Search

The application of segmental precast assembled concrete cover beams in bridge construction is beneficial to promote low carbon, green and sustainable development of construction projects. To investigate the influence of the fabrication process of large key tooth joints on the shear performance of precast assembled concrete cover girders, the damage process of large key tooth assembled prestressed concrete cover girder specimens was investigated by using ABAQUS finite element analysis (FEA). The results show that: the section precast assembled concrete beams under four-point bending loading conditions, it is in the key tooth joint area that obvious cracking occurs; the finite element model of the large key tooth assembled prestressed cover beams can be effectively used to simulate the overall stress behavior of the beams; as the key tooth depth-to-height ratio increases, the stronger the connecting effect between the damaging key tooth and the positive key tooth is, and the load carrying capacity of the assembled beams is increased by 20% compared with the single key tooth, and ductility is increased by 30%; in the range of suitable reinforcement, the change of reinforcement rate does not have a significant effect on the stress performance of the beam. [ABSTRACT FROM AUTHOR]

This research paper offers an in‐depth comparative analysis focused on the long‐term durability of shear connectors fabricated from composite materials within a composite and concrete beam structure, extending over a length of six meters. To carry out this evaluation, the experiment employs a four‐point bending test designed to rigorously assess the performance and efficacy of two distinct types of tie straps utilized within the structure. The central element of this investigation, a composite beam integrated within a concrete deck, serves as the primary test specimen, providing a realistic and applicable context for the assessment. The overarching goal of this study is to meticulously examine and compare the resilience and resistance of these shear connectors when subjected to realistic, practical loading conditions. By doing so, the research aims to shed light on the critical performance characteristics of composite shear connectors, especially their role and effectiveness in enhancing the structural integrity and durability of composite and concrete beams in various structural applications. The outcomes of this study are expected to offer significant insights and contribute valuable knowledge to the field of structural engineering, particularly in understanding and improving the performance of composite shear connectors in structural frameworks. [ABSTRACT FROM AUTHOR]

The article presents the results of a detailed experimental campaign including a compressive strength test, three- and four-point bending test (3PBT and 4PBT, respectively) of polymer fiber reinforced concrete with the addition of metakaolin. The comprehensive analysis included three Types of concrete mixture differing in amount and used polymer fibers. It was concluded that polymer fibers did not influence the maximum compressive and flexural tensile strength of concrete. On the other hand, they had a beneficial effect on the ductility, residual and equivalent flexural tensile strengths, and fracture energy of samples. The mixtures of Type 1 and 2 were characterized by softening behaviour but the mixture of Type 3 by soft-hardening behaviour. In the 3PBT, the residual flexural tensile strengths obtained according to EN 14651 did not correspond clearly with equivalent flexural tensile strengths calculated in compliance with RILEM TC 162-TDF. It is noteworthy that the effectiveness and correctness of equations presented in other work of the authors referring to dependencies between deflection, crack and tip mouth opening displacements for the 3PBT were confirmed on samples with different composition and fibers. Based on the 4PBT, the equivalent flexural tensile strengths according to JCI-SF4 standard were calculated and the correlations with the results from 3PBT were defined.

The seismic resistance of fuel cladding during the long-term core cooling after loss-of-coolant accidents (LOCAs) was investigated by performing cyclic four-point bending tests (4PBTs) of up to 1000 cycles with fresh fuel cladding samples that experienced integral thermal shock test, simulating LOCA conditions, including ballooning, rupture, oxidation, and quench. 4PBTs were performed on the samples that survived the quenching process. The results showed that up to 1000 cycles and 5.8 Nm of cyclic loading moment, there was no apparent effect on the bending fracture limit of the fuel cladding under the 4PBT. The scatter of the bending fracture limit for a given equivalent cladding reacted (ECR) evaluated by the Baker–Just oxidation rate equation (BJ-ECR) is attributed to two primary factors: first, the difference between the prescribed and the actual oxidation behavior, confirmed by comparing the BJ-ECR and the ECR evaluated based on metallographic observation (M-ECR), and second, the variated shape of the rupture-opening area after the integral thermal shock test. The strength of the α phase-dominant zone near the rupture opening seems to contribute to the bending fracture limit. [ABSTRACT FROM AUTHOR]

In this study, the effect of curing temperatures of low-temperature curable polybenzoxazole (PBO) dielectrics on the interfacial adhesion energies between the Cu redistribution layer and PBO dielectric used in advanced fan-out packaging was systematically investigated using a four-point bending test. The results revealed that the interfacial adhesion energy increased when the PBO curing temperature increased from 175 to 200 °C, whereas it decreased when the curing temperature increased from 200 to 225 °C. The increase in the interfacial adhesion energy with an increase in the PBO curing temperature from 175 to 200 °C is attributed to the polymerization of PBO. However, the decrease in the interfacial adhesion energy as the curing temperature increases to 225 °C results from thermal stress. [ABSTRACT FROM AUTHOR]

Large aggregate asphalt mixtures can absorb noise, reduce water damage, effectively improve the service life of roads, and reduce environmental pressure. In this study, the fatigue characteristics of a large-sized asphalt mixture, LSAM-30, were investigated using four-point bending tests. The fatigue performance of LSAM-30 was compared to that of AC-13 and AC-20 asphalt mixtures across a range of temperatures, frequencies, and strains. The results indicated that the temperature, frequency, and strain significantly affect the fatigue performance of LSAM-30. As the temperature or frequency increased, the disparity in the fatigue performances of LSAM-30, AC-13, and AC-20 became more pronounced. Furthermore, the variations in the strain did not exhibit a clear pattern in the fatigue performance ratio among the three asphalt mixtures, with the ratio changes being minor (<5%). Additionally, an exponential-function-based predictive equation was proposed, showing how the fatigue characteristics of LSAM-30 vary with changes in frequency and temperature. [ABSTRACT FROM AUTHOR]

