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In this study, a novel sinusoidal higher-order shear deformation thin-walled beam theory is presented to examine the effects of material properties and external load uncertainty on static responses of laminated composite thin-walled beams with open sections. The solution for the deterministic flexural analysis is based on Hamilton's principle and Ritz-type exponential shape function series. Several mechanical parameters of laminated composite materials are randomized and plugged into the beam solver to investigate the thin-walled beam's stochastic flexural behaviors. The computational cost and accuracy of the polynomial chaos expansion (PCE) method with both projection and linear regression approaches are presented and evaluated by comparing its results with crude Monte Carlo simulation (MCS). This comparison allows for a thorough assessment of the PCE method's performance. Additionally, a sensitivity analysis is conducted to compare the relative significance of the uncertainty in material properties and loads on the stochastic responses. The supervised training of the artificial neural network based on the MCS beam data is also conducted and compared to the PCE and MCS methods. The findings about the stochastic outputs are introduced in various statistical metrics and illustrations to demonstrate the influences of material properties' randomness on different laminated composite thin-walled beam configurations. [ABSTRACT FROM AUTHOR]

This research aims to study the flexural and pseudo‐ductile behavior of e‐glass biaxial and uniaxial fabric reinforced cementitious matrix (FRCM). Also, the flexural results and load–deformation curves of FRCM samples were numerically simulated using the finite element method (FEM). The experiments were started with preparation of FRCM flexural samples with different types of fabrics (biaxial and uniaxial) and their distribution in the matrix: one layer was put in the middle, two on the top, two on the bottom, and three layers were distributed equally. The surface morphology and cross‐section microstructure of the fabricated FRCM panels and cohesion of fabrics inside of them were observed using an optical microscope. Subsequently, the flexural response of the FRCM samples was measured according to standard EN 196‐1. Afterwards, based on the flexural measurements, the pseudo‐ductile behavior of the FRCM panels in terms of the ductility index (DI) was determined using energy criteria, including Naaman and Grace models. Finally, the crack propagation and flexural load‐deformation curves of FRCM samples were numerically modeled using FEM (LS‐DYNA) to validate the experiential results. The results showed that reinforcement of mortar with glass fabric leads to a significant increase in strain, especially in case of 3 layers/FRCM till 224% (uniaxial) and 110% (biaxial). Also, the uniaxial FRCM samples provided higher flexural load (3600 N) compared with mortar panel (2337 N) and biaxial FRCM (2788 N). In addition, the DI of FRCM samples was significantly improved by embedding 3 layers of uniaxial fabrics up to 152% (Naaman) and 230% (Grace), when compared with neat panel. Finally, the numerical results obtained from FEM provided a high predication to simulate the failure mode of all panels and to model the load–deformation curves with agreement >96%. Based on that, it is highly recommended to use three layers of e‐glass uniaxial fabric to reinforce the cementitious composite and to improve its flexural response. [ABSTRACT FROM AUTHOR]

This study explores the flexural behavior of continuous fiber-reinforced composite sandwich structures built entirely using material extrusion additive manufacturing. The continuous fiber additive manufacturing system used in this study works sequentially, thus enabling the addition of fiber reinforcement just in the face sheets, where it is most effective. Three-point bending tests were carried out on sandwich panel specimens built using thermoplastic reinforced with continuous glass fiber to quantify the effect of fiber reinforcement and infill density in the flexural properties and failure mode. Sandwich structures containing continuous fiber reinforcement had higher flexural strength and rigidity than unreinforced sandwiches. On the other hand, an increase in the lattice core density did not improve the flexural strength and rigidity. The elastic modulus of fiber-reinforced 3D-printed sandwich panels exceeded the predictions of the analytical models; the equivalent homogeneous model had the best performance, with a 15% relative error. However, analytical models could not correctly predict the failure mode: wrinkle failure occurs at 75% and 30% of the critical load in fiber-reinforced sandwiches with low- and high-density cores, respectively. Furthermore, no model is currently available to predict interlayer debonding between the matrix and the thermoplastic coating of fiber layers. Divergences between analytical models and experimental results could be attributed to the simplifications in the models that do not consider defects inherent to additive manufacturing, such as air gaps and poor interlaminar bonding. [ABSTRACT FROM AUTHOR]

The paper is concerned with the derivation of asymptotically consistent equations governing the long-wave flexural response of a two-layered rectangular plate with high-contrast elastic properties. In the general case, the plate is under dynamic and variable surface, volume, and edge forces. Performing the asymptotic integration of the three-dimensional (3D) elasticity equations in the transverse direction and satisfying boundary conditions on the faces and interface, we derived the sequence of two-dimensional (2D) differential equations with respect to required functions in the first two approximations. The eight independent restraints for the generalized displacements and stress resultants are considered to formulate the 16 independent variants of boundary conditions. One of the main results of the paper is the Timoshenko–Reissner type equation capturing the effect of the softer layer and taking into account the in-plane deformation induced by the edge forces. Comparative calculations of natural frequencies were carried out based on our and alternative models. [ABSTRACT FROM AUTHOR]

This study explores the flexural behavior of continuous fiber-reinforced composite sandwich structures built entirely using material extrusion additive manufacturing. The continuous fiber additive manufacturing system used in this study works sequentially, thus enabling the addition of fiber reinforcement just in the face sheets, where it is most effective. Three-point bending tests were carried out on sandwich panel specimens built using thermoplastic reinforced with continuous glass fiber to quantify the effect of fiber reinforcement and infill density in the flexural properties and failure mode. Sandwich structures containing continuous fiber reinforcement had higher flexural strength and rigidity than unreinforced sandwiches. On the other hand, an increase in the lattice core density did not improve the flexural strength and rigidity. The elastic modulus of fiber-reinforced 3D-printed sandwich panels exceeded the predictions of the analytical models; the equivalent homogeneous model had the best performance, with a 15% relative error. However, analytical models could not correctly predict the failure mode: wrinkle failure occurs at 75% and 30% of the critical load in fiber-reinforced sandwiches with low- and high-density cores, respectively. Furthermore, no model is currently available to predict interlayer debonding between the matrix and the thermoplastic coating of fiber layers. Divergences between analytical models and experimental results could be attributed to the simplifications in the models that do not consider defects inherent to additive manufacturing, such as air gaps and poor interlaminar bonding.

