Beam Specimens Research Articles

Numerical modelling of the mode I fracture behavior in composite laminates with significant R-curve effect

Significant R-curve effect is very common in the mode I fracture of composite laminates. Accurate simulation of fracture with R-curve effect is important for damage tolerance design of composite structures. However, traditional numerical methods usually do not consider the R-curve effect. In this work, four methods, including three phenomenological methods and cohesive zone model with multi-linear constitutive relation are presented. The three phenomenological methods are based on bilinear cohesive zone model, virtual crack closure technique and extended finite element method respectively with the consideration of R-curve. It is interesting to know which method is more suitable for modelling delamination growth with significant R-curve effect. To achieve this goal, double cantilever beam specimen is modeled and delamination growth is simulated using above four methods. Comparisons between the numerical results and the experimental results of laminates with different material types and stack sequences are made for these methods. Finally, the accuracy, computational efficiency and parameter acquisition of these methods are discussed with the goal of finding a suitable method for delamination modelling in laminated composites. It is shown that the cohesive zone model with multi-linear constitutive relation shows good accuracy in all studied cases.

Prediction of the complete flexural load–deflection curve of self-compacting concrete reinforced with hook-end steel fiber

The flexural performance is vital for evaluating the characteristics of steel fiber reinforced self-compacting concrete (SFR-SCC). Although the tested load–deflection curve is commonly used to predict the flexural performance, little research has been done on the tested curve prediction. In this study, the complete flexural load–deflection curves of SFR-SCC beam specimens were obtained by a four-point bending test. The hook-end steel fiber with a length about 25 mm, 30 mm or 35 mm was respectively added for SFR-SCC at volume fraction of 0.4 %, 0.8 %, 1.2 % or 1.4 %. The characteristic points of tested curves are statistically analyzed to build the prediction formulas for the initial cracking strength, the flexural strength, and the first and second residual flexural strengths. The formulas for predicting the complete flexural load–deflection curve of SFR-SCC are proposed, and verified by comparing with the test curves. Meanwhile, the distribution of steel fiber in concrete matrix of beam specimen was measured to explain the mechanisms of flexural performance of SFR-SCC.

Behavior of Steel–Lightweight Self Compacting Concrete Composite Beams with Various Degrees of Shear Interaction

This study investigated the use of lightweight self-compacting concrete (LWSCC), which represents a trend in producing high-performance concrete, as slabs in steel-concrete composite beams with headed studs as shear connectors. Three push-out test specimens were fabricated and tested to assess the shear strength and behavior of M16-headed stud connectors embedded in LWSCC. Based on the push-out test results, six steel-LWSCC composite beams were manufactured and tested as simply supported composite beams. In addition, a steel-normal weight self-compacting concrete (NWSCC) composite beam specimen with full shear interaction was manufactured and tested for comparison. The main variables taken into account in this study were the degree of shear interaction and regions of bending moment (sagging or hogging). It was observed that the increase in degree of shear interaction from 50 to 100% improved the ultimate carrying capacity, the service load, and the stiffness of the tested steel-LWSCC beam specimens by a ratio reached to 96, 95, and 122%, respectively, when subjected to sagging bending moments and by a ratio reached to 57, 59, and 134%, respectively, when subjected to hogging bending moments. In addition, it was noted that the deflection and the end slip values for steel-LWSCC specimens under a sagging bending moment are smaller than those under a hogging bending moment, which have the same degree of shear interaction and at the same load level. Moreover, the experimental results show that the ultimate carrying capacity, service load, and stiffness values for the steel-NWSCC composite beam were higher than those for the steel-LWSCC beam specimens that have the same properties, while the ultimate deflection and end slip were smaller. Doi: 10.28991/CEJ-2023-09-11-04 Full Text: PDF

Shear span behavior of reinforced concrete beams with circular and rectangular openings

In reinforced concrete (RC) beams, 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 sitffeness of the beam. This paper aims to contribute to better understanding the shear behavior of RC beam with web opening in the shear span. The study is based on an experimental program carried out on three RC beams. All beam specimens were 850 mm long with a cross section of 150 × 250 mm and a shear span to beam depth ratio (a/d) of 1.48. One beam without any openings served as the control specimen, while the remaining two beams featured circular or rectangular openings within the shear span. The test results obtained from this experimental program offer insights into the shear behavior of beams with openings. Furthermore, a simplified calculation was conducted to determine the shear strength of the test specimens, considering the influence of openings. This calculation provided a deeper understanding of how openings contribute to the reduction in the shear strength of RC beams.

