Flexural Failure Mode Research Articles

Comparison of fiber reinforcing methods of composite resin: A flexural strength and stereo microscopy study.

This study aimed to compare the effect of fiber reinforcing methods on the flexural strength and failure modes of indirect composite resins. Based on the reinforcement methods, the bar specimens (3 × 3 × 25 mm) were divided into five groups (n=20). Glass or polyethylene fibers were used for reinforcement of indirect composite resins. Fibers were either light polymerized and mixed with indirect composite resin or mixed with indirect composite resin after resin application and polymerized together. Indirect composite resin without fiber reinforcement was used as control. All five types of specimens were stored in distilled water at 37°C for 24 h. Half of the specimens were additionally thermocycled. Then the specimens were tested in a three-point bending test. Failure types were examined and categorized by using stereo microscope. The data were analyzed using two-way ANOVA and Tukey HSD test. Flexural strength was found to be significantly higher for fiber-reinforced indirect resin composites than control. However, the fiber-reinforced groups did not present any significant difference. Analysis revealed aging does not affect the flexure strength of fiber reinforcement of indirect composite resin. The study concluded that the flexure strength of indirect composite resins was improved with fiber reinforcement. Different fiber reinforcement methods demonstrated similar effects on the flexure strength of indirect composite resin. Reinforcement with glass or polyethylene fibers presented the potential to improve the mechanical properties of indirect composite resins. RESEARCH HIGHLIGHTS: Flexural strength of indirect composite resins are affected by the reinforcement of composites with glass or polyethylene fibers. Aging with thermocycling has no effect on the flexural strength of the indirect composite resins, however can cause catastrophic failures in material.

Experimental investigation on seismic performance of plain engineered cementitious composite beams

The authors proposed using plain engineered cementitious composite (ECC) in construction without aligned reinforcement. In this study, ECC with a tensile strain capacity of up to 10% was produced, which has a comparable deformability level to steel reinforcement. To demonstrate the feasibility of plain ECC construction, five plain ECC beams and two steel reinforced concrete reference beams were prepared, and four-point bending reversed cyclic loading tests were conducted on the beam specimens. The experimental tests indicated that the plain ECC beams showed more stable hysteresis loops with improved energy dissipation capacity, deformation restoring capacity, and lower stiffness degradations than normal RC beams. Two categories of failure modes were observed, i.e., flexural failure mode and shear failure mode. With the increase in the shear span ratio, the failure mode of ECC beams changed from shear failure to flexural failure. Additionally, the increase in sectional dimension had a positive influence on the stiffness and energy dissipation capacity of ECC beams. It is experimentally verified that the plain ECC beams have sufficient load-bearing capacity under static and seismic loading.

Seismic behavior of RCS frame joints applied with high-strength bolts-end plate connection

This paper proposes a novel reinforced concrete column-steel beam (RCS) joint suitable for prefabricated hybrid structures. Twelve interior RCS joint subassemblies were tested under cyclic lateral loading. The main test parameters include beam-column capacity ratio coefficient (ηbc), joint capacity ratio coefficient (ηj), and thickness (t) of the joint web plate (JWP). The results showed that the proposed joint details ensured good integrity and deformation performance of the RCS joint subassemblies. The ultimate drift ratio of most specimens was up to 4.0%. The capacity ratio coefficients were the main factors affecting the failure mode. For the specimens with ηbc less than 1, the steel beam observed flexural failure mode, and featured stable full hysteretic loops. The specimens with ηbc greater than 1, the RC column observed flexural failure mode and exhibited a stable but slightly pinched hysteretic response. The specimens with ηj of less than 1 observed concrete damage in the joint region and showed a more pinched hysteretic response. The flexural deformation of steel beams and RC columns contributed to the lateral drift of the specimens. No brittle joint shear failure occurred in specimens, which showed that the proposed joint details can meet the requirements of strong joint-weak member in seismic design.

