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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]

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.

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]

• 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]

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]

• 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]

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]

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]

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 paper examines the deflected shape assumptions built into the single-degree-of-freedom (SDOF) methodology used for analyzing structural components subject to blast loading. Design professionals use the SDOF models to analyze blast effects on components. It is common knowledge that the SDOF method is an approximation, and is not suitable for large charges with short distances (lower scaled distance -Z). Current design guidelines establish the limit of Z = 1.2 m=kg1/3 for using SDOF methodologies for blast-loaded components, which is equivalent to a peak pressure of 5,000 kPa; however, this paper shows that the limit may be significantly higher in Z value (or lower in peak pressure). Higher air-blast pressure and impulse combinations cause hinges toform before the assumed deflected shape dominates the response. Because transformation factors for SDOF are derived using static deflected shapes and the static collapse mechanism, the factors may not produce accurate or conservative responses for blast loading at lower scaled distances. Using the finite element multi-degree-of-freedom (FE-MDOF) model, the paper validates the accuracy of SDOF shape factors for large scaled distances, and shows that the static deflected shape assumptions do not apply at lower scaled distances with higher impulses. Limits to SDOF are established based on the equivalent shape factors, and the variability in the limits based on damping and mass are also discussed. [ABSTRACT FROM AUTHOR]

The results of an experimental program investigating the dynamic increase factors of light-frame wood stud walls under blast loading are presented in this paper. A total of 20 walls with two different sheathing types and thicknesses were tested to failure under static and dynamic loading. The study found that the observed failure mode for both static and dynamic loading was flexure; however, a difference in the type of flexural failure was observed. Average increase factors of 1.40 and 1.18 on the resistance and stiffness, respectively, were found. A detailed literature review combined with the test results from the current project yielded a strong correlation between the increase in strain rate and the relative increase in strength and an equation relating the dynamic increase factor (DIF) on the resistance to strain rate was proposed for strain rates in the ranges of 1.67-1.65 x 10³s-1 [ABSTRACT FROM AUTHOR]

Abstract: A simplified multi-linear stress–strain approach has been used to obtain the closed form nonlinear moment curvature response for epoxy resin materials. The model consists of constant plastic flow in tension and compression. The multi-linear stress–strain model is described by two main parameters in addition to four non-dimensional tensile and six non-dimensional compressive parameters. The main parameters are modulus of elasticity in tension and strain at the proportional elastic limit point in tension. The ten non-dimensional parameters are strain at the ultimate tensile stress, maximum strain, post elastic proportionality stiffness, and post peak strength in the tension model and strain at the proportionality elastic limit, strain at yield strength point, maximum strain, initial elastic stiffness, post elastic proportionality stiffness, and post peak strength in the compression model. Explicit expressions are derived for the stress–strain behavior of the epoxy resins. Closed form equations for moment curvature relationship are presented. The results of tension, compression, and bending tests using digital image correlation technique are presented. Load deflection response of flexural three point bending (3PB) samples could be predicted using the moment curvature equations, crack localization rules, and fundamental static equations. The simulations and experiments reveal that the direct use of uniaxial tensile and compressive stress–strain curves underestimates the flexural response. This model gives an upper bound estimate for flexural over-strength factor. [Copyright &y& Elsevier]

Abstract: Railway sleepers in a track system are usually utilised to transfer any loading from the rails to the ground support. A wide range of loading conditions has been observed but the critical loading condition is the wheel impact force, which is often due to the wheel or rail irregularities. The railway industry has been aware of a high potential that an out-of-round, single-sided wheel defect may occur and cause cracking in the railway concrete sleepers. This paper presents the dynamic effects on the railway concrete sleeper in a track system due to a single wheel impact. In this study, the railway concrete sleeper is modeled using the beam on elastic foundation theory. The dynamic finite model makes use of the elements coupling with shear and bending deformations to represent the concrete sleeper, and features the use of the tensionless elastic support as the nature of ballast. The parametric investigations focus on the influences of both magnitude and duration of the transient loading. Using the robust finite element software STRAND7, the finite element model of the railway concrete sleeper was previously established and validated against experimental data by the authors. The numerical simulations present the dynamic flexural moment magnification factor of the railway concrete sleeper under the asymmetrical wheel load patterns. [Copyright &y& Elsevier]

Abstract: This paper presents a flexural analysis of I-shaped laminated composite beams. A general analytical model applicable to thin-walled I-section composite beams subjected to vertical load is developed. This model is based on the shear-deformable beam theory, and accounts for the flexural response of the thin-walled composites for arbitrary laminate stacking sequence configuration, i.e. unsymmetric as well as symmetric. Governing equations are derived from the principle of the stationary value of total potential energy. Numerical results are obtained for thin-walled composites under vertical loading, addressing the effects of fiber angle and span-to-height ratio of the composite beam. [Copyright &y& Elsevier]

