubes and compressive strengths of concrete core was also carried out to propose a new empirical equation for estimating the confining pressure on the concrete. The predictions of ultimate strengths, behaviour and failure modes are compared with experimental results to verify the accuracy of the present model. Parameter studies indicate that both the Eurocode EC4 and Australian Standard AS 5100 approaches can be safely extended to predict the ultimate strength of concrete-filled steel columns with high strength materials. [ABSTRACT FROM AUTHOR]

High strength concrete-filled steel tube (CFST) columns have been adopted in many constructions requiring great load-carrying capacities, large floorplans, cost-effective and time-saving solutions such as modern skyscrapers or high-rise buildings, but their performance is still insufficiently understood due to the lack of experimental investigations and design specifications. The test program in this study consists of eight stub square CFST columns fabricated from high strength materials and slender sections which are beyond the permitted limits specified by many current design provisions. The failure patterns, load and moment resistances, load-mid-height deflection and load - axial strain responses were used to evaluate the overall performance of the test specimens. Furthermore, a numerical model for CFST columns, taking into account the actual factors such as the confinement on concrete cores, initial imperfections and residual stresses on steel tubular members, was developed and demonstrated a good agreement with the experimental results. A parametric study then adopted this verified model to explore the confinement effect on concrete cores and the influence of various material strengths, eccentricity ratios, section slendernesses and member slendernesses on the performance of composite columns. Finally, the load-moment interaction curves of specimens under different loading conditions obtained from experiment and numerical analysis were compared to the predictions of AISC 360-16, Eurocode 4 and AS/NZS 2327 for validating these specifications. In short, this study is expected to advance the understanding in the area of eccentrically loaded CFST columns with high strength materials and slender sections. • A study of short CFST columns with slender sections and high strength materials under eccentric loading was presented. • An accurate numerical model was also developed for a parametric study. • The accuracy of current design equations of AISC 360-16, EC 4, AS/NZS 2327 was assessed. • The benefits of using high strength materials were also highlighted. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new first-order shear deformation theory is presented for functionally graded sandwich plates composed of functionally graded face sheets and an isotropic homogeneous core. By making a further assumption to the existing first-order shear deformation theory, the number of unknowns and governing equations of the present theory is reduced, thereby making it simple to use. In addition, the use of shear correction factor is no longer necessary in the present theory since the transverse shear stresses are directly computed from the transverse shear forces by using equilibrium equations. Equations of motion are derived from Hamilton's principle. Analytical solutions for bending, buckling and free vibration analysis of rectangular plates under various boundary conditions are presented. Verification studies show that the present first-order shear deformation theory is not only more accurate than the conventional one, but also comparable with higher-order shear deformation theories which have a greater number of unknowns. [Copyright &y& Elsevier]

Abstract: Finite element model for vibration and buckling of functionally graded sandwich beams based on a refined shear deformation theory is presented. The core of sandwich beam is fully metal or ceramic and skins are composed of a functionally graded material across the depth. Governing equations of motion and boundary conditions are derived from the Hamilton’s principle. Effects of power-law index, span-to-height ratio, core thickness and boundary conditions on the natural frequencies, critical buckling loads and load–frequency curves of sandwich beams are discussed. Numerical results show that the above-mentioned effects play very important role on the vibration and buckling analysis of functionally graded sandwich beams. [Copyright &y& Elsevier]

A quasi-3D hyperbolic shear deformation theory for functionally graded plates is developed. The theory accounts for both shear deformation and thickness-stretching effects by a hyperbolic variation of all displacements across the thickness, and satisfies the stress-free boundary conditions on the top and bottom surfaces of the plate without requiring any shear correction factor. The benefit of the present theory is that it contains a smaller number of unknowns and governing equations than the existing quasi-3D theories, but its solutions compare well with 3D and quasi-3D solutions. Equations of motion are derived from the Hamilton principle. Analytical solutions for bending and free vibration problems are obtained for simply supported plates. Numerical examples are presented to verify the accuracy of the present theory. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the refined pate theory is improved to account for the effect of thickness stretching in functionally graded plates. The refined plate theory has fewer number of unknowns and equations of motion than the first-order shear deformation theory, but accounts for the transverse shear deformation effects without requiring shear correction factors. The displacement field of the refined plate theory is modified by assuming a parabolic variation of the transverse displacement through the thickness, and consequently, the thickness stretching effect is taken into consideration. Closed-form solutions of simply supported rectangular plates are presented, and the obtained results are compared with 3D solutions and those predicted by higher-order shear deformation theories. Verification studies show that the proposed theory is not only more accurate than the refined plate theory, but also comparable with the higher-order shear deformation theories which contain more number of unknowns. [Copyright &y& Elsevier]