This work focuses on examining the mechanical characteristics and flexural response of reinforced concrete (RC) beams by incorporating oil palm shell (OPS) lightweight aggregate from oil palm shell waste. The OPS aggregates are replaced in various percentages, such as 0 to 50% of natural coarse aggregate (NCA). Mechanical properties of OPS concrete were conducted, and these properties were used to quantify the flexural performance of RC beams. Five RC beams with several gradations of OPS aggregates were cast and tested for this investigation. The first cracking, ultimate strength, load-deflection behavior, ductility index, and failure patterns of OPS aggregate beams were investigated as the corresponding behaviors to the NCA concrete beam. The fresh properties analysis demonstrated lessening the slump test by varied concentrations of OPS concrete. Furthermore, compressive strength was reduced by 44.73%, 50.83%, 53.33%, and 57.22% compared to 10%, 15%, 20%, and 50% OPC substitution at 28 days. Increasing OPS content in concrete mixes decreased splitting tensile strength, comparable to the compressive strength test. Modulus of rupture and modulus of elasticity experiments exhibited a similar trend toward reduction over the whole range of OPS concentrations (0–50%) in concrete. It was revealed that the flexural capacity of beams tends to decrease the strength with the increased proportion of OPS aggregate. Moreover, crack patterns and failure modes of beams are also emphasized in this paper for the variation of OPS replacement in the NCA. The OPS aggregate RC beam's test results have great potential to be implemented in low-cost civil infrastructures. [ABSTRACT FROM AUTHOR]

Ultrahigh-performance concrete (UHPC) has been considered for a variety of structural engineering applications, owing to its superior strength and durability. Among the main properties of UHPC, flexural performance characteristics largely depend on the type and dosage of fibers incorporated into the mixture. Noting this critical aspect and the fact that the availability and cost of fibers directly contribute to choosing UHPC over other cementitious composites, this study explored the possibility of a partial replacement of steel fibers conventionally used in UHPC mixtures with synthetic fibers. With a focus on workability and strength properties, a total of 15 mixture designs were developed, investigating five different synthetic fibers, including nylon, polypropylene, polyvinyl alcohol, alkali-resistant glass, and carbon fibers. Three mixtures were prepared for each fiber type by varying the dosages of synthetic and steel fibers. From the conducted tests, load-deflection curves were extracted, further to flexural strength and toughness characteristics. To properly understand the progress of crack formation and propagation, as well as the effectiveness of various fibers in the postcracking response of UHPC, the obtained results were paired with digital image correlation data. Through holistic comparisons, the outcome of the presented study provided original information on the extent of contribution of some of the most common synthetic fibers to the strain distribution, crack resistance, and flexural performance of UHPC. [ABSTRACT FROM AUTHOR]

This study deals with the evaluation of moment-curvature response and curvature ductility of reinforced ultra high performance concrete (R-UHPC) cross-sections. Curvature ductility is calculated based on six definitions. The impact of these definitions is demonstrated through the calculation of strength reduction factors and comparisons of factored flexural strength of R-UHPC and reinforced normal strength concrete (R-NSC) cross-sections. Strategies for improving the curvature ductility of R-UHPC cross-sections are presented. A versatile framework to predict the complete moment curvature response of R-UHPC cross-sections is proposed. The proposed procedure is used to study the effect of tension reinforcement ratio, UHPC strain at crack localization, UHPC tension model, UHPC ultimate tensile strain, and compression reinforcement ratio on curvature ductility and complete moment curvature response. It is determined that for a given cross-section, changing the material from NSC to UHPC causes notable reductions in curvature ductility. This reduction applies to: 1) tension and compression reinforcement ratios that range from 0.69–2.78 % and 0 – 1.37 %, respectively; 2) UHPC tension models that feature elasto-plastic and linear strain hardening responses with and without residual branches; and 3) UHPC ultimate tensile strains that range from 0.005–0.015. Such reductions in curvature ductility render the considered R-UHPC cross-sections as members in the transition zone – a classification currently prohibited for R-NSC sections according to ACI 318–19 (22) - while their R-NSC counterparts qualify as tension-controlled. This results in lower strength reduction factors for R-UHPC cross-sections and limits the benefits of UHPC when flexural strength controls design. It is concluded that R-UHPC cross-sections that feature either the highest or the lowest reinforcement ratios provide the highest added benefit from the point of view of enhancing factored flexural strength compared to R-NSC sections. The most effective method to elevate curvature ductility is an increase in the UHPC strain at crack localization. A minimum UHPC strain at crack localization of 0.006 is required to change the classification of cross-sections from the transition zone to tension-controlled. The use of compression reinforcement - an established technique for R-NSC members to induce a change in the flexural failure mode by elevating curvature ductility - was determined to have almost no influence on the curvature ductility of R-UHPC cross-sections. • A procedure is presented to obtain the complete M − χ response of R-UHPC cross-sections. • The impact of several parameters on M − χ response and curvature ductility is examined. • R-UHPC sections exhibit much lower curvature ductility than R-NSC counterparts. • None of the considered R-UHPC sections qualifies as a tensioned controlled section. • Strategies for increasing curvature ductility of R-UHPC sections are presented. [ABSTRACT FROM AUTHOR]

Laminated composite structures, while offering weight savings compared with their metal counterparts, are susceptible to ply separation, (i.e., delamination mode of failure) due to the lack of through-thickness fiber reinforcements. In this paper, numerical simulations are used to gain an enhanced understanding of angled composite beam delamination when subjected to four-point bending consistent with the ASTM D-6415 test standard, with an expectation that the learning gained from this work is extensible to laminated composite components in general. While illustrating mesh sensitivity, manufacturing and frictional effects, four items of interest are examined: (1) the undamaged state/pre-peak load response, (2) the through-thickness peak tensile capability, (3) the post-peak load drop, and (4) the subsequent post-peak damaged response. A Finite Element Analysis (FEA) model is developed that incorporates the Smeared Crack Approach (SCA) to capture progressive failure modes within the element formulations directly, effectively eliminating the need for a priori specification of discrete delamination zones. The ability to incorporate failure directly within the element structure is particularly notable where laminates may not realistically permit a high number of interface layers or where geometry may be complex. Leveraging experimental data of curved composite laminates subject to four-point bending, the proposed approach successfully predicts the correct behavior throughout the damage progression. Additionally, this study offers an insight into effects of manufacturing-induced imperfections and frictions between the specimen and fixture on the prediction of inter-laminar strength of a curved composite part. [ABSTRACT FROM AUTHOR]

