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The article presents the results of studies on the development of fiber-reinforced concrete using composite binders and basalt fibers obtained in an experimental plasma reactor. To reduce the negative impact of Portland cement on the mineral fiber, composite binders based on Portland cement and fly ash were used in the study. To reduce the normal density in the composition of the binder, a polycarboxylate type superplasticizer was used in the work. The microstructure of cement stone was studied using SEM and IR-spectroscopy. The compressive strength was tested on cubes with an edge of 100 mm according to EN 12390-6, flexural strength – on prisms with a size of 100×100×500 mm according to EN 12390-3. The optimum content of fly ash (30 %) in the composite binder is evaluated, which allows to obtain high mechanical properties. It was revealed that the combined use of composite binder and fiber leads to an increase in compressive and flexural strength of fiber concrete. With the addition of fly ash, both hardening of the structure of the cement stone and a decrease in the alkaline effect of the basalt fiber binding on the surface are observed. Infrared spectroscopy of cement systems showed a change in the phase composition and a decrease in the basicity of the resulting calcium hydrosilicates upon addition of fly ash into the composition binder.

Fiber optical strain sensors are used to measure the strain at a particular sensor position inside the fiber. In order to deduce the strain in the surrounding matrix material, one can employ the strain transfer principle. Its application is based on the assumption that the presence of the fiber does not impede the deformation of the matrix material in fiber direction. In fact, the strain transfer principle implies that the strain in fiber direction inside the fiber carries over verbatim to the strain inside the matrix material. For a comparatively soft matrix material, however, this underlying assumption may not be valid. To overcome this drawback, we propose to superimpose the matrix material with a one-dimensional model of the fiber, which takes into account its elastic properties. The finite element solution of this model yields a more accurate prediction of the strain inside the fiber in fiber direction at low computational costs. [ABSTRACT FROM AUTHOR]

Abstract We discuss a spectral decomposition formulation for the mechanical statistical characterization of the anisotropic strain energy density of soft hyperelastic materials embedded with distributed fibers. We consider a generalized angular probability density function (PDF) of the reinforcement built upon the local eigenvalue and eigenvector system of the Cauchy–Green deformation tensor. We focus our analysis on material models dependent on the fourth pseudo-invariant of the deformation, I 4 , and on exponential forms of the fiber strain energy function. Within such a spectral reference system, we derive the closed-form expression of the PDF for I 4 by generalizing the multi-value random variable transformation procedure recently developed in Gizzi et al. 2016. Our formulation bypasses the cumbersome extension–contraction switch, commonly adopted for shutting down the contribution of contracted fibers in models based on generalized structure tensors. Accordingly, we identify analytically the support of the fibers in pure extension for significant loading conditions. We can readily compute any statistics of the fourth pseudo-invariant and we can derive the direct definition of the average second Piola–Kirchhoff stress tensor according to the second order approximation. Highlights • Spectral decomposition of statistically anisotropic strain energy density. • Generalized angular PDF based on local deformation eigenvalue and eigenvector. • Closed-form of the 4th invariant PDF by multi-value random variable transformation. • Bypass the extension-contraction switch for shutting down the contracted fibers. • Get 4th pseudo-invariant statistics & direct definition of the average stress tensor. [ABSTRACT FROM AUTHOR]

This paper investigates the strength properties of the fine-grained concrete reinforced with the amorphous fiber based on the Fe-B-C system and obtained by the "spinning" method, and concretes reinforced with commercially available types of fibers: fiber based on mineral wool, basalt fiber, fiberglass, steel and polypropylene fibers. The flexural and compressive strength tests with the fiber-reinforced concrete specimens were carried out in accordance with the standard method corresponding to the Russian State Standard. The analysis of results was made by comparison with the characteristics of the control specimens without reinforcement. The best flexural strength characteristics were shown by specimens with the amorphous fiber, while the highest compressive strength was demonstrated with the steel fiber. The addition of the amorphous fibers leads to an increase of 56 % in the flexural strength, but decreases the compressive strength by 30 % compared to the control specimens, which proves the efficiency of this fiber working in bending. The addition of the steel fiber shows an increase of 20 % in flexural strength and an increase of 14 % in compressive strength, which confirms the positive effect of adding a commercially available fiber to the fine-grained concrete. The compounds of the fiber concrete with the compression strength limit up to 38 MPa and tensile strength in bending up to 12 MPa were developed, which allows to use amorphous fiber as a compound of fine-grained concrete in the construction industry.

