Papers by Keyword: Flexural Behavior

Abstract: The presented study focuses on the theoretical and experimental analysis of slabs with non-metallic GFRP (glass fiber reinforced polymer) bars as a prestressing reinforcement in concrete structures [25]. In this study, experimentally designed GFRP-reinforced prestressed concrete slabs were developed as a lost formwork on the bridge girders. Using prestressed GFRP could effectively minimize thickness, reduce crack widths, improve flexural performance, and lower the deflections of the slabs. Due to the corrosion-resistant behavior of GFRP, it is possible to minimize the thickness of the slab by reducing the concrete cover, which leads to a reduction in the self-weight of the member. Members with GFRP reinforcements deformed approximately linearly under increasing load. The first elastic part with no cracks observed during loading is typical for small increments of deflection within the rising bending moment. The stiffness of the member reduces after crack formation. The second part of the diagram is called linear-elastic, with increasing deflection of the slab due to the linear-elastic behavior of GFRP. The results obtained were compared with analytical models for ultimate flexural resistance and load deflection behavior at each loading step evaluated using the design equations introduced in ACI 440.1R-15 and ACI 440.4R-04. For a non-linear analysis software for FEM, Atena was used, which considered geometrical and physical non-linearity. The differences in the analytically calculated models to estimate the bending capacity and deflections in the middle span of the prestressed slabs with experimental results and nonlinear FEM analysis were evaluated.

Abstract: Ultra-high-performance fiber-reinforced concrete (UHPFRC) exhibits outstanding compressive strength but tends to fail in a brittle manner under flexural loading when fibers are absent. This study evaluates the effectiveness of recycled tire steel fibers (RTSF) in improving the flexural strength, ductility, and toughness of UHPFRC beams. Thirty six doubly reinforced beams were cast and tested under three-point bending with reinforcement ratios of 0.009, 0.019, 0.028, and 0.043. The specimens were grouped as non-fiber control, mono RTSF (13 mm, 1.5% by volume), and hybrid RTSF (13 mm at 1.5% + 16 mm at 1.5%). Load deflection and stress strain responses were analyzed to assess structural performance. Beams without fibers failed abruptly, whereas those reinforced with RTSF demonstrated significantly greater ductility and energy absorption. The mono-fiber beams achieved a peak load of 264.46 kN, while the hybrid fiber beams attained a peak stress of 128.66 N/mm², 29% and 23% higher than those of the mono and non-fiber beams, respectively. These results confirm that incorporating RTSF, particularly in hybrid form, effectively mitigates brittle failure in UHPFRC and provides a sustainable, locally sourced solution for achieving superior strength, ductility, and toughness.

Abstract: The Fused Filament Fabrication (FFF) process plays a crucial role in additive manufacturing (AM), therefore the optimization of certain parameters has a significant impact on the performance of 3D-printed components. In this study, the flexural behavior of Polylactic Acid (PLA) samples manufactured by FFF process is investigated. The influence of the infill density (ID) and the outer shell (OS) on the main physical and mechanical characteristics is studied in detail. The used IDs are 10%, 30%, 50%, 70%, and 90%, and the samples are manufactured with and without OS. All samples are manufactured with rectilinear infill pattern. The geometry of the samples and the experimental program follow the ISO 178 standard. The tests were performed at room temperature, with a test speed of 5 mm/min. The results indicate that main flexural properties (stiffness, strength, strain and fracture energy) are significantly superior in OS samples. Moreover, an increase in properties is obtained with the increase of the ID, regardless of the OS configuration. It was found that specimens without OS exhibited plastic deformation at all IDs, while those with OS demonstrated a quasi-brittle fracture pattern at IDs below 50%. Further analysis of the specific properties (specific strength and specific modulus) showed that an ID of 10% is optimal for 3D-printed structures with OS, while an ID of 90% is optimal for structures without OS. Thus, the importance of ID and OS parameters should not be neglected in the design of 3D printed structural components.