The flexural behavior of textile-reinforced glass/carbon (TRGC) laminates is investigated utilizing a novel multiscale model and experiments for the application of Yacht hull structure. The multiscale model, consisting of micro, meso, and macro scales, is based on the virtual elastic-viscoplastic micromechanical data of the constituents and geometrical nonlinearities. The progressive strength analysis is performed for different stacking arrangements to obtain flexural stress-strain curves well-matched with experimental data. The scanning microscope is used to detect different damage mechanisms and their progression on the integrity of laminates. The overall energy absorption proficiency of laminates is governed by stacking arrangement and local fiber fractions. The stiffness and strength, from 10% to 85% compared to TR glass/epoxy (TRG), and toughness, from 26% to 87% compared to TR carbon/epoxy (TRC), could be enhanced by hybridization. The exterior carbon layers increase stiffness significantly and strength moderately, but result in a substantial reduction in toughness and severe through-the-thickness failure of laminates. As the carbon layers are susceptible to stress concentration, extended delamination between dissimilar adjacent layers is noticeable. Moreover, different configurations of alternative stacking arrangements, provide superior gradual-damage distribution and integrity. Two 10-layer alternative laminates based on the extended model, show improved mechanical properties and energy absorptions. • A multiscale viscoplastic model enhances the nonlinear flexural response of hybrid TRCG laminates. • Model integrates viscoplastic-material, nonlinear-geometry, and damage initiation-propagation mechanisms. • The sequence and local C:G fabric ratios determine flexural curves & delaminated areas. • Alternative laminates have the lowest thermal expansion and delaminated-area due to mixed C:G ratios and bridging-glass layers. • Microscopic scanning is used to study the fracture mechanisms and delaminated areas. [ABSTRACT FROM AUTHOR]

This experimental study investigates the flexural response of sandwich composites integrated with 3D multi-layer stitched core. Polypropylene 3D multi-layer woven fabric impregnated with an epoxy resin was selected as the core, while E-glass fiber reinforced epoxy was used for the sandwich composite face sheets. The sandwich composite exhibited a ductile behavior when loaded in three-point bending as the core layers increased. This is due to the drop in core shear strength with the increased number of core layers. The core layers that were not directly connected with the face sheets deformed most under shear, resulting in a more flexible plate behavior. The number of core layers, size of core unit-cell and stitching density were the critical design parameters determining the flexural strength and stiffness of the sandwich panel. The flexural modulus of sandwich composites with higher stitching density core stiffer than those of lower stitching density. [ABSTRACT FROM AUTHOR]

This paper presents the bending and buckling analyses of simply supported nanowires using various classical and nonclassical higher-order shear deformation theories (HSDTs). A one-dimensional structure is modeled with including the surface effects based on the Gurtin–Murdoch surface elasticity theory (nonclassical beam theory) and the small-scale effect based on the Eringen nonlocal theory (nonlocal beam theory); the transverse displacement is divided into two bending and shear components. A system of governing equations is derived with the help of the minimum total potential energy principle and resolved via Navier's solutions. Several numerical results are presented and compared with those given in the literature. The results showed that the influence of the surface effects on the bending and buckling load of nanowires is more pronounced than that of the nonlocal parameter. [ABSTRACT FROM AUTHOR]

Laminated Aluminum Composite Structure (LACS) has shown great potential for replacing traditional bulk aluminum parts, due to its ability to maintain low manufacturing costs and create complex geometries. In this study, a LACS, that consists of 20 aluminum layers joined by a structural tape adhesive, was fabricated and tested to understand its impact performance. Three impact tests were conducted: axial drop, normal and transverse three-point bending drop tests. Numerical simulations were performed to predict the peak loads and failure modes during impacts. Material models with failure properties were used to simulate the cohesive failure, interfacial failure, and aluminum fracture. Various failure modes were observed experimentally (large plastic deformation, axial buckling, local wrinkling, aluminum fracture and delamination) and captured by simulations. Cross-section size of the axial drop model was varied to understand the LACS buckling direction and force response. For three-point bending drop simulations, the mechanism causing the maximum plastic strain at various locations in the aluminum and adhesive layers was discussed. This study presents an insight to understand the axial and flexural responses under dynamic loading, and the failure modes in LACS. The developed simulation methodology can be used to predict the performance of LACS with more complex geometries.

Ultra‐high performance concrete (UHPC) is increasingly used for various engineering applications, owing to its superior strength properties. Such properties, however, can be accompanied by workability issues, especially if the dosage of steel fibers is significantly increased. As a potential solution, this study explored the use of a combination of steel microfibers and macrofibers through a holistic experimental testing program. This was to understand the effects of steel fiber combinations on the workability and flexural strength of various UHPC mixtures. The microfibers were investigated for five different dosages from 1.0% to 3.0% (with an increment of 0.5%). In parallel, two mixtures were prepared with a 2.0% dosage of macrofibers in the form of twisted wire and hooked fibers. At the next stage, six additional mixtures were prepared with a combination of microfibers and macrofibers of various dosages. Further to the measurements extracted from the workability and flexural strength tests, digital image correlation (DIC) analyses were employed to obtain firsthand information about the widths and depths of cracks observed in the flexural specimens tested under an increasing load. The outcome of this study showed how a combination of microfibers and macrofibers can contribute to improving the flexural response characteristics of UHPC, especially without having to increase the dosage of steel fibers to the ranges that can adversely affect the mixture's workability. [ABSTRACT FROM AUTHOR]

