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Additive manufacturing of composites offers advantages over metals since composites are lightweight, fatigue and corrosion-resistant, and show high strength and stiffness. This work investigates the tensile and flexural performance of continuous carbon-fiber reinforced (CCF) composites with different guide angles and number of layers. The cost and printing time analyses were also conducted. Tensile specimens with a contour-only specimen and one CCF layer with a 0° guide angle exhibited nearly comparable strength values. Increasing the number of CCF layers enhances the tensile properties. For the identical cost and reinforcement amount, 0°/0° provides a higher tensile strength and elastic modulus compared with 15°/−15°. The same phenomenon was observed for 15°/0°/−15° and 0°/0°/0°. The samples with one and two reinforcement layers had similar stiffness and maximum load values for flexural tests. For the samples with four layers, there was a considerable improvement in stiffness but a minor decrease in the maximum load. [ABSTRACT FROM AUTHOR]

Adding cement to soft soils may lead to brittle behavior and the occurrence of sudden damage. Methods to further improve the tensile and flexural properties of cemented clay are noteworthy topics. This paper mainly focuses on the effect of cement and moisture content on the strength and flexural properties of cemented clay reinforced by PVA fiber. The selected clayey soil was a kaolin with cement content of 5%, 10%, and 15% and moisture content of 50%, 56%, 63%, and 70%. The results show that the incorporation of 0.6% fiber can effectively improve the deformability of cemented clay in unconfined compression tests (UCS). The strengthening effect of fiber, as seen in the peak strength and post-peak strength of UCS, was significantly related to cement content. As the water content increased, the compressive strength of the fiber-reinforced cemented clay decreased, but its load-bearing capacity enhanced. When the cement content was 15%, the splitting tensile strength of fiber-reinforced cemented specimens increased by 11% compared to cemented soil, but the deformability of the specimens became poor. In the cement-content interval from 5% to 10%, the bending toughness was significantly improved. Sufficient cement addition ensures the enhancement of PVA fibers on strength and flexural properties of cement-stabilized clayey soil. [ABSTRACT FROM AUTHOR]

There is no unified method for deriving the tensile properties of fiber-reinforced ultra-high-performance cementitious composites (UHPCC). This study compares the most common material tests based on a large series of laboratory tests performed on a self-developed UHPCC mixture. The cementitious matrix, with a compressive strength of over 150 MPa and a matrix tensile strength of 8–10 MPa, was reinforced with 2% by volume of 15 mm long and 0.2 mm diameter straight high-strength steel microfibers. Over 100 uniaxial tensile tests were performed on three test configurations using cylindrical cores drilled out from larger prismatic specimens in three perpendicular directions. In addition to uniaxial tests, flexural tests on prismatic elements and flexural tests on thin plates were conducted, and the tensile properties were derived through digital image correlation (DIC) measurements and inverse analysis. Furthermore, splitting tensile tests on cylindrical specimens were employed to ascertain the tensile properties of the matrix. The outcomes of the diverse laboratory tests are presented and discussed in detail. The relationships between crack width and deflection in the context of flexural tests were developed and presented. In conjunction with compression tests and modulus of elasticity tests, the constitutive law is presented for the investigated materials. [ABSTRACT FROM AUTHOR]

The increasing utilization of Fiber-Reinforced Concrete (FRC) within the construction industry signifies a pivotal shift towards enhancing structural integrity and durability. Despite the predominant use of steel fibers, exploring macro synthetic fibers has gained momentum due to their potential to address critical challenges, such as workability reduction and corrosion resistance in FRC, without markedly affecting its structural performance. Among the forefronts of FRC research is developing an accurate constitutive model encompassing the diverse behavior of fibers, particularly synthetic ones. This discrepancy necessitates a distinct constitutive model for synthetic fibers to precisely characterize their tensile postcracking behavior and regulate their design specifications. In this research, a preliminary constitutive model is derived through an inverse analysis procedure employing a Generalized Reduced Gradient (GRG) optimization method to the load-displacement results of the experimental testing of twenty ASTM C1609 beam samples. The results of the inverse analysis are used to correlate the ASTM C1609 residual flexural tensile strength parameters, fL/600 and fL/150 to the stress-strain points defining the uniaxial tensile curve of macro-synthetic fibers, achieving coefficients of determination exceeding 98.5%. The model is statistically confirmed to be a valid constitutive relation for macro-synthetic fibers via successfully representing the post-cracking load-deflection behavior of standardized concrete beams, thereby outperforming traditional constitutive models in simulating the post-cracking behavior of FRC. Moreover, the model demonstrates robust predictive capabilities for the load-deflection curve of externally standardized samples, showcasing its potential for broader application in FRC design and analysis. [ABSTRACT FROM AUTHOR]

Additive manufacturing of composites offers advantages over metals since composites are lightweight, fatigue and corrosion-resistant, and show high strength and stiffness. This work investigates the tensile and flexural performance of continuous carbon-fiber reinforced (CCF) composites with different guide angles and number of layers. The cost and printing time analyses were also conducted. Tensile specimens with a contour-only specimen and one CCF layer with a 0° guide angle exhibited nearly comparable strength values. Increasing the number of CCF layers enhances the tensile properties. For the identical cost and reinforcement amount, 0°/0° provides a higher tensile strength and elastic modulus compared with 15°/−15°. The same phenomenon was observed for 15°/0°/−15° and 0°/0°/0°. The samples with one and two reinforcement layers had similar stiffness and maximum load values for flexural tests. For the samples with four layers, there was a considerable improvement in stiffness but a minor decrease in the maximum load.

