Search Results (27)

Plain concrete specimens and FRP(Fiber Reinforced Polymer)-reinforced concrete specimens were fabricated to investigate concrete’s mechanical and surface degradation behaviors reinforced with carbon, basalt, glass, and aramid fiber-reinforced polymer under coupled sulfuric acid and freeze–thaw cycles. The compressive strength of fully wrapped FRP cylindrical specimens and the flexural load capacity of prismatic specimens with FRP reinforced to the pre-cracked surface, along with the dynamic elastic modulus and mass loss, were evaluated before and after acid–freeze cycles. The degradation mechanism of the specimens was elucidated through analysis of surface morphological changes captured in photographs, scanning electron microscopy (SEM) observations, and energy-dispersive spectroscopy (EDS) data. The experimental results revealed that after 50 cycles of coupled acid–freeze erosion, the plain cylindrical concrete specimens showed a mass gain of 0.01 kg. In contrast, after 100 cycles, a significant mass loss of 0.082 kg was recorded. The FRP-reinforced specimens initially demonstrated mass loss trends comparable to those of the plain concrete specimens. However, in the later stages, the FRP confinement effectively mitigated the surface spalling of the concrete, leading to a reversal in mass loss and subsequent mass gain. Notably, the GFRP(Glassfiber Reinforced Polymer)-reinforced specimens exhibited the most significant mass gain of 1.653%. During the initial 50 cycles of acid–freeze erosion, the prismatic and cylindrical specimens demonstrated comparable degradation patterns. However, in the subsequent stages, FRP reduced the exposed surface area-to-volume ratio of the specimens in contact with the acid solution, resulting in a marked improvement in their structural integrity. After 100 cycles of acid–freeze erosion, the compressive strength loss rate and flexural load capacity loss rate followed the ascending order: CFRP-reinforced < BFRP(Basalt Fiber Reinforced Polymer)-reinforced < AFRP(Aramid Fiber Reinforced Polymer)-reinforced < GFRP-reinforced < plain specimens. Conversely, the ductility ranking from highest to lowest was AFRP/GFRP > control group > BFRP/CFRP. A probabilistic analysis model was established to complement the experimental findings, encompassing the quantification of hazard levels and reliability indices. Full article

Application of hybrid jackets consisting of comparatively stiff FRP materials for the seismic retrofit of substandard RC columns, aiming at reducing the risk of buckling and of brittle failure, which are typical to older columns, is a promising challenge. Given the sparsity of similar experimental data, the objective of this paper is to study the hybrid effect in concrete confined with conventional carbon- and glass- reinforced polymer fabrics (CFRP and GFRP, respectively). Twenty-six concrete cylinders, wrapped by one to three layers of CFRP and GFRP with different fiber configurations, were tested in compression. A clear hybrid effect was observed, consisting of a less brittle failure and an improved confinement as compared to the behavior of simple jackets. Furthermore, hybrid specimens, in which a CFRP layer is substituted by a GFRP layer, appear to display similar efficiency in confinement compared to specimens with a stiffer jacket consisting of more CFRP sheets, which are expected to experience 30 to 40% higher lateral pressure owing to the stiffer jacket. A design model to estimate peak concrete compressive strength and axial strain is proposed. The results are promising towards the potential application of similar hybrid jackets for the seismic rehabilitation of older RC columns. Full article

In this study, polyethylene terephthalate (PET) was substituted for 10%, 20%, and 30% of the sand volume in concrete. Compressive, splitting tensile, and flexural strength tests were applied to the concrete samples and stress–strain graphs were obtained. It was observed that PET substitution caused a decrease in the mechanical properties of the concrete. For this reason, the concrete with the best PET substitution rate (10%) was reinforced by wrapping it with carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP), and the same experiments were repeated. It was observed that a 10% PET substitution reduced the strength of the reference concrete by about 6%. However, wrapping the PET-substituted concrete with CFRP and GFRP increased the strength by about 1.9 and 1.5 times, respectively, surpassing that of the reference sample. In addition, this study provides a comprehensive database by bringing together experimental data from studies in which PET was used as a substitute by volume or weight instead of fine aggregate in concrete. The models proposed in this study, along with previous models, were tested for applicability. Similarly, the model suggestions in the literature for fiber-reinforced polymer (FRP)-confined concrete were tested with the experimental data in this study, and their suitability for PET-substituted concrete was discussed. Full article

