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The demand for composite materials is growing every year. In this regard, the competitiveness of a particular product is determined primarily by the price-quality ratio. The most rational option for the production of wood-filled composites is using the materials with the increased performance characteristics. To date, it is the performance characteristics of modern composite materials that are the most significant, not only for final consumers, but also for manufacturers. In this regard, to improve performance characteristics in the production of wood-filled composites, various methods of pre-treatment of wood are used – thermal modification, acetylation, furfulation, ultra-high-frequency processing, alkali treatment, the use of various additives, etc. A promising way to improve the physical and mechanical properties of wood-filled materials is acetylation, whose mechanism consists in the formation of acetyl groups in wood during processing. To reduce production costs and the cost of the final product, it is possible to use a cheaper precursor (for example, icy acetic acid instead of acetic anhydride) with the possibility of intensifying the impregnation process. This article presents the results of obtaining wood-filled composites based on acetylated birch wood flour with its various proportions in the composition. The effect of introducing acetylated wood filler into the composition on the performance properties of composites (abradability, frost-resistance, flexural strength) has been evaluated in comparison with control samples made from untreated birch wood flour. The effect of acetylation with glacial acetic acid on the structure of birch wood flour has been characterized using Fourier-transform infrared spectroscopy. The IR-spectra of the control and acetylated samples contain absorption bands belonging to the corresponding groups of cellulose and lignin of hardwoods. The abradability and frost-resistance coefficients for a wood-filled composite based on acetylated birch wood flour are on average 1.5–2 times lower for all compositions compared to control samples. The results of the research allow us to conclude that acetylation of wood flour as a method of pre-treatment of the filler in order to improve the performance characteristics of the final product is promising for implementation in the production of wood-filled materials.

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Four‐point bending tests were conducted to investigate the flexural properties of fly‐ash‐based geopolymer concrete beams. Although geopolymer concrete has a stress–strain relationship with brittle compressive softening behavior, it can be used as a flexural member because it exhibits ductile bending moment–deflection relationships when used with compression reinforcing bars and transverse reinforcement. The test results revealed that the conventional design method can be used to estimate the bending moment–deflection relationship of geopolymer concrete beams. However, the stiffness reduction ratio for yielding must be modified to consider the difference in the modulus of elasticity between geopolymer concrete and ordinary Portland cement concrete. [ABSTRACT FROM AUTHOR]

Abstract Four‐point bending tests were conducted to investigate the flexural properties of fly‐ash‐based geopolymer concrete beams. Although geopolymer concrete has a stress–strain relationship with brittle compressive softening behavior, it can be used as a flexural member because it exhibits ductile bending moment–deflection relationships when used with compression reinforcing bars and transverse reinforcement. The test results revealed that the conventional design method can be used to estimate the bending moment–deflection relationship of geopolymer concrete beams. However, the stiffness reduction ratio for yielding must be modified to consider the difference in the modulus of elasticity between geopolymer concrete and ordinary Portland cement concrete.

In this study, an experimental investigation was conducted to assess the flexural tensile strength and crack-closing performance of mortar beams containing short shape memory alloy (SMA) fibers, randomly distributed only on the tensile side. The SMA fibers were mainly composed of titanium (Ti), nickel (Ni), and niobium (Nb). In addition, the effect of tensile steel wires on the flexural strength and crack-closing performance was evaluated. A four-point bending test was performed to evaluate the post-cracking tensile strength. This study also suggested a proper model to calculate the ultimate flexural moment of the SMA fiber–embedded beams. Subsequently, a heating plate that could be installed at the bottom of the beam was used to induce the shape memory effect and measure the closed crack width. This study assessed the crack-closing performance induced by the SMA fibers at the bottom side of the beams and the resistance of the tensile wires in the beams.

This study was performed to evaluate the probabilistic characteristics of the flexural strength of reinforced concrete (RC) flexural members adopted for underground box culverts. These probabilistic models were developed to be adopted for the development of limit state load combination formats for underground RC box culverts. The probabilistic models of uncertainties inherent in the basic design variables were developed to evaluate flexural strength using field material test data as well as field survey data collected from various domestic construction sites of underground box culverts in Korea. The basic design variables include concrete strength, steel rebar strength, and section dimensions, such as slab thickness and rebar locations. Some design variables are assumed to have inherent construction error characteristics, which may be different from those inherent in the RC members for buildings and bridges. The bias models on flexural strength were evaluated based on the experimental results of four-point flexural tests on one-way RC slabs, which were fabricated following the general practice adopted in the local underground box culvert construction process. Based on the probabilistic models of basic design variables, as well as the bias models of flexural strength, Monte Carlo simulations were performed to examine the probabilistic characteristics of both ultimate flexural strength and yield moment strength of RC slab members. Some sensitivity analyses were performed to confirm the soundness of various probability models and the assumptions adopted in the development procedure. The proposed procedure may be applied to develop probabilistic resistance models for structural members, in which the construction error characteristics are assumed to be different from other practices. [ABSTRACT FROM AUTHOR]