This paper presents an experimental study on the behaviour of notched connectors with a dovetail shape. A series of three symmetrical push-out tests on connection specimens and a series of two full-scale flexural tests on slab specimens were carried out. The test results of the push-out tests showed high shear resistance and stiffness of the connectors. However, the ductility of the connectors was low, as the failure mode was governed by the shear failure of the cross layer of the CLT. In addition, it was shown in the flexural test results that the design of the composite slab is not limited by the flexural bearing capacity as a high value of the maximum bending moment was obtained in the tests. It is instead governed by the deflection of the composite slab. Besides, a modified gamma method was used to estimate the mid-span deflections and compared with the ones obtained from the flexural tests. A good agreement was obtained, validating the use of the method to estimate the stiffness of the CLT-concrete slab with Dovetail notched connection. In addition, a beam grid model was also employed in order to take into account the stiffness of the slab in the transversal direction. [ABSTRACT FROM AUTHOR]

A novel type of traditional composite member-unbonded prestressed I-shaped steel encased in a UHPC (PSRUHPC) beam is proposed to reduce the brittleness of UHPC beams and improve their bearing capacity. A PSRUHPC beam, an unbonded prestressed UHPC (PRUHPC) beam, and an I-shape steel UHPC (SRUHPC) beam were manufactured, and their flexural static performances were assessed using a flexural comparison test. The test results reveal that the flexural process of the PSRUHPC beam is similar to that of ordinary reinforced concrete beams, and UHPC crushing in the compression zone is a sign of failure. Due to the bridge coupling effect of steel fiber, the crushed concrete still maintains good integrity without bursting, the UHPC in the tension zone remains functional after cracking, and the cracking inflection point of the load–deflection curve was not obvious. The PSRUHPC beam showed a significantly improved bearing capacity and flexural stiffness, its load–deflection curve exhibited significantly more energy consumption, and its bending ductility performance was improved, with better deformation properties. Compared with PRUHPC beams, PSRUHPC beams show a bearing capacity increase of 55.3%, a cracking load increase of 11.9%, and a displacement ductility coefficient increase of 76.2%. Compared with SRUHPC beams, PSRUHPC beams show a 15.4% increase in bearing capacity, a 50.2% increase in cracking load, and a 12.1% increase in displacement ductility coefficient. The application of prestress can significantly improve the stiffness of the beam prior to cracking. The cracking loads of prestressed ordinary concrete beams and steel-reinforced concrete beams account for 20–30% of their ultimate loads, which value was 40–50% for the tested beams. The change trend of strain in the section steel and UHPC is roughly the same at the same height, and the strains of the two deviated after most of the section steel yielded under tension, but they can generally work together. When the tested beams were cracked, multiple cracks appeared, which were fine and dense. The magnetic flux sensor cable force-monitoring system can better monitor the strand stress increment of unbonded prestressed steel UHPC beams, where the prestressed strand did not yield tension under the final state; the load–strand stress increment curve was basically the same as the load–deflection curve, and the stress increment of the unbonded steel strand positively correlated with the midspan deflection. Finite element simulation was used to verify the test results, and we determined the reinforcement ratios for non-prestressed and prestressed reinforcement, as well as the ratio of a steel-containing section, the effective prestress, the height of prestressed reinforcement, the position and strength of I-shaped steel, and whether or not the prestressed reinforcement was bonded. The effects of these parameters on the bearing capacity and displacement ductility coefficient of PSRUHPC beams were studied. The results can provide a reference for subsequent theoretical design calculations. [ABSTRACT FROM AUTHOR]

There is no unified method for deriving the tensile properties of fiber-reinforced ultra-high-performance cementitious composites (UHPCC). This study compares the most common material tests based on a large series of laboratory tests performed on a self-developed UHPCC mixture. The cementitious matrix, with a compressive strength of over 150 MPa and a matrix tensile strength of 8–10 MPa, was reinforced with 2% by volume of 15 mm long and 0.2 mm diameter straight high-strength steel microfibers. Over 100 uniaxial tensile tests were performed on three test configurations using cylindrical cores drilled out from larger prismatic specimens in three perpendicular directions. In addition to uniaxial tests, flexural tests on prismatic elements and flexural tests on thin plates were conducted, and the tensile properties were derived through digital image correlation (DIC) measurements and inverse analysis. Furthermore, splitting tensile tests on cylindrical specimens were employed to ascertain the tensile properties of the matrix. The outcomes of the diverse laboratory tests are presented and discussed in detail. The relationships between crack width and deflection in the context of flexural tests were developed and presented. In conjunction with compression tests and modulus of elasticity tests, the constitutive law is presented for the investigated materials.

The traditional fishing vessels in Indonesia are usually made of wood material. The weakness of this vessel material is that it is easily weathered when exposed to seawater. For this reason, it is necessary to have vessel material engineering from composite sandwiches. This study aimed to prepare and investigate the flexural test, impact test, optical microscopy (OM), and scanning electron microscopy (SEM) observations of sandwich composites based on coconut fibre-polyester resin and wood core. The fabrication uses a hand lay-up method with a constant volume fraction (20% coconut coir fibre) and wood core variations type. The primary wood variations used are albizia chinensis, mahogany, shorea, and camphor. The Surface modification of fibre and wood core was conditioned without treatment and with treatment with about 5% NaOH solution for 2 hours. The study showed that the highest bending and impact strength was sandwich composite with camphor wood cores with alkali treatment for 39.75 MPa and 37.22 J/cm², respectively. The OM observations showed that the core and skin interface area failed to delaminate after flexural and impact tests. SEM observations also showed that the bond alkalization treatment between the matrix and the fibres was quite good. In the composite skin fracture area, there is a lot of fibre brake, and a little thread pulls out. The skin matrix also shows the presence of voids. Generally, this sandwich composite is feasible for application as a material for traditional fishing vessels. [ABSTRACT FROM AUTHOR]

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Non-biodegradability of rubber tires contributes to pollution and fire hazards in the natural environment. In this study, the flexural behavior of the Rubberized Reactive Powder Concrete (RRPC) beams that contained various proportions and sizes of scrap tire rubber was investigated and compared to the flexural behavior of the regular RPC. Fresh properties, hardened properties, load-deflection relation, first crack load, ultimate load, and crack width are studied and analyzed. Mixes were made using micro steel fiber of the straight type, and they had an aspect ratio of 65. Thirteen beams were tested under two loading points (Repeated loading) with small-scale beams (1100 mm, 150 mm, 100 mm) size. The fine aggregate is replaced by 5, 10, and 15%, respectively, with crumb rubber. While replacement of silica fume was 10, 20, 30, and 50%, respectively, with very fine rubber. Also, chip rubber was added to the mixture as coarse aggregate with 5, 10, and 15%. Five tested beams were chosen as case studies to analyze and compare the results of the ABAQUS software with the experimental results. The results showed that the flexural behavior of RRPC beams that contains rubber was acceptable when compared with the flexural behavior of the RPC beam (depending on load-carrying capacity). The crack width was decreased by including waste rubber and steel fibers. There is a satisfactory agreement between the results of the numerical analysis and the results of the experimental testing. Slight ultimate load differences are targeted between the effects of the monotonic loading and the repeated loading.