In this work, multiscale basalt fiber/epoxy composites were fabricated using silane‐modified Na+‐montmorillonite nanoclay, at various contents (0.5, 1, 3, and 5 wt% with respect to the matrix). Flexural and tribological characteristics of the composites were studied. First of all, a silane coupling agent, namely 3‐aminopropyltriethoxysilane (3‐APTS), was applied onto the surface of the nanoclay particles, and then the effects of modified nanoclay on the three‐point bending and wear properties of the basalt fiber/epoxy composites were assessed. Fourier transform infrared spectra indicated that the 3‐APTS coupling agent was successfully grafted onto the surface of the nanoclay particles after modification. The three‐point bending test results demonstrated that the basalt fiber/epoxy composite having 3 wt% modified nanoclay had the highest flexural strength and modulus. On the other hand, the pin‐on‐disk wear test results showed that the multiscale composite containing 5 wt% modified nanoclay had the highest wear resistance. Finally, the fracture and worn surfaces of the specimens were assessed to identify the dominant mechanisms. [ABSTRACT FROM AUTHOR]

This paper aims to comparatively evaluate the compressive and flexural response of high strength and ultra-high-performance polyvinyl Alcohol (PVA)- and polyethylene (PE)-reinforced ECCs at fiber contents of 1.75 vol% and 2.25 vol%, utilizing the same base mixture design. The base mixture was formulated with the objective of reducing the reliance on Portland cement by replacing 55% of it with supplementary cementitious materials (fly ash and silica fume). The flexural loading protocol consisted of monotonic loading with a displacement rate of 0.3 mm/min and 2.0 mm/min, and a repeated/cyclic loading with a displacement rate of 2.0 mm/min. The developed PVA- and PE-reinforced ECCs exhibited significant enhancements in average compressive strength, with PVA-reinforced ECC showing a 19% improvement and PE-reinforced ECC demonstrating a 39% improvement compared to the control specimen. In terms of flexural strength, PVA-reinforced ECC exhibited a 51% enhancement, while PE-reinforced ECC achieved an impressive 199% improvement. Furthermore, a digital image correlation system (DIC) was employed to characterize the cracking behavior and strain response of the specimens. The developed ECCs exhibited multiple cracking and strain-hardening behavior, exceeding a flexural strain of 3%. PE-reinforced ECCs displayed narrower cracks under low loading rates, whereas PVA-reinforced ECCs demonstrated reduced crack widths subjected to high loading rates. [ABSTRACT FROM AUTHOR]

An analytical solution has been developed developed in this research for electro-mechanical flexural response of smart laminated piezoelectric composite rectangular plates encompassing flexible-spring boundary conditions at two opposite edges. Flexible-spring boundary structure is introduced to the system by inclusion of rotational springs of adjustable stiffness which can vary depending on changes in the rotational fixity factor of the springs. To add to the case study complexity, the two other edges are kept free. Three advantages of employing the proposed analytical method include: (1) the electro-mechanical flexural coupling between the piezoelectric actuators and the plate’s rotational springs of adjustable stiffness is addressed; (2) there is no need for trial deformation and characteristic function—therefore, it has higher accuracy than conventional semi-inverse methods; (3) there is no restriction imposed to the position, type, and number of applied loads. The Linear Theory of Piezoelectricity and Classical Plate Theory are adopted to derive the exact elasticity equation. The higher-order Fourier integral and higher-order unit step function differential equations are combined to derive the analytical equations. The analytical results are validated against those obtained from Abaqus Finite Element (FE) package. The results comparison showed good agreement. The proposed smart plates can potentially be applied to real-life structural systems such as smart floors and bridges and the proposed analytical solution can be used to analyze the flexural deformation response. [ABSTRACT FROM AUTHOR]

Skew slabs have various applications, e.g. as floor of bridges and buildings. This is pertinent when it is not possible to cross a river or gap at an angle of 90°. Design aids and plans suggested by various codes are applicable for standard skew angles, i.e. 15°, 30°, 45°, etc. with selective spans only. However, in actual practices, several cases are encountered, wherein skew angle and aspect ratio of the slab panel do not fit the recommended guidelines. This occurs due to the very high land cost and space limitations. The present study proposes an analytical model for the design of skew slabs with any skew angle and aspect ratio. The developed model indicates that skew slabs simply supported along two opposite parallel sides and free along the other two sides are suitable for the construction of bridges having short diagonal larger than the span. The developed model validates the assumptions considered in terms of collapse loads and crack patterns experimentally and numerically. This shall facilitate engineers during the design of skew slab bridge for any skew angle and aspect ratio, without deviating from the alignment of the road. [ABSTRACT FROM AUTHOR]

The present study presents a generalized analysis and solution procedure for finding the flexural response of beams on viscoelastic foundations. The foundation soil is modelled as a tension membrane interconnecting a series of Burger model representing the time-dependent behaviour of saturated clayey soils and maintaining continuity of stresses and displacement beyond the loaded area as well. The governing differential equations are developed and solved using finite difference scheme. Studies were made to find the optimal mesh size for getting convergent solution matching excellently with those reported in the literature. The relative importance of the different parameters controlling the flexural response of the foundation was assessed and reported. [ABSTRACT FROM AUTHOR]

• A new steel –UHPFRC composite beam structure is proposed, aiming at the full and proper utilization of both materials. • The unique use of ① UHPFRC in both tension and compression and ② a half rolled section with continuous in-built steel dowels as shear connectors. • An experimental study is conducted to characterize the flexural and shear responses of the proposed structure. • The design principles for both flexural and shear resistance of the proposed structure are introduced based on the failure mechanism. Aiming at the full and proper exploitation of both steel and Ultra High Performance cementitious Fiber Reinforced Composites (UHPFRC) materials, this paper proposes a new steel-UHPFRC composite beam structure. The unique use of ① UHPFRC in both tension and compression and ② a half rolled section with continuous in-built steel dowels in combination with UHPFRC dowels (forming composite dowels as shear connectors) is highlighted. An experimental study consisting of two composite beams is then conducted to investigate the flexural and shear responses. In particular, the failure mode, cracking pattern, and monitoring of critical crack kinematics are discussed using digital image correlation (DIC) technology. Subsequently, the design principles for both flexural and shear resistance are introduced based on the failure mechanism: ① the determination of flexural resistance is based on the sectional analysis considering the tensile properties of UHPFRC, and ② the determination of shear resistance is based on a specific approach to the lever arm of internal forces and horizontal shear resistance of the composite dowel, considering the tensile contribution of UHPFRC. According to the experimental results, the effective interlocking between UHPFRC and the steel dowel allows efficient interaction between steel and UHPFRC components, benefiting from its higher shear resistance and ductility compared with traditional welded head studs. Both the flexural and shear response of the composite beam can be characterized into five distinguished domains, in which the quasi-elastic domain is introduced especially due to its large contribution to the resistance and high structural stiffness. Finally, the design principles are validated by the tested values. [ABSTRACT FROM AUTHOR]

