Beam Specimens Research Articles

Numerical Study of GFRP-reinforced Concrete Beams with Straight and Hooked-end Bar Lap Splices

Glass fibre-reinforced polymer (GFRP) has been increasingly used as the main reinforcement in concrete structures due to its durability and resistance to corrosion. However, there is a lack of data regarding the bond behaviour of GFRP bars with 180-degree hooked ends used in flexure concrete elements. To investigate the effects of the hooked ends of GFRP bars on the bond strength with concrete, beams reinforced with GFRP bars with straight and hooked-end lap splices at the midspan were modelled using ABAQUS/Standard software. The finite element models were validated using the experimental results of four full-size concrete beams. Two beam specimens had straight-end bars, while the other two had hooked-end bars. Sensitivity analysis was performed to find the proper values for model verification, such as dilation angle and mesh density. According to the outcomes of the parametric study conducted in this research, changing the length of the bar lap splices in the range of 15 to 40 times the bar diameter had a negligible effect on the beam’s overall behaviour. Increasing the number of reinforcing bars from 3 to 5 increased the beam flexural strength by about 33%, whereas increasing the diameter of the bars from 10 to 20 mm doubled the beam strength.

Composite Delta Beam for Slim Floor Construction

Abstract: The structural behaviour of the composite Flush Beam for slim floor as a whole has been investigated. The deformation behaviour of the structural members Steel beams with trapezoidal cross-sections and specially punched webs were developed as composite beams in slim floors. The estimation of the flexural stiffness and bending capacity of composite slim beams is rather complicated, because the influence of many factors should be taken into account. These factors include variable section dimensions, Profile of the beam, stiffness of the beam and interaction between steel and concrete. In this paper, analytical investigations have been conducted to investigate the deflection behaviour of Flush beam specimens under monotonic loading. A design procedure is developed for composite slim floor Flush beams based on cross-sectional analysis and the flexural properties of the slim floor beams are evaluated. From the analytical investigation it was found that the deflection of delta beam is 48% less than the conventional I-beam More over the stiffness of the Delta beam is 49.8% higher than the I-beam

Bending characteristics of partially reinforced aluminum/CFRP hybrid hat‐section beam structures with an adhesively bonded joint: An experimental, numerical, and analytical study

AbstractA significant feature about hybrid structures is the strengthening of critical areas in order to increase the load capacity of the beams. This research evaluates the energy absorption capability and bending collapse behavior of an aluminum hat‐section with adhesively bonded of carbon fiber reinforced plastic (CFRP) as a partial reinforcement (PR) hybrid beam. The aluminum layers and processed CFRP laminates were bonded with adhesive joints to produce the beams with varied layups for hybrid beams. The specimens showed a range of bending collapses, and the hybrid specimens' peak load and load drop differed depending on failure mechanism. The experimental results reveal that the amount of SEA of the hybrid beam specimens was higher compared with that of the aluminum beam, with Al/CFRP [0/90]S PR hybrid beam exhibiting an 85.9% improvement in SEA value. Subsequently, FE models of aluminum and hybrid beams were developed for bending collapse analysis, and the finite element results were consistent with the experimental specimens' validation. In addition, the consequences of progressive damage failure in the interface effect and transverse matrix damage in various layups were investigated. Eventually, the Kecman model is used to perform analytical modeling of hybrid and aluminum beams in order to examine the impact of CFRP partial reinforcing components based on various bending moment hinge lines.Highlight Bending characteristics of adhesively bonded partially reinforced Al/CFRP beam Experimental and numerical investigation on the beams under three‐point bending Analytical study for the prediction of energy absorption characteristics A good agreement between numerical, theoretical and experimental results

Fracture toughness of aged oil paints

The fracture toughness in opening mode GIc for selected oil paints from Mecklenburg's Paint Reference Collection after approximately 30 years of natural ageing was determined using the procedure adopted from the ASTM D5528–13 standard in which double cantilever beam specimens are split in tensile tests. The careful reglueing procedure allowed multiple fracturing tests to be carried out that not only improved statistics of the measurements but also provided insight into the variation of the fracture toughness across the paint film observed for some paints. The latter was due to pigment sedimentation or chemical change of the oil binder as a result of the easier access of oxygen from the side open to the air. For the lead white paint, used over centuries both in paint films and oil grounds, the GIc values more than doubled from 18 to 39 J/m2 for three consecutive cracks formed at an increasing distance from one side of the paint film. The study demonstrated that fracture toughness corresponding to the first crack formation in aged oil paints ranged between 10 and 40 J/m2, relatively low values compared to the animal glue-based ground in paintings. In consequence, oil paints are more vulnerable to crack initiation and growth induced by tensile stress than the ground layer. The measurements filled the gap in the knowledge required for the analysis of fracturing or delamination processes in paintings.