Composite girder is one of the main structural systems used in bridges and buildings. The same slenderness limits requirements for steel sections are used also for the composite sections in most specifications without considering the effect of concrete slabs. In fact, for composite sections under positive moments, the compression concrete slab restrains the buckling of the top flange and the compressed part of the web, in addition the steel plates behave plastically up to failure. By accounting concrete slabs attached to the steel compression elements, the section may be placed in more favorable class. The main objective of this study is to verify a reasonable relaxed slenderness limits for steel compact composite sections compared to compact steel section only and investigate the influences of the span length of girder and the concrete strength of slab, on the slenderness limits. An extensive parametric study using ANSYS, a commercial finite element (FE) software, was held using different web slenderness, various concrete strengths and girder lengths. The section classifications were evaluated, and the results were compared to the Egyptian code, Eurocode and AASHTO. A new relaxed equation and new classification limits have been developed considering the effect of the concrete slab strength. [ABSTRACT FROM AUTHOR]

In Japan, steel is mostly used to construct large-span buildings such as logistic terminals, office buildings, shopping malls, and medical facilities. However, in recent years with the fabrication cost of steel soaring, there is a concerted effort to reduce construction costs and at the same time increase productivity. Therefore, research investigations are being carried out and one of the methods involves using an innovative hybrid system where the columns are reinforced concrete and the beams are hybrid beams. In this study, concrete design strength, shear reinforcement ratio and length of RC section were altered to examine the structural performance of hybrid beams under flexural failure in a beam-column subassemblage. The results showed that ultimate flexural strength of a reinforced concrete section can be evaluated using an Architectural Institute of Japan abbreviated equation, and a coefficient of shear reinforcement of more than 2.5% will assure a plastic deformation capacity of more than 2%. [ABSTRACT FROM AUTHOR]

Concrete edge failure of a single anchor in concrete is strongly dependent on the tensile performance of the concrete, which can be greatly improved by the addition of steel fibers. This study investigated the effect of steel fibers on the shear failure mode and edge breakout resistance of anchors installed in steel fiber-reinforced concrete (SFRC) with fiber volume percentages of 0.33, 0.67, and 1.00%. The anchor used in the study was 30 mm in diameter, with an edge distance of 75 mm and embedment depth of 240 mm. In addition to the anchor specimens, beam specimens were prepared to assess the relationship between the tensile performance of SFRC beams and the shear resistance of SFRC anchors. The ultimate flexural strength of the beam and the breakout shear resistance of the anchor increased almost linearly with increasing volume fractions of fiber. Therefore, based on the ACI 318 design equation, a term was proposed using the ultimate flexural strength of concrete instead of the compressive strength to determine the concrete breakout shear resistance of an anchor in the SFRC. The calculated shear resistance of anchors in both the plain concrete and SFRC were in good agreement with the measurements. In addition to the load capacity of the SFRC anchors, the energy absorption capacity showed a linear increase with that of the SFRC beam. [ABSTRACT FROM AUTHOR]

This study was performed to evaluate the probabilistic characteristics of the flexural strength of reinforced concrete (RC) flexural members adopted for underground box culverts. These probabilistic models were developed to be adopted for the development of limit state load combination formats for underground RC box culverts. The probabilistic models of uncertainties inherent in the basic design variables were developed to evaluate flexural strength using field material test data as well as field survey data collected from various domestic construction sites of underground box culverts in Korea. The basic design variables include concrete strength, steel rebar strength, and section dimensions, such as slab thickness and rebar locations. Some design variables are assumed to have inherent construction error characteristics, which may be different from those inherent in the RC members for buildings and bridges. The bias models on flexural strength were evaluated based on the experimental results of four-point flexural tests on one-way RC slabs, which were fabricated following the general practice adopted in the local underground box culvert construction process. Based on the probabilistic models of basic design variables, as well as the bias models of flexural strength, Monte Carlo simulations were performed to examine the probabilistic characteristics of both ultimate flexural strength and yield moment strength of RC slab members. Some sensitivity analyses were performed to confirm the soundness of various probability models and the assumptions adopted in the development procedure. The proposed procedure may be applied to develop probabilistic resistance models for structural members, in which the construction error characteristics are assumed to be different from other practices.