Prefabricated internal structures of road tunnels, consisting of precast elements and the connections between them, provide advantages in terms of quality control and manufacturing costs. However, the limited construction space in tunnels creates challenges for on-site assembly. To identify feasible connecting joints, flexural tests of precast straight beams connected by welding-spliced or lap-spliced reinforcements embedded in normal concrete or ultra-high-performance fiber-reinforced concrete (UHPFRC) are first performed and analyzed. With an improvement in the strength grade of the closure concrete for the lap-spliced joint, the failure of the beam transforms from a brittle splitting mode to a ductile flexural mode. The beam connected by UHPFRC100 with short lap-spliced reinforcements can achieve almost equivalent mechanical performance in terms of the bearing capacity, ductility, and stiffness as the beam connected by normal concrete with welding-spliced reinforcements. This favorable solution is then applied to the connection of neighboring updeck slabs resting on columns in a double-deck tunnel. The applicability is validated by flexural tests of T-shaped joints, which, fail in a ductile fashion dominated by the ultimate bearing capacity of the precast elements, similar to the corresponding straight beam. The utilization of UHPFRC significantly reduces the required lap-splice length of reinforcements owing to its strong bonding strength. [ABSTRACT FROM AUTHOR]

In this work, the effects of intra-layer hybridization on the flexural properties and failure mechanisms of composite laminates were experimentally and numerically investigated. Test specimens were prepared via the thermo-forming technique with plain woven fabrics reinforced using net carbon, glass, and their intra-layer hybrids. The force–displacement curves, failure modes, and flexural properties were analyzed and compared. The experimental results revealed that the catastrophic failure modes of carbon fiber-reinforced composite laminates can be improved after hybridization with glass fibers. However, the flexural properties of the composite laminates, such as flexural strength and modulus, depended on the type of fiber along the longitudinal (i.e., load-carrying) direction. A higher flexural strain can be obtained by replacing the longitudinal carbon fiber yarns with glass fiber ones. Subsequently, finite element models that considered the inter-layer and intra-layer deformation behaviors were established and validated with the tested results. The maximum error between the experimental and predicted flexural properties was 6.15%. The fracture process and stress distribution of the specimens were predicted and analyzed to understand the failure mechanisms. Notably, it was observed that intra-layer hybridization critically affected the transverse stress distribution state across the thickness of the composites, which resulted in complicated failure behaviors among adjacent fiber yarns. Finally, the effects of interfacial properties on the flexural responses were simulated and analyzed. [ABSTRACT FROM AUTHOR]

Encasing glass fiber reinforced polymer (GFRP) beam with reinforced concrete (RC) improves stability, prevents buckling of the web, and enhances the fire resistance efficiency. This paper provides experimental and numerical investigations on the flexural performance of RC specimens composite with encased pultruded GFRP I-sections. The effect of using shear studs to improve the composite interaction between the GFRP beam and concrete was explored. Three specimens were tested under three-point loading. The deformations, strains in the GFRP beams, and slippages between the GFRP beams and concrete were recorded. The embedded GFRP beam enhanced the peak loads by 65% and 51% for the composite specimens with and without shear connectors, respectively. Moreover, a non-linear Finite Element (FE) model was developed and validated by the experimental results to conduct a parametric study. The peak loads of the composite specimen without shear studs increased by 14% and 31% and of the composite specimen with shear studs increased by 20% and 32% for the compressive strength of 35 MPa and 45 MPa, respectively. [ABSTRACT FROM AUTHOR]

A novel type of traditional composite member-unbonded prestressed I-shaped steel encased in a UHPC (PSRUHPC) beam is proposed to reduce the brittleness of UHPC beams and improve their bearing capacity. A PSRUHPC beam, an unbonded prestressed UHPC (PRUHPC) beam, and an I-shape steel UHPC (SRUHPC) beam were manufactured, and their flexural static performances were assessed using a flexural comparison test. The test results reveal that the flexural process of the PSRUHPC beam is similar to that of ordinary reinforced concrete beams, and UHPC crushing in the compression zone is a sign of failure. Due to the bridge coupling effect of steel fiber, the crushed concrete still maintains good integrity without bursting, the UHPC in the tension zone remains functional after cracking, and the cracking inflection point of the load–deflection curve was not obvious. The PSRUHPC beam showed a significantly improved bearing capacity and flexural stiffness, its load–deflection curve exhibited significantly more energy consumption, and its bending ductility performance was improved, with better deformation properties. Compared with PRUHPC beams, PSRUHPC beams show a bearing capacity increase of 55.3%, a cracking load increase of 11.9%, and a displacement ductility coefficient increase of 76.2%. Compared with SRUHPC beams, PSRUHPC beams show a 15.4% increase in bearing capacity, a 50.2% increase in cracking load, and a 12.1% increase in displacement ductility coefficient. The application of prestress can significantly improve the stiffness of the beam prior to cracking. The cracking loads of prestressed ordinary concrete beams and steel-reinforced concrete beams account for 20–30% of their ultimate loads, which value was 40–50% for the tested beams. The change trend of strain in the section steel and UHPC is roughly the same at the same height, and the strains of the two deviated after most of the section steel yielded under tension, but they can generally work together. When the tested beams were cracked, multiple cracks appeared, which were fine and dense. The magnetic flux sensor cable force-monitoring system can better monitor the strand stress increment of unbonded prestressed steel UHPC beams, where the prestressed strand did not yield tension under the final state; the load–strand stress increment curve was basically the same as the load–deflection curve, and the stress increment of the unbonded steel strand positively correlated with the midspan deflection. Finite element simulation was used to verify the test results, and we determined the reinforcement ratios for non-prestressed and prestressed reinforcement, as well as the ratio of a steel-containing section, the effective prestress, the height of prestressed reinforcement, the position and strength of I-shaped steel, and whether or not the prestressed reinforcement was bonded. The effects of these parameters on the bearing capacity and displacement ductility coefficient of PSRUHPC beams were studied. The results can provide a reference for subsequent theoretical design calculations.