Textile Types, Number of Layers and Wrapping Types Effect on Shear Strengthening of Reinforced Concrete Beams with Textile-Reinforced Mortar versus Carbon-Fiber-Reinforced Polymer

In the scope of this study, the strengthening of reinforced concrete beams with different types of composite materials was investigated experimentally and analytically. For the experimental part of the study, a total of seventeen reinforced concrete beams, one with high shear strength and sixteen with low shear strength, were fabricated. The beam with high shear strength and one of the beams with low shear strength were chosen as reference beams. The remaining fifteen beam specimens were strengthened with textile-reinforced mortar (TRM) and carbon-fiber-reinforced polymer (CFRP). While light and heavy carbon mesh were used for strengthening with TRM, unidirectional carbon textile was used for strengthening with CFRP. Other experimental parameters were the spacing of strips, the number of layers (one or two) and the way of wrapping (strip or full). Simply supported beam specimens were tested under three-point loading. Beam specimens were compared in terms of failure mode, ultimate load capacity, ductility index and energy dissipation capacity.

Scalable, roll-to-roll manufacturing of multiscale nanoparticle/fiber composites using electrophoretic deposition: Novel multifunctional in situ sensing applications

Multiscale composites, where traditional fiber reinforcements are combined with nanoscale reinforcements, have emerged as multifunctional materials and have found potential for in situ strain and damage sensing, and energy harvesting/storage applications. Critical to the advancement of future applications is the development of manufacturing techniques that are industrially scalable. Electrophoretic deposition (EPD) can uniformly coat functionalized nanoparticles, such as carbon nanotubes (CNT), on conductive and non-conductive fiber substrates, producing multiscale composites with controlled microstructures and functional properties. In this research, a pilot-scale roll-to-roll EPD system is developed to continuously manufacture CNT-integrated fabrics for in situ sensing applications. Based on fundamental knowledge of CNT deposition mechanisms, key experiments are conducted to determine electrode configurations to optimize deposition yield in the roll-to-roll process. Functionalized CNTs are then deposited on 4–6 m long continuous rolls of randomly oriented non-woven glass fiber veil with different areal weights, and the CNTs form a continuous, conductive fiber-level coating. The thin and open fabric microstructure allows embedded sensors that are minimally invasive to the composite structure and allow ultraviolet (UV) light transmittance for use with UV-curable resins. The electrically conductive CNT network created on the fabric allows for the integration of sensing functionality. Short beam specimens with the CNT sensors embedded at the midplane showed no deterioration in strength. Multiple functionalities, including strain sensing and flow/UV cure monitoring during vacuum infusion are demonstrated. Sensors tested under flexural loading demonstrated sensitivity in tension and compression, and during resin infusion, the sensors could track resin flow and cure progression.

Performance of Epoxy-Injection and Microorganism-Based Crack-Healing Techniques on Cracked Flexural Members

Reinforced concrete (RC) members are designed to crack and the crack width usually remains within the service limit; however, these micro-cracks make structures susceptible to the infiltration of aggressive substances, especially near the coastline. Thus, the healing of these cracks is necessary before they further widen and spread. This study focused on the development and application of a crack-healing solution using microorganisms of the class bacillus; healing was observed through a crack-sensing camera. The aim was to regain the load-carrying capacity of the concrete member to meet the serviceability limit state requirements after healing the crack. The performance of the crack-healing solution was compared with the epoxy-injection method. Five full-scale RC beams of 100 × 200 × 1800 mm in dimension were cast using concrete designed with a cylindrical compressive strength of 21 MPa. After curing for up to 28 days, the beam specimens were tested and subjected to four-point bending to produce a flexural crack of width 1–3 mm. One of the beams was treated to fill the crack by injecting epoxy, while the three other similar beams were treated using a crack-healing solution consisting of bacteria (Bacillus subtilis), nutrient (calcium nitrate), and transporting agents. The healing solution was applied directly to the opened crack with silica gel and with cement slurry in three similar beams cracked under flexural load. The cracks in the beam treated with the crack-healing solution were sealed and kept moist for a further 14 days. After curing, all of the beams including the control (without treatment) were tested again and were subjected to four-point bending until failure to observe the effect of the crack repairs on the flexural response. It was observed that both systems were equally good at enhancing the serviceability limit state and improving the load-carrying capacity.