Mechanical and Microstructural Properties of Ultra-High Performance Concrete with Lightweight Aggregates

Although ultra-high-performance concrete (UHPC) presents superior mechanical properties and durability compared to conventional concrete; its spalling resistance to elevated temperatures is much lower compared to conventional concrete due to the high compactness and absence of capillary pores. This paper investigated the influence of lightweight aggregate (LWA) on the strength properties and microstructure of UHPC to enhance its resistance to elevated temperatures. UHPC specimens prepared with LWA as a partial replacement of silica sand were produced. The study evaluated the compressive and flexural strengths, failure mode, mass loss, and microstructure of the specimens, using SEM. The results showed that the compressive strength of the UHPC specimen was reduced with increasing the content of LWA at ambient temperature, but the compressive strength of the UHPC specimens prepared with LWA improved when exposed to elevated temperatures. The replacement of 10% of the silica sand with LWA led to an increase in the compressive strength from 100 MPa to 110 MPa after exposure to 200 °C; however, the flexural strength decreased from 23.6 MPa to 18.3 MPa. On the contrary, the flexural strength of UHPC increased with the inclusion of LWA at an ambient temperature but reduced with high-temperature exposure. The failure mode of UHPC was not significantly affected by the variation in LWA content and temperature. In addition, the SEM result confirms that LWA is an effective internal curing material for enhancing the microstructure and compressive strength of UHPC

Investigation of CFRP Reinforcement Ratio on the Flexural Capacity and Failure Mode of Plain Concrete Prisms.

The utilization of carbon-fiber-reinforced polymer (CFRP) composites as strengthening materials for structural components has become quite famous over the last couple of decades. The present experimental study was carried out to examine the effect of varied widths of externally bonded CFRP on the debonding strain of CFRP and the failure mode of plain concrete beams. Twelve plain concrete prims measuring 100 mm × 100 mm × 500 mm were cast and tested under identical loading conditions. The twelve specimens include two control prisms, i.e., without CFRP strips, and the remaining ten prisms were reinforced with CFRP strips with widths of 10 mm, 20 mm, 30 mm, 40 mm, and 50 mm, respectively, i.e., two prisms in each group. Four-point loading flexural testing was carried out, and the resulting data are presented in the form of peak load vs. midpoint displacement, load vs. concrete strain, and load vs. CFRP strain. The peak load was directly recorded from the testing machine, while the midpoint deflection was recorded through the linear variable differential transducer (LVDT) installed at the midpoint. To measure the strain, two separate strain gauges were installed at the bottom of each concrete prism, i.e., one on the concrete surface and the other on the surface of the CFRP strip. The results of this study indicate that the debonding strain is a function of CFRP strip width and that the failure patterns of beams are significantly affected by the CFRP reinforcement ratio.

Flexural behaviour of composite modular wall systems under uniformly distributed and concentrated loads

The flexural behaviour of glass fiber-reinforced polymer (GFRP) composite modular wall systems was evaluated experimentally and analytically. Full-scale wall panels were tested under uniformly distributed and concentrated loads to investigate the effects of wall sheathing, types of connections between sheathing and frame, inter-panel connections, and loading direction. The results show that the investigated parameters had a significant effect on the flexural capacity and failure modes of the composite wall panels but very limited effect on their flexural stiffness. Moreover, under uniformly distributed load, the panels effectively used the high-strength properties of composite materials by minimising localised failure. The adhesive connection provided higher composite action between the frame and sheathing than riveted connections. Furthermore, bolting the wall panels together resulted in pseudo ductile failure behaviour compared to the brittle failure of the adhesive inter-panel connection. This study demonstrated the high potential of fiber composite materials for modular wall systems, but careful attention should be given to the loading conditions and panel connection details to effectively take advantage of their high strength properties.

Experimental and Numerical Study on the Flexural Behavior of Cold-Formed Steel Multi-Limb Built-Up Section Beams

Cold-formed steel (CFS) is a typical green building material with the merits of being low-cost, lightweight, high-strength, and recyclable. CFS built-up section beams are widely used in CFS frames owing to their outstanding mechanical properties. However, a simplified and accurate method for calculating the flexural moment capacity of multi-limb built-up beams is missing in specifications. In this study, the flexural behaviors of CFS four-limb built-up beams with closed and open sections are investigated via experiments and finite element (FE) modeling. Firstly, the flexural moment capacities and failure modes of the beams are obtained by four-point bending experiments. The ultimate load capacity of the new open section beam is found to be higher than that of the closed section beam, and the failure mode is local buckling of the web and upper flange. Then, the FE models validated by the tests are developed to conduct an extensive parametric study. Numerical results show that the flexural moment capacity increases with the thickness and web depth. Finally, a simplified calculation method for the flexural moment capacities of the closed and open section beams is proposed by considering the reduction factor of gross section modulus of the built-up section.