This article presents the experimental methodology and results of laboratory tests and numerical modeling in order to determine the values of bearing capacity and stiffness of fiber cement board (FCB) within a frame of curtain wall system. The performance of a panel as a part of a system is taken into account for evaluation of the stress-strain state of a cladding. An analysis included 2 stages: an experimental study of a full-size fragment of a curtain wall system with fiber cement cladding and its numerical simulation by means of finite element method (FEM). The dependences of the deflection of the panel on a value of uniformly distributed load were obtained, and the experimental results converged with numerical calculation. The maximum values of the uniformly distributed (simulating wind impact) loads acting on the panel under which the panel satisfies the requirements stated by Ultimate and Serviceability Limit States were calculated also. It can be concluded that onset of Ultimate Limit State is characterized by appearance of cracks due to the stresses in the panel exceeding the value of flexural strength in the area of fastening to curtain wall frame. The results demonstrated that the stress-strain state of the cladding depends on the structural scheme of the supporting frame of the curtain wall system and its rigidity, therefore it is recommended to perform tests on the cladding in conjunction with the supporting frame.

In this study, twelve reinforced concrete (RC) T-beams were tested to failure under two-point flexural loading to investigate the influence of shear span-to-effective depth ( a/d) ratio on their ultimate resistance and failure modes. All test specimens had exactly same cross-section and longitudinal steel ratio without any transverse stirrups along their lengths. The percentage of steel fibers used in the concrete mix ranged from 0 to 1.5 %, whereas the values of a/d ratio were varied as 1.6, 2.5 and 3.0 for each case. Steel fiber reinforced concrete (SFRC) specimens exhibited the higher ultimate resistance, displacement ductility and flexural toughness as compared to the RC beams without steel fibers for all values of a/d ratio. The diagonal-tension (shear) mode of failure is noticed in the RC specimen for the a/d ratio of 3.0, whereas the flexural mode of failure is noticed for the SFRC specimen with 1 % steel fibers for the a/d ratio of 1.6. The flexural strengths of SFRC specimens as noted in the experiments are compared with the theoretical values predicted using the ultimate design approach. [ABSTRACT FROM AUTHOR]

The present investigation shows new development on assembled permanent formwork using ultra high toughness cementitious composites with low permeability and high crack resistance. A bidirectional keel formwork is designed to act as surface cover to prevent corrosion of steel reinforcements for structures under aggressive environment. Main attention is focused on mechanical aspects of a reinforced concrete specimen made with permanent formwork in this article. The flexural behavior of specimen is measured with four-point bending test and experimental results are then presented. A method is proposed to predict the load capacity and displacement of specimen and theoretical prediction shows a coincidence with test results. Furthermore, a series of design details and suggestions are discussed. The results of this investigation show that specimen made by ultra high toughness cementitious composite assembled permanent formwork presents higher load-carrying capacity and more ductile behavior compared with reinforced concrete specimen. [ABSTRACT FROM AUTHOR]

We discuss analytical and numerical tools for the statistical characterization of the anisotropic strain energy density of soft hyperelastic materials embedded with fibers. We consider spatially distributed orientations of fibers following a tridimensional or a planar architecture. We restrict our analysis to material models dependent on the fourth pseudo-invariant I 4 of the Cauchy–Green tensor, and to exponential forms of the fiber strain energy function Ψ aniso . Under different loading conditions, we derive the closed-form expression of the probability density function for I 4 and Ψ aniso . In view of bypassing the cumbersome extension–contraction switch, commonly adopted for shutting down the contribution of contracted fibers in models based on generalized structure tensors, for significant loading conditions we identify analytically the support of the fibers in pure extension. For uniaxial loadings, the availability of the probability distribution function and the knowledge of the support of the fibers in extension yield to the analytical expression of average and variance of I 4 and Ψ aniso , and to the direct definition of the average second Piola–Kirchhoff stress tensor. For generalized loadings, the dependence of I 4 on the spatial orientation of the fibers can be analyzed through angle plane diagrams. Angle plane diagrams facilitate the assessment of the influence of the pure extension condition on the definition of the stable support of fibers for the statistics related to the anisotropic strain energy density. [ABSTRACT FROM AUTHOR]