Influence of the Oriented Configuration of the BarChip Fibre Polypropylene to the Ductility Factor of the Reinforced Concrete Beam

Abstract
 Bending and shear strength of fiber reinforced polimer concrete beams was studied in this research project. The reinforced concrete beam behaves in brittle structure in the certain reinforcement configuration. BarChip fibre polypropylene as the material for enhancement of the ductility factor is applied to the concrete beam. Three types of BarChip fibre configuration were examined: randomly spreading, placing at the mid-span area, and concentration on the tension zone. The experimental program included five beam specimens. Two of the beams were control specimens in which one was reinforced with no fibre, while the other one did not have any Barchips polypropylene. Each one of the other three specimens was reinforced with one of the above mentioned fibers by 0,4% volumetric ratio. Investigating the following issues for medium-high concrete strength was the goal of this study. In order to determine whether adding 0.4% volumetric ratio of polypropylenes as additional bar reinforcement in beams would provide adequate strength and stiffness properties comparable to reinforcing steel used as minimum bar reinforcement, it was necessary to first assess the effectiveness of each type of oriented fiber configuration on the bending strength, then to look into each beam's bending strength, shear strength, toughness, crack patterns, and near ultimate load crack width. The findings demonstrated that the bending capacity of the beam specimens was raised by all three types of polypropylene configuration more than by the beam reinforced with the fewest amount of bar reinforcement. Additionally, some of the employed fibers may cause failures other than pure shear. It is reccomended to spread the polypropylene within the tension zone of the reinforced concrete beam on the bottom mid span.
 Keywords: Fibrous Concrete, Polypropylene, Ductility, Reinforced, Beam

A Rate-Temperature-Dependent Visco-Hyperelastic Constitutive Model for UD CF/PEEK Prepregs During a One-Step Hot Stamping Forming Process

An anisotropic visco-hyperelastic constitutive model for rate-temperature-dependent deformation during one-step hot stamping forming simulation of unidirectional (UD) CF/PEEK prepregs is presented. This constitutive model is based on strain energy decomposition and a multiplicative decomposition of the deformation gradient. Two simple Maxwell models are used to characterize the viscoelastic behavior of the melted PEEK matrix and longitudinal shear deformation, respectively, and a shear invariant of [Formula: see text] is proposed to calculate the shear deformation. Moreover, the fiber stretching deformation is modeled by an anisotropic hyperelastic model. To obtain the model parameters, tensile tests at different strain rates and temperatures above the melt temperature of PEEK are performed on [Formula: see text], [Formula: see text], and [Formula: see text] CF/PEEK prepreg specimens, respectively. In parallel, the [0]8 and [45]8 curved beam specimens are experimentally fabricated to validate the constitutive model. The VUMAT subroutine is developed according to the proposed constitutive model and applied for a [Formula: see text] off-axis tensile simulation and hot-stamping forming simulation of CF/PEEK prepregs. The experimental and simulation results show that the materials flow, distribution of strain and stress, forming defects (wrinkles and overlap) of CF/PEEK curved beam can be captured by the proposed model.

Bond-Slip Behaviors Between BFRP Bar and Ecological High Ductility Concrete Using the Beam Test

To better understand the design parameters of bridge deck link slab made by basalt fiber reinforced polymer (BFRP) bar and ecological high ductility concrete (Eco-HDC), the bond behaviors of BFRP bar embedded in Eco-HDC using beam test based on RILEM standard were studied. The beam specimens had variable factors namely diameter of BFRP bar, embedment length and cover thickness. The results indicate that most beam specimens display a failure mode of BFRP bar pulled out with specimen splitting. Besides, with the increase of diameter and embedment length, the bond strength decreases. While as the cover thickness increases, the bond strength and first bond stress show an increasing trend. The free end slip increases as the embedment length or cover thickness increases. In addition, the strain at loaded end is larger than that at free end as the load increases. Moreover, the formulas of bond strength and peak slip are proposed based on the test data of specimens. At last, embedment length and cover thickness of BFRP bar in the bridge deck link slab are recommended.