Seismic performance of flexure-dominated reinforced-engineered cementitious composites coupled shear wall

The feasibility of using engineered cementitious composites (ECC) to improve the seismic performance of coupled shear walls was investigated experimentally and analytically. Reinforced-ECC (RECC) coupled shear wall was tested under cyclic loading for comparative study with its RC counterparts. Important seismic performance indicators, such as the deformation mode, damage pattern, stiffness, ductility and energy dissipation of the two coupled shear walls were compared and analyzed. The RECC shear walls and RC shear walls exhibited flexural failure modes with different damage patterns. The damage was concentrated mainly in the plastic hinge area, which include the bottom of the wall and the ends of the coupling beams. The RECC shear wall exhibited smeared cracking characteristics with a significantly smaller crack width. The RECC members showed ductile failure mode without crushing or spalling, and provided effective restraint to the longitudinal rebar, which delayed the buckling of the longitudinal rebar. The deformation capacity of the RECC shear wall was twice that of the RC shear wall, and the energy dissipation capacity of RECC shear wall also improved significantly compare to RC shear wall. The RECC shear wall exhibited a slightly higher load-bearing capacity compared with its RC counterpart. The ultimate strength of the RECC and RC coupled shear walls were estimated based on the compression–bending mechanism. The calculated results agreed well with the test results. The estimated yield and ultimate displacement of the RECC and RC shear walls were close to the test results.

Analysis of Flexural Bearing Capacity and Failure Mode of Precast LSFRC Pavement Slab

To promote practical use of the top-and-bottom layered steel fiber reinforced concrete (LSFRC) plates, an appropriate constitutive model is selected using ABAQUS software to analyze the bearing capacity, failure pattern, and deformation of the LSFRC plates. An LSFRC plate model is established for the analysis and calculation. Meanwhile, a test was carried out to measure the bearing capacity of 10 LSFRC plates. The results show that, after going through the elastic stage, crack growth, and failure stage, when the maximum crack width reaches 0.1 mm, the load of the LSFRC plates can be used as the ultimate bearing load. When failure appears to be bending the LSFRC plates, the neutral axis will shift upwards, showing a pseudoplastic failure. There is a larger tensile stress area after the first crack appears at the bottom of the steel fiber concrete. The change before and after the maximum load is relatively gentle. After becoming plastic, the plate witnesses a rapid crack growth on its bottom. With similar results from the test and numerical simulation, small errors can be minimized by further analysis to provide a more accurate model for the subsequent bearing capacity analysis of the LSFRC plates.

Investigation of flexural and shear failure modes of tapered castellated steel beams using expansion plates

Using modern technologies for fabricating steel, I-beams can be easily made by welding, and hot-rolled beams can often be produced at an economical price with slender webs and equal flanges. Experimental and theoretical studies of the behavior of tapered castellated steel beams were carried out. Due to the cost reductions associated with tapered castellated steel beams, they are a feasible alternative to prismatic components. This study assessed the influence of tapered castellation on the bending capacity and flexural stiffness of tapered castellated steel beams (TCBs) with simply supported end conditions experimentally and theoretically. Four three-point bending tests on TCBs with H/h values of 1, 1.2, 1.4 and 1.6 were conducted utilizing a standard parent I-section beam (IPE140) as the control specimen. The test findings include the ultimate load vs. mid-span deflection response curves and failure mechanisms. The testing findings indicated that the TCBs' ultimate load capacity might be up to 140 percent of that of the parent section. The Abaqus program was used to conduct a finite element (FE) analysis of TCB, which allows for material and geometric nonlinearity. The derived finite element models exhibit excellent agreement with the experimental results in terms of ultimate load capacity vs. mid-span deflection response and failure mechanisms. Based on the results of the work, TCBs can be used for increasing the strength and stiffness of the I-section parent beam with adding expansion plates. The maximum load capacity of TCBs can be enhanced when adding expansion plates up to 40 % above that of the parent beam. A TCB has lower ductility than its parent beam. Moreover, a TCB fulfills serviceability requirements since its mid-span depth exceeds that of its parent beam.