Growing public environmental awareness leads to an increased focus on utilizing green and sustainable materials in infrastructure construction. Geopolymer concrete (GPC) and basalt macro fibres (BMFs) are promising construction materials due to their eco-friendly merits and excellent mechanical properties. In this study, a new type of BMFs reinforced GPC (BMF-GPC) was developed, and the compressive and flexural properties of BMF-GPC were investigated. The effects of BMF content and length on the mechanical properties of GPC were studied. It was found that with the addition of 2 % BMFs, the compressive and flexural toughness (energy absorption capacities) of GPC were greatly enhanced by up to 126 % and 965 %, respectively. Increasing the content and length of BMFs resulted in favourable outcomes for strain softening of GPC under compression and post-cracking behaviour of GPC under flexural loads, whilst having limited effects on the modulus of elasticity and flexural strength. Additionally, an analytical model was proposed to predict the compressive stress-strain behaviour of BMF-GPC, which could be used for the design of BMF-GPC structures. • New Basalt Macro Fibre reinforced Geopolymer Concrete (BMF-GPC) is proposed. • Compressive and flexural properties of BMF-GPC are revealed. • Effects of BMF content and length on mechanical properties are examined. • Analytical model is proposed to predict its compressive stress-strain behaviour. [ABSTRACT FROM AUTHOR]

To explore the effect of adding bamboo fiber and steel wire mesh to BFRP bar-reinforced concrete beams on their flexural performance, we designed and fabricated six test beams with different parameters. Through flexural tests and numerical simulations, the effects of bamboo fiber length and steel wire mesh layout on the crack resistance, deformation capacity, and flexural ultimate bearing capacity of BFRP bar concrete beams were assessed. The feasibility of the simulation and the calculation method of flexural capacity of such specimens were considered. The research results showed that the addition of bamboo fiber can increase the cracking load and global stiffness and reduce the deformation of the test beam, but this had little effect on the ultimate flexural bearing capacity of the test beam. The cracking load, global stiffness, and ultimate flexural bearing capacity of the test beams were improved by the addition of steel wire mesh, and the stiffness and ultimate flexural bearing capacity of the test specimens with steel wire mesh in the whole beam were improved. Although the composite effect of bamboo fiber and steel wire mesh showed some improvement in these indicators, the improvement effect was not ideal. [ABSTRACT FROM AUTHOR]

This paper presents the test results of four static full-size four-point bending tests to investigate the flexural behaviour of a recently developed prefabricated steel-concrete composite ultra-shallow flooring system (PUSS®). The flooring system comprises of T-ribbed concrete floors partially-embedded within and connected to side C-channel beams and horizontally-oriented shear connectors. This study investigates the effects of three parameters on the flexural behaviour of PUSS® and the performance of the shear connectors under bending. The parameters under study are the type of concrete, degree of shear connection and depth of the slab. Four 4 m span test specimens are constructed using two types of concrete, two with reinforced normal weight concrete (NWC) and the remaining two with reinforced lightweight aggregates concrete (LWC). Three of the test specimens employ the unique shear connection system composed of horizontally-oriented steel dowels with horizontally-oriented web-welded shear studs (dowels with WWSS) while the last one employs horizontal steel dowels only. The contribution of the above parameters on flexural behaviour and failure mechanisms are examined. The study concludes that replacing NWC with LWC of similar strength does not affect the flexural behaviour of PUSS® in terms of slab capacity, ductility and failure mechanism. However, LWC demonstrates lower initial stiffness and leads to the development of larger cracks as loads increases. Also, reducing the degree of shear connection lowers the moment capacity of the slabs and results in failure of some shear connectors during testing. PUSS® units exhibit ductile behaviour under bending conditions regardless of the degree of shear connection. • Flexural tests on PUSS® with innovative web-welded horizontal shear connection system. • Failure mechanism of prefabricated ultra-shallow composite slabs under bending. • Replacing NWC with LWC of similar strength does not affect the flexural behaviour of PUSS. • Contribution of degree of shear connection in the load capacity of composite slabs. • Shear connection system enables composite slab to behave ductility as a single rigid body. [ABSTRACT FROM AUTHOR]

This paper presents the results of a parametric finite element (FE) study that investigates the flexural behaviour and bending capacity of a recently developed steel‐concrete composite flooring system subjected to static bending tests. The flooring system is composed from prefabricated ultra‐shallow slab units (aka PUSS) that consist of T‐ribbed concrete floors encased within and connected to two C‐channel steel edge beams with horizontally oriented shear connections. The study considers three unique types of shear connection systems, that compose of only horizontally oriented web‐welded shear studs (WWSS), only horizontal steel dowels or a combination of horizontal steel dowels with WWSS. The failure mechanism, the shear resisting capacity of the shear connection systems and their behaviour under flexural loads are examined. The present work explores the influence of variable parameters on the performance of the PUSS flooring system. In particular, the parameters under critical investigation are the type, arrangement, and size of the shear connectors (WWSS and steel dowels) as well as the location of the main pressure caused by the applied load. Based on the results, the location of the applied loads contributed greatly to the behaviour of the shear connectors, moment resistance capacity and failure mechanism of the slabs. In addition, horizontal dowels provided greater bond between concrete and steel in comparison to WWSS. [ABSTRACT FROM AUTHOR]

To explore the effect of adding bamboo fiber and steel wire mesh to BFRP bar-reinforced concrete beams on their flexural performance, we designed and fabricated six test beams with different parameters. Through flexural tests and numerical simulations, the effects of bamboo fiber length and steel wire mesh layout on the crack resistance, deformation capacity, and flexural ultimate bearing capacity of BFRP bar concrete beams were assessed. The feasibility of the simulation and the calculation method of flexural capacity of such specimens were considered. The research results showed that the addition of bamboo fiber can increase the cracking load and global stiffness and reduce the deformation of the test beam, but this had little effect on the ultimate flexural bearing capacity of the test beam. The cracking load, global stiffness, and ultimate flexural bearing capacity of the test beams were improved by the addition of steel wire mesh, and the stiffness and ultimate flexural bearing capacity of the test specimens with steel wire mesh in the whole beam were improved. Although the composite effect of bamboo fiber and steel wire mesh showed some improvement in these indicators, the improvement effect was not ideal.