Strength, durability, and impact behavior of recycled aggregate concrete with polypropylene aggregate

Massive consumption and production of plastic is expected to have a significant environmental impact in the near future. Plastic waste from landfills can be refined and recycled as aggregates in concrete through subsequent processing. Several studies have already been conducted using plastic scraps as aggregate in concrete. However, more research is needed before it can be incorporated into structural concrete. Therefore, this study aims to investigate the static and dynamic behavior of concrete made with polypropylene plastic aggregate (PPA) obtained from waste plastic materials. Natural coarse aggregate (NCA) and recycled concrete aggregate (RCA) are partially replaced with PPA in this study and drop impact tests are performed after the samples are exposed to room and elevated temperatures (200 °C and 400 °C). PPA replacement percentages are 0, 5, 10, and 15 %. The drop impact test is performed on both cylinders (150 mm × 63.5 mm) and beams (100 × 100 × 500 mm) specimens. Different mechanical and durability tests are also investigated. The impact energy decreases by up to 68 percent as the PPA percentage increases at room temperature. Furthermore, when the specimens are heated to 200 °C or 400 °C, the impact blows are significantly reduced (6–13 no). After being heated to 200 °C and 400 °C, the 15 percent NCA replaced cylinder loses 87 percent and 91 percent of its impact energy, respectively. In terms of mass loss, the control cylinder has a higher loss than the PPA cylinders, indicating that the presence of PPA in concrete causes less damage. In terms of mechanical properties, the 5 percent PPA-based concrete outperforms the control. Depending on the concrete age and coarse aggregate types, a 5 % PPA content increases compressive strength by up to 11.6 percent. In terms of durability, the water absorption tendency increases with increasing PPA content, and all-natural PP concrete (NPC) and recycled PP concrete (RPC) exhibit moderate to very low chloride ion penetrability. Overall, it is proposed that 5 % PPA be used with NCA and RCA for structural applications.

The ductility performance of concrete using glass fiber mesh in beam specimens

Abstract It is known that concrete with high ductility reduces fatalities because it absorbs more energy during an earthquake. The aim of this study is to increase the ductility of concrete by using glass fiber mesh (GFM) left over from the use of plaster in structures and to support sustainability by reusing waste materials in concrete. Another aim is to contribute to the economy by using waste fibers instead of expensive fibers such as carbon and polypropylene in concrete. Two types of concrete were used: class C25 concrete and self-compacting concrete. The specified number of GFM materials was cut into 3 cm wide pieces and placed in 10 cm × 10 cm × 50 cm concrete beam specimens in varying numbers. It was found that the flexural values of the obtained specimens gave slightly better results than the prepared reference specimen. In addition, the increasing stress zones in the beams were visualized using the ANSYS software.

Ferrocement-Timber Composite Beams Loading capacity

This paper presents an experimental study of simply supported ferrocement timber composite members. An adherently bound link is investigated. As a shear connector layer, an appropriate length for this type of composite beam was chosen to study the effect of shear strength on the impact of one point load (1.2 m). Sikadur 31 thixotropic epoxy resin adhesive is used. The research's primary goal is to collect data and provide information on the structural behavior of proposed ferrocement timber composite (FTC) beams. The thickness and width of timber beams, the presence and absence of a bonding layer on the shear connector, and the influence of sagging and hogging bending moments were also investigated. FTC beams are a relatively new civil engineering solution, and their behavior should be investigated to develop relevant methods for calculating their resistance. Two push-out tests were used to tentatively resolve the connector's slip and pinnacle load limits. The stiffness and strength of the connection utilized to bind a ferrocement slab to a timber beam were investigated by the authors. These criteria are critical for composite beam planning because the solidity and quality of a composite beam framework's connections determine its performance. A three-point loading test was performed on the composite beam specimens. Measurements also demonstrate that the connection is near-perfect because the slide is minimal during the test (except at failure). Converting from sagging to It has been witnessed that converting from sagging to hogging bending reduces the ultimate load by up to 24%. The suggested beams' loading It has been witnessed that Converting from sagging to hogging bending reduces the ultimate load by up to 24%.shown to be excellent when compared to their weight in tests. Epoxy resin (Sikadur 31) can be used to provide adequate bonding between the components. The highest gain in the loading capacity was 48% when the timber thickness was increased from 90 to 190 mm.