Lack of knowledge about the performance of emerging sewer rehabilitation technologies represents a critical shortcoming in the water infrastructure industry. This has led the leading aging water infrastructure research organizations to develop pipe rehabilitation technology demonstration programs. Specific scenarios of interest include technologies applicable to challenging site conditions and pipes with challenging configurations. The results of these programs are intended to enhance the industry's awareness of available technologies and their capabilities. This paper describes the demonstration of an emerging ultraviolet (UV)-cured, glass fiber-reinforced (GFR) cured-in-place pipe (CIPP) technology used to rehabilitate 271 m (888 ft) of 250-mm (10-in.) clay pipe in Frisco, Texas. This technology met the utility owner's requirements, and mechanical testing showed that the liner exceeded the minimum design requirements. A key takeaway from this project was the importance of using the proper test method when evaluating the liner's structural properties. These findings are valuable for water infrastructure system engineers in need of alternatives to traditionally disruptive pipeline renewal methods. [ABSTRACT FROM AUTHOR]

In the context of multiscale-oriented computational analyses of fiber-RC (FRC) structures, the modeling of single fiber pullout behavior represents the basic constituent to provide traction-displacement relations to be used for the modeling of FRC on a macroscopic scale. This essential ingredient needs to be formulated such that it only requires minimal computational effort. To this end, an analytical model for the pullout behavior of single fibers embedded in a concrete matrix for various configurations of fiber type, matrix strength, and embedment condition is proposed. An interface law is developed for the frictional behavior between the fiber and matrix. In the case of inclined fibers, the plastic deformation of the fiber and the local damage of concrete are also considered. For hooked-end fibers, the anchorage effect due to the deformed topology of the fiber ends is taken into account in the formulation. By combining these submodels, the pullout response of single fibers embedded in a concrete matrix is predicted. In addition, numerical simulations of pullout tests are performed to obtain insight into the local fiber-concrete interactions and provide supporting information for analytical modeling. The model is successfully validated by means of representative experimental results. [ABSTRACT FROM AUTHOR]

Concrete structures deteriorate for various reasons and upgrading is needed to ensure their continued safe working conditions. Retrofitting reinforced concrete (RC) beams have been accomplished using various techniques, namely, steel plates, external posttensioning, externally bonded fiber-reinforced polymer (FRP), and near-surface-mounted FRP systems to increase flexural and shear capacity. The objective of this paper is to investigate the feasibility of fabric-reinforced cementitious-matrix (FRCM) materials as an alternative external strengthening technique for RC members. The FRCM is a composite material consisting of one or more layers of cement-based matrix reinforced with dry-fiber fabric. The experimental program consists of testing 18 RC beams strengthened in flexure with two different FRCM schemes (one and four reinforcement fabrics). An analysis and design are conducted following the well-established formulation to calculate the flexural capacity of the beams and compare their results with the experimental database. [ABSTRACT FROM AUTHOR]

The effect of randomly oriented discrete synthetic fiber inclusions on the properties of soils treated with proprietary liquid chemical stabilization additives was evaluated in a laboratory-based investigation. Mercia mudstone, Oxford clay, and limestone quarry fines were stabilized with a proprietary polymer and reinforced with discrete fibers. The findings were compared with untreated and reinforced specimens, which served as the control. Test results showed that the inclusion of randomly oriented discrete synthetic fibers had no significant effect on the compaction characteristics of the soils examined. However, it did result in significant improvements in the toughness of all soils examined and load retention after peak strength for Mercia mudstone and Oxford clay. Polymer/sulphonated oil-stabilized and fiber-reinforced Mercia mudstone and Oxford clay specimens were found to be highly susceptible to moisture, while polymer-stabilized and reinforced limestone quarry fines specimens demonstrated good durability when submerged in water and retained 21 to 33% of their air-cured strengths. [ABSTRACT FROM AUTHOR]