Various materials and reinforcement technologies have been created for concrete structures. However, there is no uniform methodology to compare the mechanical characteristics of different reinforcement systems. In structural systems, residual stiffness can estimate the efficiency of the reinforcement. This study introduces a simplified approach for the flexural stiffness analysis. It employs a new testing layout designed with the purpose to form multiple cracks in a small laboratory specimen. The achieved solution requires neither iterative calculations nor a description of the loading history. Several composite reinforcement schemes, including internal glass fibre reinforced polymer (GFRP) bars, carbon fibre reinforced polymer (CFRP) sheets and near-surface mounted (NSM) strips are considered. The analysis of the test results reveals a substantial efficiency of the external CFRP reinforcement systems. Article in English. Skirtingomis kompozitinėmis sistemomis armuotų betoninių elementų lenkiamojo standumo lyginamoji analizė Santrauka Betono konstrukcijoms armuoti naudojamos įvairios medžiagos ir technologijos, tačiau unifikuotos metodikos, kuria būtų galima palyginti skirtingų armavimo sistemų mechanines savybes, nėra. Konstrukcinės sistemos armavimo efektyvumas gali būti vertinamas atsižvelgiant į elementų liekamąjį standumą. Šiame straipsnyje pateikiamas supaprastintas lenkiamojo standumo analizės metodas. Jis apima naują bandymų schemą, kuria siekiama gauti tolygų plyšių pasiskirstymą mažame laboratoriniame bandinyje. Siūlomas analitinis sprendimas nereikalauja nei iteracinio skaičiavimo, nei detalaus apkrovos istorijos aprašymo. Nagrinėjamos kelios kompozitinio armavimo sistemos: taikant stiklo pluoštu armuotus polimerinius (GFRP) strypus, išdėstytus elemento viduje, anglies pluoštu armuotus polimerinius (CFRP) lakštus, priklijuotus elemento išorėje, ir sijų paviršiuje tvirtinamas anglies pluoštu armuotas polimerines (NSM) juostas. Tyrimo rezultatai rodo anglies pluoštu armuotų polimerų (CFRP) sistemų, išdėstytų elementų išorėje, efektyvumą. Reikšminiai žodžiai: betono kompozitas, armavimas, liekamasis standumas, analitinis modelis, lenkimo bandymai.

Various materials and reinforcement technologies have been created for concrete structures. However, there is no uniform methodology to compare the mechanical characteristics of different reinforcement systems. In structural systems, residual stiffness can estimate the efficiency of the reinforcement. This study introduces a simplified approach for the flexural stiffness analysis. It employs a new testing layout designed with the purpose to form multiple cracks in a small laboratory specimen. The achieved solution requires neither iterative calculations nor a description of the loading history. Several composite reinforcement schemes, including internal glass fibre reinforced polymer (GFRP) bars, carbon fibre reinforced polymer (CFRP) sheets and near-surface mounted (NSM) strips are considered. The analysis of the test results reveals a substantial efficiency of the external CFRP reinforcement systems. [ABSTRACT FROM AUTHOR]

Featured Application: The proposed numerical analysis principles are applicable for a design for serviceability of fibre-reinforced polymer (FRP)–concrete elements. Advanced materials have been created for structural application during the past decades. Engineers, however, faced severe problems due to the absence of a reliable technique for ensuring the required structural properties minimising the amount of material used. A lack of constitutive models for the analysis of the structural systems also exists. Residual stiffness of flexural concrete elements subjected to short-term load is the focus of this research. Tension-stiffening models were developed to represent the deformation response of the members reinforced with internal bars. This study examines the suitability of the tension-stiffening modelling approach for simulating the deformation behaviour of the composite specimens comprising glass fibre-reinforced polymer (GFRP) pultruded profile adhesively bonded to the tensile surface of the concrete beam. The study employs a nonlinear finite element approach and analytical model to simulate the deformation behaviour of the flexural elements. [ABSTRACT FROM AUTHOR]

The application of an innovative real-time structural health monitoring system is studied through tests performed on flexural and shear-critical reinforced concrete elements subjected to monotonic and cyclic loading. The test set-up involves a Wireless impedance/Admittance Monitoring System (WiAMS) that comprises specially manufactured small-sized portable devices to collect the voltage frequency responses of an array of smart piezoelectric transducers mounted on structural members of reinforced concrete constructions. Damage detection and evaluation is achieved using the in-situ measurements of the integrated piezoelectric sensors/actuators signals at the healthy state of the member and at various levels of damage during testing. Three different installations of Piezoelectric lead Zirconate Titanate (PZT) transducers are examined: (a) epoxy bonded PZTs on the surface of the steel reinforcing bars of the flexural elements, (b) PZTs embedded inside the concrete mass of the shear-critical beams and (c) externally epoxy bonded PZTs attached to the concrete surface of the tested elements. The smart piezoelectric materials have been pre-installed before testing based on the potential flexural and shear cracking of the elements. Quantitative assessment of the examined damage levels using values for the statistical damage index is also presented and discussed. Voltage signals and index values acquired from the PZTs’ measurements using the proposed wireless monitoring technique demonstrated obvious discrepancies between the frequency response of the healthy and the examined damage levels for every tested element. These differences clearly indicate the presence of damage, whereas their gradation reveals the magnitude of the occurred damage. Promising results concerning the prediction of the forthcoming fatal failures at early damage stages have also been derived.

In the last decades, fiber reinforced concrete have emerged as the possible key to revolutionize civil engineering. Among different types of fibers employed in concrete technology to date, the application of recycled steel fibers produced from end-of-life car tires appears to be a viable approach towards environmentally friendly construction. In this study, we demonstrate the laboratory research and numerical analysis of concrete reinforced with waste steel fibers recovered during the recycling process of end-of-life car tires. Concrete mixes with the following fiber contents: 0.5%, 0.75%, 1.0%, 1.25%, and 1.5% per volume were prepared and then tested in three-point bending conditions. The laboratory investigation revealed highly boosted properties of concrete under flexure. We further performed the finite element method (FEM) analysis of 2D models using Atena software in order to develop a material model allowing the numerical modelling of recycled steel fibers reinforced concrete (RSFRC) behavior. The parameters of RSFRC material model have been modified using the inverse analysis until matching the experimental performance of the material. The results, being in good agreement with the laboratory investigation, have indicated a high potential of RSFRC for real scale construction applications.

