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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]

Composite sandwich panels were developed for the sail boat hull using glass-fibre/epoxy composite facing and polyurethane foam core. These light weight structures were tested through four-point bending tests to characterize their flexural behaviour. The material exhibited an initial linear elastic behaviour followed by non-linear behaviour. Finite element analysis of the sandwich panels, accounting for the materials and geometrical nonlinearity as well as the cohesive nature of the skin-core interaction, was performed to analyse the flexural behaviour of the structure. Good agreement has been observed between the numerical and experimental response up to the failure. Moreover, the experimental results were compared with the predictions of the classical sandwich theory. The theoretical predictions well represented the linear flexural response of the sandwich panels, while deviates as the load increase up to failure due to the theory limitations. [ABSTRACT FROM AUTHOR]

The outer rise on the distal periphery of a subduction system is caused by emplacement of an accreted load onto the flexed oceanic lithosphere. By examining the bathymetry and free-air gravity anomaly data collected by satellite observations and marine reflection seismic data collected during the TAIGER project, we demonstrate the characteristics of the flexural outer rise seaward of the Manila Trench. The region of the outer rise on the westernmost periphery of the Manila subduction system is characterized by the positive free-air gravity anomaly seaward parallel to the Manila Trench and the morphological rise at the south of the Manila subduction system. A flexure simulation is performed based on the flexural profiles along the southern Manila Trench-outer system and the resulting effective elastic thickness values may provide an alternative aspect for the spreading rates of the South China Sea basin. Since both the western periphery of the Taiwan collision belt and Manila subduction belt are dominated by the strain regime of extension of flexural origin, it appears that the strain regime of flexural extension associated with the flexural forebulge of the Western Taiwan Foreland Basin to the north, and the strain regime of flexural extension associated with the outer rise seaward of the Manila Trench to the south are meridionally interconnected. This revised understanding of the strain regime of flexural extension origin west of the Taiwan-Luzon convergent belt provides an alternative point of view on the strain regime offshore SW Taiwan. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper the experimental results relative to three-point bending tests on multilayer glass beams and on semi-rigid connections realised with stainless double web angles are presented and discussed. Small and medium size glass beams were tested and load–deflection curves and crack patterns at failure were recorded. The laminated glass specimens, of equal cross-section, were characterised by three different combinations of annealed float and fully thermally tempered glass plies and different interlayers. Steel joints constituted by double web angles to connect two glass beams were tested adopting several geometrical configurations and using stainless steel bolts preloaded with two different preloading values. The results obtained highlight the brittleness of glass beams with fail safe mechanism in the case of multilayer glasses with PVB. The joints tested were the semi-rigid type, which only make it possible to activate small percentages of the flexural capacity of beams. In all cases examined brittle failure in the glass beams was observed due to stress concentration near the hole, highlighting the importance of the choice of an adequate distance from the hole and the edges of the beams and of the study of an appropriate interface material for connections between glass panels and steel members in the case of both preloaded and non-preloaded bolts. [Copyright &y& Elsevier]

Abstract: Externally bonded carbon fiber reinforced polymer (CFRP) sheet has shown excellent performance to repair, restore and increase the load-carrying capacity of RC structures. In this paper results of an experimental test are presented in which fourteen RC beams strengthened with CFRP epoxy bonded sheets in flexure and time-dependent tests are subjected to four-point bending and sustained load respectively. The test variables included different degrees of strengthening scheme and two types of sustained load for both un-cracked and cracked beams. For flexural strengthening, the increase of ultimate strength provided by CFRP was assessed by varying the layers of laminates and incorporating end anchorage. In time-dependent test, deflection reduction coefficient in concrete tension stiffening model is proposed to evaluate the stiffness of the section after cracking for RC beams. It is found that the analytical values based on effective modulus method (EMM) are in general gives conservative estimates of the experimental results. [Copyright &y& Elsevier]

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]

Traditional building materials may not be appropriate in view of the urgency in dealing with flash flood victims which need for immediate replacement of destroyed housing at a reasonable cost. Thus, the solution lies in making the best use of lightweight sandwich composite technology for flash flood victims lost residence in a short time. Therefore, this research focuses on comprehensive comparisons in bending of LWF sandwich/concrete (RC) composite beams. The flexural response of the LWF/RC beams is investigated in terms of crack load, load–deflection curves, stiffness, energy absorption capacity, ductility index, ultimate flexural load-to-weight ratio, load–strain curves, crack patterns, number of cracks, average crack width, crack spacing, and the failure mode. The test results reveal the remarkable enhancement in the flexural behavior and potential application for reconstruction of flash flood victims lost residence utilizing lightweight sandwich composite technology. The method outlined by ACI Building Code is used to compute ultimate moment capacities. The results obtained using this method are compared with the experimental results. [ABSTRACT FROM PUBLISHER]

