Flexural Deflection Research Articles

Numerical Investigation of a Hybrid FRP-Geopolymer Concrete Beam

Over the past years, numerical investigations have gained more attention and success in analysing the overall performance of hybrid FRP-concrete structures in civil engineering applications. In this study, a hybrid FRP-geopolymer concrete beam, which consists of high-strength geopolymer concrete filled into a rectangular hollow section pultruded GFRP profile, has been investigated numerically using the commercial software ABAQUS. A non-linear finite element model has been developed to simulate the flexural behavior of this hybrid beam under four-point static loading. Different material models were employed to describe the materials used for the hybrid beam members. The numerical results including the flexural capacity and load deflection curves are compared and verified with published experimental data from literature. The determination of dilation angle of geopolymer concrete and the effect of mesh dimensions are also compared and reported in this study. A reasonable agreement between experimental data and the numerical result is obtained, which indicates the finite element model developed in this numerical investigation is able to predict the non-linear behavior of this hybrid beam.

Flexural experiment and stiffness investigation of reinforced concrete beam under chloride penetration and sustained loading

This paper presents an experimental study conducted to characterize the effect of corrosion and sustained load on structural behavior of reinforced concrete (RC) beam. The effects of loading level on corrosion of reinforcing steel, the flexural deflection and residual loading capacity of the test beams were investigated. In the first scenario, two non-corroded beams were tested to determine the maximum load levels that were required by the beams to reach their deflection limits and that were also tested for the sustained levels of the applied loads. For the second experiment, the corrosion was accelerated through the application of external direct current whilst the beams were under the load equivalent to 0%, 50%, 65% and 80% of the ultimate load. The results indicate that load levels have a significant effect on the rise of steel corrosion level, the decrease of flexural stiffness and the degradation of flexural capacity. The mechanical properties like the strength and ductility are significantly impaired due to simultaneous effect of loading and corrosion in comparison to the effect of the single parameter at a time. Considering the corrosion situation of different position of steel bar, the formula of the ratios of the different position of steel bar corresponding with different sustained loading levels was given. An equation was deduced to calculate the flexural stiffness of corroded reinforced concrete and can be served as a reference for deflection calculation of corroded reinforced concrete beams.

Multifrequency force microscopy using flexural and torsional modes by photothermal excitation in liquid: atomic resolution imaging of calcite

We introduce a new multifrequency atomic force microscopy (AFM) method which involves the excitation of flexural and torsional eigenmodes of the microcantilever probe in liquid environments. The flexural and torsional deflection signals are mostly decoupled in the majority of commercial AFM setups, so they can be relatively easily recorded and processed. The use of torsional modes provides additional surface information at the atomic scale, with respect to flexural mode imaging alone, although the flexural modes are the only ones capable of ‘true’ atomic resolution imaging. In our experiments, the torsional modes are shown to be particularly sensitive to protruding oxygen surface atoms on the calcite plane. The high lateral resolution capability of the flexural modes, combined with the high sensitivity of the torsional modes to specific surface features in liquid environments, can thus offer the means of observing chemical contrast at the atomic level using purely mechanical measurement AFM techniques, even in the absence of tip functionalization.

Flexural Behavior of Posttensioned Flat Plates Depending on Tendon Layout

This paper discusses the experimental results on the flexural behavior and deflections of posttensioned concrete flat plates depending on tendon layout. One reinforced concrete flat plate and two posttensioned concrete flat plates were manufactured and tested. One-way posttensioning layout and two-way posttensioning layout were considered in this paper. The load-deflection behavior and modes of crack are presented from the test results. Posttension systems effectively controlled crack and deflection. One-way and two-way posttensioning layouts both showed similar maximum load. However, serviceability improved with two-way posttensioning layout compared to one-way posttensioning layout. Also, the yield-line theory was applied to predict the ultimate load for the posttensioned flat plates. The comparison between the test results and estimation by yield-line analysis generally showed good agreement.

Behavior of the sandwich beam subjected to bending as a function of the core density

The sandwich beam can be considered as the multi-layered structure with a symmetrical cross-section. In this paper is assumed that the structure is created by periodical repetition of a unit cell. The influence of its size on the beam’s static behavior in bending was analyzed. The variation of the unit cells number affects the size of the cell, so the static analysis was performed – the flexural stiffness and the beam’s deflection were determined as functions of the unit cells number. The two configurations of the sandwich beams were considered: the beam with the constant cross-section along its length and the beam with the periodically variable cross-section. The graphs of the beam’s flexural stiffness and deflection variations in terms of the unit cells number were obtained. It was concluded that after a certain number of the cells, the core’s density does not further influence the behavior of the sandwich beam, under the given loading conditions. The conclusion from comparison of the two configurations is that the sandwich beam with the variable cross-section behaves somewhat better than the beam with the constant cross-section. The FEM analysis has verified all the conclusions from the analytical solution about the sandwich beams behavior when subjected to bending.

