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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]

Ultrahigh toughness cementitious composite (UHTCC) is a new class of high performance fiber-reinforced cementitious composites which exhibits pseudostrain hardening and multiple cracking phenomena. The main objectives of this paper are to investigate the compressive properties of UHTCC and to develop the constitutive models to describe it. The complete study includes an experimental phase and an analytical phase. In the experimental phase, the stress-strain curves were directly obtained, and the compressive parameters, i.e., strength, average strain at maximum stress, elastic modulus, and Poisson's ratio, were calculated. The relationships of compressive parameters as a function of compressive strength were proposed according to the test results. The comparisons between UHTCC and matrix were carried out to understand the fiber effect on the compressive parameters. In the theoretical phase, comparisons were conducted between experimental results and existing models. As a result, two analytical relationships were proposed for design purpose under ultimate limit state conditions and nonlinear analysis of UHTCC structures. The research should lead to better understand the compressive properties of UHTCC and the mechanisms of fiber reinforcement for UHTCC and to provide analysis models for design or analysis of UHTCC structural members. [ABSTRACT FROM AUTHOR]

This paper presents tests that were performed on square large-scale steel-fiber-reinforced high-strength concrete (HSC) columns under concentric compression loading. The experimental program was mainly designed to examine the effect of the volumetric steel-fiber ratio on the behavior of reinforced HSC large-scale elements subjected to axial compression loading. The test program was also designed to examine the combined confinement effect of steel fibers and transverse steel reinforcement. Thus, the test variables studied herein are the steel-fiber volumetric ratio and the volumetric ratio, yield strength, and spacing of the transverse steel ties. The results show that adding discrete fibers to HSC mixtures in reinforced concrete columns not only prevents the premature spalling of the concrete cover but also increases the strength and ductility of the axially loaded reinforced member. This behavior was predicted by the proposed fiber-reinforced concrete stress-strain model, which takes into account most of the parameters that influence confinement effectiveness: the concrete strength; the spacing, yield strength, volumetric ratio, and configuration of the transverse reinforcement; the distribution of the longitudinal reinforcement; and the diameter, length, shape, volumetric ratio, and frictional bond strength of the fibers. Predictions were found to be in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

The “Design Research Laboratory (DRL)-10 space pavilion” has been built in the early 2008 on Bedford Square, London, on the occasion of the 10th anniversary of the DRL Department at the Architectural Association Architecture School. The pavilion has been a great success and it has attracted huge interest in the architectural scene as well as in the general public. The pavilion consists of 850 individually cut fiber reinforced panels and over 2,000 joints. Its complex geometry was controlled by architects Alan Dempsey and Alvin Huang using a highly parametrized digital model. This paper is written from the point of view of the structural engineer, challenged not only by the complex geometry but also by the rather uncommon application of fiber reinforced concrete as a construction material. Physical tests on the proprietary fiber-C elements by Austrian firm Rieder as well as tests on their joints are described. Further, the paper gives information on the structural model and insight to a number of structural options that have been investigated during the design process. [ABSTRACT FROM AUTHOR]

This article presents the implementation of a new inelastic damage model able to carry out simulation of initiation and evolution of damage in the Z-pinned laminated composite structures with friction effects. The classical elastic damage model is modified to an inelastic model with friction effects obeying the simple Coulomb friction criterion. The main idea is the modification of strain energy parameter by introducing sliding and friction parameters. The simulations of single Z-fiber pull tests highlight the effectiveness of the proposed model for micro-scale predictions. [ABSTRACT FROM AUTHOR]

Distributed optical fiber strain sensors have attracted increasing attention in research and applications related to civil engineering because no other tools can satisfactorily detect the locations of unpredictable events. For instance, for crack detection, it is necessary to employ a fully distributed sensor because crack locations are a priori unknown. The Brillouin optical correlation domain analysis (BOCDA) system, a distributed sensor that offers high spatial resolution by using stimulated Brillouin scattering, has undergone significant development over the last decade, during which it has been used in a wide range of civil engineering applications. In this paper, we demonstrate how a BOCDA-based optical fiber strain sensor can be employed to monitor cracks in fiber-reinforced concrete. Crack monitoring is important for checking the structure of such high-performance concrete, which has enhanced strength and toughness since it incorporates fibers. In particular, early detection of tiny cracks is essential for preventing crack growth and dispersion. We carried out a concrete beam-bending test to detect crack-induced strain distribution during loading. For this purpose, we employed an improved BOCDA system that provides enhanced measurement length with high spatial resolution; hence, BOCDA can detect a tiny crack before visual recognition. Moreover, we demonstrate a field application of the BOCDA system to ensure a flawless pedestrian deck made of fiber-reinforced concrete. [ABSTRACT FROM AUTHOR]