This study investigates the influence of elastic properties and nodes on the flexural behaviour of bamboo culms by comparing different characterization techniques and theoretical approaches. The most representative parts of the bamboo culm were selected using microscopic images of bamboo cross-sections. These were sliced from the bottom, middle, and top parts of a single culm and were analyzed with Digital Image Processing. Four-point bending tests were conducted on twelve culms of Phyllostachys aurea, subdivided into groups of untreated (UN) and heat-treated (HT) samples. The axial modulus of elasticity (Eb) and the shear modulus (G) were determined experimentally using four different mathematical models: (i) a global deflection model using the Euler-Bernoulli beam theory according to the ISO Standard; (ii) a global deflection model using the Timoshenko beam theory; (iii) a global deflection model based on the Timoshenko beam theory but accounting for the presence of nodes; and finally, (iv) a local model using extensometry. The dominant failure modes for UN and HT samples are described and discussed, and were influenced by the moisture content (MC). Approaches (i) and (ii) showed good agreement, giving reliable parameters to assess Eb. The third approach (iii) indicated that the nodes significantly influence the flexural behaviour of the culms. Approach (iv) was appropriate for determining G, but resulted in higher values of Eb, typically not representative of the material.

AbstractThe four-point bending test has inherent errors in measuring the flexural stiffness of tubes. The size of loading noses/supports could affect the response of equivalent bending moment on the tested tubes’ transverse section. The asymmetric axial strain distribution on the tested tubes’ transverse section depends on the tube’s thickness to diameter ratio. Based on the above phenomena, a four-point bending test with small-sized loading noses/supports and a characterization formula of tube’s flexural stiffness were proposed. The proposed methods were conducted on a thin-walled steel tube and a composite tube respectively. The errors between theoretical and experimental results were discussed. [ABSTRACT FROM AUTHOR]

The article presents the results of a detailed experimental campaign including a compressive strength test, three- and four-point bending test (3PBT and 4PBT, respectively) of polymer fiber reinforced concrete with the addition of metakaolin. The comprehensive analysis included three Types of concrete mixture differing in amount and used polymer fibers. It was concluded that polymer fibers did not influence the maximum compressive and flexural tensile strength of concrete. On the other hand, they had a beneficial effect on the ductility, residual and equivalent flexural tensile strengths, and fracture energy of samples. The mixtures of Type 1 and 2 were characterized by softening behaviour but the mixture of Type 3 by soft-hardening behaviour. In the 3PBT, the residual flexural tensile strengths obtained according to EN 14651 did not correspond clearly with equivalent flexural tensile strengths calculated in compliance with RILEM TC 162-TDF. It is noteworthy that the effectiveness and correctness of equations presented in other work of the authors referring to dependencies between deflection, crack and tip mouth opening displacements for the 3PBT were confirmed on samples with different composition and fibers. Based on the 4PBT, the equivalent flexural tensile strengths according to JCI-SF4 standard were calculated and the correlations with the results from 3PBT were defined. [ABSTRACT FROM AUTHOR]

In the last two decades, the utilization of timber in construction has gained increasing attention among researchers and sustainable building designers. Therefore, studies of climate impact on timber structures have been conducted, many of them focusing on the moisture content caused changes in timber. In the present study, four-point bending tests have been performed on three testing groups, containing 30 samples each. The first group has been tested under its natural conditions, while the second and the third groups were fully saturated with water. The third group was glazed with a protection material. The results show the changes in the modulus of elasticity and the modulus of rupture caused by the moisture content increase. In the same time the material behavior changed from brittle to semi-ductile or ductile for some samples. [ABSTRACT FROM AUTHOR]

The full-depth reclamation with Portland cement (FDR-PC) technology embodies an environmentally friendly approach to solving the damage to old asphalt pavement. Fatigue failure emerges as the predominant mode of degradation for FDR-PC pavement. The fatigue characteristics of the full-depth reclamation with Portland cement cold recycled mixtures were evaluated through four-point bending tests. Three contents (4%, 5%, 6%) of cement and three base-to-surface ratios (10:0, 8:2, 6:4) were utilized. The fatigue equations were derived for the mixtures using a two-parameter Weibull distribution. The results indicate that all correlation coefficients of the Weibull distribution model surpass 0.88, effectively projecting the lifespan of FDR-PC. With increases in cement contents and base-to-surface ratios, the fatigue life of the mixture extends, though with an augmentation of stress sensitivity. Comparative analysis with the fatigue equation model parameters of the current Chinese specifications for the design of highway asphalt pavement reveals that mixtures with a 4% cement content and combinations of a 5% cement content with a low base-to-surface ratio meet the requirements for inorganic-binder-stabilized soil. Additionally, mixtures with a 5% cement content and a high base-to-surface ratio, along with those with a 6% cement content, fulfill the specifications for inorganic-binder-stabilized granular materials. [ABSTRACT FROM AUTHOR]