Tensile Stress‐Strain Relationship for UHPFRC based on notched 3‐point‐bending tests Both the tensile strength and the residual tensile strengths of fibre reinforced concrete are generally determined indirectly by flexural tests. For this purpose, a force‐deformation curve has to be converted into a tensile stress‐strain curve. For ultra‐high performance fibre reinforced concrete (UHPFRC) there is currently no regulated conversion procedure due to the lack of valid standards and guidelines in Germany. To analyse the tensile stress‐strain behaviour of UHPFRC, notched 3‐point‐bending tests according DIN EN 14651 were carried out at iBMB, Division of Concrete Construction of the TU Braunschweig. A conversion procedure for UHPFRC based on the Model Code 2010, which regulates normal‐ and high‐strength fibre reinforced concrete, was developed taking into account the test results. The finite element method (FEM) was applied for validation. [ABSTRACT FROM AUTHOR]

A standard approach is presented to obtain analytical solutions for deflection field of determinate beams subjected to conventional loading patterns. The solutions are based on a trilinear moment–curvature response using a deflection hardening behavior characterized by flexural crack initiation, inelastic response due to crack extension, and full plastic hinge formation. Methodology for full span deflection and rotation distributions are presented for multiple cases that include three‐ and four‐point bending, uniform load, concentrated moment, and cantilever beams. The proposed approach provides analytical expressions for the curvature, rotation, and deflection at any point along the beam, and correlated to stress or strain distribution. The procedure can therefore be integrated into a serviceability‐based design approach. A parametric study of the effects of model parameters on the stages of the response is addressed. Several case studies involving steel fiber reinforced concrete (SFRC), textile reinforced concrete (TRC) and ultra‐high performance concrete (UHPC) are conducted and the simulated load‐deflection responses are verified against the experimental data from several published experiments. Size effect on the serviceability limits of beams with spans ranging from 0.22 to 8.6 m is studied by tracking the full‐range moment–curvature and load‐deflection responses. [ABSTRACT FROM AUTHOR]

The object of this study was to evaluate the flexural strength of glass fiber reinforced polyurethane composites under variable displacement rates. Flexural tests have been conducted at a range of displacement rates included 0.2, 2, 20, 100, 200, 1000 mm/min. Specimens with identical geometry have been used in all the tests. This particular composite has viscoelastic behavior with both elasticity modulus and ultimate flexural strength being strongly dependent of the displacement rate. Results showed that, both the flexural modulus and the ultimate flexural strength are increased with the increasing in the displacement rate.

The capability to bend in a controlled manner Grès Porcelain stoneware tiles passing by a processes of pyroplastic deformation opens up new opportunities in utilisation of this important family of ceramics. A bent tile can be used in innovative applications, such as stairs, shelves, benches and even radiators, turning this element from a simple piece of furnishing in a modern functional component. But this change in functionality requires a new and different approach to the quality control that can no longer be limited to the validation tests as specified in the regulations used for traditional ceramics (e.g. colour, porosity, hygroscopic ...). Starting from a brief description of the first and only device devised for the verification of flexural resistance of curved tiles, this paper investigates the limitations and possibilities of use of that innovative equipment for product/process quality monitoring. Thanks to a careful modelling of its mechanism of operation, accompanied by various simulations comparing the limit cases of use, it has been possible to verify the incidence of some of the potential weaknesses of the equipment as well as to carry out a sensitivity analysis of this new tool for measure.

This paper presents the experimental and analytical results of a new composite girder that consists of a steel girder and hybrid fiber-reinforced concrete (HFRC) slab. First, six push-out tests were performed, and the test results were used to verify the interface behaviors of two composite girders. Then, the composite behavior between the steel girder and HFRC slab was investigated under sagging moment. It was found that the composite girder with HFRC slab exhibited a much greater ductility and a slightly smaller ultimate moment capacity, and the probability of cracking was also significantly reduced compared with the normal concrete (NC) slab. Finally, equations introducing the reinforcement indexes to determine the capacity, degree of shear connector, and effective moment of inertia of the steel-HFRC composite girders with partial interaction were proposed. It was found that the analytical results of the equations had a fairly good agreement with experimental results. [ABSTRACT FROM AUTHOR]

Nanocomposites based on a cross-linked epoxy matrix with the addition of a reinforcing organically modified boehmite nano-phase were realized and characterized with the aim to produce systems possessing enhanced properties over commercial epoxy systems. Different amounts of a commercially available organically modified boehmite were added to a diglycidyl ether of bisphenol A (DGEBA) epoxy matrix. The rheological characteristic and kinetic behavior of the liquid nano-filled mixtures were analyzed and compared to those displayed by the un-filled resin. A mathematical model was applied to the experimental rheological data in order to assess the aspect ratio of the nano-filler. A proper equation was employed to model the cure kinetics of the nano-filled epoxy systems. The nanocomposites were heat-cured in the presence of an aromatic amine hardener. They were, then, characterized by scanning electron microscopy with EDS analysis, dynamic mechanical thermal analysis, differential scanning calorimetry, and Flexural and Hardness tests. Significant increase in the glass transition temperature, Shore D hardness and maximum flexural strength was found. The experimental results demonstrated the effectiveness of the o-boehmite nano-filler to improve the physical and mechanical properties of the epoxy resin. Further studies are in progress to verify the protective efficiency of the epoxy-boehmite nanocomposite when applied on different substrates as adhesive or coating for construction materials, such as porous stones, concrete, wood, and metal. [ABSTRACT FROM PUBLISHER]

The use of fiber reinforced concrete in tunnel linings, with or without conventional rebars, has increased in the two last decades, especially with regard to precast tunnel segmental linings. In addition, there is a general growing interest in the scientific community on macro-synthetic fibers for use in underground structures. Within this framework, the present study investigates the possibility of using polypropylene (PP) fiber reinforcement in hydraulic precast tunnel segments by means of an experimental program on six full-scale segments of Monte Lirio hydraulic tunnel (Panama). Three different reinforcement solutions were studied both under flexure and point load test: typical conventional reinforcement generally adopted in practice (reference samples, RC); PP fibers only (PFRC specimens); combination of PP fibers and conventional reinforcement (hybrid solution, RC + PFRC segments). Based on the loading configurations considered, experimental results showed that PP fibers (with or without reinforcing bars, depending on loading conditions) represent an efficient reinforcement for hydraulic precast tunnel segments. PP fibers can be used as flexural, splitting and minimum shear reinforcement, while concerning the spalling reinforcement, only PP fiber reinforcement could be used even if the combination with conventional reinforcement (hybrid solution) guarantees a better control of spalling cracks for high load levels. [ABSTRACT FROM AUTHOR]