Abstract: This paper describes the results of an investigation on the resistance of plain and fibre reinforced cement-based foams to sulphate exposure. A synthetic foaming agent was used to produce foamed cementitious composites with essentially a closed cellular structure at 1200kg/m3, 750kg/m3, and 475kg/m3. Polymeric microfibres were introduced at 0% and 0.2% volume fraction to result in 6 mixes. Prismatic specimens were immersed in a sodium sulphate solution to be tested in flexure, after specific intervals of exposure, according to ASTM C1609. A comparison with the response of unexposed specimens reveals that the heavier cement-based foams are more susceptible to sulphate attack and perform poorly with an increase in the duration of exposure. On the other hand, the lightest of the mixes—at 475kg/m3—registered higher flexural strength and toughness factors up to 30days of exposure before succumbing to sulphate attack. This self-healing response was attributed to the space available in such highly porous composites that allows for the unhindered growth of ettringite without attendant cracking. The presence of microfibres facilitated self-healing, as evident from the flexural toughness factor. [Copyright &y& Elsevier]

Abstract: The mechanical properties of electrolytic oxide layers elaborated on aluminium substrate in oxalic–sulphuric acid bath were optimized using a four variables doehlert experimental design (bath temperature, anodic current density, sulphuric acid and oxalic acid concentrations). Thickness measurements and flexural tests were conducted. A sudden decrease of the load, indicative of film failure, was observed upon the load–deflection curve. The deflection at failure and the maximum load for each layer were deduced from the corresponding load–deflection curve. The isoresponse curves study and the optimum path study of the three retained responses: thickness, maximum load and deflection at failure, showed that the experimental conditions, where the three optima were found, were opposite. In order to maximize in the same time the three responses, multicriteria optimization using the desirability function was achieved. In so doing, the determined optimal anodizing conditions were: C ox =13.6gL−1, T =21.4°C, j =2.48Adm−2, C sul =186.3gL−1, while the corresponding estimated response values were 57.6μm, 775N and 4.16mm for thickness, maximum load and deflection at failure, respectively. Finally, a morphological study of the aluminium oxide layer after flexure test was conducted using optical microscopy examination. [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]

The application of aluminium alloys in structural engineering is growing owing to their high strength-to-weight ratio, aesthetic appearance and excellent resistance to corrosion. However, the low modulus of elasticity of aluminium poses adverse effects on the flexural response of structural members made of aluminium alloys. In case of tubular members, the performance can be improved with the addition of concrete infill. Research on the flexural response of concrete-filled aluminium alloy tubes is still minimal. This study presents experimental and numerical investigations on the behaviour of concrete-filled and bare 6082-T6 aluminium alloy tubular members under in-plane bending. In total 20 beams, including 10 concrete-filled aluminium alloy tubular (CFAT) and 10 bare aluminium alloy tubular (BAT) specimens, were tested. The specimens comprised of square and rectangular hollow sections and were filled with 25 MPa nominal cylinder compressive strength concrete. The experimental results are reported in terms of failure mode, flexural strength, flexural stiffness, ductility and bending moment versus mid-span deflection curve. Compared to the BAT specimens, the counterpart CFAT specimens have shown remarkably improved flexural strength, stiffness and ductility due to the concrete infill and the improvement is more pronounced for the specimens with thinner sections. Finite element models of BAT and CFAT beams were developed by taking into account the nonlinearities in geometry and material and validated against the experimental data. A parametric study considering a broad range of cross-sections and different concrete grades was conducted based on the validated models. The FE results have shown that the flexural strength of the BAT and CFAT members increases with the increase of cross-sectional aspect ratio, wall thickness and concrete grade. The results obtained from experiments and numerical analysis for BAT members were used to assess the flexural capacity predictions and the applicability of the slenderness limits provided in the European standards. It was demonstrated that the slenderness limits provided by Eurocode 9 are conservative for Class A aluminium sections. Hence, revised Class 1, Class 2 and Class 3 limits are proposed which appear to be better applicable to Class A aluminium alloys. In the absence of design specifications for CFAT flexural members, the design rules for concrete-filled steel tubular flexural members provided by Eurocode 4 were adopted and the material properties of steel were replaced with those of aluminium alloy. It was shown that the proposed design methodology is suitable for the design of CFAT flexural members. Moreover, a slenderness limit for compact sections of CFAT flexural members is proposed based on Eurocode 4 framework. • Flexural response of concrete-filled and bare 6082-T6 aluminium alloy tubes is investigated. • 20 simply supported beam tests are performed. • A parametric study, including 36 CFAT and 36 BAT beams is conducted based on validated finite element models. • Applicability of European design standards is assessed. • Revised slenderness limits are proposed. [ABSTRACT FROM AUTHOR]

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]