The repair and retrofit/rehabilitation of existing concrete and masonry structures have traditionally been accomplished with externally bonded fiber-reinforced polymer (FRP) systems, steel plates, reinforced concrete (RC) overlays, and posttensioning, just to name some of the many techniques presently available. Fabric-reinforced cementitious-matrix (FRCM) composites have recently emerged as an additional strengthening technology. FRCM is a composite material consisting of a sequence of one or more layers of cement-based matrix reinforced with dry-fiber fabric. This paper has three objectives: (1) to review existing guidelines for tensile testing and calculation of FRCM material properties to be used in analysis; (2) to report on some of the results of an experimental program intended to characterize the tensile behavior of FRCM coupons; and (3) to discuss the performance and analysis of concrete RC slab-type elements strengthened with FRCM. The laboratory results demonstrate the technical viability of this new composite material system for strengthening flexural RC members. [ABSTRACT FROM AUTHOR]

In this paper, experimental and numerical studies are conducted to study the damage and failure behavior of a laminated T700/BA9912 composite under low-velocity impact. The three-dimensional (3D) Hashin damage criterion and the cohesive zone model are used in the finite-element analysis, and the numerical simulation reveals the delamination, matrix damage, and fiber breakage process in the material. To show the capacity and fidelity of the numerical model, a drop-weight test and a nondamage inspection (NDI) are performed, and the model predictions are compared with the test results. The numerical model is able to predict the load versus impact time responses of the specimens. The predicted size and shape of the delamination area show excellent agreement with the NDI result, and the predicted through-thickness matrix failure directly below the impactor and the fiber breakage in the bottom layers of the laminates are in good agreement with the experimental observations. [ABSTRACT FROM AUTHOR]

In the last decade, a new strengthening methodology has been developed for reinforced concrete (RC) frames with hollow clay tile (HCT) infill walls by means of diagonally applied carbon fiber-reinforced polymer (CFRP) fabrics. In the experimental part of a study conducted by the authors, this user-friendly methodology was experimentally investigated considering different aspect (height/width) ratios of the infill walls. In this study, first a numerical model of the FRP strengthened infill walls strengthened with the proposed methodology is developed. Afterwards, the numerical simulation results are validated by use of experimental response curves and finally, a parametric study, which further investigates the effect of aspect ratio of HCT infill walls is presented. [ABSTRACT FROM AUTHOR]

Unreinforced masonry (URM) walls have been constructed for the past millennia and are still widely used today. URM walls have proven to have low shear strength and are prone to brittle failure when subjected to in-plane loads caused by earthquake or wind. Retrofitting URM walls is accomplished internally and externally using current techniques, such as placing steel bars in the cavities and grouting, posttensioning with steel tendons, stitching, and adhering fiber-reinforced polymers (FRP) to increase capacity and enhance pseudoductility. In this study, a fabric-reinforced cementitious matrix (FRCM) system is applied to URM walls to determine its feasibility as an alternative external strengthening technology. The experimental program consists of testing a total of nine clay brick walls under diagonal compression. Two FRCM strengthening reinforcement schemes are applied, namely, one and four reinforcement fabrics. An analytical model is used to calculate the shear capacity of strengthened URM walls and compare its results with the experimental database. The effect of limitations in design approach on shear capacity of strengthened walls is discussed. [ABSTRACT FROM AUTHOR]