Deformation Behavior and Fracture Strength of Single‐Crystal 4H‐SiC Determined by Microcantilever Bending Tests

In this study, the deformation behaviors and mechanical properties of 4H‐SiC single crystals are investigated using microcantilever beam specimens with two different sizes, A and B (A < B). Tensile stress is applied along <20> direction. Plastic deformation, or nonlinearity, is observed in the stress–strain curves, and yield stress, or proportional limit, coincides between the two specimens at ≈25 ± 2 GPa. Scanning transmission electron microscopy and transmission electron microscopy studies show that the plastic deformation is due to dislocation activities; multiple‐dislocation pileup areas are observed in both the specimens. Assuming {100}/<110> prismatic slip which most plausibly occurs in the <20> stress application, the critical resolved shar stress is estimated to be 10.9 GPa, which agrees well with the previous studies. Measured fracture strength is 41.9 ± 2.8 and 33.5 ± 2.4 GPa for the A and B, respectively. Dislocation–fracture relationship is discussed on the basis of dislocation‐based fracture mechanics, etc. It is suggested that cracks form within the multiple‐dislocation pileup area, by interaction with dislocation pileups, and act as fracture origins. A's strength is close to an ideal tensile strength of 4H‐SiC in the <110> direction, 47–55 GPa.

The Impact of Silver Diamine Fluoride Only or Simultaneously With Potassium Iodide Treatment on the Bond Durability of Resin Composite Material on Primary Teeth.

We aim to evaluate the bond strength between resin composite and primary demineralized dentin, pretreated with silver diamine fluoride (SDF) and simultaneous SDF with potassium iodide (KI) after thermal aging. In this in vitrostudy, human carious-free primary molars were randomly assigned into three groups and prepared by exposing the superficial dentin. The primary dentin of each molar was demineralized. The first group (the control) received saline treatment before bond application. SDF was pretreated for the second group, whereas SDF and KI were used for the third. After that, the pretreated dentin was immediately built with resin composite bonded with a universal adhesive and kept wet for 24 hours. Then, the pretreated molars were prepared into beam specimens for microtensile bond strength (µTBS), 16 for each group, and subjected to thermal aging. Lastly, they were tested using a universal testing machine, and the resulting data were analyzed using one-way analysis of variance (ANOVA) followed by Tukey's post hoc test. It was found that the SDF-KI group had a significant difference with both the control and SDF groups (p < 0.05), while the control and SDF groups showed no significant differences (p =0.310). The SDF-KI group had the highest mean value of 11.73 ± 4.39 megapascal (MPa). In contrast, the control group had the lowest mean value of 9.31 ± 3.41 MPa. Post hoc pairwise comparison results showed that SDF-KI pretreatment had a significantly higher strength value than the control and SDF groups. Pretreatment of demineralized primary dentin with SDF-KI does not negatively affect the immediate loading of resin composite. However, under the limitation of this study, KI application after SDF pretreatment is recommended to enhance the bond's durability of resin composite to demineralized dentin.

Experimental investigation on the effect of hoop spacing and crosstie configuration on the cyclic performance of reinforced concrete beams