Objective This study evaluated the flexural strengths of reinforced denture base resins subjected to long-term water immersion. Materials and methods Acrylic denture base resin reinforced with metal wire or glass fiber-reinforced composite (FRC), and without reinforcement were tested. Bar-shaped specimens were fabricated. Half of the specimens were stored in 37 °C distilled water for 50 hours (h), the other half were stored in 37 °C distilled water for 180 days (d) before testing. Ten specimens were fabricated per group for each reinforcement/water immersion period combination. The ultimate flexural strength and flexural strength at the proportional limit of reinforced denture base resin were tested. Results The 180 d bulk specimen possessed significantly lower ultimate flexural strength compared with the 50 h bulk specimen (p 0.05). The 180 d bulk specimen had a significantly lower flexural strength at the proportional limit compared to the 50 h bulk specimen. The 180 d reinforced specimens of metal and FRC were not significantly different from each of the 50 h specimens. Conclusion The flexural strengths of a reinforced denture base resin did not change after long-term water immersion.

Concrete edge failure of a single anchor in concrete is strongly dependent on the tensile performance of the concrete, which can be greatly improved by the addition of steel fibers. This study investigated the effect of steel fibers on the shear failure mode and edge breakout resistance of anchors installed in steel fiber-reinforced concrete (SFRC) with fiber volume percentages of 0.33, 0.67, and 1.00%. The anchor used in the study was 30 mm in diameter, with an edge distance of 75 mm and embedment depth of 240 mm. In addition to the anchor specimens, beam specimens were prepared to assess the relationship between the tensile performance of SFRC beams and the shear resistance of SFRC anchors. The ultimate flexural strength of the beam and the breakout shear resistance of the anchor increased almost linearly with increasing volume fractions of fiber. Therefore, based on the ACI 318 design equation, a term was proposed using the ultimate flexural strength of concrete instead of the compressive strength to determine the concrete breakout shear resistance of an anchor in the SFRC. The calculated shear resistance of anchors in both the plain concrete and SFRC were in good agreement with the measurements. In addition to the load capacity of the SFRC anchors, the energy absorption capacity showed a linear increase with that of the SFRC beam.

This study evaluated the flexural mechanical properties of various thermoplastic denture base polymers (six polyamides, four acrylic resins, polyester, polypropylene, and polycarbonate) by three different testing conditions; specimens were tested in water bath at 37®C (Wet/Water, by ISO 20795-1), or in ambient air (Wet/Air) after being immersed in distilled water for 50 h, or after desiccation for 7 days (Dry/Air). The mean ultimate flexural strength (UFS) and flexural modulus (FM) for most products ranged from 27 to 61 MPa and from 611 to 1,783 MPa respectively, which failed to meet the minimum requirements of the international standard, except for polycarbonate (89 and 2,245 MPa). The mean UFS and FM values were ranked Dry/Air>Wet/Air>Wet/Water (p<0.05). In conclusion, the flexural mechanical properties of denture base polymers varied with the products and were significantly affected by the testing medium (air or water) and specimen conditions (wet or dry). [ABSTRACT FROM AUTHOR]

ObjectiveThis study evaluated the flexural strengths of reinforced denture base resins subjected to long-term water immersion. Materials and methodsAcrylic denture base resin reinforced with metal wire or glass fiber-reinforced composite (FRC), and without reinforcement were tested. Bar-shaped specimens were fabricated. Half of the specimens were stored in 37 °C distilled water for 50 hours (h), the other half were stored in 37 °C distilled water for 180 days (d) before testing. Ten specimens were fabricated per group for each reinforcement/water immersion period combination. The ultimate flexural strength and flexural strength at the proportional limit of reinforced denture base resin were tested. ResultsThe 180 d bulk specimen possessed significantly lower ultimate flexural strength compared with the 50 h bulk specimen (p < 0.05). The ultimate flexural strength of the 50 h metal, 50 h FRC, 180 d metal and the 180 d FRC reinforcement specimens were not significantly different from each other (p > 0.05). The 180 d bulk specimen had a significantly lower flexural strength at the proportional limit compared to the 50 h bulk specimen. The 180 d reinforced specimens of metal and FRC were not significantly different from each of the 50 h specimens. ConclusionThe flexural strengths of a reinforced denture base resin did not change after long-term water immersion. [ABSTRACT FROM AUTHOR]