Study on mechanical properties of poplar timber bending members of ancient buildings strengthened with CFRP sheets embedded

The reduction of the section area of timber beams in ancient buildings leads to the decline of their flexural mechanical properties. In order to study the effect of the reinforcement method with near-surface mounted CFRP sheets, three groups of 14 scaled poplar timber beam specimens were designed for static loading tests, and the strengthening effects of the new members replacing the damaged members and the concealed CFRP sheets strengthening the damaged members were compared. The results show that the ultimate flexural capacity and flexural stiffness of the strengthened timber beams are significantly improved compared with the simulated damaged beams; the bending performance of the optimum strengthened timber beam is equivalent to that of the undamaged beam. The distribution of the section strain of the strengthened timber beam along the height of the beam section basically conforms to the plane section assumption. A formula for calculating the ultimate flexural capacity of poplar timber beams strengthened with CFRP sheets is proposed. The calculated results are in good agreement with the experimental results.

Impact resistance and flexural behavior of U-shaped concrete specimen retrofitted with polyurethane grout

Normal concrete-polyurethane grout (NC-PUG) composite U-shaped and beam specimens were developed in this study to evaluate the capability and efficacy of PU grouting material prepared from mixing bio-based polyurethane (PU) and quartz sand as a coating material. The composite specimens were subjected to dynamic and flexural loads using U-shaped drop-weight impact test (USDWIT) and three-point bending test, respectively. Various PUG overlaid thicknesses and configurations were adopted to improve the impact and flexural behavior of the concrete. Weibull distribution analysis was performed on the USDWIT result. The result indicated that the reference NC-PUG beam exhibited the highest load-carrying capacity of 18.26 kN and the lowest ultimate deflection of 0.52 mm compared to the composite NC-PUG specimens. While, the NC beam retrofitted with a 10 mm thickness overlaid at the top surface (NC-PUGT10) revealed a reduced ultimate load-carrying capacity compared to the reference NC-PUG specimen. The impact performance of the composite U-shaped NC-PUG specimen have remarkably improved due to the influence of PU grouting materials overlaid, with a higher ductility index, which tends to change the brittle nature of concrete to a ductile state. The energy absorption capacity at the failure stage of the NC-PUGT5 is 16 times that of the reference U-shaped NC-PUG specimen. The NC-PUGTB5 and NC-PUGT10 revealed impact strength, which is 52.28 times and 68.1 times more than the reference specimens, respectively. Reliability analysis indicated that about 80% of the U-shaped NC-PUG specimen can withstand 63 impact times at the failure stage. The finding showed that retrofitting concrete structures with PUG material is a promising and sustainable method to protect the concrete structure against dynamic loads

Experimental Torsional Capacity of Plain Concrete Beams Made from Crushed Clay Brick and Recycled Brick Concrete as Coarse Aggregate

Concrete was made with four different types of coarse aggregate, i.e., natural stone aggregate concrete (NSAC), crushed virgin clay brick aggregate concrete (VBAC), crushed recycled brick concrete aggregate concrete (RBAC), and crushed recycled stone concrete aggregate concrete (RSAC). Beam specimens prepared from these four types of concrete were subjected to pure torsional moment up to failure. From this experimental procedure, ultimate torque at failure along with twisting angle were observed. From the torque vs. twisting angle curves, torsional stiffness and torsional toughness were also evaluated for these four types of concrete. It was observed that ultimate torque of VBAC and RBAC was 95% and 90% of that of NSAC, respectively. The torsional toughness of VBAC was found to be 68%–72% of that of NSAC. In addition, experimental torques were compared with predictions of torsional strength as per five commonly used models. For VBAC, the ultimate torque prediction made by skew bending theory was found to be the closest to the experimental findings.