There is a renewed interest in using steel fiber reinforcement within the critical hinging regions of reinforced concrete (RC) members as a means for improving their seismic response. Examples include beam-column joints, structural walls, and shear walls coupling beams. The presence of steel fiber reinforcement in these regions confines the concrete, improves the bond strength of the steel bars, and reduces the bond degradation, leading to reduced damage and increased energy absorption and dissipation capacities under cyclic loading. This paper presents a synthesis of the results of a series of experimental and analytical investigations undertaken by the writer on the use of steel fiber reinforcement for improving the bond capacity and bond stress-slip response of steel bars under static and cyclic loading and its implication on the static and seismic response of RC members. The experimental results are discussed, a design expression for evaluating the effect of fiber reinforcement on the bond or development/splice strength of steel bars in tension is described, and a new model of the local bond stress-slip response under generalized (cyclic) excitations is presented. [ABSTRACT FROM AUTHOR]

In recent years, advanced fiber-reinforced polymer (FRP) composites have been steadily developed and used in a wide spectrum of infrastructure applications. It is, however, recognized that many polymer resins soften rapidly when heated above 82°C(180°F). Hence fire vulnerability may become a future obstacle with the widespread use of FRP materials. In this paper, initial findings from an on-going project, aimed at developing temperature-resistant cement-based composite sheets for structural retrofit, were reported. Following a similar installation procedure to that of FRP sheets, it is essential to examine the effect of mix compositions on the rheological properties of the cement slurry and to develop suitable cement slurries for making thin fiber-reinforced cement sheets on the job sites. Retrofit efficiency of using both epoxy-based and cement-based thin sheets is investigated. Preliminary results are presented and discussed in this paper. It is confirmed that cement sheets could be very likely made in situ and provide a similar retrofit capacity to their FRP counterparts. [ABSTRACT FROM AUTHOR]

In steel fiber-reinforced composites materials, fiber and matrix are bonded together through a weak interface. The study of this interfacial behavior is important for understanding the mechanical behavior of such composites. Moreover, with the outcome of new composites materials with improved mechanical properties and advanced cement matrices, such in the case of steel fiber reinforced self-compacting concrete, the study of the fiber/matrix interface assumes a new interest. In the present work, experimental results of both straight and hooked-end steel fibers pullout tests on a self-compacting concrete medium are presented and discussed. Emphasis is given to the accurate acquirement of the pullout load versus end-slip relationship. The influence of fiber embedded length and orientation on the fiber pullout behavior is studied. Additionally, the separate assessment of the distinct bond mechanisms is performed, by isolating the adherence bond from the mechanical bond provided by the hook. Finally, analytical bond-slip relationships are obtained by back-analysis procedure with an interfacial cohesive model. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) materials possess inherently high strength-to-weight ratios, but their effective elastic moduli are low relative to civil engineering (CE) construction materials. While elastic modulus may be comparable to that of some CE materials, the lower shear modulus adversely affects stiffness. As a result, serviceability issues are what govern GFRP deck design in the CE bridge industry. An innovative solution to increase the stiffness of a commercial GFRP reinforced-sinusoidal honeycomb sandwich panel was proposed; this solution would completely replace the GFRP honeycomb core with a hexagonal honeycomb core constructed from commercial steel roof decking. The purpose of this study was to perform small-scale tests to characterize the steel hexagonal honeycomb core equivalent elastic moduli in an effort to simplify the modeling of the core. The steel core equivalent moduli experimental results were compared with theoretical hexagonal honeycomb elastic modulus equations from the literature, demonstrating the applicability of the theoretical equations to the steel honeycomb core. Core equivalent elastic modulus equations were then proposed to model and characterize the steel hexagonal honeycomb as applicable to sandwich panel design. The equivalent honeycomb core will enable an efficient sandwich panel stiffness design technique, both for structural analysis methods (i.e., hand calculations) and finite-element analysis procedures. [ABSTRACT FROM AUTHOR]