Abstract: Using cement as the primary material for making concrete, around 7%-15%, requires a significant amount of energy and generates abundant waste, thus significantly impacting the environmental conditions. Innovative materials are needed as alternatives to cement. Fly ash, as an environmentally friendly material, can be a solution to minimize the use of cement. The selected fiber is Poly-Vinyl Alcohol (PVA) fiber due to its high tensile strength, which can effectively inhibit the rate of crack development occurring in the beams. The research process was divided into two stages: geopolymer mortar compressive strength testing and beams flexural testing. Compressive strength testing of geopolymer mortar was conducted on 50x50x50 mm cube samples, tested at ages of 3, 7, and 28 days using both air curing and moist curing methods. Geopolymer mortar was created using fly ash as the base material, along with activators such as Sodium Hydroxide (NaOH) and Sodium Silicate (Na₂SiO₃). Meanwhile, flexural beams were tested in 5 samples of 150x200 mm beams with a length of 3300 mm each. The samples consisted of a control beam, a beam reinforced with commercial grouting mortar, a beam reinforced with commercial grouting mortar and PVA geopolymer fibers, a beam reinforced with geopolymer mortar, and a beam reinforced with geopolymer mortar and PVA fibers. The research results indicated that adding PVA fibers to geopolymer mortar could enhance the maximum load-bearing capacity and stiffness of the beams. Regarding failure modes, beams reinforced with PVA-free geopolymer mortar experienced delamination failure, whereas beams reinforced with PVA-containing geopolymer mortar encountered debonding failure.

Abstract: In this study, an experiment was performed on flexural behavior of RC beam that experienced spalling due to corrosion. The spalled concrete was repaired using grouted mortar, while the lost reinforcement area was replaced with Glass Fiber Reinforced Polymer (GFRP) sheets. The effectiveness of these repairs relied heavily on the bond between the existing and new concrete, ensuring no delamination occurred under maximum load. To enhance this bond, connectors or dyna-bolt anchors were incorporated into the joint area. Eight RC beam were prepared, each with a cross-section of 150 mm x 200 mm and length of 3300 mm, consisting of 1) two existing beams (BE), 2) two beams repaired with grouting and GFRP sheet (BGS), 3) two beams with grouting, GFRP sheet, and the addition of 4 anchors (BGS-DN4), and 4) two beams with grouting, GFRP sheet, and the addition of 8 anchors (BGS-DN8). The repaired area was 2700 mm long and 50 mm thick, and then flexural testing using four-point loads was conducted on all specimens. The results showed that RC beam repaired with mortar grouting and GFRP sheets, along with the inclusion of 4 dyna-bolt anchors in the connection area (BGS-DN4), could increase the maximum load by 61% compared to BE. This repair method improved the bond between the existing concrete and the repair material, effectively preventing delamination.

Abstract: Glass Fiber Reinforced Polymer (GFRP) Composite are increasing rapidly in Aerospace Industry, Civil and Wind energy sectors, where they can frequently be exposed to different temperature conditions. As the constituent polymer matrix is highly affected by temperature, extreme temperature conditions are critical for GFRP composite structural design. Researchers have recently found nanofillers such as graphene and carbon nanotubes with excellent multifunctional mechanical properties. Graphene Nanoplatelets (GnP) consist of several layers of graphene. GnP is considering an attractive nanofillers as it has improved polymer matrix properties. In this study, the weight percentage of GnP added in GnP-GFRP laminate is 0.25% and 0.5%.GFRP and GnP-GFRP laminates are fabricated by using the hand lay-up method, and the specimens are subjected to a three-point bending test in a thermal chamber with varying the temperature, i.e., 30°C, 50°C, 75°C, and 100°C. This paper investigates the effect of graphene nanoplatelets on the flexural behavior of glass fiber-reinforced polymer composites subjected to different temperatures. Flexural strength and modulus are evaluated, and the appropriate conclusions are determined. GFRP with 0.25% GnP shows higher strength than the neat and 0.5% GnP-GFRP. Here, it has also been shown that flexural strength and modulus decrease significantly with increasing temperature.