This study presents an integrated numerical and experimental investigation of a laminated aluminum composite structure. The laminated aluminum composite structure was created by attaching structural tape adhesive in between aluminum layers and curing it in an oven. Three point bending tests were conducted on samples with different span lengths and thicknesses and their effect on the flexural response was observed and discussed. Using realistic material fracture models, simulations were performed to capture the different failure modes that were observed experimentally (large plastic deformation, wrinkling, and delamination). Good agreement was observed between the simulations and experiments. The delamination mechanism in the simulations was also discussed in detail. The developed simulation methodology can be used as a robust tool to predict the performance of laminated aluminum composite structures with more complex geometries. [ABSTRACT FROM AUTHOR]

Composite sandwich structure possesses unique characteristics in which the facings' material provides a high in-plane stiffness/strength, while the core material keeps the facings a part to enhance the flexural stiffness/strength. However, sandwich structure is susceptible to shear failure due to the weak bond between the facings and the core materials. This article addresses this issue and provides an efficient semi-circular shear keys concept to be inserted in the interfacial surface between the sandwich structural elements to improve the facings–core interaction with marginal sacrifice in the strength-to-weight ratio. Composite sandwich panels composed of glass fibre–reinforced polymer skins and polyurethane foam core material have been investigated in this study. Mechanical tension, compression and shear tests were performed on the facings, while compression tests were conducted on the core materials to define the elasto-plastic response of the constituent's materials. Four-point bending tests were performed on the conventional composite sandwich panel and panels incorporated with shear keys concept. Considerable improvement in the flexural stiffness and strength along with detouring the crack path was noticed for the samples incorporated with shear keys. A non-linear finite element analysis was established to verify the experimental results. Comparisons between the experimental and finite element results were presented and showed good agreement between both results which justified the parameters used in the finite element models and their capabilities to capture the mechanical behaviour and the damage mode of the investigated models. [ABSTRACT FROM AUTHOR]

This paper presents the effect of sustained service loading at elevated temperatures on the residual flexural response of reinforced concrete (RC) T-beams after exposed to elevated temperatures of 700 and 900°C (1292 and 1652°F) for 3 hours and then cooled in air. Two beams were subjected to a constant simulated service loading equal to 22.6% of undamaged (unheated) flexural strength, while the counterpart beams were exposed to fire without any applied sustained load. The test results showed that the bottom (tension) steel reinforcements in all fire-exposed beams had experienced the peak temperatures that were higher than a critical value (593°C [1099°F]) before the post-fire static test. The post-fire static test results showed that the sustained loading has a detrimental effect on the post-fire flexural response of RC beams. The effect was more pronounced on the post-fire stiffness and ductility than on strength. In the paper, simplified finite element models for predicting the temperature response and post-fire load-deflection relationships of fire-exposed RC beams are also described. [ABSTRACT FROM AUTHOR]

Abstract Ultra-high performance concrete (UHPC) mixtures demonstrating more than 150 MPa compressive strength and 20 MPa flexural strength are proportioned with commonly available cement replacement materials (30% or 50%, mass-based replacement levels) and steel fibers using a recently developed combined binder and aggregate optimization approach. The compressive (axial) stress-strain responses of the unreinforced and fiber-reinforced UHPC mixtures, along with the calculated volumetric strains, are used to define two critical stress states – viz., crack initiation and crack damage stresses. The crack damage stress, being the threshold value at which unstable crack propagation begins, is suggested to be used as the true strength of UHPC in structural design. The influence of matrix composition and fiber volume on these parameters is brought out, to better elucidate the influence of material design on properties. Digital image correlation (DIC) on unnotched beams under flexure is used to show the fundamental differences in the matrix properties that lead to differences in strain localization. The beneficial influence of fibers on strain localization in UHPC mixtures is also brought out. [ABSTRACT FROM AUTHOR]

Highlights • An FE model for predicting the flexural behaviour of UHPC was investigated. • The numerical approach was validated with 21 UHPC specimens. • The FE model accurately traces the flexural performance of the tested specimens. • The simulated and experimental ultimate load and deflection agree well. Abstract This paper presents a finite element (FE) modelling to predict the behaviour of ultra-high performance concrete (UHPC) members under static flexural loading. A plasticity-based constitutive model for concrete and an implicit solver in LS-DYNA were adopted in the numerical simulation. Experimental data for 21 UHPC specimens tested in the present study and in previous works were used to calibrate and validate the proposed FE model and modelling technique. The simulation was able to accurately predict the experimentally obtained ultimate strength, stiffness, and hardening and softening behaviours of the specimens. This demonstrates the effectiveness and adequacy of the developed FE model and modelling technique. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flexural behaviour of non-prestressed and pre-stressed basalt textile reinforced concrete isinvestigated and discussed. • A practical prestressing rig for application to textile reinforced concrete composites is developed and presented. • The role of reinforcement ratio, location, number of layers and plies are explored. • The role of prestressing level, prestressing release day and curing time are explored and presented. While the recently emerged textile-reinforced concrete (TRC) composites offer a more durable alternative to conventional reinforced concrete, these composites are susceptible to cracking and high deformations under service loads, which hinders their widespread application for the development of load-bearing structural components. Aiming at addressing this issue, the present paper experimentally investigates the flexural response of non-prestressed and prestressed basalt-based textile-reinforced concrete plates. Basalt is chosen as an emerging low-carbon reinforcement for TRC composites. The first series of tests is focused on non-prestressed TRCs and consists of eleven reinforcement configurations considering the role of reinforcement ratio, position and coating on the flexural behaviour of TRCs. The second series, focused on prestressed TRCs, considered the role of prestressing level (13%, 25% and 35% of the fabric's ultimate tensile load), releasing time, testing age and coating type on the flexural behaviour. [ABSTRACT FROM AUTHOR]