To minimize the consumption of virgin aggregates during concrete production, and to utilize the high volume of construction waste, a limited number of studies have been devoted to the potential use of multi-generation recycled aggregate concrete (MGRAC). To date, these studies have been restricted to quantifying aggregate and material properties, and no research has investigated behaviour at the member level or assessed the applicability of code specified design approaches. To investigate the impact of MGRAC at the member level, in this work, four generations of concrete are manufactured, the first using virgin aggregates (VA) and then three subsequent recycled aggregate generations (RA-1 to RA-3) with 100% replacement ratios. The flexural behaviour of MGRAC is tested through a series of small-scale reinforced concrete beams, where for each generation beams with two different reinforcement ratios are tested. Throughout testing, member load-deflection and crack-width are recorded. The study further assesses the feasibility of using standard code approaches to design MGRAC beams at different limit states and quantifies the global warming potential (GWP) of each generation of concrete. The results show member level behaviour at the ultimate limit state is not negatively impacted by the use of MGRAC, but tension stiffening and cracking are influenced at the serviceability limit state. Standard design approaches are able to predict member strength but under predict member deflection. Life-cycle assessment demonstrates little variation in GWP between each generation of concrete manufacture, but as expected, show significant savings in virgin material usage. [ABSTRACT FROM AUTHOR]

This paper presents experimental testing and numerical analysis of durable composite girder systems consisting of hybrid carbon/glass fiber-reinforced polymer (HFRP) I-girders and precast ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs. Epoxy adhesive and/or bolt shear connectors (SCs) were used to transfer horizontal shear forces from the UHPFRC slabs to the HFRP I-girders. Push-out tests were performed to evaluate the shear interaction at the slab/girder interface. The results of the push-out tests were used to design five large-scale composite girders. The experimental variables included two types of bolt SCs (straight and inclined bolt SCs) and different slab geometries. The composite behavior between the HFRP I-girder and the UHPFRC slab was examined. The test results showed that the combined use of the bolt SCs and the epoxy adhesive was essential to achieve a full interaction between the HFRP I-girder and the UHPFRC slab. The use of the epoxy adhesive resulted in improving the strength and stiffness of the composite girders, reducing the stress concentration around the bolt-holes, and increasing the shear strength of the bolt SCs. The girders with the inclined bolt SCs showed a more ductile behavior than those with the straight headed bolt SCs. A three-dimensional finite element (FE) analysis of the HFRP-UHPFRC composite girder was carried out that considered slip effects at the slab/girder interface and the nonlinear behavior of the bolt SCs. Comparisons between the experimental results and the FE analysis were performed and a fairly good agreement was found. A companion paper shows derivations of analytical equations to predict composite behaviors of the HFRP-UHPFRC girders with varying levels of interaction at the slab/girder interface. [ABSTRACT FROM AUTHOR]

This papers addresses the disparities that exist in measuring the constitutive properties of thin section cement composites using a combination of tensile and flexural tests. It is shown that when the test results are analyzed using a simplified linear analysis, the variability between the results of tensile and flexural strength can be as high as 200-300%. Experimental results of tension and flexural tests of laminated Textile Reinforced Concrete (TRC) composites with alkali resistant (AR) glass, carbon, aramid, polypropylene textile fabrics, and a hybrid reinforcing system with aramid and polypropylene are presented. Correlation of material properties is studied analytically using a parametric model for simulation of flexural behavior using a closed form solution based on tensile stress-strain constitutive relation. The flexural load carrying capacity of TRC composites is computed using a back-calculation approach, and parameters for a strain hardening material model are obtained using the closed form equations. While the parametric model over predicts the simulated tensile response for carbon and polypropylene TRCs, predictions are however consistent with experimental trends for aramid and glass TRCs. Detailed discussion of the differences between backcalculated and experimental tensile properties is presented. Results can be implemented as average moment-curvature relationship in the structural design and analysis of cement composites. [ABSTRACT FROM AUTHOR]

Design and production of industrial components and materials are nowadays a compromise between the required performances and the environmental impact. In the case of structural concrete, the existing ecological approaches are mainly focused on sustainability, regardless of mechanical performances. Tailoring a new generation of concretes, capable of maintaining acceptable mechanical properties with a reduced ecological impact, is therefore the big challenge that construction industry has to face. Accordingly, new instruments, based on both mechanical and environmental performances, need to be introduced in place of the classical life cycle assessment procedure. This is the case of the so-called eco-mechanical index (EMI), described in the present paper and applied to different series of plain and fiber-reinforced self-compacting concretes. The basic mechanical properties, such as compression and flexural strengths, and the related post-peak curves, are taken into account by the proposed EMI. Conversely, water, embodied energy consumption and the amount of carbon dioxide, necessary for the production of concrete, are here assumed to represent the environmental performance. As a result, in presence of fiber-reinforced concrete, despite the higher ecological impact than plain concrete, the best eco-mechanical performances are generally measured at each stage of concrete life. [ABSTRACT FROM AUTHOR]