A novel demodulation method with a reference signal for operational modal analysis and baseline-free damage detection of a beam under random excitation

A novel demodulation method with a reference signal is developed for operational modal analysis and damage detection of a beam structure under random excitation. The novel demodulation method can process measurements of the beam by a continuously scanning laser Doppler vibrometer (CSLDV) system and measurements of a reference point on the beam by a single-point laser Doppler vibrometer to estimate its modal parameters, such as damped natural frequencies and undamped mode shapes. Damped natural frequencies of the beam are estimated from fast Fourier transforms of measurements of the CSLDV system. A cross-correlation function between a measurement of the CSLDV system and a measurement of a single-point laser Doppler vibrometer is calculated, and the cross-correlation function is multiplied by a sinusoidal signal whose frequency is an estimated damped natural frequency of the beam. The processed cross-correlation function is filtered by a low-pass filter to obtain the undamped mode shape of the beam that corresponds to the estimated damped natural frequency of the beam. Smooth polynomials are used to fit estimated undamped mode shapes, which can be considered as undamped mode shapes of an undamaged beam. Curvatures of estimated undamped mode shapes and polynomials are compared by curvature damage indices to determine the location of a damage in the beam. The novel demodulation method with a reference signal is investigated for baseline-free damage detection from both finite element simulation and experiment. Modal parameters of a finite element model of the damaged beam and a damaged beam specimen, which are under random excitation, are successfully estimated, and locations of damages in the beam model and beam specimen are accurately determined.

Optimal Shear Strengthening of Severely Deficient RC Beam Using JFRP Laminate with Anchor

High-strength jute fibre-reinforced polymer (JFRP) laminates have recently been introduced to strengthen RC beams against shear. In contrast to synthetic-based composites, JFRP laminates would be more ductile, compatible with steel shear rebar and effective in reducing debonding due to their lower modulus of elasticity. The prime objective of this research was providing an optimal solution to strengthen a severely deficient RC beam against shear using an externally bonded JFRP laminate with anchor. Fabrication of the JFRP laminate was carried out with the maximum fibre content of 37.5% to obtain high tensile strength. Five full-scale RC beam specimens were cast. Shear strengthening was done by an externally bonded JFRP laminate with double connector, multiple connector and embedded-bar anchor systems. The dimensions of JFRP laminate were obtained based on proposed guidelines. Based on the experimental test, the average tensile strength of the fabricated JFRP laminate was found to be 162 MPa. Results also showed that the JFRP laminate with multiconnector anchor increased the maximum shear capacity of deficient RC beams by 89% and the beams had failed by the fracture of laminate. Beams strengthened with embedded-bar anchor had shown flexural ductile failure. Both beams failed after yielding of flexural bar. The proposed guidelines could be used for shear strengthening of severely deficient beams to enhance the maximum shear capacity using full strength of JFRP laminate with anchor. KEYWORDS: RC beam, Shear strengthening, JFRP laminate, Anchor, Optimal design

On the Cover: A Composite Rigid Double Cantilever Beam Specimen for Assessing the Traction–Separation Response of Mode I Delamination in Composite Laminates

On the Cover: A Composite Rigid Double Cantilever Beam Specimen for Assessing the Traction–Separation Response of Mode I Delamination in Composite Laminates

Application of Mangrove Timber in Reinforcing Concrete

Use of mangrove timber beams for supporting floor slabs in historic buildings in Zanzibar Stone Town is still applied although the available structural data on mangrove timber is inadequate. This concern has called for an investigation on the structural properties of mangrove timber, so that the information obtained could help to establish the structural strength of the existing floor slabs in historic buildings. Hence, mangrove timber specimens were sampled from Zanzibar, and tested in the laboratory for their strengths in tension, compression and shear. The test results showed that mangrove is a hardwood timber of strength class D70, the highest rank of timber classification. Also, concrete beam specimens reinforced with mangrove timber rods, and others reinforced with structural steel were studied. The obtained test results showed that beams reinforced with mangrove timber rods with enlarged ends performed better than those reinforced with uniform mangrove rods. The strength of the beams reinforced with mangrove timber was found to be 50% of the beams reinforced with steel bars, implying that mangrove timber can be used to reinforce concrete beams.