• The complete flexural response of composite UHPC filled HSS sections is characterized. • A procedure to compute this response is presented and validated. • The proposed procedure captures the effect of steel element local buckling. • Three failure modes are identified and a formulation is presented for future identification. • Contribution of UHPC to flexural response is discussed for each failure mode. • Closed form equations are presented to predict flexural capacity. • Impact of HSS grade, section size, and UHPC properties on flexural response is presented. A mechanics based analytical method for obtaining the complete moment–curvature response of composite hollow structural steel (HSS) and ultra high performance concrete (UHPC) cross-sections is presented. Flexural response at the cross-sectional level is traced past the local buckling of the steel elements and up to the exhaustion of UHPC and steel material capacity. The proposed method is validated using experimental data from seven flexural tests on composite HSS-UHPC beams. Flexural failure mode is classified as either a UHPC compression-controlled failure, UHPC fiber tension-controlled failure, or a balanced failure. Behavioral differences between the cross-sections that fall into these three categories are discussed in terms of flexural capacity, curvature ductility, and relative contributions of HSS and UHPC to flexural capacity. Flexural response of the composite HSS-UHPC cross-section is compared to that of the bare HSS cross-section. The enhancement in flexural capacity and curvature ductility, for UHPC fiber tension-controlled sections compared to the bare HSS cross-section, was 52% and 79%, respectively. For composite cross-sections that feature a balanced failure, the increase in flexural capacity and curvature ductility, compared to the bare HSS cross-section, was 37% and 35%, respectively. Closed form formulations are proposed to identify the flexural failure mode and predict flexural capacity. The influence of various parameters, such as HSS material grade, size of cross-section, and UHPC material characteristics on the complete flexural response of the cross-section is investigated. The average ratio and corresponding coefficient of variation (COV) of tested to computed flexural strength obtained using the proposed procedure was 1.06 and 21.28%, respectively. Similarly, the average ratio and COV of tested to calculated flexural strength obtained using the proposed closed form formulations was 1.07 and 22.18%, respectively. [ABSTRACT FROM AUTHOR]

• Flexural behavior of 15 BFRP, GFRP, and steel reinforced normal (NSC) and high strength concrete (HSC) beams investigated. • Cracking and ultimate moments, deflection and crack widths compared with ACI 440 Guidelines. • BFRP bars exhibited 15% higher stress level at failure in HSC beams with elastic response and cracking moments similar to NSC beams. • Modified empirical equation based on earlier version of ACI 440 proposed to enhance the deflection predictions at service load. • The bond coefficient k b for predicting the crack width for BFRP reinforced normal and high-strength beams proposed. Basalt fiber-reinforced polymer (BFRP) bars are emerging as potential non-metallic reinforcements for concrete structures due to the wide availability of their raw materials, their environmentally friendly manufacturing process, and their excellent mechanical and durability properties. This paper focuses on the flexural and deflection response of normal and high-strength concrete (HSC) beams reinforced with BFRP bars. A total of fifteen simply supported concrete beams were tested under four-point loading on a flexural span of 2.5 m. The study parameters were the reinforcement ratio, BFRP bar size, concrete strength and bar type (BFRP, GFRP and Steel). The experimental results were compared to ACI 440.1R-15 predictions. The prediction of ultimate moment capacity was in good agreement with the experimental result, while the cracking moment was overestimated. Furthermore, the mid-span deflection was significantly underestimated at service and ultimate loads. Modification in the empirical equations was proposed to enhance the predictions of mid-span deflection at service load. The bond coefficient k b used for predicting the crack width was estimated at 0.89 and 1.12 for BFRP-reinforced normal and high-strength beams. [ABSTRACT FROM AUTHOR]

Highlights • Addition of polymer causes concrete to behave in more ductile manner. • Addition of fibers into PMC are able to improve flexural responses and toughness. • Water penetration resistance of FRPMC depends on fiber volume fraction and length. • At low volume fraction, water penetration resistance remains in similar ranges to plain PMC. • Penetration resistance decreases markedly as fiber volume fraction increase to 1.0%. • Fiber length provides negative effect on the water penetration resistance of FRPMC. Abstract In this study, the effects of fiber on the properties of polymer modified concrete (PMC) were investigated. Hooked end steel fibers with two different lengths but similar aspect ratios were used at 0.5% and 1.0% by volume fraction. Acrylic polymer was added into concrete at 2 different weight ratios, 7.5% and 15% by weight of cement. Four experiments were carried out: slump, compression, flexural and water penetration tests. Results indicated that both fiber content and length, and polymer content played an important role on the properties of fiber reinforced polymer modified concrete (FRPMC) in different ways. In term of workability, the slump increased with the increasing polymer content and decreased when the fiber was added into PMC. For mechanical properties, fiber addition enhanced the load response of PMC and increased the strength and fracture toughness. In term of compressive strength, regardless of PCM type, the strength of FRPMC was found to increase up to about 15% as compared to plain PCM. The effect of fibers was more pronounced under bending load than under compression. The increase in flexural load up to 34% was observed in FRPMC as compared to plain PMC. For water penetration test, fiber at low volume fraction had a negligible effect on the water tightness. However, when the fiber volume fraction was increased to 1.0%, the water tightness was reduced significantly. [ABSTRACT FROM AUTHOR]

The flexural response of the box-girder bridges, having curvature and skewness together referred as skew-curved bridges, cannot be predicted by simply superimposing the individual effect of skewness and curvature due to the coupling of these effects. Moreover, the complexity of such thin-walled box-girder bridges increases under eccentric vehicular loads causing additional torsional and warping stresses in the box-sections. The present study focuses on predicting the flexural response of simply supported single cell skew-curved concrete box-girder bridges. In order to investigate the effect of curvature and skewness, the central curvature angle has been varied from 0° to 48° at an interval of 12° while the skew angle is swept from 0° to 50° at an interval of 10°. Three-dimensional analysis models of the bridges are created using CSiBridge and a finite element analysis has been carried out for gravity loads and Indian Road Congress (IRC) specified Class 70R tracked vehicular Live Load (LL) plying at a minimum specified clearance from the kerb. The parametric study results indicate that the flexural response of the inner girder (web) becomes more pronounced in case of skew-curved bridges. In general, it has been observed that presence of skewness in highly curved bridges significantly improves the flexural response of the bridge. Furthermore, the critical position of LL producing the absolute maximum longitudinal moment as well as the location of the critical section for moment has been found significantly affected by skewness and curvature. These critical positions have been presented in the framework of newly developed ‘skew-curve’ coordinate system for systematic representation. [ABSTRACT FROM AUTHOR]