According to ACI 318-19(SI), in the plastic hinge zone of RC beams, the longitudinal reinforcement at each corner and every other longitudinal reinforcement must be enclosed by the corner of the closed hoop or the hooks of crossties. However, in RC construction practice, the longitudinal reinforcement of RC beams is densely arranged, making construction difficult. In this study, four large RC beam specimens were designed and fabricated to conduct experiments to verify the effect of hoop spacing and crosstie configuration on the cyclic performance of reinforced concrete beams. It is found that: (1) The crosstie configuration with seismic hook engaging the longitudinal reinforcement at the bottom is recommended and that during construction, within the range of twice the beam depth from the RC column outer face, the bottom and side formwork should be completed after the crossties are assembled, which should solve the problem of difficult construction. (2) The transverse reinforcement spacing between 4 and 6 times the smallest longitudinal reinforcement diameter of RC beams may have no significant effect on the cyclic performance of RC beams. (3) The requirement that in the plastic hinge zone of RC beams, every corner and alternate longitudinal bar on the perimeter must have lateral support provided by the corner of a tie or crosstie in ACI 318-19(SI) may not have a major impact on the cyclic performance of the RC beam. (4) The ultimate drift angle of each specimen in the negative direction was between 4.3% rad and 4.5% rad; thus, all the specimens satisfied the ACI requirement. However, the cyclic performance (plasticity rotation angle) of all specimens basically did not meet the requirement of 3.0% rad for earthquake-resistant structures.

Experimental study on the effectiveness of strengthening of reinforced concrete beams with opening in shear span using CFRP sheets

In reinforced concrete beams, the opening is frequently required for the passage of utility ducts and/or pipes. The presence of such web openings leads to a reduction of the strength and stiffness of the beam. To ensurethe safety of the reinforced concrete beam, a strengthening system around the opening is necessary. This paperaims to contribute to a better understanding of the shear behavior of reinforced concrete beams with openingsin the shear span, strengthened with Carbon fiber-reinforced polymer (CFRP) sheets. The study is based on anexperimental program carried out on six beams. All beam specimens were 850 mm long with a cross-sectionof 150 × 250 mm and a shear span to beam depth ratio (a/d) of 1.48. One beam without any openings served asthe control specimen, while the remaining five beams featured circular or rectangular openings within the shearspan and with/without shear strengthening using CFRP sheets around the openings. The test results obtainedfrom this experimental program provide insights into the shear behavior of beams with openings, both with andwithout strengthening using CFRP sheets. Additionally, the potential advantages and effectiveness of employingCFRP strengthening techniques for opening strengthening are investigated and discussed.

Investigation on the size effect of compacted clay mode I fracture based on NDB specimens

The size effect is closely related to the cracking resistance of compacted clay, which is crucial in engineering applications, but little attention has been given to it in previous studies. This study investigated the size effect on mode I fracture behaviors of compacted clay using single-edge notched deep beam (NDB) specimens. Through the digital image correlation (DIC) method, the crack initiation mechanism of compacted clay was analyzed. The results showed that the specimen size and dimensionless crack length did not change the failure pattern, while peak load, peak displacement, and fracture energy gradually increased with the increase of specimen size. Based on the load–displacement curves and the horizontal strain evolution laws, the three horizontal strain stages at the crack tip crack initiation point were defined, i.e., the steady strain growth stage, the nonlinear strain growth stage, and the nonlinear strain intensification stage. Through the Bažant size effect model (SEM), the fracture process zone length Cf and mode I fracture toughness KIC of compacted clay without the size effect were inferred. The separated form of SEM was applied, and the contribution ratios of the strength criterion and linear elastic fracture mechanics were quantitatively analyzed. Combing the characteristics of the NDB specimens, a prediction model considering the support spacing, specimen structure parameters, and fracture toughness was established.

Experimental study of failure of glulam-concrete composite beams

AbstractThis paper is dedicated to the memory of Dr. Miklós Iványi, who instilled in the authors an appreciation for experimental investigations, which are foundational to understanding material and structural behavior. Timber-concrete composite structures are increasingly adopted for new buildings due to their favorable sustainability parameters and the increased availability of cross laminated timber. For larger spans, however, solid timber floors lead to higher timber volumes and the use of glulam beams may become necessary for a more efficient use of wood. This paper presents laboratory tests of glulam-concrete composite beams and is the first in a series of two papers on investigating the associated failure mechanisms. Three full-scale glulam-concrete beam specimens were studied. The glulam and concrete are monolithically interconnected using a continuous layer of adhesive. Shear reinforcement was added to the glulam beams to allow for failure mode control. Static load tests to failure were conducted along with acoustic emission monitoring to track the progression of the failure. The results indicate that the shear reinforcement of the glulam layer affects the load capacity of the composite beam through shifting the failure from a shear to a tension failure mode. Similar glulam-concrete beams can enable larger span applications for buildings and bridges while maintaining an attractive sustainability performance.