Abstract: This paper presents a zeroth-order shear deformation theory for bending and vibration analyses of functionally graded plates resting on elastic foundation. In the present theory, the shear deformation effect is incorporated in the in-plane displacements through the use of shear forces instead of rotational displacements as in existing shear deformation theories. Equations of motion and boundary conditions are derived from Hamilton's principle. Analytical solutions of simply supported plates are presented, and the obtained results are compared with available solutions to verify the accuracy of the present theory. Numerical results show that the present theory gives a very good prediction of bending and vibration responses of functionally graded plates resting on elastic foundation. [Copyright &y& Elsevier]

Abstract: In this paper, a simple first-order shear deformation theory is presented for laminated composite plates. Unlike the existing first-order shear deformation theory, the present one contains only four unknowns and has strong similarities with the classical plate theory in many aspects such as equations of motion, boundary conditions, and stress resultant expressions. Equations of motion and boundary conditions are derived from Hamilton’s principle. Analytical solutions of simply supported antisymmetric cross-ply and angle-ply laminates are obtained and the results are compared with the exact three-dimensional (3D) solutions and those predicted by existing theories. Comparison studies show that this new first-order shear deformation theory can achieve the same accuracy of the existing first-order shear deformation theory which has more number of unknowns. [Copyright &y& Elsevier]

In this paper, various efficient higher-order shear deformation theories are presented for bending and free vibration analyses of functionally graded plates. The displacement fields of the present theories are chosen based on cubic, sinusoidal, hyperbolic, and exponential variations in the in-plane displacements through the thickness of the plate. By dividing the transverse displacement into the bending and shear parts and making further assumptions, the number of unknowns and equations of motion of the present theories is reduced and hence makes them simple to use. Equations of motion are derived from Hamilton's principle. Analytical solutions for deflections, stresses, and frequencies are obtained for simply supported rectangular plates. The accuracy of the present theories is verified by comparing the obtained results with the exact three-dimensional (3D) and quasi-3D solutions and those predicted by higher-order shear deformation theories. Numerical results show that all present theories can archive accuracy comparable to the existing higher-order shear deformation theories that contain more number of unknowns. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an efficient analysis method considering both geometric and material nonlinearities is proposed for predicting the ultimate strength and behavior of multi-span suspension bridges. The geometric nonlinearities of the cable members due to sag effects are captured using the catenary element, while the geometric nonlinearities of the beam-column members due to second-order effects are captured using the stability functions. The material nonlinearities of the cable and beam-column members are considered using elastic–plastic hinge and refined plastic hinge models, respectively. A simple initial shape analysis method is presented to determine the deformed shape and initial cable tension of the bridge under dead loads. Numerical examples are presented to verify the accuracy and efficiency of the proposed method. In addition, a case study on a four-span suspension bridge is carried out to show the capability of the proposed method in estimating the strength and behavior of very large scale structures. [Copyright &y& Elsevier]

Abstract: In this paper, finite element formulation of various four unknown shear deformation theories is presented for the bending and vibration analyses of functionally graded plates. The present theories have strong similarity with the classical plate theory and accounts for shear deformation effects without using any shear correction factors. A four-node quadrilateral finite element is developed using Lagrangian and Hermitian interpolation functions to describe the primary variables corresponding to the in-plane displacements and transverse displacement, respectively. Material properties are assumed to be graded in the thickness direction according to a power-law distribution in terms of volume fractions of the constituents. Convergence test and comparison studies are performed for thin and very thick plates to demonstrate the accuracy of the present formulation. [Copyright &y& Elsevier]

