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The Tension-Stiffening Contribution of NSM CFRP to the Behavior of Strengthened RC Beams.

ABSTRACT: Tension stiffening is a characteristic behavior of reinforced concrete (RC) beams which is directly affected by the bond-slip property of steel bar and concrete interfaces. A beam strengthened with a near-surface mounted (NSM) technique would be even more affected by tension stiffening, as the NSM reinforcement also possess a bond-slip property. Yet assessing how much the tension stiffening of NSM contributes to the behavior of RC beams is difficult due to the fact that bond-slip effects cannot be directly incorporated into a strain-based moment-curvature analysis. As such, the tension stiffening is typically incorporated through various empirical formulations, which can require a great deal of testing and calibrations to be done. In this paper a relatively new method, which can be called the mechanics-based segmental approach, is used to directly simulate the tension stiffening effect of NSM reinforcements on RC beams, without the need for empirical formulations to indirectly simulate the tension stiffening. Analysis shows that the tension stiffening of NSM fiber reinforced polymer (FRP) contributes a significant portion to the stiffness and strength of the strengthened RC beam not only during serviceability, but at all load levels.

SUBMITTER: Shukri AA

PROVIDER: S-EPMC5455669 | biostudies-other | 2015 Jul

REPOSITORIES: biostudies-other

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Strut deformation in CFRP-strengthened reinforced concrete deep beams.

Project description:Strut-and-tie model (STM) method evolved as one of the most useful designs for shear critical structures and discontinuity regions (D-regions). It provides widespread applications in the design of deep beams as recommended by many codes. The estimation of bottle-shaped strut dimensions, as a main constituent of STM, is essential in design calculations. The application of carbon fibre reinforced polymer (CFRP) as lightweight material with high tensile strength for strengthening D-regions is currently on the increase. However, the CFRP-strengthening of deep beam complicates the dimensions estimation of bottle-shaped strut. Therefore, this research aimed to investigate the effect of CFRP-strengthening on the deformation of RC strut in the design of deep beams. Two groups of specimens comprising six unstrengthened and six CFRP-strengthened RC deep beams with the shear span to the effective depth ratios (a/d) of 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00 were constructed in this research. These beams were tested under four-point bending configuration. The deformation of struts was experimentally evaluated using the values of strain along and perpendicular to the strut centreline. The evaluation was made by the comparisons between unstrengthened and CFRP-strengthened struts regarding the widening and shortening. The key variables were a/d ratio and applied load level.

| S-EPMC4147263 | biostudies-literature

The effect of different levels of pre-damage loading on the strength and structural behavior of CFRP strengthened R.C. beams: Experimental and analytical investigation.

Project description:In order to investigate the effect of pre-loading damage on the structural performance of Carbon Fiber Reinforced Polymer (CFRP) strengthened Reinforced Concrete (R.C.) beams, experimental and Finite Element Modelling (FEM) investigation was carried out on six R.C. beams. Five of the R.C. beams were damaged up to different levels of strain in the main steel bars before Flexure CFRP strengthening. One of the R.C. beams loaded up to failure and was kept as a control beam for comparison. The experimental results showed that the failure mode of the CFRP strengthened specimen was controlled by CFRP debonding followed by concrete crushing; however, the control beam failed in concrete crushing after yielding the steel bars, which is a ductile failure. The CFRP sheet increases the strength and initial stiffness of the R.C. beams and reduces ductility and toughness. Also, CFRP application increases the first crack and yielding steel bars load by 87.4% and 34.4%, respectively. Furthermore, the pre-damage level does not influence the strength and ductility of the strengthened R.C. beams except for the highest damage levels, which experienced a slight decrease in load capacity and ductility. However, the initial stiffness decreases with increasing pre-damage levels by 40%. Design guideline ACI 440.2R (2004) predicts the ultimate load capacity marvelously for externally bonded Fiber-Reinforced Polymer (FRP) beams compared to the experimental maximum load capacity. The excellent agreement between experimental and FEM results indicates that the constitutive models used for concrete and reinforcement and the cohesive interface model can well capture fracture behavior. However, The FEM analysis predicts the beam to be slightly stiffer and more robust, probably because of the assumed perfect bond between concrete and reinforcement. The developed FEM can be used for further parametric study.

| S-EPMC8717972 | biostudies-literature

Flax, Basalt, E-Glass FRP and Their Hybrid FRP Strengthened Wood Beams: An Experimental Study.