Experimental study and theoretical analysis of ECC type I fatigue fracture after subjected to sub-high temperature

Three-point bending (TPB) fatigue fracture tests were conducted on Engineered Cementitious Composites (ECC) prefabricated notched beam specimens at three target temperatures (T = 20℃, 100℃, 200℃) and three stress levels (S = 0.7,0.8,0.9). The fatigue life, maximum crack opening displacement (CMODmax), and stiffness attenuation were characterized. The evolution of cracks is recorded in real time. The fatigue crack growth curve (af-N) is obtained by fitting a logistic function, and the crack growth rate is determined based on its first derivative. It is found that compared to 20℃, there is a slight increase in the fatigue life of ECC, and the critical crack growth rate decreases after 100℃. After 200℃, the fatigue life of ECC decreases, the brittleness increases, and the crack growth rate increases. This is mainly related to the degradation of PVA fibers at 200℃, with most fibers being pulled off during fatigue loading, which leads to a decrease in crack propagation resistance.

Bond between deformed steel rebars and concrete at elevated temperatures

This paper presents an experimental study on the bond behavior between deformed steel rebars and concrete at elevated temperatures, focusing on the effect of heating rate on the flexural bond strength. Most of the earlier research on this topic involved axial pull-out tests in cooled-down conditions. None of the earlier research has studied flexural bond behavior in hot conditions. Also, there is a lot of variability in the test conditions used in these studies. To overcome these challenges, a number of beam specimens whose flexural behavior was governed by bond failure were prepared and tested at elevated temperatures. Two different rebar diameters (12 mm and 20 mm), and two different rates of heating (2 °C/min and standard fire curve) were used in these tests. The results indicate that a rapid rate of heating affected the bond strength more significantly. Also, the 20 mm-diameter rebar had lower bond strength per unit surface area in comparison to the 12 mm-diameter rebar. The bond ductility reduced more rapidly than the bond strength as the interface temperature rose.

Bayesian analysis of acoustic emission data for prediction of fatigue crack growth in concrete

Acoustic emission (AE) is a valuable technique for non-destructive testing, enabling real-time monitoring and measurement of fatigue crack growth in engineering structures. The present study focuses on investigating the fatigue crack growth behaviour in plain concrete specimens through Bayesian analysis of AE data collected during the testing of beam specimens under three-point bending. A log-linear relationship is established between parameters extracted from AE waveforms and the fatigue crack growth in concrete. Additionally, AE energy is identified as the most suitable parameter for characterising the fatigue behaviour of concrete. Bayesian regression is employed for estimating model parameters and their posterior distributions. The proposed model is validated through post-processing and Bayesian analysis of experimental data from the literature. Furthermore, it is demonstrated that the estimated model parameters remain unaffected by the frequency of fatigue loading and the size of the specimen.

A numerical study on a novel demountable cold-formed steel composite beam with profiled steel sheeting

Cold-formed steel composite beams are known for their unique advantages, like being lightweight and ease of installation. The use of profiled steel sheeting in cold-formed composite beams reduces construction time and costs by acting as a permanent formwork in the composite beams. The current study presents a 3D finite element model of cold-formed steel composite beam specimens comprising a cold-formed double-lipped channel section, profiled steel sheeting, concrete slab, and bolted shear connector. Employing bolted shear connectors, structural components can be deconstructed and replaced after their service life expires or if they are damaged. The characteristics of the materials obtained from an experimental program were assigned to the finite element model. Geometric characteristics, material nonlinearities, and loading procedures were attentively simulated, and a dynamic explicit procedure was employed for the numerical analyses. A comparison of the results obtained from the finite element models and the available experimental results validated the precision of the models. Then, numerical studies were conducted to investigate the effects of various parameters, including compressive strength of concrete, thickness of concrete slab, height and grade of cold-formed steel section, thickness of profiled steel sheeting, number and diameter of shear connectors, on the behavior of the composite beam. The results showed that the height and grade of the cold-formed steel section and compressive strength and thickness of the concrete slab have a significant effect on increasing the capacity of the composite beam.