The concept, design, and experimental validation of the new Avançon Bridge in Bex, Switzerland, are described. The lightweight glass fiber-reinforced polymer (GFRP) sandwich bridge deck adhesively bonded to steel girders, reduced the traffic disruption period by approximately 40 days or 80% compared to a cast-in-place concrete bridge, and also enabled the bridge to be widened to two lanes. The semi-integral bridge concept allows the application of a continuous asphalt layer across the abutments without expansion joints and thus facilitates and reduces maintenance. The GFRP sandwich deck with structural balsa core fulfils all the requirements concerning serviceability, ultimate limit state, and fatigue. The bridge deck dimensions significantly depended on the selected and applied design recommendation. In the case of the Avançon Bridge, the German and British recommendations provided the most conservative sets of material factors, the Dutch recommendation specified the least conservative, with the Eurocomp recommendation lying somewhere in between. In particular, the selected material factor applied to stiffness influenced the deck composition and material consumption. [ABSTRACT FROM AUTHOR]

This paper presents the uniaxial compression behavior of steel-polypropylene hybrid fiber-reinforced concrete (HFRC). A total of 30 batches of specimens with different fiber-reinforcement indices in terms of volume fraction and aspect ratio are investigated by the orthogonal experimental method. A variance analysis is conducted to obtain the optimum proportion of hybrid fiber in terms of compressive strength and corresponding peak strain. It is observed from the experimental results that the uniaxial compression behavior of plain concrete can be improved by inclusion of hybrid fibers; it is also noted that the hybrid effect between volume fraction and aspect ratio of steel fiber as well as the volume fraction of polypropylene fiber should be considered as influential factors on uniaxial compressive strength. Furthermore, in comparison to single fiber-reinforced concrete, HFRC exhibits more ductility at postpeak performance. Subsequently, the results are used to develop predictive equations for the strength, deformation, and the complete stress-strain relation of HFRC under uniaxial compression. The developed equations for compressive strength and stress-strain relationship account for the effect of varying fiber volume fractions and aspect ratios; the results obtained by the equations are found in satisfactory agreement with the experimental results. It is believed that the proposed equations can be useful for further analytical investigations and practical engineering simulations. [ABSTRACT FROM AUTHOR]

Based on the experimental background of 75 true triaxial compression tests conducted on cubic specimens, a plasticity constitutive model for hybrid steel-polypropylene fiber-RC (HFRC) is developed in this study, aiming to accurately predict the strength and deformation of HFRC under various loading scenarios. A five-parameter Willam-Warnke failure surface is modified to account for the presence of hybrid fibers. The evolution of the loading surface is characterized by uncoupled hardening and softening regimes determined by the accumulated equivalent plastic strain, and a Drucker-Prager nonassociated plastic flow is used to describe the plastic deformation. Various model parameters are mainly calibrated on the basis of true triaxial compression test data. Subsequently, the responses of the constitutive model are verified by multiaxial compression test results of both plain concrete and fiber-RC reported by various researchers. It is observed that a good estimation of the strength and the deformation capacity of HFRC with varying fiber volume fractions and aspect ratios can be achieved by the proposed model. [ABSTRACT FROM AUTHOR]

Enhancement of local soils with fibers and cement for the construction of stabilized pavement bases, canal lining, and support layers for shallow foundations shows great economical and environmental advantages, avoiding the use of borrow materials from elsewhere, in addition to the need of a spoil area. In previous studies, a unique dosage methodology for cemented soils has been established based on rational criteria in which the porosity-to-cement ratio plays a fundamental role in the assessment of the target unconfined compressive strength (). The present paper extends previous work by quantifying the influence of the amount of cement, the porosity, and the porosity-to-cement ratio in an assessment on tensile strength () and compressive strength of a fiber-reinforced artificially cemented sand, in addition to the evaluation of the relationship. A program of splitting tensile tests and unconfined compression tests considering four distinct dry densities and five cement contents, varying from 1-7%, was carried out in the research reported in this paper. The results show that a power function adapts and values well with increasing cement content and reducing porosity of the compacted mixture. The porosity-to-cement ratio is an appropriate parameter to assess both tensile strength and unconfined compressive strength of the fiber-reinforced sand/cement mixture studied. Finally, the relationship is unique for the fiber-reinforced sand/cement studied, being independent of the porosity-to-cement ratio. [ABSTRACT FROM AUTHOR]