Flexural response of steel-fiber-reinforced concrete beams: Effects of strength, fiber content, and strain-rate

This study aims to investigate the flexural behavior of steel-fiber-reinforced concrete (SFRC) beams under quasi-static and impact loads. For this, a number of SFRC beams with three different compressive strengths (fc' of approximately 49, 90, and 180 MPa) and four different fiber volume contents (vf of 0, 0.5, 1.0, and 2.0%) were fabricated and tested. The quasi-static tests were carried out according to ASTM standards, while the impact tests were performed using a drop-weight impact test machine for two different incident potential energies of 40 and 100 J. For the case of quasi-static load, enhancements in the flexural strength and deflection capacity were obtained by increasing the fiber content and strength, and higher toughness was observed with an increase in the fiber content. For the case of impact load, an increase in the load carrying capacity was obtained by increasing the potential energy and strength, and an improvement in the post-peak behavior was observed by increasing the fiber content. The increases in fiber content and strength also led to enhancements in residual flexural performance after impact damage. Finally, the flexural strength became less sensitive to the strain-rate (or stress-rate) as the strength of concrete increased.

Effect of Plasma and Fiber Position on Flexural Properties of a Polyethylene Fiber-Reinforced Composite.

The aim of this study was to evaluate the effect of plasma treatment using argon and oxygen gases, combined with fiber position on flexural properties of a fiber-reinforced composite. Eleven groups were evaluated, a non-reinforced control group and 10 groups reinforced with InFibra, a woven polyethylene fiber, varying according to the plasma treatment and fiber position. The samples were prepared using a stainless steel two-piece matrix. The three point bending test was performed in an EMIC testing machine. Flexural strength (FS) and flexural deflection (FD) were calculated from initial (IF) and final (FF) failure. Data were evaluated statistically using Kruskal-Wallis and Mann-Whitney tests (p<0.05). For IF, in all groups with fibers placed on the base, the FS and FD values were significantly higher than those positioned away from the base. The highest value of FS was obtained in the group treated with O 3 min (296.2 MPa) and the highest value of FD was obtained in the group treated with 1 min (0.109 mm). For FF the FS and FD values obtained for the groups with fibers positioned away from the base were similar or higher than those placed on the base. The highest FS value was obtained in the group treated with 1 min (317.5 MPa) and the highest FD value was obtained in the group treated with O 3 min (0.177 mm). Plasma treatment influenced FS and FD. Fiber position and plasma treatment affected the flexural properties of a fiber-reinforced composite.

Flexural performance evaluation of composite steel deck one-way slab system with SFRC

The slab is one of the most important members in building structures because it covers the largest area of the building. The structural type and construction method of a slab can have a large influence on the construction period and the amount of structural materials. This study investigates a simplified one-way slabsystem with simple construction procedures. The simplified slab system consists of a composite steel deckplate and steel fiber reinforced concrete (SFRC) without conventional steel reinforcing bars. The compositesteel deck plate can replace the tensile reinforcing bars and concrete form, and the SFRC makes temperaturereinforcement unnecessary. Four specimens were tested to analyze the flexural performance and serviceability.The test results were analyzed from the viewpoints of flexural performance regarding flexural load capacity,stiffness, deflection, crack development, and failure mode. The test results indicate that the overallflexural performance of the system was suitable in slab members, even though reinforcing bars were not used.It has higher flexural stiffness and shows lower crack height than a conventional RC slab.