Development of three-dimensional woven weft interlock carbon-fiber-reinforced plastic composites and experimental investigation on their out-of-plane flexural performance

Developing three-dimensional (3D) woven composites using various woven structures is important in the advanced composite research field. In this study, carbon-fiber 3D woven textile-reinforced epoxy–resin composites using four different woven structures (such as 2.5D, 3D-a, 3D-b, and 3D-c) were designed and fabricated based on a dobby-weaving loom, and vacuum-assisted resin transfer molding technology. In these 3D woven structures, part of weft insertions serves as binder yarns with a special weft interlock structural design, different weft-to-binder yarn ratios are obtained. Out-of-plane quasistatic three-point bending tests and dynamic low-velocity drop-weight impact tests were conducted on these woven composites to study the effect of woven structure on their flexural performance. Nondestructive ultrasonic C-scan and X-ray microcomputed tomography were applied to characterize the failure modes of the post impacted composites. We found that woven structures affect the flexural performance and failure mode of the developed composites, these structures with lower in-plane and binder yarn waviness exhibited higher quasistatic–flexural performance; 3D-c structure with serious in-plane yarn waviness combined with through-thickness binder yarn path exhibited superior impact resistance than other structures and survived more from composite through-thickness cracks and binder yarn breakage failures. Proper structural design is a key to improving flexural performance in specific engineering applications.

Critical study of steel beams with web openings

ABSTRACT In this study, experimental and numerical approaches are adopted to comprehensively investigate the flexural strength capacity and failure modes of I-shaped steel members with various web openings geometry. To validate the results, the finite element models are established using ABAQUS with the same configurations as the test specimens. Based on the experimental and numerical investigation it is observed that, the web openings not only weaken the practical section but also destroy its continuity. The common mode of failure observed in beams with web openings is excessive bending, Vierendeel mechanism and web post buckling. When the opening ratio exceeds 0.75, the openings greatly affect the stability of the components, which results in reduction in strength capacity of perforated beams. In contrast, when the opening ratio is less than 0.5, the openings have negligible impact on the stability and strength component. The web openings also have a significant impact on the bearing strength of the members when the provided web post width is less than 200 mm. In contrast, when the web post width exceeded 200 mm, the web opening ratio had only a small effect on the member bearing capacity. The response of the perforated beams was presented in terms of load-deflection and moment-deflection curves. .

Flexural fatigue behavior of novel co-curing damping composite structures

In order to investigate the flexural fatigue performance of novel carbon fiber reinforced bismaleimide resin matrix damping sandwich composite structure prepared by co-curing process, three-point flexural fatigue tests were carried out on composite structure embedded with damping films of different thickness. The flexural fatigue failure mode, fatigue life and damage evolution law of sandwich beam were obtained, and different damage mechanisms of sandwich beam under flexural fatigue load were analyzed. The S-N curves of undamped composite were fitted by three-point flexural fatigue test. The fatigue characteristics of the undamped composite and damping composite were compared and analyzed. The results showed that the fatigue life of damping composite decreased with the increase of damping layer thickness under the same cyclic load. A numerical simulation model of three-point flexural fatigue performance of damping composite was established. The fatigue life variation trend of damping composite under different damping layer parameters (number of damping layers, location of damping layers, distribution of damping layers) was further simulated, which provided theoretical basis for the fatigue design of damping composite.

Experimental Research on Flexural Mechanical Properties of Ultrahigh Strength Concrete Filled Steel Tubes

Based on the project of the Guansheng Qujiang Bridge, the flexural mechanical properties of an ultrahigh strength concrete filled steel tube (UHSCFST) were discussed. A total of six UHSCFST beam specimens were tested, and the cube strength (fcu) of the core concrete reached 80.3–115.2 MPa. The effects of concrete strength on flexural bearing capacity, deformation characteristics, and failure modes of UHSCFST specimens were discussed. Test results showed that the bending failure modes of UHSCFST specimens were the same as those of ordinary ones. The failure of UHSCFST specimens was attributed to excessive deflection, and local buckling occurred in the compression zone. Moreover, the bending capacity of the specimens did not decrease, even if they had yielded. Although ultrahigh strength concrete was poured, all of the specimens displayed outstanding bending ductility. The main function of core concrete was to provide radial restraint for the steel tube to avoid premature buckling. When the steel content of the specimen section was constant, the strength increases of core concrete had a slight impact on the bending failure mode, bearing capacity and ductility of UHSCFST specimen. The research results can deepen the understanding of the mechanical behaviors of the UHSCFST composite truss structure.