Although abundant plastic waste contaminating the environment may be utilized as reinforcing materials, a potential pozzolanic material (rice husk ash blended with lime) possesses superior properties in stabilizing soils. Engineering behavior of the stabilized clayey/silty soil reinforced with randomly distributed discrete plastic waste fibers is investigated in this paper. The results indicate that the proposed method is very effective to improve the engineering properties of the clayey/silt soil in terms of compressive, tensile, and shear strength, which further enhanced the stability and durability of the soil. Based on the compressive strength, California bearing ratio (CBR), shear strength, and failure characteristics, the optimum amount of fiber mixed in soil/lime/rice husk ash mixtures ranges from 0.4-0.8% of the dry mass. [ABSTRACT FROM AUTHOR]

Abstract: This paper aims to investigate and model the post-cracking behavior of steel fibre reinforced concrete (SFRC) elements, which is characterized by more distributed, narrower and closely spaced cracks with respect to ordinary reinforced concrete. A numerical procedure based on non-linear fracture mechanics concepts has been developed to take into account the main mechanisms governing the problem, namely the tension softening, related to the bridging effect provided by aggregates and fibers across cracks, and the tension stiffening between steel bars and surrounding concrete. The effectiveness of the proposed approach has been then verified through comparisons with significant experimental tests available in technical literature concerning SFRC slabs, tension ties and beams. [Copyright &y& Elsevier]

In the study described here, reinforced and unreinforced specimens of reactive powder concrete were scanned using an X-ray computed tomography (CT) imaging system that allowed characterization and measurement of internal features. The X-ray CT imaging was done in conjunction with three-point bending tests of notched beam specimens. Unreinforced specimens were used to measure specific fracture energy in a way that accounts for the irregular shape of the fracture surface. For fiber-reinforced specimens, 3D digital image analysis techniques were used to measure fiber volume fraction, as well as the orientation of each individual fiber. In postfracture scans, the total amount of internal cracking was measured, as was the degree of fiber pullout relative to undamaged specimens. Measurements show that with a nominal steel fiber volume fraction between 3.5 and 4.0% there can be a greater than a 100-fold increase in the net work of load. Through quantitative analysis of the tomographic images, we could account for close to 90% of that increase. The analysis shows that roughly half of the internal energy dissipation comes from matrix cracking, including the crack branching and multiple crack systems facilitated by the fibers, while the remaining energy dissipation is a result of fiber pullout. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study on the mechanical behavior of concrete columns strengthened with fiber-reinforced polymer (FRP) and subjected to concentric and eccentric compression loading. A numerical analysis model was developed based on the effectively confined concrete area and the stress-strain relationship of the confined concrete established based on compression tests of circular plain concrete columns. The model was verified against the test results of square concentrically loaded plain concrete columns and square eccentrically loaded reinforced concrete columns. An analytical formula of the maximum compression load of square or rectangular fiber reinforced polymer strengthened concrete columns, with respect to the same but nonstrengthened columns, was developed based on the parametric study results by using the verified model. The analytical formula was further verified with the test results of 23 square and rectangular fiber reinforced polymer strengthened columns reported in the literature. Good agreement was achieved. It was found that the increase of the maximum compression load of FRP-strengthened concrete columns, with respect to the same but nonstrengthened columns, increases linearly with the amount of FRP sheets used and decreases linearly with the load eccentricity and exponentially with the concrete compression strength. The last observation implies that the FRP strengthening technique (through wrapping) is most suitable for low-strength concrete buildings. [ABSTRACT FROM AUTHOR]

Abstract: The ideal tensile stress–strain curve of ultra high toughness cementitious composites (UHTCC) shows trilinear stress–strain relationship. And its strain hardening process can be divided into multiple cracking zone and post multiple cracking zone. In this paper, the general expression of the fiber bridging stress laws in the crack plane is presented, and the stress–strain models are established for both zones based on the law. Furthermore, the critical fiber length between fiber pull-out and fiber rupture in the post multiple cracking zone are deduced. And the precondition to guarantee the post multiple cracking zone is deduced. [Copyright &y& Elsevier]