• Unidirectional GFRP improves the behaviour of studs and light-frame walls. • Simple tension GFRP reinforcement did not increase the ductility (i.e., brittle). • U-shaped GFRP reinforcements resulted in ductility ratios ranging 1.4–3.9. • Weaker specimens experienced greater increases when reinforced with GFRP. • Four GFRP reinforced walls were subjected to simulated blast loading. An experimental program was undertaken to investigate the flexural performance of forty-eight unreinforced and glass fibre-reinforced polymer (GFRP) reinforced Spruce-Pine-Fir No. 2 grade individual wood studs. In general, it was found that the GFRP contributed to reducing the damage region, especially when both reinforcement and confinement were utilized. The simple tension reinforcement did not provide any significant improvement to the post-peak behaviour and resulting in a brittle failure, similar to that observed in the unreinforced studs. Other reinforcement options, particularly those consisting of U-shaped reinforcement on the tension face with and without confinement, significantly increased the average flexural strength and stiffness of the stud by a factor of 2.4 and 1.8 times those obtained in the unreinforced studs, respectively. Significant ductility ratios, in the range of 1.4–3.9, were also observed in these reinforced configurations. Weaker specimens experienced greater increases in strength and reduction in variability when reinforced. Based on these observations, six full-scale light-frame stud walls reinforced with FRP were tested dynamically under simulated blast loading. The results showed that the walls reinforced with FRP performed better and had relatively less damage while dissipating, on average, twice the energy dissipated by the unreinforced walls. The observed failure modes of the reinforced walls were consistent with the static failure modes of the individual reinforced studs. [ABSTRACT FROM AUTHOR]

• Unretrofitted glulam beams have little to no significant post-peak resistance. • Multi-directional GFRP localized damage and significantly enhanced the performance. • Ductility ratios ranging 2.3–3.6 are obtained using multidirectional FRP fabrics. • An average increase in wood ultimate tensile failure strain of 1.21 is observed. • An approach that considers strain rate dependency and empirical knowledge is proposed. An experimental program, investigating the potential of using multi-directional fibre-reinforced polymers (FRPs) as a strengthening option for glulam beams when subjected to blast loading, was undertaken. A total of ten different retrofit configurations were investigated and compared to the behaviour of unretrofitted glulam members. In general, the use of multi-directional GFRP contributed to significant performance enhancement, where ductility ratios in the range of 2.3–3.6 were obtained. The use of bidirectional GFRP fabrics localized the damage in the wood section to a small area, and provided confinement which helped delay the failure of the retrofitted specimen. The FRP fabrics also contributed to an increase in wood ultimate tensile failure strain. A two-step approach was proposed to predict the resistance function of the retrofitted specimens. The model predicted the peak resistance and deflection at peak resistance reasonably well. The approach was able to predict the ultimate failure deflection when the experimental ductility ratios were used. An approach for design using a lower-bound ductility ratio was proposed. [ABSTRACT FROM AUTHOR]

This article investigates the effect of cell architecture on the bending behavior of architected cellular beams subjected to a thermo-mechanical load. The architected functionally graded cellular (FGC) beam is made of porous cells whose properties vary across the thickness or length of the beam. The FGC beam is modeled according to Reddy's third-order shear deformation theory (TSDT), and the effective thermo-mechanical properties are obtained by standard mechanics homogenization. The governing equations are solved by a finite element method, and deflection curves are presented for the architected cellular beams with relative density gradients, subjected to thermal and mechanical loads. Numerical results demonstrate that tailoring relative density through the thickness of an FGC beam can reduce the lateral deflection of lightweight beams to less than half; consequently, tuning the flexural stiffness of cellular structures without changing their total weight. Interestingly, numerical results reveal that the flexural deformation of an FGC beam subjected to a thermo-mechanical load can be controlled by means of the variation function of cell architectures. We also present the optimized architectural variation and cell topologies leading to the least flexible architected cellular beams for alternative thermo-mechanical loading conditions. This paper sheds light on the application of cellular-based mechanical metamaterials for programming the multifunctional behavior of lightweight meta-structures. [ABSTRACT FROM AUTHOR]

Most of the composite materials that are used in aerospace structures have been manufactured using a thermostable matrix, as epoxy resin. The region of stability of these polymers is defined by the glass transition temperature (Tg). However, operating temperatures close and above the Tg can cause a variation in the properties of the polymer and consequently, modify the mechanical properties of the composite material. Therefore, it is necessary to understand the failure mechanisms that occur in the material in order to ensure stability and durability. The effect of temperature and time of exposure on the impact and flexural mechanical responses of carbon/epoxy composites are studied in this work. For that purpose, ageing treatments at temperatures below and above the Tg have been considered and then, impact and flexural tests have been performed. It was observed that thermal ageing cause two different effects: at temperatures below the Tg, there is an increase of the maximum strength because of a post-curing effect; however, the mechanical properties decrease at higher temperatures of thermal ageing due to the thermo-oxidation of the epoxy resin and the loss of adhesion in the matrix/fibre interface. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental program, where a total of eight retrofitted walls were subjected to blast loading, simulated by shock waves using the University of Ottawa's shock tube. Four different external retrofit options were considered and their behavior in terms of failure mode, stiffness, and strength were documented. Nonlinear single-degree-of-freedom (SDOF) modeling was performed using material models developed specifically for each retrofit. In general, good agreement was found between the predicted level of damage and calculated displacement using the model and the measured behavior. The study shows that a significant increase in stiffness and strength can be achieved. [ABSTRACT FROM AUTHOR]