The nature of cracking in flexural specimens made using ultra-high-performance concrete (UHPC) is studied in the context of mechanisms of enhanced strength and ductility. The effect of fibers on the suppression of cracking and the attendant toughening mechanisms are addressed at two different fiber contents to elucidate the strain-softening and strain-hardening responses. Results indicate that the first crack strength is directly related to the fiber content, with fibers extending the stable crack growth region at high fiber contents such that flexural strengths as high as 20 MPa are obtained. Fiber bridging results in resistance to crack growth, stabilization, as well as multiple crack formation, all of which contribute to toughening. Using a combination of experimental results, digital image correlation (DIC) measurements of crack extension, and an analytical model for the flexural response, the stress and strain distributions across the depth of the specimens are determined, leading to stress-crack width relationships, and consequently, the relationship between tensile and flexural stresses in fiber-reinforced UHPCs. The results are also used to determine the tensile and compressive strain and stress distributions. Using back-calculated tensile properties from the flexural response and the 3-D DIC results, crack width profile and the stress-crack width relationship in tension are obtained for UHPCs, leading to a comprehensive understanding required for the structural design using such high-ductility materials. [ABSTRACT FROM AUTHOR]

• A novel residual tensile stress to crack width model was developed. • The tensile model utilized a normalization process to account for fiber dosage and fiber geometry. Mechanical properties at the material scale are required for the efficient design of structural concrete members constructed using steel fiber reinforced concrete (SFRC). Simple analytical models are desired which define and correlate the mechanical properties based on the macro-scale parameters for the mix including the density, compressive strength and fiber dosage. This paper describes a study conducted to understand the relationship between the compressive, flexural and direct shear responses for SFRC containing hooked-end steel fibers at 0 to 1% by volume. Three different concrete matrices were considered: a regular concrete, a lightweight aggregate concrete with similar compressive strength, and a high strength concrete that was 2.4 times as strong. Fibers were found to be effective in enhancing the direct shear strength of regular concrete where the cracks progressed around the aggregates. Less improvement in direct shear strength for high-strength and lightweight matrices was observed as cleavage through the aggregates was more prevalent. Further exploration of the flexural test data allowed development of a novel relationship between the residual tensile stresses across cracks relative to the crack opening through a normalization process with key mix composition parameters. The novel relationship is presented in a format that is suitable for use in member-scale structural design. [ABSTRACT FROM AUTHOR]

• UHPC have been developed using local sand and basalt aggregates. • Analytical model has been developed to design UHPC bridge deck connections. • The hybrid connection produced with local UHPC showed moment capacity increased more than 80% compared to NSC. Although using of UHPC improves the mechanical properties of concrete, it is not widespread used, due to several factors; for instance, its high material cost, special curing requirements, and lack of widely accepted design guidelines. This study aims to find an appropriate Ultra-High-Performance Concrete (UHPC) mixture, using locally available materials. In addition, the flexural response of this locally made UHPC mixture in hybrid bridge deck connections has been studied. The effect of different parameters such as percentage of silica fume, fine aggregate type, glass powder content and steel fiber volume fraction were investigated. The compressive strength results showed that a 28 days-strength of 140.3 MPa (20.35 ksi) has been achieved by using basalt as fine aggregate and 20% silica fume by weight. To investigate the applicability of this locally produced UHPC in bridge joints closure, two full scale, 8 ft. clear span, hybrid bridge deck slabs with UHPC closure were constructed and tested under monotonic loading. The load–deflection behavior of the hybrid connection confirmed that the deflection increased linearly until the initiation of cracks, after that it was increased non-linearly up to the failure of the connection. UHPC experienced less strain than high strength concrete (HSC) under compression. The hybrid connection produced with local UHPC showed moment capacity increase by more than 80% compared to NSC. The Moreover, a moment–curvature analytical model of hybrid bridge deck connection was developed to predict ductility, curvature, and stress distributions in closure connections. The model was able to predict initial stiffness and ultimate flexural moments of UHPC composite connections very well. [ABSTRACT FROM AUTHOR]

• Locally available fine river sand (RS) was used instead of micro silica sand (MS) to produce the ECC matrix. • Stone slurry powder (SSP) waste was incorporated as partial substitution of fine aggregates. • Mechanical, durability and environmental impact assessment of ECC mixes were evaluated. • SSP can be utilized as alternate of RS and MS to produce the durable and eco-friendly ECC. The current investigation focuses on utilization of stone slurry powder waste (SSP) in engineered cementitious composite (ECC) as alternate substitution of locally available river sand (RS) and micro silica sand (MS). Performance of various ECC mixes was judged by assessing the compressive, tensile, flexural, electrical resistivity (ER), air permeability, sorptivity and environmental characteristics. The effect of chemical exposure on ECC under chloride, sulphate and combined (chloride-sulphate) immersion was assessed through compressive strength, tensile response and ER behaviour. From this study, it has been concluded that the ECC containing SSP promote the superb characteristics of ECC under normal and chemical exposure conditions. [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]