Fiber reinforcement can help to enhance soil strength, stabilize near-surface soil layers, and mitigate the risk of soil liquefaction. Evaluation of the strength of fiber-reinforced soils needs a proper failure criterion. This study presents a three-dimensional failure criterion for fiber-reinforced sand. By assuming that the total strength of the composite is a combination of the shear resistance of the host soil and the reinforcement of fibers, a general anisotropic failure criterion is proposed with special emphasis on the effect of isotropically/anisotropically distributed fibers. An anisotropic variable, defined by the joint invariant of the deviatoric stress tensor and a deviatoric fiber distribution tensor, is introduced in the criterion to quantify the fiber orientation with respect to the strain rate/stress direction at failure. With further consideration of the fiber concentration and other factors such as aspect ratio, the proposed criterion is applied to predicting the failure of fiber-reinforced sand in conventional triaxial compression/extension tests for both isotropically and anisotropically distributed fiber cases. The predictions are in good agreement with the test results available in the literature. The practical significance of using this criterion for such problems as inclined slope stabilization is briefly discussed. [ABSTRACT FROM AUTHOR]

Several models have been suggested to estimate the improvement brought by fibers to the shear strength of fiber-reinforced sands. To date, the effectiveness and reliability of these models have not been the subject of a comprehensive evaluation. The objectives of this paper are to (1) compile the experimental data available in the literature on the behavior of fiber-reinforced sands into a comprehensive state-of-the-art database, (2) quantify the model uncertainty and bias of current strength prediction models for fiber-reinforced sands, and (3) provide insight regarding possible modifications that could be made to the formulation of available models to improve their predictive effectiveness and reduce their model uncertainty. Two models that are considered to present the best available approaches to predicting sand-fiber shear strength were evaluated, namely, the 'energy-based' model and the 'discrete' model. The energy-based model was found to underestimate the measured friction coefficient on average by about 10%, while the discrete model overestimated the friction coefficient by 6%, with associated coefficients of variation on bias values of 0.20 and 0.17, respectively. With the introduction of minor modifications to these models, the average bias error was eliminated, and the coefficients of variation in the ratio of predicted to measured shear strength (bias) were reduced to 0.17 and 0.12, respectively, for the two models. [ABSTRACT FROM AUTHOR]

Crack propagation in strengthened concrete disks is a problem that has not yet been addressed properly. To investigate it, a cracked half-infinite disk of concrete is strengthened with a linear elastic material bonded to the surface, and analyzed using two different finite element modeling approaches. The first method is 3D modeling of strengthening, interface and disk, and the second method is modeling of an equivalent disk in 2D, with an effective cohesive crack, equivalent thickness and equivalent stiffness. The 2D modeling approach simplifies modeling of the problem significantly and reduces the computational efforts and time. A good prediction of the cracking response, global response and load was obtained with the 2D model, whereas prediction of the size and shape of the interface debond was only approximate. It is concluded that the effective cohesive modeling approach can be used instead of 3D calculations to predict the response of a structure and that it opens up for simpler evaluation of strengthened concrete structures using the finite element method. [ABSTRACT FROM AUTHOR]

Abstract: Delamination is one of the most critical damage mechanisms in laminated composites. A fracture test, referenced in the following as Tensile Flexure test on Notched Specimen, is proposed in this work to characterize the propagation of delamination. After the description of the experimental procedure, experimental results on carbon/epoxy specimens are presented to describe the capabilities and advantages of the test to characterize delamination. Then, a new propagation law is proposed to describe the evolution of the fracture toughness. Finally, a non-deterministic analysis is performed to determine the influence of the measured parameters on the toughness identification. [Copyright &y& Elsevier]