Experimental study on the mechanical properties and structural performance of the rapid hardening concrete

Rapid-hardening concrete (RHC) is becoming more popular as a cast-in-place jointing material in precast concrete bridges and buildings due to its high tensile strength and crack resistance. RHC’s technical properties are highly regarded due to the working conditions of mega projects. The study assessed the impact of modern modifiers on concrete in order to select a composition of rapid-hardening concrete (RHC) with superior mechanical properties. Following an analysis of previous studies by other authors, microsilica and a polycarboxylate ether-based chemical additive was chosen as basic modifiers in the manufacture of RHC. In addition, four reinforced rapid-hardening concrete beams were tested for operational reliability and durability after 3 days of casting. The structural performance of RHC beams was evaluated in comparison to normal concrete beam specimens, and it was determined that crack distribution, load deflection, reinforcement strains, ductility, and toughness were all important factors in the evaluation. RHC beams exhibit higher ductility, toughness, ultimate loads, and deformability than NC beams. The tensile strength analysis revealed a positive impact of RHC, but the shrinkage crack related to heat hydration was crucial.

Three-Dimensional Probabilistic Semi-Explicit Cracking Model for Concrete Structures

This paper introduces a three-dimensional (3D) semi-explicit probabilistic numerical model for simulating crack propagation within the framework of the finite element method. The model specifically addresses macrocrack propagation using linear volume elements. The criteria governing the macrocrack propagation is based on the softening behavior observed in concrete under uniaxial tension. This softening behavior corresponds to a dissipated cracking energy that is equal to the mode I critical fracture energy (GIC) used in the Linear Elastic Fracture Mechanics theory (LEFM). The probabilistic nature of this model revolves around the random distribution of two mechanical properties: tensile strength (ft) and fracture energy, which varies based on the volume of finite elements. The scattering of the fracture energy increases as the volume of finite elements decreases in order to consider the strong heterogeneity of the material. This work primarily aims to estimate the relationship between the standard deviation of GIC and the volume of finite elements through the development of the numerical model. For this purpose, an inverse analysis is conducted based on a fracture mechanical test simulation. This test involves macrocrack propagation in a large Double Cantilever Beam (DCB) specimen with a crack length exceeding two meters. The proposed inverse analysis procedure yields highly significant results, indicating that the numerical model effectively evaluates both crack length and crack opening during propagation.

Epoxy-Printed Circuit Board Interfacial Fracture Reliability Under Three-Point and Four-Point Bend Loading After Sustained Elevated Temperature Exposure

Abstract The survivability and reliability of commercial electronic components under very high thermo-mechanical loads are improved using underfilling and potting methods. Potting protects from operating conditions such as moisture, water, or corrosive agents. Furthermore, potting offers damping against shock and vibrations, heat dissipation, and structural support. Being one of the most cost-efficient methods, potting greatly increases reliability and therefore reduces costs for replacements and repairs. It also addresses trapped hot air issues better than other restraint technologies. In potted electronic assemblies, interfacial delamination at the epoxy and printed circuit board (PCB) interface has been one of the major failure modes. Interfacial delamination happens at the epoxy/PCB interface under dynamic shock loads, which leads to failures at the solder interconnects of the electronic components. Sustained operation and storage at elevated temperatures change the interfacial characteristics at the epoxy/PCB interface. This research is focused on interfacial failure mechanics at epoxy/PCB interfaces with high-temperature isothermal aging. In the selection of the epoxy potting material and the reliability assessments of the supplemental restraint systems, fracture parameters such as steady-state strain energy release rate stress and fracture toughness are critical. Rectangular beam specimens of the epoxy/PCB interface are fabricated for different potting compounds, and the fracture behavior is studied under quasi-static monotonic three-point and four-point bend loads. One of the main differences between three-point and four-point bend loading is that the maximum bending stress occurs at the midpoint under the point of loading of the specimen in three-point bending, whereas the peak stress is distributed over the section of the specimen between the loading points in four-point bending. Four different potting compounds with diverse properties have been studied. The recommended curing schedule from the manufacturer has been chosen and followed for all the potting compounds. The epoxy/PCB interfacial samples are aged at a high temperature of 100 °C for 30–180 days. Damage has been assumed to happen at the epoxy/PCB interface under dynamic loads. The critical load of crack initiation for the epoxy/PCB interface has been determined from the experimental findings, and it is used in the computation of fracture toughness values. The fracture toughness values are compared for the various epoxy/PCB systems based on the number of days of thermal aging and the method of flexure testing. A cohesive zone model has been constructed for predominantly mode-I delamination with four-point bend stress to predict the interfacial delamination behavior at the epoxy/PCB interfaces. It has been assumed that the bulk material is linear elastic during the bending load. The cohesive zone has been modeled at the interface, where the interfacial fracture has been assumed to occur. The fracture behavior in the simulation is predicted based on the fracture parameters determined through the experiment. The computed cohesive zone parameters are unique to the interfaces, and they can be used across various applications with the same epoxy/PCB interface to predict interfacial delamination and to select a more suitable potting material.