Computational Approach to Investigation of Crack Behaviour under Vehicular Loading of A Typical Concrete Pavement (A Case Study of Mbagathi Road in Nairobi)

Nairobi County has nearly 100% road network as bituminous roads and only 4km road network (Mbagathi Road) is concrete road. This road was a pilot project that was implemented by Kenyan Government between the years 2005 and 2007 at a total construction cost of over 400 million Kenya Shillings. The design was done based on South Africa design procedure on a 210 mm thick PJCP pavement. Performance of Plain Jointed Concrete Pavement (PJCP) depends on aggregate interlock, which is the mechanism by which loads are transferred from one slab to the adjacent one. This study attempted to use the information on load transfer mechanics in order to quantify the effect of aggregate properties to crack size as well as the propagation of any cracks formed in service. This research was undertaken in two different ways namely experimental and computer simulation. The experimental approach entailed measuring widths and depths of cracks existing in Mbagathi road, and also involved setting up concrete beams in the laboratory and loading them to failure with predetermined loads and measuring sizes of resulting cracks. On the other hand, the computational approach was verified by experimental results entailed simulating crack widths and depths with recent devised fracture models. Cracks were experimentally noticed to occur due to loading the pavement with vehicular loads bigger than safe load. Cracks generated had crack width equivalent to the measured flexural deflection and for an ideal concrete pavement crack width and crack depth exhibited an exponential relationship. It was found that vehicular loads induce stresses in concrete pavements which exceed permissible tensile stresses, hence a better understanding of the resultant cracks, as well as their propagation. This research will lead to an improvement of the design of concrete pavements in Kenyan environment.&#x0D;

강섬유보강 콘크리트를 사용한 무배근 연속슬래브의 구조성능

Slab is one of the most important members in the building structures because it covers the largest area of the building. But, amount of reinforcement in this member is relatively small because of its small supporting loads. And large exposed area in slab can induce the cracks. To improve this characteristics, the new slab system consist of structural deck-plate and fiber reinforced concrete was suggested for improving construction ability and reduction of construction period. Basic concept of this slab system is that structural deck-plate can replace the tensile reinforcing bars and concrete form, and fiber reinforced concrete can replace the temperature reinforcement. But, previous study was limited because it tested only simply supported slab specimens. This study tested various continuous slab specimens to find the applicability of the suggested new slab system without any additional reinforcement. Design concept is that structural design of slab is assumed as simply support slab, but it should keep the negative moment cracks under allowable crack width in service load conditions. Four continuous slab specimens in total were tested for analyzing the flexural strength, stiffness, deflection, crack development and failure pattern. Test results indicated that suggested new slab system appeared to be better flexural capacity and stiffness than normal reinforced concrete slab with negative moment reinforcement. And it can control the cracks under the allowable crack width upto the service and factored loads.

Improved finite element modeling of piezoelectric beam with edge debonded actuator for actuation authority and vibration behaviour

The main emphasis of the present work is to model a piezoelectric beam with edge debonded actuator by employing finite element method based layerwise shear deformation theory, to improve the accuracy with which the actuation authority and natural frequencies are computed. The surface-bonded piezoelectric actuators and the host beam are considered to rotate individually due to shear deformation, while they are assumed to undergo the same flexural deflection and slope. These modeling aspects have improved the accuracy of the computed results. Edge debonding of actuator is accounted in the model by modeling healthy and debonded regions of the beam individually and subsequently applying the displacement continuity conditions at the interfaces of different regions. The investigations are carried out to find the effect of different extents of edge debonding on the actuation authority and natural frequencies of the debonded piezoelectric beam. It is found from the numerical results that the behaviour of the beam with edge debonded actuator is affected considerably as regards to the actuation authority and marginally with respect to natural frequencies. Further it has been shown that, when an actuator is edge debonded it introduces the local modes besides displaying significant reduction in its actuation authority.

A hydromechanical approach to assess CO2 injection-induced surface uplift and caprock deflection

This study focuses on the derivation of a semi-analytical approach for the evaluation of surface uplift and caprock deflection induced by underground injection of CO2. The adopted methodology includes the development of a mathematical model that incorporates the deformable behaviour of the storage reservoir and the flow of two immiscible fluids (CO2 and brine) within the aquifer while the surface rock or the caprock layer is modelled as a thin plate. Governing equations are solved for the axisymmetric flexural deflection due to a constant rate of CO2 injection. Both developed solutions are applied to a representative CO2 storage case solved numerically by the finite element method, and good agreement between results is observed. When benchmarking to the In Salah surface uplift, the developed semi-analytical approach can capture a high rate of surface uplift caused by the pressure build-up during the early stage of CO2 injection. The required calculation time is very short compared to a classical finite element approach. This method can be employed as a design tool for the analysis of uncertainty in parameters such as the injection rate, porosity, rock properties and geological structures. This semi-analytical approach also provides an efficient means of estimating the influence of high injection rates of CO2 on surface uplift.