The structural system of a horizontally curved steel I-girder bridge consists of a number of curved girders that are laterally braced by interconnected cross-frames. The modeling and nonlinear analysis procedures of large and complex systems of curved bridges are time consuming and demand a high computational cost. In order to facilitate the preliminary design procedures, it is suggested that the complicated bridge system might be replaced by simple single curved I-girders. In this paper, the applicability of single-girder models in determining the flexural response, elastic stiffness and the ultimate strength of curved bridge girders is examined. In addition, a series of finite element parametric studies is conducted to consider the effect of curvature on the accuracy of single-girder models. It is observed that the spread of plasticity, flexural strength and failure mechanism of bridge girders can be well predicted by the use of equivalent single-girder models. Yet, single-girder models cannot accurately predict the elastic stiffness and vertical and lateral and deflections of horizontally curved steel bridge girders. [ABSTRACT FROM AUTHOR]

According to unique mechanical properties of Reactive Powder Concrete (RPC) and numerical methods, an analysis program is developed to reveal the structural behavior of the RPC members, with which 44 groups of nonlinear full-range flexural curves were calculated. Failure modes and influence of reinforcement parameters were analyzed. The results show that members will experience balance failure with a reasonable mix of reinforced bars and tendons, but the members would have a brittle failure with too much or too little reinforcement. In addition, applicable laws were suggested as follows: The reinforced bars and tendons both can increase the ultimate flexural strength independently and the ultimate flexural strength is linked to the total amount of reinforced bars and the tendons. However, the cracking strength is only dependent on the ratio of the tendons. Consequently, it is imperative that we control the ratio parameter of reinforced bars and tendons to guide the design. [ABSTRACT FROM AUTHOR]

Highlights: [•] Increasing the content of UPOFA will increase the flexural strength. [•] Increasing the content of UPOFA will increase the direct tensile strength. [•] UPOFA can considered as an efficient pozzolanic mineral admixture. [Copyright &y& Elsevier]

The ultimate flexural strengths of bisymmetric and monosymmetric I-girders subjected to local bend-buckling in webs have been investigated by nonlinear finite element analysis incorporating post-buckling behaviors. The plate girders fabricated with high performance steel (HPS) and conventional steel were modeled three-dimensionally with thin shell elements and ultimate strength analyses were conducted utilizing versatile nonlinear techniques provided by a commercial finite element analysis (FEA) package program, ABAQUS. The constitutive relationship for both HPS and conventional steel was assumed to be elasto-plastic strain-hardening, and the initial imperfections were considered in the web panels and the residual stresses were imposed on the hypothetical built-up sections. The ultimate flexural strengths of girders with various slenderness of web were evaluated from the nonlinear FEA and compared with values predicted by the specifications in AASHTO LRFD and Eurocode 3. It has been found that the current flexural strength formulas for conventional steel girders from AASHTO LRFD and Eurocode 3 can be extended to application for HPS girders without modification. [ABSTRACT FROM AUTHOR]