Composite materials are increasingly used in aircraft structural components with complex structures like L, C, or T shapes, which can cause delamination failure in the thickness direction under complex loading. This research focuses on the experimental investigation of the effect of different adhesive reinforcement phases with an adhesively bonded external patch to examine the residual strength and delamination resistance of repaired glass/epoxy curved samples. The damaged region in curved samples was repaired using adhesive reinforcement phases like neat epoxy, chopped glass fiber, and particulate glass fiber, along with adhesively bonded external patches like hybrid patches of glass/Kevlar (HP G/K), glass/carbon (HP G/C), and intraply patch carbon/Kevlar (IP C/K). The findings show that chopped glass fiber HP G/C patch-repaired curved samples had a curved beam strength (CBS) and interlaminar tensile strength (ILTS) recovery of 222.87% and 149.54%, respectively, as compared to damage area removed samples. In addition, it exhibited higher peak force, residual strength, and less elongation when compared to HP G/K and IP C/K patch-repaired curved samples. According to the findings of this research, composite angle brackets in aircraft structural components can be repaired utilizing an adhesively bonded HP G/C patch filled with chopped glass fiber at the dressed site. Highlights • The effect of patch hybridization on repaired curved laminates was studied. • Four-point bending test was conducted on indented and repaired samples. • Residual strength and delamination behavior were studied. • Chopped glass fiber HP G/C patch repaired samples had higher CBS and ILTS. • Delamination onset and propagation were assessed using Photographic images. [ABSTRACT FROM AUTHOR]

Composite slabs, consisting of a precast plank and a cast-in-situ concrete topping, are the most commonly used horizontal structural components in prefabricated buildings. In order to solve the problem that the precast plank of composite slab is easy to crack and a lot of vertical supports are needed in its construction, this study proposes a new type of composite slab with a joint. The precast plank of this novel composite slab is fully prefabricated in the midspan area, and concrete is poured on-site only at the surrounding joints. In this paper, the bending performance of three composite slabs with a joint in different shapes of concrete topping and one cast-in-situ slab was investigated. The test results showed that the novel composite slabs with a joint in T-shape and trapezoidal concrete topping had similar properties as the cast-in-situ slab, including bearing capacity and cracking load, which can meet practical requirement. The use of bent-up steel bars and roughening of the interface between the precast plank and topping concrete can ensure effective transmission of internal forces at joint. The bearing capacity of the composite slabs with a joint in T-shape and trapezoidal concrete topping was evaluated using the formula in GB50010–2010, and the experimental values were 1.06 and 1.1 times the theoretical values, respectively, which provides a foundation for the design of two types of composite slabs with a joint. Meanwhile, based on the FEA software ABAQUS, numerical simulation was conducted on the composite slab with a joint in T-shaped concrete topping. The numerical finding exhibit close agreement with experimental results in terms of load-midspan deflection curve and the crack distribution.

The present study aims to explore the feasibility of employing 3D printing technology in reinforcing High Performance Concrete (HPC). To this end, the mechanical characteristics of HPC reinforced with four types of 3D-printed trusses (Pratt, Howe, Warren and Warren with vertical members) made from Polylactic Acid (PLA) have been evaluated. The 3D-printed truss reinforcements were plotted with the aid of 3D Max software. Then, they were produced using the Fused Deposition Modeling (FDM) technique and were placed into the molds. After that, the HPC mixture was poured into the molds and the specimens were cured for 28 days. Finally, the four-point bending tests were conducted on the specimens. The results showed that the employment of different 3D-printed trusses reduced the weight of the control samples between 0.5 and 2.5 kg. In addition, the application of 3D-printed Warren truss had the best performance among other types of trusses in terms of the flexural strength so that it increased the flexural strength of the control sample from 24.4 to 27.9 kN. Finally, all types of 3D-printed trusses increased the energy absorption capacity and were able to alter the fracture mechanism of HPC from brittle to ductile.

Mechanical tests on bone plates are mandatory for regulatory purposes and, typically, the ASTM F382 standard is used, which involves a four-point bending test setup to evaluate the cyclic bending fatigue performance of the bone plate. These test campaigns require a considerable financial outlay and long execution times; therefore, an accurate prediction of experimental outcomes can reduce test runtime with beneficial cost cuts for manufacturers. Hence, an analytical framework is here proposed for the direct estimation of the maximum bending moment of a bone plate under fatigue loading, to guide the identification of the runout load for regulatory testing. Eleven bone plates awaiting certification were subjected to a comprehensive testing campaign following ASTM F382 protocols to evaluate their static and fatigue bending properties. An analytical prediction of the maximum bending moment was subsequently implemented based on ultimate strength and plate geometry. The experimental loads obtained from fatigue testing were then used to verify the prediction accuracy of the analytical approach. Results showed promising predictive ability, with R2 coefficients above 0.95 in the runout condition, with potential impact in reducing the experimental tests needed for the CE marking of bone plates. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of specimen size on the flexural fatigue behaviour of two different locally-sourced pavement materials stabilised with 3% general purpose (GP) cement, viz., cement-stabilised Holcim road base (CSHRB) and cement-stabilised quartzite (CSQRT). Three different sizes of geometrically similar beams were tested under both static and dynamic four-point loading conditions. A suitable load pulse shape that simulates the critical stress response of the cement-treated base (CTB) under standard axe loading was generated for each beam size to perform stress-controlled flexural fatigue tests. The flexural fatigue test results showed the existence of a fatigue endurance limit in cement-stabilised pavement materials (CSPMs) at 28 days curing period. The analysis of experimental data revealed that the flexural properties of CSHRB (i.e. flexural strength and flexural fatigue performance) are appreciably affected by the size of the beam specimen employed in the flexural test while the flexural properties of CSQRT did not show a clear trend for increasing beam size. Bažant's size effect law is in good agreement with the flexural strength results obtained in this study for CSHRB. For materials that exhibit size dependence on flexural strength, an empirical relation is proposed in this study to determine the flexural strength of any given beam size using the flexural strength of standard beam size or indirect tensile strength of the beam material. Furthermore, a stress-based fatigue model incorporating the size effect is proposed to predict the flexural fatigue life of CSPMs in service. The factors that give rise to erroneous strain-based fatigue models were critically discussed on the basis of the results of this study. [ABSTRACT FROM AUTHOR]