Protecting coastal regions is crucial due to high population density and significant economic value. While numerous strategies have been proposed to mitigate scouring and protect coastal structures, existing techniques have limitations. This paper introduces a novel approach, SEAHIVE^®, which enhances the performance of engineered structures by utilizing hexagonal, hollow, and perforated concrete elements externally reinforced with glass fiber-reinforced polymer (GFRP). Unlike conventional steel bars, GFRP offers superior durability and requires less maintenance, making it a sustainable solution for any riverine and coastal environment. SEAHIVE^® aims to provide robust structural capacity, effective energy dissipation, and preservation of natural habitats. Although some research has addressed energy dissipation and performance in riverine and coastal contexts, the structural performance of SEAHIVE^® elements has not been extensively studied. This paper evaluates SEAHIVE^® elements reinforced with externally bonded GFRP longitudinal strips and pretensioned GFRP transverse wraps. Testing full-size specimens under compression and flexure revealed that failure occurred when the pretensioned GFRP wraps failed in compression tests and when longitudinal GFRP strips slipped in flexure tests. Strength capacity was notably improved by anchoring the GFRP strips at both ends. These findings underscore the potential of the SEAHIVE^® system to significantly enhance the durability and performance of coastal and riverine protection structures. FEM simulations provided critical insights into the failure mechanism and validated the experimental findings. In fact, by comparing FEM model results for cases before and after applying GFRP wraps under the same compression load, it was found that maximum stresses at crack locations were significantly reduced due to compression forces resulting from the presence of pretensioned GFRP wraps. Similarly, FEM model analysis on flexure samples showed that the most vulnerable regions corresponded to the locations where cracks started during testing. Full article

The hybridisation of fibre-reinforced polymers (FRPs), particularly with the combination of natural and synthetic fibres, is a prominent option for their development. In the context of the construction industry, there is a notable gap in research on the use of jute and glass fibres for the strengthening of concrete structures. This paper presents comprehensive experimental results from tests on seven reinforced concrete (RC) beams strengthened for shear using synthetic, natural, and hybrid jute–glass FRP composites. The beams were reinforced using the externally bonded reinforcement (EBR) technique with U-wrap bonding. A beam without any strengthening was tested and set as a reference for the other beams. Two beams were tested with synthetic FRP shear strengthenings, one with carbon fibre-reinforced polymer (CFRP) and another with glass fibre-reinforced polymer (GFRP). The remaining tests were on RC beams strengthened with natural jute fibre-reinforced polymer (JFRP) and hybrid jute–glass FRP. The paper discusses the experimental behaviour of the tested beams in terms of vertical displacements, crack widths, and strains on steel bars, concrete, and FRP. The experimental strengths are also compared with theoretical estimates obtained using ACI 440.2R and fib Bulletin 90. The tests confirm the effectiveness of natural jute FRP and jute–glass hybrid FRP as an option for the shear strengthening of reinforced concrete beams. Full article

In the Middle East, wall-like reinforced concrete (RC) columns are a common choice in multistory buildings. Sometimes, these columns need axial retrofitting for increased load capacity. In practice, unstrengthened columns bear their load, and if retrofitting is necessary, the load is released before the upgrade—unlike in past research studies that overlooked this real-world scenario. This study aimed to investigate the response of preloaded wall-like RC columns after being retrofitted using different configurations. In the experimental campaign, two half-scale columns were cast and axially loaded to 80% of their capacity, and the load was then totally released. After that, these specimens were strengthened with two different schemes, and hence, they were concentrically loaded until failure. In both schemes, the section shape was not modified. The first scheme comprised wrapping carbon FRP (fiber-reinforced polymer) sheets together with near-surface mounted (NSM) steel rebars. However, the second technique was composed of wrapping glass FRP (GFRP) sheets together with NSM steel rebars and bolted steel plates. The second scheme was found to be superior to the first one due to the extra confinement provided by the bolted steel plates. This scheme improved the peak load, stiffness, and dissipated energy by 115%, 75%, and 524%, respectively. Other than the testing campaign, nonlinear numerical modeling was undertaken to examine the behavior of tested specimens. The models were utilized to conduct a parametric study, exploring the influence of the percentage of preloading and the amount of load release on the response of columns strengthened with the second scheme. Full article