Abstract: In this work, an experimental test series was carried out in order to evaluate the influence of the geometry of the specimen and stacking sequence on macroscopic behavior and the failure modes. A CFRP prepreg unidirectional was used to perform the tested specimens according to ASTM D790 standard. Five main lay-up configurations have been analyzed: [0]₁₂, [±30]_3s, [±45]_3s, [±80]_3s, and [0/90]_3s subjected to flexural loading. The macroscopic behavior was followed by an MTS machine equipped with a bending fixture. A digital microscope is used to follow the microscopic failure modes during loading. These laminates exhibit a more complex behavior due to coupling effects and the combination of different failure modes. However, the most predominant damage observed is delamination accompanied with matrix cracking. Furthermore, the present work has shown a linear behavior of [0]₁₂, [±80]_3s, [0/90]_3s, and a distinctive behavior of [±45]_3s and [±30]_3s laminate under flexural loading due to its pseudo ductile behavior.

Abstract: There are several different types, shapes and geometries of profiled steel decking that are available in the market for composite slabs construction. The application of the system in construction industry usually depends on the design tables provided by the manufacturer of steel decking. Engineers and builders use the design tables according to the required spans and thicknesses in order to facilitate the design of composite slabs for their construction. However, architectural designs might be an obstacle toward applying the system directly because of the limitation toward spans and thicknesses that can be provided by the design tables. In this research, reinforced profiled steel deckings using cold formed C-channel were used to construct full-scale composite slabs with a purpose to increase the span provided by manufacturer design tables and the capacity of the system for in-situ construction. The full-scale composite slabs system was simply-supported and tested in four-point bending with single control shear spans. The structural behaviour of the reinforced slabs system was investigated. The test comprises 12 specimens which include control (CD slabs) and reinforced decks (RD slabs) samples. The composite slab flexural behaviour was monitored using the LVDT instruments toward bending deformation at the critical points and toward slip displacement between the metal decks and the concrete. The load was applied until total damage was observed for the composite slabs system. The performances of the tested RD slabs were comparable with the corresponding CD slabs which indicated by the samples load carrying capacity, end-slippage, and concrete-steel composite action.

Abstract: The good mechanical performance of bamboo, coupled with its sustainability, has boosted the idea to use it as a structural material. In some areas of the world it is regularly used in constructions but there are still countries in which there is a lack of knowledge of the mechanical properties of the locally-grown bamboo, which limits the spread of this material. Bamboo is optimized to resist to flexural actions with its peculiar micro structure along the thickness in which the amount of fibers intensifies towards the outer layer and the inner part is composed mostly of parenchyma. The flexural strength depends on the amount of fibers, whereas the flexural ductility is correlated to the parenchyma content. This study focuses on the flexural strength and ductility of six different species of untreated bamboo grown in Italy. A four-point bending test was carried out on bamboo strips in two different loading configurations relating to its microstructure. Deformation data are acquired from two strain gauges in the upper and lower part of the bamboo beam. Difference in shape and size of Italian bamboo species compared to the ones traditionally used results in added complexity when performing the tests. Such difficulties and the found solutions are also described in this work. The main goal is to reveal the flexural behavior of Italian bamboo as a functionally graded material and to expand the knowledge of European bamboo species toward its use as a structural material not only as culm but also as laminated material.

Abstract: Cold-formed profiled steel decking composite slab is one of the most widely used system of slab after conventional concrete slab for building structure. It is cost effective, straightforwardly designable and readily available in the market for construction. However due to modern architectural desire of large span building, this system weakness that is the requirement of temporary propped support may have an impact toward its cost effectiveness. Generally more propped support are required with the increase of slab span design.This paper present the result of laboratory test on the behavior of reinforced profiled steel decking under loading to increase the span for unpropped composite slabs construction. The load capacity of the steel decks was amplified by reinforcing cold formed C channel on the top flange of steel decks. The experimental program comprises 12 full-scale tests of three length with a set of modification of profiled steel decking using cold formed C channel.The result shown experimental evidence of the role played by the cold formed C channel on altering the cross section properties which supporting the bending capacity of the steel decks. The flexural response of the steel deck was examined using the LVDT instruments to capture the deformation at three points. The finding delivered by the experimental data for the performance of reinforced profiled steel decking are set as the base for the future verification of finite element model.