In nature, there are widely distributed bi-modulus materials with different deformation characteristics under compressive and tensile stress states, such as concrete, rock and ceramics. Due to the lack of constitutive model that could reasonably consider the bi-modulus property of materials, and the lack of simple and reliable measurement methods for the tensile elastic parameters of materials, scientists and engineers always neglect the effect of the bi-modulus property of materials in engineering design and numerical simulation. To solve this problem, this study utilizes the uncoupled strain-driven constitutive model proposed by Latorre and Montáns (2020) to systematically study the distributions and magnitudes of stresses and strains of bi-modulus materials in the three-point bending test through the numerical method. Furthermore, a new method to synchronously measure the tensile and compressive elastic moduli of materials through the four-point bending test is proposed. The numerical results show that the bi-modulus property of materials has a significant effect on the stress, strain and displacement in the specimen utilized in the three-point and four-point bending tests. Meanwhile, the results from the numerical tests, in which the elastic constitutive model proposed by Latorre and Montáns (2020) is utilized, also indicate that the newly proposed measurement method has a good reliability. Although the new measurement method proposed in this study can synchronously and effectively measure the tensile and compressive elastic moduli, it cannot measure the tensile and compressive Poisson's ratios.

Extruded polystyrene (XPS) is frequently used in the construction of many different structures. Therefore, it is necessary to appropriately characterize its mechanical properties to ensure the safety of said structures. Among the available characterization tests, static bending tests are simple and easy to perform; owing to these characteristics, they should be performed more frequently than other tests. In static bending tests on XPS, there are several challenges owing to the high flexibility of XPS, and the chosen testing method and sample configuration affect the accuracy of characterization. For cellular plastics, including XPS, three-point bending (TPB) test methods are standardized by the International Organization for Standardization (ISO) and Japanese Industrial Standards (JIS) as in ISO 1209-2:2007 and JIS K 7221-2:2006, respectively, where the sample configurations are determined. Therefore, TPB tests of cellular plastics have been conventionally performed based on these standardized methods to characterize the bending properties. In contrast, investigations on the effects of testing methods and sample configurations have often been neglected due to the existence of these standardized methods. However, to characterize the bending properties of XPS accurately, the effects of the testing method and sample configuration must be examined in detail. In this study, three bending properties (Young’s modulus, proportional limit stress, and bending strength) of samples cut from an XPS panel were determined using three-point bending (TPB), four-point bending (FPB), and compression bending (CB) tests with varying sample span/depth ratios from 5 to 50 at intervals of 5, and statistical analyses were performed to determine the relevance of the tests. The effect of sample configuration on Young’s modulus could be reduced when the span/depth ratio range was 25–50, 25–50, and 15–50 in the TPB, FPB, and CB tests, respectively, whereas that on the proportional limit stress was reduced in the span/depth ratio range of 5–50, 20–50, and 15–50 in the TPB, FPB, and CB tests, respectively. Additionally, the effect on the bending strength was reduced when the span/depth ratio range was 5–50, 20–50, and 5–50 in the TPB, FPB, and CB tests, respectively. Therefore, these results suggest that the TPB and CB tests were more feasible than the FPB test when the span/depth ratio was determined as being 25–50 and 15–50, respectively. However, clear differences were observed in the sample bending properties determined in these tests. In light of these findings, further studies should be conducted to elucidate these differences.

Through the use of the material test system (MTS), bending fatigue tests are conducted in this work in order to investigate the attenuation law of fatigue performance of asphalt pavement in the end-stage of service. Response surface methodology (RSM) is used to analyze the effects of strain, frequency, and temperature on the asphalt surface layer's initial stiffness, fatigue life, phase angle, and cumulative dissipated energy when there is a 50 % reduction in the initial stiffness. Through multi-factor coupling analysis, the optimal combination is found and verified by the MTS-810 test system. Based on this, the data of the initial stiffness declining to 20 % was used for analysis on the AC-13C asphalt surface mixture of the APT full-size test road in the laboratory. At 15 °C and 10 Hz, the evolution law of the flexural stiffness, the residual stiffness, phase angle, and cumulative dissipated energy of the asphalt mixture was investigated. Analysis of the asphalt mixture's damage evolution under the single stage of loading and various strain levels revealed changes in the fatigue cracking crack. Beam specimens were made from asphalt mixture field test beams of AC-13C (laboratory accelerated pavement test road), AC-20C, and AC-25C (Ji-Qing expressway) to conduct four-point bending fatigue test (4PB). According to the constant strain fatigue prediction equation, and the residual fatigue life of prediction localized model was established. The results show that the influence of frequency and temperature on the initial stiffness and phase angle is more significant than strain, and the influence of strain on number of fatigue is more significant. The flexural stiffness of the asphalt mixture shows an obvious S-curve, and larger the tensile strain at the bottom of the asphalt layer, shorter the time needed to reach the termination condition, that is, the faster the fatigue failure occurs. When the damage termination condition is reached, under the strain level of 200–300 με, 60 % of the number of loading produce about 35–40 % damage, and the remaining 20 % of the number of loading lead to 10–20 % damage.