This study presents an experimental framework with seventeen beams to investigate the impact of loading type, configuration, and through-bolt anchorage on LC-GFRP (Low-Cost Glass-Fiber-Reinforced Polymer) confinement performance. Beams underwent three-point and four-point bending, with LC-GFRP applied in various ways, including U-shaped, side-bonded, and fully wrapped, with and without anchors. The performance of LC-GFRP was compared to CFRP (Carbon-Fiber-Reinforced Polymer) and sisal wraps. LC-GFRP in side-bonded and U-shaped configurations without anchors under three-point bending showed no shear failure, while those under four-point bending without anchors experienced shear failure. With anchors, U-shaped configurations successfully prevented shear failure. The side-bonded, U-shaped, and U-shaped configurations along the full span with anchors demonstrated peak capacity enhancements of 72.11%, 43.66%, and 68.39% higher improvements than the corresponding configurations without anchors, respectively. Wrapping all sides of the beam with LC-GFRP or CFRP prevented shear failure without additional anchors, with complete wrapping being the most efficient method. When anchors were used, significant capacity enhancements were observed. Existing shear strength prediction models were evaluated, highlighting the need for more tailored expressions for LC-GFRP confinement, especially for non-U-shaped configurations. Full article

This research aims to address a post-earthquake urgent strengthening measure to enhance the residual seismic capacity of earthquake-damaged reinforced concrete wall structures with coupling beams. The study consists of a series of tests on half-scale prototype coupling beams with various detailing options, including confined with reduced confinement, partially confined, and unconfined bundles, under cyclic loading conditions. The methodology employed involved subjecting the specimens to displacement-controlled reversal tests, and carefully monitoring their response using strain gauges and potentiometers. The main results obtained reveal that GFRP wrapping significantly enhances the seismic performance of earthquake-damaged coupling beams, even in cases where specimens experienced strength loss and main reinforcement rupture. The strengthened beams exhibit commendable ductility, maintaining high levels of deformation capacity, and satisfying the requirements of relevant seismic design codes. The significance of the study lies in providing valuable insights into the behavior and performance of damaged coupling beams and assessing the effectiveness of GFRP wrapping as a rapid and practical post-earthquake strengthening technique. The findings can be particularly useful for developing urgent post-earthquake strengthening strategies for high-rise buildings with structural walls. The method may be particularly useful for mitigating potential further damage in aftershocks and eventual collapse. In conclusion, this study represents a significant advancement in understanding the post-earthquake behaviors of coupling beams and provides valuable guidance for practitioners in making informed decisions regarding post-earthquake strengthening projects. The findings contribute to the overall safety and resilience of structures in earthquake-prone regions. Full article

Reinforced concrete (RC) wall-like columns are commonly employed in structures in Saudi Arabia. These columns are preferred by architects owing to their minimum projection in the usable space. However, they often need strengthening due to several reasons, such as the addition of more stories and increasing the live load as a result of changing the usage of the building. This research aimed to obtain the best scheme for the axial strengthening of RC wall-like columns. The challenge in this research is to develop strengthening schemes for RC wall-like columns, which are favored by architects. Accordingly, these schemes were designed so that the dimensions of the column cross-section are not increased. In this regard, six wall-like columns were experimentally examined in the event of axial compression with zero eccentricity. Two specimens were not retrofitted to be used as control columns, whereas four specimens were retrofitted with four schemes. The first scheme incorporated traditional glass fiber-reinforced polymer (GFRP) wrapping, while the second one utilized GFRP wrapping combined with steel plates. The last two schemes involved the addition of near-surface mounted (NSM) steel bars combined with GFRP wrapping and steel plates. The strengthened specimens were compared with regard to axial stiffness, maximum load, and dissipated energy. Besides column testing, two analytical approaches were suggested for computing the axial capacity of tested columns. Moreover, finite element (FE) analysis was performed for evaluating the axial load versus displacement response of tested columns. As an outcome of the study, the best strengthening scheme was proposed to be used by practicing engineers for axial upgrading of wall-like columns. Full article