Project description:In this study, the structural behavior of small-scale wood beams externally strengthened with various fiber strengthened polymer (FRP) composites (i.e., flax FRP (FFRP), basalt FRP (BFRP), E-glass FRP ("E" stands for electrical resistance, GFRP) and their hybrid FRP composites (HFRP) with different fiber configurations) were investigated. FRP strengthened wood specimens were tested under bending and the effects of different fiber materials, thicknesses and the layer arrangements of the FRP on the flexural behavior of strengthened wood beams were discussed. The beams strengthened with flax FRP showed a higher flexural loading capacity in comparison to the beams with basalt FRP. Flax FRP provided a comparable enhancement in the maximum load with beams strengthened with glass FRP at the same number of FRP layers. In addition, all the hybrid FRPs (i.e., a combination of flax, basalt and E-glass FRP) in this study exhibited no significant enhancement in load carrying capacity but larger maximum deflection than the single type of FRP composite. It was also found that the failure modes of FRP strengthened beams changed from tensile failure to FRP debonding as their maximum bending load increased.

| S-EPMC6723195 | biostudies-literature

Influence of Tension Stiffening on the Flexural Stiffness of Reinforced Concrete Circular Sections.

Project description:Within this paper, the assessment of tension stiffening effects on a reinforced concrete element with the circular sections subjected to axial and bending loads is presented. To this purpose, an enhancement of an analytical model already present within the actual technical literature is proposed. The accuracy of the enhanced method is assessed by comparing the experimental results carried out in past research and the numerical ones obtained by the model. Finally, a parametric study is executed in order to study the influence of axial compressive force on the flexural stiffness of reinforced concrete elements that are characterized by a circular section, comparing the secant stiffness evaluated at yielding and at maximum resistance, considering and not considering the effects of tension stiffness.

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Crack Identification in CFRP Laminated Beams Using Multi-Resolution Modal Teager-Kaiser Energy under Noisy Environments.

Project description:Carbon fiber reinforced polymer laminates are increasingly used in the aerospace and civil engineering fields. Identifying cracks in carbon fiber reinforced polymer laminated beam components is of considerable significance for ensuring the integrity and safety of the whole structures. With the development of high-resolution measurement technologies, mode-shape-based crack identification in such laminated beam components has become an active research focus. Despite its sensitivity to cracks, however, this method is susceptible to noise. To address this deficiency, this study proposes a new concept of multi-resolution modal Teager-Kaiser energy, which is the Teager-Kaiser energy of a mode shape represented in multi-resolution, for identifying cracks in carbon fiber reinforced polymer laminated beams. The efficacy of this concept is analytically demonstrated by identifying cracks in Timoshenko beams with general boundary conditions; and its applicability is validated by diagnosing cracks in a carbon fiber reinforced polymer laminated beam, whose mode shapes are precisely acquired via non-contact measurement using a scanning laser vibrometer. The analytical and experimental results show that multi-resolution modal Teager-Kaiser energy is capable of designating the presence and location of cracks in these beams under noisy environments. This proposed method holds promise for developing crack identification systems for carbon fiber reinforced polymer laminates.

| S-EPMC5554037 | biostudies-other

Experimental Research on Concrete Beams Reinforced with High Ductility Steel Bars and Strengthened with a Reactive Powder Concrete Layer in the Compression Zone.

Project description:The article describes four-point bending tests of three reinforced concrete beams with identical cross-sections, spans, and high-ductility steel reinforcement systems. Two beams were strengthened in the compressed section with a thin layer of reactive powder concrete (RPC) bonded with evenly spaced stirrups. Their remaining sections, and the third reference beam, were made of ordinary concrete. Measurements of their deflections, strains and axis curvature; ultrasonic tests; and a photogrammetric analysis of the beams are the main results of the study. For one of the beams with the RPC, the load was increased in one stage. For the two remaining beams, the load was applied in four stages, increasing the maximum load from stage to stage in order to allow the analysis of the damage evolution before reaching the bending resistance. The most important effect observed was the stable behaviour of the strengthened beams in the post-critical state, as opposed to the reference beam, which had about two to three times less energy-absorbing capacity in this range. Moreover, thanks to the use of the RPC layer, the process of concrete cover delamination in the compression zone was significantly reduced, the high ductility of the rebars was fully utilized during the formation of plastic hinges, and the bending capacity was increased by approximately 12%.

| S-EPMC7560432 | biostudies-literature

Experimental Study of Flexural Behavior of Reinforced Concrete Beam Strengthened with Prestressed Textile-Reinforced Mortar.