Fiber-reinforced polymers (FRPs) have received considerable research attention because of their high strength, corrosion resistance, and low weight. However, owing to the lack of ductility in this material and the quasi-brittle behavior of concrete, FRP-reinforced concrete (FRP-RC) beams, even with flexural failure, do not fail in a ductile manner. Because the limited deformation capacity of FRP-RC beams depends on the ductility of their compression zones, the present study proposes using a precast confined concrete block (PCCB) in the compression zone to improve the ductility of the beams. A control beam and four beams with different PCCBs were cast and tested under four-point bending conditions. The control beam failed due to shear, and the PCCBs exhibited different confinements and perforations. The goal was to find an appropriate PCCB for use in the compression zone of the beams, which not only improved the ductility but also changed the failure mode of the beams from shear to flexural. Among the employed blocks, a ductile PCCB with low equivalent compressive strength increased the ductility ratio of the beam to twice that of the control beam. The beam failed in pure flexure with considerable deformation capacity and without significant stiffness reduction. [ABSTRACT FROM AUTHOR]

The objective of this study is to explore the application of polymer‐based materials in composite bridges. The paper incorporates both theoretical and practical insights from the field of composite bridges, with a specific focus on shear connectors. The primary aim of this research is to substitute steel with polymer‐based materials in the composite cross‐section. The paper will primarily concentrate on the experimental aspect of the study, employing mechanical analysis through a four‐point bending test. The outcomes of the experiment will encompass the maximum deformation and strength of the composite beam. Such results serve as an impetus for further research and establish the theoretical foundation for designing composite bridges utilizing more environmentally friendly, lightweight, and sustainable materials. [ABSTRACT FROM AUTHOR]

This paper investigates the fracture behavior of high‐performance grouting materials in the grouted connection section of marine structures, where they are subjected to complex stress states. This study utilizes a combination of experimental and numerical simulation methods to establish a reliable numerical simulation technique for the fracture process of high‐performance grouting materials. The mixed mode fracture behavior is analyzed using six different types of specimens, and the strain contour is analyzed using the Digital Image Correlation technique. An extended peridynamics model is proposed for the numerical simulation, which adopts a fracture criterion based on strain energy density. The accuracy of the model is verified qualitatively and quantitatively, and the simulation results are consistent with the experiments. Overall, this study provides insights into the fracture behavior of high‐performance grouting materials in complex stress states and presents a reliable numerical simulation technique for the fracture process. Highlights: Different fracture criteria were used to analyze the four points bending test results.Digital Image Correlation technique was adopted to predict the crack initiation position and failure mode.The failure mode, failure angle, and fracture toughness of material were discussed.An extended peridynamics model is established for failure analysis of grouted material. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Southeast University / Dongnan Daxue Xuebao is the property of Journal of Southeast University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Concrete is a widely used material in various industries, including hazardous waste management. At the same time, its production creates a significant carbon footprint. Therefore, intensive research is being conducted to create more eco-friendly concrete, for example, partially replacing cement with by-products such as oil shale ash (OSA) or improving properties by adding dispersed fibers such as basalt fibers (BFs). The article consists of experimental testing of nine types of concrete and the modeling of crack propagation in bending. The basic trends of crack propagation in samples of concrete with OSA and BFs are simulated using a two-dimensional Finite Element (FE) model considering only material degradation on the opening crack surface and experimental data of three- and four-point bending tests. Crack propagation is modeled using the bridging law approach. A surrogate model for predicting the peak loading as a function of tensile strength and fracture work was created. An examination of the results of the FE model shows that the bilinear and nonlinear bridging law functions best describe the crack growth in the analyzed material. A comparison of experimental and modeled results showed that the length of the composite BF strongly affects the accuracy of the numerical model. [ABSTRACT FROM AUTHOR]

Due to permanent ground deformation (PGD) such as earthquakes and liquefaction, water supply pipes and connected joints may experience rotation and deflection through losing its function and complex water contamination. Since the specifications of joints are different in each country, evaluating joints are difficult to manage the functional maintenance of water network system. In this study, two metallic and three non-metallic pipe joints were selected through the joints commonly used in Korea. PGD simulation could be conducted through Four-point bending test which derives the result of deflection angle, moment, and strain value for damaged pipes. Each component showed above M-1 grade which resulted based on the grade of ISO 16134. To compare metallic pipe results, collar joint showed stronger binding force than the mechanical joint, but in deflection angle result mechanical showed higher value. In non-metallic pipe test, since its material contains large flexibility, strain value mainly affected its result. Based on this study, functional evaluation of water supply pipeline regarding the PGD was identified through comparing tendency of each joint characterization. Moreover, these data can be expected to be utilized as the basis of performance evaluation and critical component in piping design. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation that focuses on the flexural behavior of an innovative reinforced concrete–ultra-high performance concrete slab with an expanded polystyrene lightweight concrete core. This type of slab is proposed to serve the semi-precast solution, in which the bottom layer is ultra-high performance concrete working as a formwork during the construction of semi-precast slab, the expanded polystyrene lightweight concrete layer is used for the reduction of structure self-weight, and the top layer is normal concrete designed to withstand compressive stress when the slab is loaded. Two similar large-scale specimens with dimensions of 6200 mm × 1000 mm × 210 mm were fabricated and tested under four-point bending conditions to investigate the flexural behavior of composite slab. Test results indicated that three different layers of materials can work effectively together without separation. The bottom ultra-high performance concrete layer leads to the high ductility of the slab and has a good effect in limiting the widening of the crack width by forming other cracks. According to design code ACI 544.4R, a modified distribution stress diagram on the composite section was proposed and proven to be suitable for the prediction of flexural strength of the composite section with an error of 3.4% compared to the experimental result. The effect of the ultra-high performance concrete layer on the flexural strength of the composite slab was clearly demonstrated, and for the case in this study, the ultra-high performance concrete layer improves the flexural strength of the slab by about 11.5%. [ABSTRACT FROM AUTHOR]

Glulam is a construction material widely used all over the world. Common glulam often exhibits brittle damage under bending loads due to natural defects in the wood, which results in low load-bearing and deformation capacities. To improve the flexural performance of glulam beams, a new type of glulam longitudinally strengthened with flax-fiber reinforced polymer (FFRP) composites is proposed. Eighteen full-scale timber beams with and without FFRP were tested, where the bonding length and the bonding layers of the FFRP are varied for FFRP strengthened beams. Results demonstrate that the flexural performance of strengthened beams improves significantly with increasing bonding length. The number of layers of FFRP had a minor effect on the flexural performance when the bonding length was 2700 mm. Moreover, the reliability of load capacity of beams can be improved by bonding FFRP with lengths over 1400 mm. A theoretical calculation predicts the ultimate flexural capacity of the strengthened beam, and exhibits good agreement with the experimental results. Finally, a cost analysis is made to evaluate the economics of various reinforcement methods, indicating that three-layer FFRP of 2700 mm strengthening length significantly increases the flexural performance at lower cost than other strengthened types. [ABSTRACT FROM AUTHOR]