Study on structural performance of repaired reinforced concrete beams with partially debonded longitudinal rebars

In order to evaluate the structural performance of repaired RC beams with partially debonded longitudinal rebars, structural experiments were conducted. In the experiments, real-scale and half-scale RC beam specimens underwent cyclic loading of 1.0% or less in terms of deformation angle, repaired with epoxy resin injection method, and multiple cyclic loading again. As a result of the experiments, damage was suppressed in specimens with partially debonded longitudinal rebars even after repairs. Further, the specimens with partially debonded longitudinal rebars exhibited high recovery of initial stiffness after repair compared to the specimen with bonded longitudinal rebars. In addition, from study of the costs required to repair cracks, it was confirmed that RC beams with partially debonded longitudinal rebars used smaller quantities of materials used for repairs and could potentially reduce repair cost by approximately 50% compared to RC beams having standard bonding properties.

Flexural strengthening of RC beams by advanced concrete canvas

AbstractIn this study, concrete canvas (CC) layers were used as a novel method to strengthen reinforced concrete (RC) beams because of their flexibility, rapid installation, fast curing, and rapid strengthening. Due to the importance of the CC mechanical properties, various combinations of cement including ordinary (OPC) and High Alumina (HAC), as well as silica fume, were investigated to determine the optimal mixture for strengthening RC beams. The results indicate that substituting 75% of HAC with OPC significantly boosted flexural strength by 33%, and increased tensile strength in the warp and weft directions by 25% and 21%, respectively. The study examined six RC beam specimens in a four‐point flexural test, assessing their flexural properties, ductility, cracking behavior, and energy dissipation. The number of CC layers and the bonding method, which involved either the conventional externally bonded reinforcement (EBR) technique or the externally bonded reinforcement on grooves (EBROG) technique were studied. The experimental results revealed the superiority of the EBR method over the EBROG technique due to the uniform bond between CC and the concrete surface. Using the EBR technique, improvements of 35% and 51% were observed in the load‐carrying capacity of the beams strengthened with one and two CC layers, respectively. It is while for the beam with an improved loading capacity of 51%, the crack width decreased from 5.3 to 2.1 mm, and the energy dissipation increased by three times compared to the control specimen. Theoretical analysis also was performed to calculate the load‐carrying capacity of the RC beams strengthened with CC layers.

Shear Capacity of RC Beam with Opening Strengthened Using CFRP Sheet and Plate

This paper investigates the use of carbon fibre-reinforced polymer (CFRP) sheets and plates for the bi-directional reinforcement of reinforced concrete beamswith transverse single and double symmetrical openings. The dimensions of the under-reinforced specimens are 1900mm in length, 150mm in width, and 300mm in height, with 3H12 tension reinforcement, 2H6 compression reinforcement, and R6-300 stirrups. This study aims to compare the maximal shear capacity of each CFRP configuration to that of conventional beams andevaluate the deflection profiles, failure modes, strain distribution, and crack patterns under shear loads. The beams are created using in-situ casting, and the openings are treated using post-drilling techniques to simulate real-world procedures. The beam specimens are subjected to a four-point stress test following the application of Sikadur-330 and CFRP. The principal findings indicate that the application of CFRP sheets increases the ultimate shear strength compared to conventional beams with openings, whereas the application of CFRP plates has the opposite effect. Nevertheless, the control beam with no openings has the greatest ultimate shear capacity. In addition, the sheet reinforced CFRP specimens exhibit less deflection than the control beam and conventional beams. The use of both CFRP sheets and plates aids in the transition from shear failure to flexural failure.