Abstract: Closed-form solution for buckling analysis of thick functionally graded plate resting on elastic foundation is presented using the third-order shear deformation theory. It is assumed that the plate rests on Pasternak foundation and its material properties vary through the plate thickness as a power function. By decoupling the governing equations, the neutral surface position for such plate is determined, and the third-order shear deformation theory based on exact neutral surface position is employed to derive the governing equations. Comparing with the middle surface based formulations, the neutral surface based formulations do not exhibit the stretching–bending coupling; hence, the values of buckling load can be obtained by eigenvalue analysis. Closed-form solutions are obtained for rectangular with different boundary conditions. Numerical results are presented and discussed for a wide range of plate and foundation parameters. [Copyright &y& Elsevier]

Abstract: Analytical solutions for bending, buckling, and vibration analyses of thick rectangular plates with various boundary conditions are presented using two variable refined plate theory. The theory accounts for parabolic variation of transverse shear stress through the thickness of the plate without using shear correction factor. In addition, it contains only two unknowns and has strong similarities with the classical plate theory in many aspects such as equations of motion, boundary conditions, and stress resultant expressions. Equations of motion are derived from Hamilton’s principle. Closed-form solutions of deflection, buckling load, and natural frequency are obtained for rectangular plates with two opposite edges simply supported and the other two edges having arbitrary boundary conditions. Comparison studies are presented to verify the validity of present solutions. It is found that the deflection, stress, buckling load, and natural frequency obtained by the present theory match well with those obtained by the first-order and third-order shear deformation theories. [Copyright &y& Elsevier]

Abstract: A simple refined shear deformation theory is proposed for bending, buckling, and vibration of thick plates resting on elastic foundation. The theory accounts for parabolic distribution of transverse shear stress, and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. The number of unknowns of present theory is two as against three in the case of other shear deformation theories. The elastic foundation is modeled as two-parameter Pasternak foundation. Equations of motion are derived from Hamilton's principle. Analytical solutions are obtained for rectangular plates with two opposite edges simply supported and the other two edges having arbitrary boundary conditions. Comparison studies are presented to verify the validity of present solutions. It can be concluded that the proposed theory is accurate and efficient in predicting the bending, buckling, and vibration responses of thick plates resting on elastic foundation. [Copyright &y& Elsevier]

Abstract: This paper presents a simple first-order shear deformation theory for the bending and free vibration analysis of functionally graded plates. Unlike the conventional first-order shear deformation theory, the present first-order shear deformation theory contains only four unknowns and has strong similarities with the classical plate theory in many aspects such as governing equations of motion, boundary conditions, and stress resultant expressions. Equations of motion and boundary conditions are derived from Hamilton’s principle. Closed-form solutions of simply supported plates are obtained and the results are compared with the exact 3D and quasi-3D solutions and those predicted by other plate theories. Comparison studies show that the present theory can achieve the same accuracy of the conventional first-order shear deformation theory which has more number of unknowns. [Copyright &y& Elsevier]

• New design mixes for ultra-high strength concrete (UHSC) are proposed. • Cost-benefit analysis is performed to find the optimised mix deisgn. • A database of over 300 specimens of UHSC is collected. • A new equation for predicting elastic modulus of UHSC is proposed. The use of ultra-high strength concrete (UHSC) could significantly increase the load-carrying capacity of a structural member, and thus reducing the amount of materials used as well as expanding the floor area of buildings due to a reduction in member size. Despite these benefits of UHSC, its practical applications are still limited because of its complicated and uneconomical manufacture. This study therefore investigates different mix designs for UHSC using conventional manufacture methods with commonly used raw materials. An experimental study was also conducted to determine the optimised mix design in terms of the manufacturing cost. Modifications to improve the strength of current UHSC mixes were also suggested. In addition, an empirical equation for predicting the elastic modulus of UHSC was proposed based on an experimental database newly collected from about 300 tests with the cylinder compressive strength in the range from 100 MPa to 200 MPa. By comparing with the equations from current design codes and existing equations, it can be concluded that the proposed equation is not only simple but also gives the best predictions among existing equations. [ABSTRACT FROM AUTHOR]