A refined geometrically nonlinear theory of sandwich plates and shells with a flexible soft core and composite facing layers having low shear and compressive stiffness was introduced. It is based on the refinement of the shear model of S.P. Timoshenko taking into account transverse compression, as well as on the use of simplified three-dimensional equations of the theory of elasticity for a transversely flexible core. By integrating the equations over the transverse coordinate to describe the stress-strain state of the core, two two-dimensional unknown functions were introduced, which are transverse shear stresses, constants by thickness. For describing the static deformation process with high variability of the parameters of the stress-strain state of the core, two variants of two-dimensional geometrically nonlinear equations were derived. In the first one, the geometric nonlinearity was considered in the standard approximation by retaining the terms containing only the membrane forces in the facing layers. In the second variant additional geometrically nonlinear terms of a higher order of smallness were kept. Using the compiled equations, a geometrically and physically nonlinear problem of four-point bending of the sandwich specimen was formulated with regard to the physically nonlinear relationship between the transverse shear stresses and the corresponding shear strains in the facing layers. A numerical method stemming from the finite sum method (integrating matrix method) was developed for its solution and post-buckling behavior of specimen was investigated. It was shown that when the specimens are tested, their failure can be caused by the transverse shear buckling mode of the facing layer near the loading roller.

As regard to cementitious composite materials added a certain dosage of fiber, estimation of tensile constitutive law through inverse analysis methods is no longer extraordinary. However, development or improvement to achieve an effective method for estimating such a tensile behavior of fiber reinforced concrete (FRC) or Ultra high-performance concrete (UHPC) is still an interesting topic to researchers. In this respect, the paper presents a development of inverse analysis method developed by Lopez to obtain the stress-strain behavior of UHPC from the four-point bending test. By applying optimization algorithm into the iterative procedure of method, an improvement could be obtained for the inverse analysis with a high degree of automation in calculation. A post-process treatment for inverse analysis results is also proposed to bring a finer agreement between the tensile behavior curve obtained by the inverse analysis and result curve of uniaxial tensile test (UTT). The effectivity of process is shown through a comparison between the result obtained by the proposed method and the result in Lopez’s public paper.

The presented study investigates the effect of a recently developed multiaxial geocomposite made of polypropylene geogrid and non-woven fabric on the delay of crack propagation, based on four-point bending tests of large asphalt concrete beams – both for reinforced and non-reinforced specimens. Several approaches are described in this study, including analysis of stiffness modulus decrease and analysis of crack propagation using dissipated energy. The study also includes investigation of the impact of reinforcement on shear resistance of the inter-layer bond. The reinforced system displays reduced decrease in stiffness during cyclic loading; it is able to bear loads over a longer period, in contrast to the unreinforced system. An increase in fatigue life by a factor of 10–22 is possible, as compared to the unreinforced system. The factor of relative increase in the number of cycles to the first initiation of crack in lower asphalt layer when reinforcement is introduced ranges from 5 to 10. [ABSTRACT FROM AUTHOR]

Desert sand foamed concrete (DSFC), which offers advantages, such as fire resistance, sound insulation, construction convenience, and environmental benefits, has not been used in cold-formed steel (CFS) composite floors. In this study, four full-scale specimens were designed and tested under four-point bending to investigate the effect of foamed concrete filling and holes. The load–deflection curves and strain distribution at mid-span were measured and analyzed. The experimental results indicated that the failure modes of the CFS composite floors were local buckling at the top flange for specimens without holes and tensile failure at the bottom flange for specimens with holes, respectively, which differed from the web crippling observed in non-composite floors. Moreover, due to the presence of foamed concrete, the flexural stiffness was significantly improved by 117.6% and 73.6% for the specimens without holes and with holes, respectively, while ultimate capacity increased by 224.9% and 121.8%, respectively. Through the nonlinear finite element models validated against experimental results, it was found that the flexural behavior was improved with the increase in CFS thickness and foamed concrete strength. The impact of the holes was not obvious for specimens infilled with holes. [ABSTRACT FROM AUTHOR]

The present paper experimentally investigates the flexural behavior of steel-concrete-steel (SCS) composite beams with lightweight polypropylene fiber-reinforced concrete core and corrugated-strip shear connectors. For this purpose, the four-point bending tests have been performed on 11 specimens. This aims to investigate the influence of lightweight concrete core on the performance of the beams, and therefore all the parameters in the tested beams are kept constant except the type of concrete core. Based on the results of the performed quasi-static loading tests, the observed failure modes and force-displacement curves are reported and analyzed to achieve a deeper understanding of the influence of lightweight fiber-reinforced concrete on the flexural behavior of SCS beams. It was found that the utilization of polypropylene fiber has an improving influence on the performance of SCS beams, and especially enhances their toughness and ultimate deflection. A positive linear relationship between the fiber content (up to 2 %) with the specimen’s toughness was detected. It was also found that the addition of micro-silica to the lightweight fiber-reinforced concrete core results in considerable improvement in the flexural load capacity of the tested SCS beams. In addition, numerical finite element models including detailed material and geometric modeling of SCS beams are developed using the general software package ABAQUS. The accuracy of the developed models is validated using the attained experimental results. The numerical models can be used to simulate the load-deflection behavior and ultimate strength of SCS sandwich beams.