The impact of a thin layer of a ductile fiber-reinforced concrete referred to as engineered cementitious composites (ECC) on unreinforced masonry (URM) prisms and beams has been evaluated. The objective of the research was to characterize the performance and potential benefits of using ECC to retrofit URM with eventual application to masonry infill walls in non-ductile reinforced concrete frames. Compression tests of masonry prisms and flexural tests of masonry beams with different ECC retrofit schemes were conducted. The variables studied were the use of wall anchors to improve the ECC-masonry bond and alternate steel reinforcement ratios within the ECC layer in the form of welded wire fabric. The ECC retrofit was found to increase the strength and stiffness of URM prisms by 45 and 53 %, respectively compared to those of a plain specimen. When wall anchors were installed on the masonry specimens, the bond between the ECC layer and the masonry surface was improved. Four-point bending tests indicated that the strength and more importantly the ductility of an ECC retrofitted brick beam are increased significantly, especially when light reinforcement is added to the ECC layer, relative to an URM beam. Analytical models for estimating the strength and stiffness of ECC retrofitted masonry specimens are proposed and evaluated. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the flexural strength of welded sections based on a series of flexural tests performed on H-sections fabricated from steel plates of thickness 6.0mm with nominal yield stress of 315.0MPa. Thin-walled flexural members undergo local, lateral-torsional or their interactive buckling according to the section geometries and lateral boundary conditions. Flexural members with the flanges or the web of large width-to-thickness ratios may undergo local buckling before lateral-torsional buckling and their interaction before the final collapse of the section. The local buckling has a negative effect on the flexural strength based on the lateral-torsional buckling. This phenomenon should be considered in the estimation of the nominal flexural strength of thin-walled flexural members. Welded H-section beams composed of the flanges and the web with various width-to-thickness ratios were tested to failure. The initial imperfections in local and lateral buckling mode, and residual stresses were included in the FE analyses. Simple design flexural strength formulas for the direct strength method (DSM) were proposed based on the test and FE results of welded sections to account for interaction between local and lateral-torsional buckling. The design strength curves were compared with the AISC specifications (2005), Eurocode3 (2003) and test results. The adequacy of the strength curve for the DSM was confirmed. A set of conclusions on the flexural strength and structural behavior of thin-walled welded H-sections was drawn from the experimental studies. [Copyright &y& Elsevier]

The effect of different amine/epoxy ratios on different properties of an epoxy resin was evaluated. Also, different amounts of carbon nanotubes (CNT) were added in order to analyse which of these two factors is more relevant. Dynamic thermomechanical analysis and flexural tests were carried out. The results obtained for the epoxy resin are in agreement with that reported by several researchers. The glass transition temperature of the resin and composites is maximal for the amine/epoxy stoichiometric ratio, while the highest glassy storage and flexural modulus correspond to the epoxy-rich systems, showing that the most crosslinked network is not the stiffest one. The effect of changing the stoichiometry is more relevant than adding CNT to the epoxy resin used in this work. However, the addition of CNT causes more remarkable changes in the epoxy-rich resin, promoting an increase of the glass transition temperature and the elastic modulus. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a total of 13 FRP-strengthened reinforced concrete beams were tested in flexure and analyzed using the finite element method. The various variables included bonding or no bonding of the FRP, the anchorage system, the amount of prestressing, and the span length. The experiments consisted of one control beam, two non-prestressed FRP-bonded beams, four prestressed FRP-unbonded beams, four prestressed FRP-bonded beams, and two prestressed FRP-unbonded beams with different span lengths. All the beams were subjected to three-point and four-point bending tests under deflection control, with the loading, deflection and failure modes recorded to the point of failure. A nonlinear finite element analysis of the tested beams was also performed using the DIANA software; this analysis accounted for the nonlinear concrete material behaviour, the reinforcement, and an interfacial bond-slip model between the concrete and CFRP plates. The aim of this investigation was to study the flexural performance of reinforced concrete members strengthened using CFRP plates, employing different FRP bonding and prestressing methods. The failure mode of the prestressed CFRP-plated beams was not debonding, but FRP rupture. For the reinforced concrete members strengthened with externally bonded prestressed CFRP plates, debonding of the composite laminates occurred in two stages. After the debonding of the CFRP plates that occurred in the bonded cases, the behaviour of the bonded CFRP-plated beams changed to that of the unbonded CFRP-plated beams due to the effect of the anchorage system. The flexural test results and analytical predictions for the CFRP-strengthened beams were compared and showed very good agreement in terms of the debonding load, yield load, and ultimate load. The ductility of the beams strengthened with CFRP plates having the anchorage system was considered high if the ductility index was above 3. [Copyright &y& Elsevier]

Polyester resin based composite materials are widely used in the manufacture of fiberglass boats. Production time of fiberglass laminate components could be strongly reduced by using an intense energy source as well as microwaves. In this work a polyester resin was used with 2% by weight of catalyst and reinforced with chopped or woven glass fabric. Pure resin and composite samples were cured by microwaves exposition for different radiation times. A three point bending test was performed on all the cured samples by using an universal testing machine and the resulting fracture surfaces were observed by means of scanning electron microscopy (SEM). The results of mechanical and microscopy analyses evidenced that microwave activation lowers curing time of the composite while good mechanical properties were retained. Microwaves exposition time is crucial for mechanical performance of the composite. It was evidenced that short exposition times suffice for resin activation while long exposure times cause fast cross linking and premature matrix fracture. Furthermore high-radiation times induce bubbles growth or defects nucleation within the sample, decreasing composite performance. On the basis of such results microwave curing activation of polyester resin based composites could be proposed as a valid alternative method for faster processing of laminated materials employed for large-scale applications. [ABSTRACT FROM AUTHOR]

The article presents a research study about corrosion-induced bond strength degradation in reinforced concrete. The research provides analytical and empirical models to show the effect of reinforcement corrosion on bond strength reduction. It proposed the empirical models by considering a wide range of published experimental investigations about bond strength degradation. The estimation of various bond strength parameters, which includes corrosion pressure, and modeling of tensile behavior, was adopted for the analytical model. The research examined the performance of the models based on their ability to recreate experimental trends. It discovered that the proposed models can give estimates of predicted bond strength of corroded reinforcement.

A theoretical study was carried out to investigate stress along tensile lap-spliced spaced or bundled fibre reinforced polymer (FRP) bars in concrete. R. Tepfers developed a mathematical model, which could be applied for any type of reinforcing bar, based on the modulus of displacement theory. The mathematical model can predict the bond stress and stresses in the reinforcing bars and the surrounding concrete. In this paper, the model developed by Tepfers was represented by applying the modulus of displacement theory, and theoretical predictions are compared with the experimental results from testing 16 large-scale concrete beams. Good agreement between the theoretical values and experimental results was observed at three stages of loading. Recommendations for investigating the modulus of displacement from pullout tests have been included. Lastly, the maximum average bond stress of spliced FRP bars can be estimated using the ultimate failure pattern analysis, in which the contributions of the splitting resistance were included. [ABSTRACT FROM AUTHOR]