Abstract: This article deals with the effective dynamic behavior of elastic materials periodically reinforced by stiff linear slender elastic inclusions. By assuming a small scale ratio between the period section size and the characteristic size of the system global strain, and by weighing the constituents stiffness contrast by powers of , the dynamic macroscopic behavior at the leading order is derived through the asymptotic homogenization method of periodic media considering different frequency ranges. A two order stiffness contrast () is shown to lead to a dynamic macroscopic behavior spatially non-local in the transverse direction, where the system behaves as a generalized inner bending continuum, and temporally non-local in the axial direction, where the system behaves, at higher frequency, as a metamaterial in which internal resonance phenomena take place. The consequences of such non-localities on the reinforced medium modes are examined. The system axial and transverse modes are shown to be significantly different from those of usual composites. [Copyright &y& Elsevier]

In Part I of this two-part study, a theory is provided for the extension of the lattice discrete particle model (LDPM) to include fiber reinforcing capability. The resulting model, LDPM-F, is calibrated and validated in the present paper by comparing numerical simulations with experimental data gathered from the literature. The analyzed experiments include direct tension, confined and unconfined compression, and notched three-point bending tests. [ABSTRACT FROM AUTHOR]

Abstract: The structural potential for cracking of externally strengthened concrete tension members, can be predicted with three parameters, describing the structural cracking potential based on fracture mechanical properties of the of concrete and interface between concrete and strengthening medium. With these parameters, it is possible to design reinforcement and obtain a required cracking behavior of a given structure. Design recommendations for single and multiple cracking of the tension specimen are given in terms of fracture mechanical parameters, and a structural stiffness parameter. [Copyright &y& Elsevier]

This paper reviews progress in acoustic emission (AE) research and its applications to high performance composite materials and structures. The achievement and inadequacy in understanding of AE from composites are examined along with cases of successful usage in commercial and aerospace fields, taking into account limitations due to high attenuation and anisotropy. New goals for the future are also discussed in view of new analytical tools and vastly advanced instrumentation. [ABSTRACT FROM AUTHOR]

A concrete tension member strengthened with fiber reinforced polymer plates on two sides is analyzed with non-linear fracture mechanics. The analysis of the strengthened tension member incorporates cohesive properties for both concrete and interface between concrete and strengthening medium, and results in closed form solutions for the load-crack opening relationship. To distinguish between single and multiple cracking in a design process, structural classification parameters are derived. The minimum reinforcement ratio for obtaining multiple cracking derived from the structural classification parameters, is investigated in a non-dimensional analysis, and found to depend strongly on the ratio between interfacial and concrete fracture energies. [ABSTRACT FROM AUTHOR]

Abstract: We provide a simple proof of the bifurcation criteria for a membrane cylinder subjected to combined axial loading and internal pressure. Three modes of bifurcation are discussed: a prismatic mode, a bulging mode and a composite mode. The bulging mode of bifurcation is further exploited in the context of aneurysm formation with cylindrical geometry in cardiovascular diseases. In particular, the bulging mode is taken as the initiation of aneurysm formation. The role that the collagen fibers inside the arterial walls play is established. It is shown that healthy collagen fibers stabilize the artery and avoid aneurysm formation. Collagen fibers give the anisotropic character to the mechanical response of arteries. The presence of these fibers also give rise to the so called strain stiffening mechanism. We show here that loss of tissue anisotropy associated with a strain softening mechanism of the collagen fibers may play an important role in the initiation of aneurysms. [Copyright &y& Elsevier]

Pavement systems provide critical infrastructure services to society but also pose significant impacts related to large material consumption, energy inputs, and capital investment. A life-cycle model was developed to estimate environmental impacts resulting from material production and distribution, overlay construction and preservation, construction-related traffic congestion, overlay usage, and end of life management. To improve sustainability in pavement design, a promising alternative material, engineered cementitious composites (ECC) was explored. Compared to conventional concrete and hot-mixed asphalt overlay systems, the ECC overlay system reduces life-cycle energy consumption by 15 and 72%, greenhouse gas emissions by 32 and 37%, and costs by 40 and 47%, respectively. Material, construction-related traffic congestion, and pavement surface roughness effects were identified as the greatest contributors to environmental impacts throughout the overlay life cycle. The sensitivity analysis indicated that traffic growth has much greater impact on the life-cycle energy consumption and environmental impacts of overlay systems compared to fuel economy improvements. [ABSTRACT FROM AUTHOR]