The sudden occurrence of an earthquake induces a liquefaction effect on foundation soil, which causes a substantial increase in the uplift pressure acting on piles and causes structural damage to superstructures. This forms the basis of the necessity of experimenting with the behaviour of piles subjected to uplift loads and predicting their load-carrying capacity or resistance. Fibre-reinforced polymer (FRP) wraps are widely used for strengthening and retrofitting piles subjected to damage. The current study is aimed at determining the uplift load-carrying capacity or resistance of piles wrapped with basalt fibre-reinforced polymer (BFRP) and glass fibre-reinforced polymer (GFRP) sheets by experiment. Preliminary tests were conducted to identify the influence of BFRP and GFRP wraps on the mechanical strength properties of concrete. The mechanical strength of the specimen with the double wrapping of basalt and glass fibres in the perpendicular direction outperformed all other specimens. Moreover, the piles were wrapped with laminates and experimented on for their uplift capacity in dry and submerged conditions. The results indicate a considerable improvement in the uplift resistance of the piles compared with the unconfined piles. The BFRP and GFRP wraps improved the uplift resistance of the piles by 35.56% and 15.56%, respectively, higher than the unconfined pile for dry conditions. The angle of the interfacial friction in dry and submerged states was observed to be the maximum for the perpendicular direction for both of the FRP wraps, and the failure modes were compared. The simulated model showed a significant correctness for determining the uplift resistance of FRP-wrapped piles in dry and submerged states. The degree of agreement in the dry condition for the experimental results and finite element method was more than 94% for all fibre wraps. Full article

Plantation softwood timber poles are associated with low natural durability, and it is also not clear what the effects of the high humidity environment on the long-term performance of composite action integrity of such a system. This paper presents a durability study for the proposed composite poles using (GFRP) glass fiber-reinforced polymer as a confinement system on wooden poles sourced from plantation softwood timber. Radiata pine poles of 6 m length were wrapped with multiple layers of 0°/90° woven roving biaxial E-glass fiber sheets through a wet layup process as confinement. The prepared GFRP softwood poles were then subjected to high humidity environmental conditions of up to 95 ± 2% relative humidity and 22 ± 2 °C temperature for a period of 30 months. Various lengths of confinement were considered in this study ranging from 0% to 70% of the span length. The poles had a span length of 5.4 m and were tested using a three-point bending test. Results showed that the proposed confinement system of GFRP-softwood provided a satisfactory long-term performance and the high humidity environment did not greatly affect the improvement in the mechanical performance that the GFRP system provided. Full article

The evaluation of frost resistance varies with different reinforcement methods, but it is a hot research topic for concrete reinforced with Fiber-Reinforced plastic (FRP). Freezing and thawing tests of FRP-reinforced concrete prisms and cylinders are presented to simulate beams and piers of buildings in cold climates. To evaluate the specimens’ frost resistance, tests with various reinforcement techniques, morphological analysis, weight tests, and relative dynamic modulus of elasticity tests were used. Examined also were the variations in stress–strain curves for axial compression tests and load–displacement curves for bending tests following various freeze–thaw cycles. The findings indicated that after 100 freeze–thaw cycles, the weight of unreinforced concrete cylinders decreased by 9.7%, and its compressive strength decreased by 27.6%. On the other hand, CFRP-reinforced concrete cylinders (Carbon-Fiber-Reinforced Plastics) and GFRP (Glass-Fiber-Reinforced Plastics) gained 1.1% and 1.58% in weight, respectively, while the compressive strength decreased by 7.4% and 8%. After 100 freeze–thaw cycles, the weights of concrete prisms with reinforcement, without reinforcement, and with CFRP reinforcement decreased by 12.13%, 8.7%, and 9.6%, respectively, and their bending strength was reduced by 20%, 42%, and 53%, respectively. The frost resistance of the two FRP-reinforced concrete types had significant differences under freeze–thaw cycles because the prismatic specimens were not fully wrapped with FRP materials. Finally, finite element software ABAQUS was used to simulate the freeze–thaw cycle test of the two specimens. Calculated values were compared to experimental results for the load–displacement curve and the axial stress–strain curve under bending load. The comparison of peak displacement produced a maximum error of 8.6%, and the FRP-reinforced concrete model validity was verified. Full article