Abstract: Formation of initial delaminations and growth of existing delaminations in L-shaped laminates made of plies of a unidirectional carbon fiber reinforced epoxy resin is investigated computationally and experimentally. For this purpose an experimental test is designed which allows to realize load states for which delamination is the dominant failure mechanism. Two types of test specimens, with and without initial delaminations, are investigated and good agreement is obtained between the computational predictions and the experimental results concerning delamination emergence, delamination growth, growth stability, the structural response, and the maximum principal strains. [Copyright &y& Elsevier]

Two 381 mm (15 in. nominal) diameter fiber reinforced cement pipes have been tested under embankment loading conditions to study pipe response in both low stiffness, fine grained backfill, and a high stiffness graded granular backfill. Pipe deformations and strains were measured and interpreted to provide insight into the effect of soil backfill on the deformations and moments that develop. Not surprisingly, the use of silty clay backfill resulted in greater pipe deflections while the stiffer granular backfill lead to greater load transfer to the surrounding ground. Calculations using elastic soil-pipe interaction theory were effective in estimating the observed changes in pipe diameter at typical service loads (overburden pressures of 100 kPa, i.e., 14.4 psi in the lower stiffness backfill and 200 kPa, i.e., 28.8 psi in the high stiffness backfill). Measured strain distributions show that the fiber reinforced pipe exhibited ovaling response similar to that seen for flexible and semiflexible pipes. As expected, tensile strains were observed on the outer surface at the springlines and the inner surface at the crown. Strains observed at the haunch were negligible, indicating that the bending moments within the pipe have conventional “hourglass” distribution, with negligible moments at shoulders and haunches. Differences in strain measured at the inner and outer surfaces were used with the elastic pipe modulus to calculate the experimental bending moments. Comparisons of those experimental bending moments with the bending moment calculated for a rigid pipe indicate that these FRC pipe structures are semirigid so that moments are reduced as a result of support provided by the surrounding soil. A design expression for moment arching factor (MAF or moment divided by the rigid pipe moments) developed in an earlier paper was found to provide reasonable estimates for the experimental moment values. Moment estimated using the design soil moduli of McGrath and MAF provide moment values that are reasonable and conservative relative to those that were observed. [ABSTRACT FROM AUTHOR]

Thermal buckling analysis of laminated smart composite plates subjected to uniform temperature distribution has been presented. Shape memory alloy (SMA) fibers whose material properties depend on temperature have been used as a smart material. A three-dimensional layerwise plate model has been employed in developing the system equations using variational approach. Finite-element method has been adopted for discretization of the laminate. Lagrangian interpolation functions have been used to approximate the displacement components along the thickness as well as in the in-plane direction. The actual variation of prebuckling stresses has been accounted for in the derivation of the geometric stiffness matrix of the laminates. An incremental load technique has been used in the analysis to take into account the nonlinearity in the material properties of the SMA arising due to their temperature dependence. The effects of thickness ratio, orthotropic ratio, fiber orientation, aspect ratio, stacking sequence and various boundary conditions on the critical buckling temperature have been examined in details. The results have been validated with those available in the literature. [ABSTRACT FROM AUTHOR]

In recent years, research has been devoted to the control of permanent deformations in flexible pavements. In order to prevent rutting, fatigue, and low-temperature cracking, different types of polymer modifiers have been utilized. The use of polypropylene (PP) fibers as a modifier in pavement mix that can be found locally and at low cost compared to other modifiers is an attractive option. This paper reports on the Marshall design and the optimum bitumen content for asphalt concrete with the addition of polypropylene fibers. Different types of PP fibers were used in order to determine the optimum bitumen content and the optimal PP fiber dosage. Marshall specimens were tested using the universal testing machine to determine the creep behavior of dense bituminous mixtures under repeated loading. The results from the analysis of the tested specimens show that the addition of polypropylene fibers improves the behavior of the specimens by increasing the life of samples under repeated creep testing. [ABSTRACT FROM AUTHOR]