Project description:In this study, nine specimens were experimentally tested to analyze the strengthening efficiency of textile-reinforced mortar (TRM) and the difference in flexural behavior between prestressed and non-prestressed TRM-strengthened reinforced concrete beam. The test results show that TRM strengthening improves the flexural strength of TRM-strengthened reinforced concrete beams with alkali-resistant-(AR-) glass textile as well as that with carbon textile. However, in the case of textile prestressing, the strengthening efficiency for flexural strength of the AR-glass textile was higher than that of the carbon textile. The flexural stiffness of AR-glass textiles increased when prestressing was introduced and the use of carbon textiles can be advantageous to reduce the decreasing ratio of flexural stiffness as the load increased. In the failure mode, textile prestressing prevents the damage of textiles effectively owing to the crack and induces the debonding of the TRM.

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Bending Behavior of Lightweight Wood-Based Sandwich Beams with Auxetic Cellular Core.

Project description:The work concerns a three-point bending test of beams made of plywood, high density fibre boards, cardboard, and wood-epoxy mass. The goal of the investigation was to determine the effect of thickness and type of wood-based facings on stiffness, strength, ability to absorb, and dissipate the energy of sandwich beams with an auxetic core. The cognitive goal of the work was to demonstrate the possibility of using recycled materials for facings and cores instead of popular wood composites. Experimental studies and numerical calculations were performed on correctly calibrated models. Experimental studies have shown that the beams with HDF facings (E = 1528 MPa, MOR = 12.61 MPa) and plywood facings (E = 1248-1395 MPa, MOR = 8.34-10.40 MPa) have the most favourable mechanical properties. Beams with plywood facings also have a good ability to absorb energy (1.380-1.746 J), but, in this respect, the beams manufactured of HDF (2.223 J) exhibited better capacity. The use of an auxetic core and facings of plywood and cardboard significantly reduces the amount of dissipated energy (0.0093 J, 0.0067 J). Therefore, this type of structures can be used for modeling beams carrying high deflections.

| S-EPMC7465774 | biostudies-literature

Evaluation of Fatigue Strength Improvement by CFRP Laminates and Shot Peening onto the Tension Flanges Joining Corrugated SteelWebs.

Project description:Corrugated steel web with inherent high out-of-plane stiffness has a promising application in configuring large span highway bridge girders. Due to the irregularity of the configuration details, the local stress concentration poses a major fatigue problem for the welded flange plates of high strength low alloy structural steels. In this work, the methods of applying CFRP laminate and shot peening onto the surfaces of the tension flanges were employed with the purpose of improving the fatigue strength of such configuration details. The effectiveness of this method in the improvement of fatigue strength has been examined experimentally. Test results show that the shot peening significantly increases hardness and roughness in contrast to these without treatment. Also, it has beneficial effects on the fatigue strength enhancement when compared against the test data of the joints with CFRP strengthening. The stiffness degradation during the loading progress is compared with each treatment. Incorporating the stress acting on the constituent parts of the CFRP laminates, a discussion is made regarding the mechanism of the retrofit and related influencing factors such as corrosion and economic cost. This work could enhance the understanding of the CFRP and shot peening in repairing such welded details and shed light on the reinforcement design of welded joints between corrugated steel webs and flange plates.

| S-EPMC5455533 | biostudies-other

Comparison of Ductile-to-Brittle Transition Behavior in Two Similar Ferritic Oxide Dispersion Strengthened Alloys.

Project description:The ductile-to-brittle transition (DBT) behavior of two similar Fe-Cr-Al oxide dispersion strengthened (ODS) stainless steels was analyzed following the Cottrell-Petch model. Both alloys were manufactured by mechanical alloying (MA) but by different forming routes. One was manufactured as hot rolled tube, and the other in the form of hot extruded bar. The two hot forming routes considered do not significantly influence the microstructure, but cause differences in the texture and the distribution of oxide particles. These have little influence on tensile properties; however, the DBT temperature and the upper shelf energy (USE) are significantly affected because of delamination orientation with regard to the notch plane. Whereas in hot rolled material the delaminations are parallel to the rolling surface, in the hot extruded material, they are randomly oriented because the material is transversally isotropic.

| S-EPMC5509083 | biostudies-other

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