Full-scale experimental investigation on the seismic performance of PC columns before and after repair of grouting defects

This research focused on investigating the influence of insufficient grouting on the seismic performance of precast concrete (PC) columns, connected using grouted sleeves, and validating the feasibility and reliability of the repair method for insufficient grouting. To realize these, five full-scale PC columns were tested under cyclic loads, including one specimen without grouting defects, two specimens with defect ratios of 45% and 60%, respectively, which were determined by previous cyclic test results of grouted sleeve connections (GSCs), and two repaired specimens which had initial defect ratios of 45% and 60%, respectively. The effects of defect ratios and repair actions were analyzed, and the test results indicated the following: 1) The bar slip dominated the failure of two specimens with defect ratios as expected, rather than the flexural failure mode for the specimen without defects. A rocking phenomenon was observed since the occurrence of bar slip, and the pinching phenomenon appeared for the corresponding hysteretic curves. The load-bearing, deformation and energy dissipation capacities were significantly lower than those of the specimens without defects. The increase in the defect ratio decreased the drift ratio associated with the bar-slip phenomenon, but the influence of the defect ratio on the seismic performance after the bar slip was negligible. 2) The bar-slip behavior was effectively prevented after the repair of insufficient grouting. Hence, the repaired specimens exhibited the expected flexural failure mode, and the load-bearing, deformation, and energy dissipation capacities were generally comparable with those of the specimen without defects. Rocking behavior and pinching phenomenon were not observed after repair. The negative influences of insufficient grouting were almost eliminated, thus validating the reliability of the repair method. The research outcome can serve as a reference for quality control of PC structures using GSCs.

Influences of wrinkles induced by tows’ offset in automated fiber placement on the bending properties of composites

This paper studies the influence of wrinkles caused by tows’ offset on the bending performance of composite laminates during Automated Fiber Placement (AFP) manufacturing. In this paper, the different distances of tows’ offset are set to prepare laminates containing various wrinkles and obtain the characteristics of different wrinkles through the feature recognition algorithm. Then a three-point bending test is conducted to investigate the influences of different wrinkles on the flexural strength and failure mode of laminates. The results indicate that wrinkle defects reduce the flexural strength of the laminate by about 12% to 15%, and the flexural strength is positively correlated with the wrinkle smoothness S. As the wrinkles increase, the failure mode of the laminate gradually changes from local collapse under the punch to instantaneous shear failure in the wrinkle area, and the degree of warping and delamination increases. Therefore, avoiding wrinkle defects can effectively maintain flexural strength and reduce the extent of warping and delamination.

Analytical Investigation on Behaviour of Cold Formed Deep Joist Channel Section

The application of cold formed steel elements in construction is becoming very popular due to several advantages like Speedy construction, higher strength to weight ratio, dimensional stability and recycled material. CFS is proposed to use as building components as beams, columns, Joists, wall panels etc. The load carrying capacity of cold-formed steel (CFS) joists can be enhanced by employing optimization techniques. Recent research studies have mainly focused on optimizing the bending capacity of conventional channel with and without lips that are used as joists. The objective of the study is to examine the flexural strength, failure mode and load-deflection of the cold formed steel double furred channel section with and without web openings under flexure.

Comparison of flexural behaviors between plain and steel-fiber-reinforced concrete beams with hybrid GFRP and steel bars

This study investigates the flexural behavior of steel-fiber-reinforced concrete (SC) beams with hybrid glass fiber reinforced polymer (GFRP) and steel bars. The experimental results of current SC beams are compared with those of the plain concrete (PC) beams conducted in our previous research. Taking account of the differences in nominal reinforcement ratio and reinforcement layout of seven tested SC beams, the test results including cracking load, ultimate load, failure mode, crack spacing and width, and mid-span deflection were firstly discussed. Then, a comprehensive comparison of flexural behaviors between SC beams and PC beams with same reinforcements was conducted in this paper. Especially, the crucial effects of type and strength of concrete on flexural capacity and failure mode of test beams were analyzed in detail. Finally, for concrete beams reinforced with hybrid (GFRP and steel) bars, the optimization of two balanced nominal reinforcement ratios was proposed to ensure the beam’s flexural failure in an appropriate-reinforced mode without rupture of GFRP bars.