Grid stiffened composite structures have been maturely developed in aircraft and automobile industries due to their excellence properties such as high specific strength, high specific stiffness, excellent energy absorption capability and corrosion resistance. In the current investigation, the effect of multi-walled carbon nanotubes addition in various weight percentages (0, 0.1, 0.25 and 0.4) on the flexural response of anisogrid composite panels was evaluated. For fabrication of the composite specimens, hand lay-up method was used where plain weave E-glass fibers and unidirectional carbon fibers impregnated to the epoxy resin that modified with multi-walled carbon nanotubes were used in the skin and rib parts, respectively. Experimental results from three-point bending test showed that with the addition of 0.4wt.% of multi- walled carbon nanotubes, the maximum flexural load, flexural stiffness and energy absorption of anisogrid composite panels increased by 24%, 35% and 25%, respectively. Microscopic analyses revealed that the improvement in the flexural properties of anisogrid composite panels with the addition of multi-walled carbon nanotubes was due to improvement in the interfacial properties of matrix and fibers. [ABSTRACT FROM AUTHOR]

An exact analytical model based on a higher-order beam theory (HBT) is developed for an accurate prediction of the flexural response of two layered composite beams with partial shear interactions. This is achieved by taking a third order variation of the longitudinal displacement over the beam depth for the two layers separately. The deformable shear connectors joining the two different material layers are modelled as distributed shear springs along the beam length at their interface. The principle of virtual work is used to derive the governing equations which are solved analytically using a Navier type solution technique. To assess the performance of the proposed model, numerical examples of composite beams are solved using the model. The results predicted by the model are compared with published results and the numerical results produced by a one dimensional finite element model based on HBT as well as a detailed two-dimensional finite element modelling of composite beams. [ABSTRACT FROM AUTHOR]

The purpose of the work was the study of the structural safety of R.C. beams subjected to corrosion processes though the derivation of moment-curvature diagrams and moment-to-shear interaction diagrams. Normal-strength reinforced concrete beams with longitudinal bars in the presence of transverse stirrups and subjected to corrosion processed are considered. Experimental results available in the literature related to corrosion processes, for steel bars, crack openings and bond degradation due to rust formation are reviewed. Then analytical laws relating to crack opening, bond degradation with attack penetration depth, through a rearranged form of Faraday’s law, are presented. An analytical model for cross-section analysis and shear strength prediction including the main effect due to rust formation is developed and verified against experimental data. Finally, a case study is added giving moment-curvature diagrams and moment-to-shear interaction diagrams to show the effects of different scenarios of natural corrosion increasing with time on beam elements. [ABSTRACT FROM AUTHOR]

Steel plate shear walls (SPSWs) have been increasingly used in lateral load resisting system since the post-buckling strength of web plates was realized and considered in practical design. Diagonal tension field is formed in the web plate to resist the lateral force induced by winds and earthquakes. The force is anchored by the surrounded horizontal boundary elements (HBEs) and vertical boundary elements (VBEs) and eventually transferred to the ground. Therefore, the response of HBEs, especially anchor HBEs, is essential to ensure that SPSWs could exhibit the required strength, ductility, and energy dissipation capacity. This paper presents the results of theoretical studies into the flexural behavior of the anchor HBEs of SPSWs and can be regarded as an extension to the previous work by Qu and Bruneau (2011) and Qin et al. (2017). The boundary effect was considered to reflect the actual stress state at the HBE-to-VBE connection, which assembled the method by Qin et al. (2017). Furthermore, more proper distributions of the vertical component of tension field for the positive and negative flexure cases, respectively, were proposed comparing to the work by Qu and Bruneau (2011). The hand calculation approach for the plastic flexural capacity of the anchor HBEs was given by the summation of the contributions from the flanges and the web. The developed equations are compared with previous data and good agreement was found between them. Meanwhile, comprehensively discussions are conducted to evaluate the influence of key parameters on the flexural behavior of anchor HBE. It was found that the plastic flexural capacity of anchor HBE decreases from unity to the minimum as a result of the increase in shear force, axial force and vertical stresses. Moreover, the flexural response of anchor HBE is most vulnerable to the change in shear force. This indicates that boundary effect is significantly important and cannot be ignored in the analysis. The research in this paper provides basis for the capacity design of anchor HBE. [ABSTRACT FROM AUTHOR]

Biot's poroelastic theory is used with classic plate theory and plane stress theory to determine the constitutive relationships for a thin poroelastic plate. The dynamic equations for the thin poroelastic plate are derived from the extended Hamilton's principle. The dynamic equations are then transformed to frequency domain and Galerkin's finite element method is used to derive the stiffness matrix of a triangular plate element. When impulsive loads and elastic boundary conditions are applied, the finite element frequency domain analysis for the thin poroelastic plates is achieved. Vibration behavior of thin elastic and poroelastic circular plates is accurately predicted. [ABSTRACT FROM AUTHOR]

This paper provides closed-form expressions for the process zone lengths and load-displacement responses of cohesive zone modeling, for the popular mode I double cantilever beam (DCB) test, the mode II end notched flexure (ENF) test and the mixed-mode I/II bending (MMB) test of composite materials. By incorporating traction-separation laws that consist of only one quasi-brittle softening segment, the problems are formulated and analytically solved for homogenous material or mid-plane symmetric laminates within the framework of classical lamination theory (CLT). The solutions of the MMB test are obtained by the superposition method. Having been known as depending on the mode mixity, the material and interfacial fracture properties, the process zone length is found as a system parameter that is also influenced by the specimen geometry, including the thickness and the crack length, especially for mode II. Based on the parametric studies and the comparison against finite element (FE) simulations, suggestions for estimating the process zone length are provided. [ABSTRACT FROM AUTHOR]