In this study, two machine learning (ML) algorithms including support vector regression (SVR) and artificial neural network (ANN) are employed to predict the ultimate strength of rectangular and circular concrete-filled cold-formed steel tubular (CFCFST) columns under concentric and eccentric loading. In total, 730 test results on CFCFST columns are compiled and used to train the algorithms. In addition, 720 rectangular and circular CFCFST columns subjected to concentric and eccentric loading are modelled and analysed using finite element (FE) method to expand the training data. The accuracy of the developed FE models is verified by comparing the simulation results with existing experimental results. To develop the predictive models with the best performance, hyperparameter tuning is performed through random search. The results show that the ANN models have relatively better accuracy than that of SVR ones. Using the well-trained ANN models, a graphical user interface (GUI) is developed to predict the ultimate strength of CFCFST columns. To make the GUI applicable to practical application, reduction factors are proposed by performing reliability analysis using Monte Carlo simulation (MCS). The reduction factors are in accordance with load standards of America, Europe and Australia/New Zealand. • We develop empirical equations for the practical design of CFCFST columns using two machine learning algorithms. • A comprehensive test database of 730 specimens is collected for testing and training. • An additional numerical database of 720 columns is also developed using ABAQUS. • Monte Carlo simulation-based reliability analysis is also carried out to derive the reduction factors for real world applications in design. • A Graphical User Interface (GUI) tool is developed to benefit end-users. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a simple quasi-3D theory for the bending analysis of functionally graded plates. This theory accounts for both shear deformation and thickness stretching effects by a sinusoidal variation of all displacements through the thickness. By dividing the transverse displacement into bending and shear parts, the number of unknowns and governing equations of the present theory is reduced, and hence, makes it simple to use. The governing equations and boundary conditions are derived using the principle of virtual displacements. Analytical solutions are obtained for simply supported plates. The accuracy of the present theory is verified by comparing the obtained results with 3D and quasi-3D solutions and those predicted by higher-order shear deformation theories. The comparison studies show that the obtained results are not only more accurate than those obtained by higher-order shear deformation theories, but also comparable with those predicted by quasi-3D theories with a greater number of unknowns. [Copyright &y& Elsevier]

A finite element model based on sinusoidal shear deformation theory is developed to study vibration and buckling analysis of composite beams with arbitrary lay-ups. This theory satisfies the zero traction boundary conditions on the top and bottom surfaces of beam without using shear correction factors. Besides, it has strong similarity with Euler-Bernoulli beam theory in some aspects such as governing equations, boundary conditions, and stress resultant expressions. By using Hamilton's principle, governing equations of motion are derived. A displacement-based one-dimensional finite element model is developed to solve the problem. Numerical results for cross-ply and angle-ply composite beams are obtained as special cases and are compared with other solutions available in the literature. A variety of parametric studies are conducted to demonstrate the effect of fiber orientation and modulus ratio on the natural frequencies, critical buckling loads, and load-frequency curves as well as corresponding mode shapes of composite beams. [ABSTRACT FROM AUTHOR]

Abstract: A new sinusoidal shear deformation theory is developed for bending, buckling, and vibration of functionally graded plates. The theory accounts for sinusoidal distribution of transverse shear stress, and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. Unlike the conventional sinusoidal shear deformation theory, the proposed sinusoidal shear deformation theory contains only four unknowns and has strong similarities with classical plate theory in many aspects such as equations of motion, boundary conditions, and stress resultant expressions. The material properties of plate are assumed to vary according to power law distribution of the volume fraction of the constituents. Equations of motion are derived from the Hamilton’s principle. The closed-form solutions of simply supported plates are obtained and the results are compared with those of first-order shear deformation theory and higher-order shear deformation theory. It can be concluded that the proposed theory is accurate and efficient in predicting the bending, buckling, and vibration responses of functionally graded plates. [Copyright &y& Elsevier]