Comparison of Various Techniques for Flexural Strengthening of Thin Concrete Members Using Continuous Carbon Fibers

This paper deals with flexural performance of thin concrete members reinforced with continuous carbon fibers in the form of filament yarns. The laboratory specimens were tested under static loading conditions to investigate the effects of three different strengthening techniques on flexural stress, mid-span deflection and modes of failure. The specimens were strengthened in flexure using carbon fiber yarns as near-surface mounted, externally bonded and placed in the geometric center of the specimen, respectively. Based on this investigation, the advantages and shortcomings of individually strengthening technique can be drawn.

Predicting the post-cracking behavior of normal- and high-strength steel-fiber-reinforced concrete beams

In this paper, the results of analytical and experimental analyses for the flexural response of steel-fiber-reinforced concrete (SFRC) beams are presented. In the analytical part, to predict the flexural response of SFRC beams according to the strength of concrete and steel fiber content, a model for compression was adopted from a previous research and a trilinear tension-softening curve (TSC) was suggested based on inverse analysis. To obtain the TSC, a number of notched SFRC beams with two parameters such as (1) strength of concrete (normal- and high-strengths) and (2) steel fiber content (0.0%, 0.5%, 1.0%, 2.0%) were fabricated and tested in accordance with the Japan Concrete Institute (JCI) standard. The suggested models were verified through a comparison of the previous four-point flexural test results and the sectional analyses. For the experimental part, the compressive strength and elastic modulus showed negligible changes with the inclusion of steel fibers, while the strain capacity and post-peak behavior were improved by including steel fibers. The addition of more than Vf of 1.0% steel fibers resulted in the significant improvement of flexural strength, deflection capacity, and post-peak ductility, while the increase of compressive strength led to an increase in the flexural strength and a decrease in the post-peak ductility. Lastly, the fracture energy increased with the increase in the fiber content and the decrease in the strength.

Flexure behavior of composite cantilevers subjected to different environmental conditions

Abstract This publication presents an experimental study which was conducted to examine the effects of various types of environments on the flexural stress and load-deflection relationships of the composite cantilever beams subjected to a single force at their free end for different exposure times. The study includes the testing of five different conditions which are cold, hot, humid, seawater environments and room temperature. Maximum flexure stresses and deflections of cantilever beam are presented analytically, numerically and experimentally. ANSYS FEA program is used for numerical analysis of composite materials. The test results carried out after generally one and two months of exposure to the different environmental conditions show that the flexure stress and deflection of the beams are affected at different levels. Moreover, it is shown that the analytical and numerical results are consistent with the experimental data.

Evaluating the mechanical properties of E-Glass fiber/carbon fiber reinforced interpenetrating polymer networks

A series of vinyl ester and polyurethane interpenetrating polymer networks were prepared by changing the component ratios of VER (Vinyl ester) and PU (Polyurethane) and the polymerization process was confirmed with Fourier Transform infrared spectroscopy. IPN (Inter Penetrating Polymer Network - VER/PU) reinforced Glass and carbon fiber composite laminates were made using the Hand lay up technique. The Mechanical properties of the E-glass and carbon fiber specimens were compared from tests including Tensile, Compressive, Flexural, ILSS (Inter Laminar Shear Strength), Impact & Head Deflection Test (HDT). The IPN Reinforced Carbon fiber specimen showed better results in all the tests than E-Glass fibre reinforced IPN laminate with same thickness of the specimen, according to ASTM standards. It was found that the combination of 60%VER and 40%PU IPN exhibits better impact strength and maximum elongation at break, but at the slight expense of mechanical properties such as tensile, compressive, flexural, ILSS properties. The morphology of the unreinforced and reinforced composites was analyzed with help of scanning electron microscopy.

Bending Capacity Analysis of High-strength Reinforced Concrete Beams Using Environmentally Friendly Synthetic Fiber Composites