Purpose: The aim of this in vitro study was to assess the efficacy of fiber reinforcement to enhance flexural strength of the transitional implant‐supported fixed dental prosthesis (TISFDP). Materials and methods: One hundred and forty denture acrylic resin plates (64 mm × 12 mm × 5 mm) with two 7 mm diameter holes were fabricated using heat‐polymerized type (Lucitone 199) and CAD‐CAM prepolymerized type (AvaDent) materials to simulate a chair‐side reconstruction of the TISFDP. Specimens were divided into 7 groups (n = 10) according to the airborne‐particle abrasion of titanium cylinder (Straumann) surface and locations of fiber reinforcement ribbons (Ribbond‐ULTRA). No cylinder surface abrasion and no fiber added acrylate specimens were used as the controls. The prosthetic screws were hand‐tightened on a custom fixture with analogs. Specimen hole and cylinder were joined using a 50:50 mixture of chemically polymerized resin (QYK‐SET; Holmes Dental) and repair resin (Dentsply Sirona). Ten acrylate specimens with no holes were fabricated from each tested material and assigned as positive controls. A modified four‐point bending test (ASTM standard‐D6272) was conducted using a universal testing machine and a custom fixture with a crosshead speed 1 mm/min. The maximum failure loads were recorded. Data were statistically analyzed using 2‐way ANOVA and the Tukey tests at α = 0.05. Results: The flexural strength values ranged from 55.4 ±8.3 to 140.9 ±15.4 MPa. The flexural strength decreased significantly when fiber was attached on the titanium cylinder surface (p < 0.05). There were no statistically significant differences in flexural strength values between specimens with and without titanium cylinder surface abrasion (p > 0.05). Statistically significant improvement in flexural strength was observed in specimens with fibers attached around the specimen holes (p < 0.05) buccally and lingually. The obtained values were not statistically significantly different from the positive controls (p > 0.05). Some fixation screw fractures were observed before catastrophic failure of specimens during testing. Conclusions: Fiber reinforcement significantly improved the flexural strength of denture acrylic resins only if placed around the specimen holes on the tension side at the site of initiation of crack propagation. Even when the specimens underwent catastrophic failure, the segments remained attached to each other with the attached fibers. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, experimental and statistical analyses were conducted to reveal the effect of micro steel and/or polypropylene (PP) fibre with macro steel fibre as binary and ternary hybridization on the fresh, mechanical and flexural performance of hybrid fibre reinforced self-compacting concrete (HFR-SCC). For this purpose, some tests were conducted related to fresh and hardened properties. It was seen that PP had negative effect on the fresh properties of HFR-SCC mixtures compared to micro steel fibre. Moreover, multiple linear regression (MLR) was used to estimate the fresh and hardened properties of HFR-SCC as function of the percent of fibres by volume while ANOVA analysis determined the contributions of parameters. It was obtained from statistical analysis that there was a good correlation between experimental results and predicted values with approximately R2=0.91 except for compressive strength. Finally, the use of PP with micro steel fibre as ternary hybridization increased the compressive, splitting, flexural tensile strengths, toughness and ductility of HFR-SCC with 1.1%, 13.2%, 18.8%, 14.9% and 26.3%, respectively, while the inclusion of PP into the mixture as binary hybridization had less positive effect on the hardened properties compared to binary steel fibre reinforced SCC with 0.25% micro steel fibre. [ABSTRACT FROM AUTHOR]

Textile-reinforced concrete (TRC) is a cement-based composite material that uses textile as a reinforcement material. The weft-direction fiber bundles in the traditional orthogonally arranged warp–weft textile hardly bear force, and its bonding strength with the weft fiber bundle is not ideal. Under the action of force, a small included angle between the stressed fiber bundle and the stressed direction can effectively increase the anchoring effect of their fibers in the matrix, resulting in higher bonding and reinforcement efficiency. To improve the utilization rate of fibers and the bonding strength between the textile and the concrete matrix, an arrangement along the diagonal of the grids was proposed in this paper. The flexural properties of basalt TRC plates with orthogonal grids (OG-BTRC) and plates with nonorthogonal grids (NOG-BTRC) with different grid angles and grid sizes with different laying methods, namely, a side layout (SL) and diagonal layout (DL), were studied through four-point bending tests. A comparative analysis was carried out with an ABAQUS simulation and the test results. The results showed that with a decrease in the grid angle, the BTRC specimens gradually showed a failure mode of multiple cracks, and most of the cracks appeared in the pure bending area; as the grid angle decreased, the BTRC specimens exhibited excellent flexural bearing capacity, good ductility, and high toughness. The total number of cracks on the specimen increased when it failed, while the spacing of the cracks decreased, and the fracture morphology appeared as fine and uniform features. The toughness of the specimen with a small grid angle using the DL laying method was greater than that using the SL laying method. The software simulation value matched the test data well, which proved that the test result was reliable. [ABSTRACT FROM AUTHOR]

This paper presents the numerical strength prediction of externally carbon fibre reinforced polymer (CFRP)- strengthened concrete beams using a traction-separation law. From reported experimental observations, the externally CFRP-strengthened concrete beams are prone to exhibit mixed-mode cohesive failure within the adhesive layer before beam separation. Testing series comprised of different strengthening schemes and CFRP plate length indicated that all specimens failed in cohesive delamination (debonding). This study performed a numerical modelling framework by using a combination of extended finite element method (XFEM) within the concrete beam and cohesive zone model (CZM) within the adhesive layer to explicitly demonstrate debonding phenomenon as seen in experimental observations. The results showed that the modelling technique was able to capture the debonding failure and the crack propagation of the concrete beam, consistent with experimental observations. Hence, the combination of the XFEM-CZM approach yields good agreements with experimental datasets. It was found that discrepancies of maximum load-bearing capacity between numerical modelling and previous experimental work are below 17 % were found in all testing series. However, due to the unavailability of fracture energy properties of tested concrete, the current approach used values of similar concrete grade from other literature. It is expected that better results would be obtained if the fracture energy of the investigated concrete beam was independently measured.