Polycarbosilane (PCS) heat-treated (preheated) at low temperatures (500 - 600°C) was chosen as the raw material for the production of porous SiC ceramics. The PCS was ground in a ball mill, shaped by slip casting, and sintered at 1000°C. Due to the semi-organic structure of the preheated PCS, the milled powders can be shaped and then sintered at 1000°C without the use of other binders; this made possible to create the above-mentioned porous SiC ceramics. The pore size, open porosity, and ultimate flexural strength of the SiC ceramics that were obtained were studied. It was found that an increase in the temperature at which the PCS is heat-treated impedes its shaping and reduces the open porosity and ultimate flexural strength of the resulting SiC ceramics. Information is also presented from a study of the fracture surface of the porous SiC ceramic. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the resilience, glass transition temperature (Tg), ultimate flexural strength (UFS), and penetration coefficient of 3 composite adhesives (Concise, Transbond, and Right On) and a glass ionomer cement (Fuji Ortho LC). For 25 minutes after initial set, the composite materials were significantly more resilient than Fuji Ortho LC (P = .000). Resilience values for all materials increased for up to 90 minutes after initial set, reflecting a continuation of their setting reaction. Right On remained the most resilient material at 90 minutes after initial set (P = .01). At 120 minutes, there was no significant difference in the resilience of Concise, Right On, and Fuji Ortho LC. However, Transbond was significantly less resilient than these materials (P = .01). The composite materials recorded significantly higher glass transition values (89-123°C) than Fuji Ortho LC (54°C). The composite materials were also significantly stronger (61-68 MPa) than Fuji Ortho LC (35 MPa) in flexion. The penetration coefficients of Concise and Transbond were significantly higher (P = .001) than Right On and Fuji Ortho LC. However, the relative penetration coefficients of the materials studied did not appear to influence the degree of bracket base penetration achieved by the cements. In conclusion, Fuji Ortho LC offered a reduced energy-absorbing capacity immediately after bracket placement and reduced cohesive and mechanical adhesive strength. In addition, the glass transition temperature of Fuji Ortho LC was low; this may result in compromised attachment at temperatures above 60°C. Significant differences in the penetration coefficient of the materials studied have been recorded. However, the penetration of the 4 cements into a range of bracket base morphologies was uniformly good. Therefore, the differences in penetration coefficient recorded should not influence the quality of the bracket cement interface provided. [ABSTRACT FROM AUTHOR]

This study presents a strengthening method for reinforced concrete (RC) columns. The proposed method, which consists of a pair of steel rods, two reverse-threaded couplers, and four corner blocks, is feasible and straightforward. A quasi-static cyclic loading test was performed on the columns externally strengthened by the steel rods. It was found that the corner blocks and the external steel rods with a low prestress level effectively confined the concrete on the compression side of plastic hinges, which eventually induced flexural failure with a ductility higher than three in the strengthened columns. In addition, an analytical approach to predict the shear strength and ultimate flexural strength of the externally strengthened columns was applied. The comparison of analytical and experimental results showed that the analytical approach provided highly accurate predictions on the maximum strength and the failure mode of the externally strengthened columns. It is expected that the application of the proposed method will improve the seismic performance of damaged or deteriorated RC structures, thereby increasing their lifespan expectancy and sustainability. [ABSTRACT FROM AUTHOR]

This study evaluated the flexural mechanical properties of various thermoplastic denture base polymers (six polyamides, four acrylic resins, polyester, polypropylene, and polycarbonate) by three different testing conditions; specimens were tested in water bath at 37°C (Wet/Water, by ISO 20795-1), or in ambient air (Wet/Air) after being immersed in distilled water for 50 h, or after desiccation for 7 days (Dry/Air). The mean ultimate flexural strength (UFS) and flexural modulus (FM) for most products ranged from 27 to 61 MPa and from 611 to 1,783 MPa respectively, which failed to meet the minimum requirements of the international standard, except for polycarbonate (89 and 2,245 MPa). The mean UFS and FM values were ranked Dry/Air>Wet/Air>Wet/Water (p<0.05). In conclusion, the flexural mechanical properties of denture base polymers varied with the products and were significantly affected by the testing medium (air or water) and specimen conditions (wet or dry).

Objective : This study evaluated the reinforcing effect of glass fiber-reinforced composite (FRC) reinforcement on flexural strength at the proportional limit (FS-PL) of a repaired denture base resin. Materials and methods : Repaired denture base resins reinforced with metal and with FRC reinforcement, and that without reinforcement were tested. The ultimate flexural strength, the FS-PL and the elastic modulus of repaired denture base resins were tested. The joint efficiency (times) of the repaired denture base resins on the intact denture base resin was evaluated. Results : The repaired denture base resins reinforced with metal reinforcement and with FRC reinforcement had significantly higher ultimate flexural strength than the repaired denture base resin without reinforcement ( p < 0.05) and were not significantly different from each other ( p > 0.05). The FS-PL of a repaired denture base resin reinforced with the FRC reinforcement was similar to that with the metal reinforcement ( p > 0.05), and these were significantly higher than the FS-PL of a repaired denture base resin without reinforcement ( p < 0.05). The elastic modulus of the repaired denture base resin reinforced with the FRC reinforcement was significantly lower than that with metal reinforcement ( p < 0.05) and was significantly higher than that without reinforcement ( p < 0.05). The joint efficiency of the FRC reinforced specimen was 0.98. Conclusion : The FRC reinforcement had a reinforcing effect on the FS-PL of a repaired denture base resin., Competing Interests: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.