The research was conducted to determine the bending capacity of high-strength reinforced concrete beams with the addition of three environmentally friendly synthetic fibers i.e., polypropylene fiber, tie wire fiber, and used rubber tires fiber. Four beams with a dimension of 15 x 30 x 220cm were tested, including a beam for specimen without fiber as comparison. Specimens were designed to experience bending failure. Yield point of steel (fy) used for flexural and shear reinforcement was 407.43MPa. The diameter of flexural tensile reinforcement was 15.8mm, 11.9mm for the compressive reinforcement, as well as 11.9mm for the shear reinforcement. Concrete proportion incorporated 8% silica fume and 1.5% polycarboxylate ethers based superplasticizer ViscoCrete 10 from the cement weight. The maximum diameter of split was 15.9mm, having 550kg/m3 cement content and w/c-ratio 0.30. The target compressive strength was 70MPa for cylinder 15/30cm. The results showed that all beams experienced flexural failure as planned. Addition of fibers enhanced the bending behavior significantly, especially in flexural capacity, deflection and ductility. In comparison with high-strength reinforced concrete beam without fibers, the beam with polypropylene fiber had the increase of flexural strength of 115.24%, deflection of 306.56% and ductility of 298.9%; with tie wire fibers resulted in the increase of flexural strength of 117.39%, deflection of 160.52% and ductility of 148.0%; as well as with used rubber tires fiber produced the enhance of flexural strength of 112.13%, deflection of 184.56% and ductility of 178.3%. It can be concluded that the use of such environmentally friendly synthetic fibers can reduce the brittleness of high strength concrete, in which polypropylene fiber had delivered the best value and can be used very effectively than the other two types of fibers.

Computational Approach to Investigation of Crack Behaviour under Vehicular Loading of A Typical Concrete Pavement (A Case Study of Mbagathi Road in Nairobi)

Nairobi County has nearly 100% road network as bituminous roads and only 4km road network (Mbagathi Road) is concrete road. This road was a pilot project that was implemented by Kenyan Government between the years 2005 and 2007 at a total construction cost of over 400 million Kenya Shillings. The design was done based on South Africa design procedure on a 210 mm thick PJCP pavement. Performance of Plain Jointed Concrete Pavement (PJCP) depends on aggregate interlock, which is the mechanism by which loads are transferred from one slab to the adjacent one. This study attempted to use the information on load transfer mechanics in order to quantify the effect of aggregate properties to crack size as well as the propagation of any cracks formed in service. This research was undertaken in two different ways namely experimental and computer simulation. The experimental approach entailed measuring widths and depths of cracks existing in Mbagathi road, and also involved setting up concrete beams in the laboratory and loading them to failure with predetermined loads and measuring sizes of resulting cracks. On the other hand, the computational approach was verified by experimental results entailed simulating crack widths and depths with recent devised fracture models. Cracks were experimentally noticed to occur due to loading the pavement with vehicular loads bigger than safe load. Cracks generated had crack width equivalent to the measured flexural deflection and for an ideal concrete pavement crack width and crack depth exhibited an exponential relationship. It was found that vehicular loads induce stresses in concrete pavements which exceed permissible tensile stresses, hence a better understanding of the resultant cracks, as well as their propagation. This research will lead to an improvement of the design of concrete pavements in Kenyan environment.

Experimental Study on Flexural Response of FRP Strengthened Masonry Beams

This paper presents experimental study on flexural response of strengthened masonry beams using Engineered Cementitious Composites (ECC), strips and carbon fibre laminates. Five sets of eleven samples were tested for flexure in four-point loading set up. Two test samples made up a set of control beams. Set two consists of three test samples strengthened using ECC strips of two centimetres thick. Four test samples strengthened using ECC strips of three centimetres thick constituted the third set. Sets four and five comprise of one test sample each; termed [i] un-plastered, strengthened using carbon fibre laminates, and [ii] plastered, strengthened, using fibre laminates of carbon respectively. In terms of bending or flexural strength, deflection ductility and energy ductility parameters, samples strengthened using ECC strips and carbon fibre laminates exhibited higher values than there were for reference beams. Increased thickness of ECC strengthening strips from 2cm to 3cm resulted in increase in values of deflection ductility and energy ductility by 10.70% and 22.23% respectively. http://dx.doi.org/10.4314/njt.v34i1.11

Stress relaxation behavior of starch powder‐epoxy resin composites

ABSTRACTThe purpose of the present study is to investigate the quasi‐static and the viscoelastic behavior of epoxy resin reinforced with starch powder. An increase in the elastic modulus on the order of 42% was achieved; a behavior that was predicted by the modulus prediction model (MPM). Next, the composite was subjected to flexural relaxation experiments, in order to determine the relaxation modulus, at different filler‐weight fractions and flexural deflections imposed. The viscoelastic models of the standard linear solid, the power law model and the residual property model (RPM) were applied in order to simulate/predict the stress relaxation curves. Predicted values derived from the application of the above models were compared to each‐other as well as to respective experimental findings. From the above comparison it was proved the superiority of the RPM model in predicting both the linear and the nonlinear viscoelastic response of the materials investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41697.