One of the main factors that lead to the deterioration of reinforced concrete structures is the corrosion of reinforcing steel. The aluminum alloy (AA) bars, which have favorable characteristics such as good ductility, low specific weight, good corrosion resistance, and recyclability, can be used as an alternative to steel reinforcement to increase service life of concrete structures. This study investigates the feasibility and performance of AA reinforced concrete beams. A total of nine specimens reinforced with AA bars and two specimens reinforced with plain steel bars, which serve as benchmark, were fabricated and tested under four-point bending up to failure. The longitudinal reinforcement ratio and the concrete strength were the main test variables for the specimens. The load-deflection curves, failure modes, crack patterns, crack width, and reinforcement strains were evaluated and discussed for each specimen. A modified section analysis and a strut-and-tie model were used to predict the load carrying capacities of AA reinforced beams for flexural and shear failure modes. The results indicate that the AA bars, if properly treated, can be utilized as reinforcement in concrete beam with satisfactory performance. [ABSTRACT FROM AUTHOR]

Closed-form solutions for cohesive zone modeling within the framework of classical lamination theory (CLT), for the popular mode I double cantilever beam (DCB) test, the mode II end notched flexure (ENF) test and mixed-mode I/II bending (MMB) test are provided in this paper. Zero-thickness virtual multi-linear traction–separation laws are introduced to simulate the cohesive interactions between potential crack surfaces. The problem is formulated by solution forms corresponding to each segment of the cohesive laws and using appropriate boundary and continuity conditions. Detailed algorithms for each case are provided to clearly show the influence of the cohesive zone law on the ensuing crack growth. The superposition method used for mixed-mode growth in the MMB test for homogenous material or mid-plane symmetric laminates is proved both theoretically and numerically. Comprehensive parametric studies are performed on the crack growth response and the process zone length, revealing their relations to the delamination length, cohesive parameters, the shape of the traction–separation laws and the mode mixity. With applicability to general multilayered structures, and the capability to incorporate arbitrary, piecewise linear cohesive constitutive laws, the closed-form solutions can serve as a tool to determine the accuracy of numerical solutions used in conjunction with finite element simulations. [ABSTRACT FROM AUTHOR]

The objective of this work is the characterization and the assessment of the damage in CFRP composite laminates with different stacking sequences subjected to low velocity impact and flexural loading. Charpy impact test and three-point bending test were used in order to obtained the impact response and flexural behavior of different laminates. An experimental test series was carried out to determine impact energy absorption, flexural strength and stiffness and failure mechanisms of composite laminates made from M 21 E / IMA , an unidirectional prepreg used in Airbus A350 XWB primary structures. It is important to note that both elastic moduli and strength in the principal material directions are different under tension and compression. The flexural modulus is expected to have an intermediate value between the tensile and compression moduli. We analyze the effect of this type of multimodulus materials [1–3] in order to evaluate the influence of the geometry of the specimen on the failure modes (shear or flexural failure modes) observed in the three-point bending test and compare the results with tensile and compression behavior. Two main lay-up configurations have been analyzed: Unidirectional laminates [ 0 ] 12 , [ 90 ] 12 , [ 45 ] 12 and multidirectional laminates (cross-ply [ 0 / 90 ] 3 s , angle-ply [ ± 45 ] 3 s and quasi-isotropic laminates [ 0 / 90 / ( ± 45 ) 2 ] s ). Unidirectional laminates are rarely used in structural components but help to assess the different types of damage (splitting, matrix cracking, delamination) and response of the specimens under low-velocity impact and flexural loading. They are usually combined with plies of varying orientation in multidirectional laminates. These laminates exhibit a more complex behavior due to coupling effects and the combination of different failure modes. In this study, both impact and flexural response for the different laminates have been compared. Special attention is paid in the response of multidirectional laminates under flexural (and impact) loading. Shear effects are very important in this type of laminates. Only a limited number of experimental studies have been developed in this context [4–7]. Additionally, the failure modes observed under impact and flexural loading were correlated with fracture energy absorption and load–deflection behavior respectively for the unidirectional and multidirectional laminates. The results have shown that the effect of the stacking sequences on the impact and flexural response depicted similar trends than in the case of tensile response studied in previous works [8–11]. Furthermore, the present work has shown a distinctive behavior of [ ± 45 ] 3 s angle-ply laminate.under impact loading due to its pseudo-ductile behavior. This laminate exhibited the best impact performance in terms of averaged absorbed energy but the flexural strength and stiffness drastically decreased compared to [ 0 ] 12 laminate. Finally, SEM and optical micrographs of fracture surfaces were used to gain an insight into the assessment of different type of damage of the previous laminates. [ABSTRACT FROM AUTHOR]

This manuscript summarizes an experimental program investigating the cyclic flexural behavior and energy dissipation of C-shaped cold-formed steel structural framing members experiencing global, distortional or local buckling. Understanding the cyclic flexural moment-rotation ( M – θ ) response of individual members is essential in developing analytical models that can facilitate analysis-based design of cold-formed steel building systems. Specimen cross-section dimensions and lengths were selected to isolate specific buckling modes (i.e., local, distortional or global buckling). A cyclic loading protocol was adapted from FEMA 461 with targets based on elastic buckling properties. Abrupt drops in flexural strength after peak moment were observed with subsequent stiffness degradation and pinching of the moment-rotation response associated with straightening of buckling deformations during loading direction reversals. Members experiencing local and distortional buckling accumulated damage at the compressed web and flanges within the leading buckled half-wave that spread throughout the cross-section forming flexural hinges after several cycles. In members experiencing lateral-torsional buckling, damage localized at the C-section flange-stiffening lip but distinct flexural hinges were not observed. Energy dissipation per cycle in members undergoing lateral-torsional buckling remained constant through large flexural rotations because the failure mechanism involved mid-span cross-section rigid body motion without plastic deformations spreading across the cross section. Local and distortional buckling specimens resulted in more dissipated energy per cycle compared to global buckling specimens, but the energy dissipation rapidly decreased as applied displacements increased. Energy dissipation within the damaged half-wave(s) is higher for lower cross-sectional slenderness and increasing section modulus, key trends that will be useful for generally defining cyclic hysteretic response of thin-walled cold-formed steel members in planned future work. [ABSTRACT FROM AUTHOR]