Adobe mixtures reinforced with fibrillated polypropylene fibers: Physical/mechanical/fracture/durability performance and its limits due to fiber clustering

This study assesses the feasibility of the incorporation of fibrillated polypropylene fibers (FPFs), an engineered multidimensional and multifilament fiber mostly used to reinforce concrete mixtures, into adobe mixtures (AMs), a traditional and manually-made material used to produce adobe blocks. The incorporation of FPFs was assessed using increasing dosages (0%, 0.25%, 0.5%, and 1% in wt% of clay soil) of FPFs. These fibers were gradually added and mixed with the clayey soil prior to incorporation of water to promote uniform mixtures with adequate fiber distribution to reduce the formation of fiber clusters. The impact of FPFs was evaluated in terms of its effects on the bulk density (physical), compressive and flexural strength (mechanical), flexural toughness indices (fracture) and water erosion resistance (durability) of AMs. Results indicate that increasing dosages of FPFs monotonically reduce average values of bulk density, as well as compressive and flexural strength of AMs. On the other hand, these increasing dosages of FPFs monotonically increase average values of water erosion resistance as well as flexural toughness indices, varying the flexural failure mode from brittle (unreinforced AM) to ductile (reinforced AMs) because of the adequate bonding and FPF-bridging effect after the crack generation as confirmed by instrumentation as well as digital image correlation evaluations implemented in this study. The significant reductions of bulk densities and compressive and flexural strengths obtained for fiber-reinforced AMs were related to the increasing number of fiber clusters found for increasing dosages of FPFs within the fiber-reinforced mixtures, which was evaluated using scanning electron microscopy analyses. For example, positively the AM incorporating 1% of FPFs increased, on average, the flexural toughness by 674% and reduced the bulk density and water erosion depth by, on average, 9% and 64%, respectively, when compared to the unreinforced AM. However, this large dosage of FPFs also generated a significant reduction of the compressive strength (60% on average) and the flexural strength (43% on average) when compared to the plain mixture. On the other hand, a small dosage of FPFs (0.25%) generated less significant improvements in terms of flexural toughness, bulk density, and water erosion (on average, increment of 58% and reductions of 2% and of 38%, respectively, when compared to the unreinforced AM). Yet, the latter mixture presented reductions, on average, of compressive and flexural strengths of 24% and 16%, respectively, when compared to the plain mixture, and these reductions were significantly smaller than the reductions obtained by the largest FPF dosage, due to the significantly smaller number of fiber clusters presented by the 0.25% dosage when compared to the 1% dosage. Finally, the mechanical performance limitations exhibited by the incorporation of FPFs, especially in large dosages, are related to generated fiber clusters due to the inherent morphology of these FPFs as well as the traditional manual confection process of AMs. Therefore, this study recommends the implementation of FPFs in AMs, but in small dosages and/or suggests the implementation of a mechanical mixing/compaction process that guarantee a more uniform fiber distribution that reduces the generation of fiber clusters.

Seismic performance of double skin composite wall under maximum considered far-field earthquake loading protocol

In order to evaluate the realistic seismic performance of double skin composite wall (DSCW) under earthquakes, 4 full-scale experiments of DSCW were conducted using the maximum considered far-field earthquake loading protocol. The methodology for developing the loading protocol was described, and all necessary assumptions and decisions of the development were briefly introduced. The effect of boundary columns thickness and axial compression ratio of DSCW were taken into consideration. The experimental results showed that all DSCW specimens underwent a similar damage process and exhibited the flexural failure mode. The DSCW component has desirable ductility under the maximum considered earthquakes. Improving the thickness of boundary columns increases the peak strength and ultimate strength of DSCW but significantly decreases the displacement ductility. Increasing the axial compression ratio enhances the peak strength and initial stiffness of DSCW but reduces the displacement ductility of DSCW significantly. The thickness of boundary column has a negligible impact on the energy dissipation capacity of DSCW. However, the DSCW with the thicker thickness of boundary columns gains less energy dissipation cycles due to its lower displacement ductility. Increasing the axial compression ratio improves the energy dissipation capacity of DSCW but reduces the energy dissipation cycles.