Acoustic emission (AE) and 4D X-ray computed tomography (4D XCT) were used simultaneously to study crack initiation and propagation in two different types of quartz-rich sandstones during the four-point bending experiments. Statistical analysis of the AE response indicated the failure mechanisms and their dynamics. The characteristic changes observed in the AE response defined the timing of the bending interruptions for XCT scanning to reveal the development of the crack. It was possible to quantitatively describe the developing cracks in their dimensions and volume and relate this information to the rate of decrease in the post-peak region of the material response. It could be concluded that the combination and concurrent use of AE and XCT techniques represents a highly effective and reliable instrument for observation, description, analysis of the crack propagation process, and rock disintegration in detail at a microscale level. With regard to the specific sandstones studied, Mšené sandstone is softer, respectively, less brittle, while Kocbeře sandstone is characterised by a more brittle behaviour accompanied by an AE signal with higher amplitudes compared to those of Mšené. • Simultaneous AE and 4D XCT tests provide a data set on crack propagation in stones. • Crack propagation dynamics identified by statistical analysis of AE data. • Quantification of crack characteristics using 4D computed tomography. [ABSTRACT FROM AUTHOR]

Ultra-high performance concrete (UHPC) has been widely used in wet joints of precast bridge deck panels (PBDPs) due to its remarkable compressive strength, excellent tensile strength, and exceptional durability properties. However, there is a lack of consistent understanding regarding the mechanical properties of PBDPs with UHPC wet joints, especially shear behavior. To investigate the shear performance of PBDPs with UHPC wet joints, a total of seven bridge deck panels (BDPs) were designed and conducted by four-point bending tests. The test parameters included reinforcement types (straight bar and U-bar), lap details (contact lap and non-contact lap), joint widths (150 mm, 200 mm, 250 mm, and 500 mm), and filling materials (NC and UHPC). According to the test results, the shear behavior of seven BDPs was analyzed. The experiment results showed that all specimens exhibited shear failure, with critical shear cracks occurring in the shear span. For PBDPs with U-bars, the shear capacity of 200-mm-wide UHPC wet joints was 1.5 % higher than that of 500-mm-wide NC wet joints. In addition, the failure pattern had a tendency to gradually shift from shear failure to flexural failure when the width of UHPC wet joints was reduced from 250 mm to 150 mm. To establish 3D finite element (FE) models, a cohesion-friction hybrid model was proposed. The FE models had good simulation accuracy, with a maximum deviation of 7.0 %. Furthermore, a parametric analysis was performed to assess the influence of critical parameters on shear performance. The results showed that longitudinal reinforcement has a greater influence on the shear performance of PBDPs. Finally, shear capacity formulas in the design codes were verified in comparison with test results. The deviation of theoretically calculated values from test results was within 10 %. • Seven BDPs were designed to investigate the shear behavior of wet joints. • It is feasible to replace 500-mm-width NC wet joints with 200-mm-width UHPC wet joints for PBDPs with U-bars. • As the width of UHPC wet joints decreased, the failure mode shifted from shear failure to bending failure. • The cohesion-friction hybrid model was proposed to simulate the behavior of joint interfaces. [ABSTRACT FROM AUTHOR]

Laminated glass beams are used as supporting structural elements for glass roofs or glass facades to maximize their transparency. Their failure is rather brittle, with a residual load-carrying capacity ensured by the interlayers significantly lower than the initial glass fracture resistance. By adding ductile tendons as reinforcement elements along the glass edges subjected to tensile stresses, both the initial glass fracture resistance and especially the residual load-carrying capacity can be improved. An additional post-tensioning of the beams by pre-stressing the tendons can increase the initial glass fracture resistance even further. In most previous research, mechanically pre-stressing the tendons and subsequently fixing them to steel parts at the ends of the beams was used for obtaining post-tensioned laminated glass beams. This paper presents investigations on a novel approach for post-tensioning laminated glass beams with adhesively bonded iron-based shape memory alloy tendons along both longitudinal glass beam edges. This allows a relatively easy post-tensioning process by, first, adhesively bonding pre-strained tendons to the glass beam edges and, second, triggering the shape memory effect of the tendons through electrical resistive heating. Experimental and simulation results are presented for laminated glass beams without reinforcement, reinforced laminated glass beams and post-tensioned laminated glass beams subjected to four-point bending. Two different adhesives, an epoxy and a methacrylate, are investigated for bonding the tendons to the glass beam edges. The results show that a post-tensioning of laminated glass beams is feasible by electrical resistive heating of the iron-based shape memory alloy tendons, but also indicate an optimization potential of the applied process. Moreover, the contribution of the tendons, with and without post-tensioning, to improving the initial glass fracture resistance and the residual load-carrying behaviour are evaluated and advantages and disadvantages of the two different adhesives are highlighted. The applied simulation approach, covering both the post-tensioning and the four-point bending, allows a relatively good prediction of the initial and residual force versus displacement behaviour, and of the glass crack patterns for the different types of beams. • Electrical resistive heating allows for post-tensioning glass beams with Fe-SMA tendons. • Adhesively bonded Fe-SMA tendons increase initial load-carrying resistance of glass beams. • Activation of Fe-SMA tendons further increases load-carrying capacity of glass beams. • Adhesively bonded and activated Fe-SMA tendons lead to high residual load-carrying capacity. • Finite element simulations allow structural behaviour prediction of post-tensioned glass beams. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)