Pultruded fiber-reinforced polymer (PFRP) profiles have started to find widespread use in the structure industry. The position of the web openings on these elements, which are especially exposed to axial pressure force, causes a change in the behavior. In this study, a total of 21 pultruded box profiles were tested under vertical loads and some of them were strengthened with carbon-FRP (CFRP) and glass-FRP (GFRP). The location, number and reinforcement type of the web openings on the profiles were taken into account as parameters. As a result of the axial test, it was understood that when a hole with a certain diameter is to be drilled on the profile, its position and number are very important. The height-centered openings in the middle of the web had the least effect on the reduction in the load-carrying capacity and the stability of the profile. In addition, it has been determined that the web openings away from the center and especially the eccentric opening significantly reduces the load carrying capacity. Furthermore, when double holes were drilled close to each other, a significant decrease in the capacity was observed and strengthening had the least effect on these specimens. It was also determined that the specimens reinforced with carbon FRP contribute more to the load-carrying capacity than GFRP. Full article

Many structural elements are subjected to a significant torsional moment that affects the structural design and may require strengthening. This paper presents different effective strengthening techniques to enhance the torsional capacity of reinforced concrete (RC) beams. An experimental and numerical investigation was undertaken to evaluate the efficacy of utilizing various strengthening systems. The experimental program included six full-scale RC beams with a cross-section dimension of (150 mm × 300 mm) and a length of 1500 mm, split into one beam without strengthening as a control beam, and six beams strengthened with various materials. The various strengthening materials were wrapped aluminum strips with anchorage bolts, wrapped stainless steel strips with anchorage bolts, wrapped glass fiber reinforcement polymer (GFRP), one layer of wrapped steel wire, and two layers of wrapped steel wire meshes along the beam. The results showed that the ultimate torque of the beam strengthened by wrapped aluminum strips and the beam strengthened by wrapped stainless steel strips was larger than the control beam by about 32% and 40%, respectively, because the strips acted as an external reinforcement. In addition to the strengthening systems, using aluminum strips and stainless steel strips is effective in raising the capacity to a similar degree despite the high cost of the stainless steel strips. The ultimate torque of the beams strengthened by GFRP, one-layered wrapped steel wire meshes, and two-layered wrapped steel wire meshes along the beam is larger than the control beam by about 62%, 118%, and 163%, respectively, in addition to the ultimate angle of twist, which was larger than the control beam by about 53%, 93%, and 126%, respectively. This showed that the strengthening using the two-layered wrapped steel wire meshes along the beam would be very significant in increasing the ultimate torque strength. Moreover, the strengthened beam by two-layered fully wrapped steel wire meshes along the beam developed the highest ductility factor compared to all strengthened beams; in contrast, the beam strengthened by GFRP had less ductility. To verify the outcomes of the experimental tests, a finite-element program, ABAQUS, was performed. Finally, an excellent agreement between the experimental and numerical results was obtained. Full article

Timber elements, such as timber bridges, are exposed to heavy loads. Therefore, reinforcement might be useful. Due to a lack of wood supplies, poplar, a fast-growing tree, could be used to construct CLT (cross-laminated timber). The low density of fast-growing wood species directly impacts the mechanical properties of CLT. Therefore, in this study, a CLT panel was reinforced with GFRP (glass-fiber-reinforced polymer), and the lateral resistance of double shear lap joints in reinforced CLTs with 0-90-0° arrangements in two strength directions was investigated. Lag screws (Ø = 8 mm) at the end distances of 1 and 3 cm were employed for making the lateral test specimens. First, the effect of the number of GFRP layers on lateral resistance of the joints was investigated. The results revealed that, as the number of GFRP layers changed from one to three, the lateral resistance increased by 45.47%, and then, by four layers, it decreased by 1.3%. Since the joints with three layers of FRP had the highest strength, the effects of the end distance and the CLT panel strength directions on the lateral performance of the reinforced and non-reinforced specimens were investigated. The results indicated that the lateral resistance of reinforced CLTs with GFRP was about 26.5% more than the unreinforced ones. Moreover, CLTs in the major strength direction showed 4.2% more lateral resistance than those in the minor strength direction. Moreover, lag screws at the end distance of 3 cm had 60% more lateral resistance than those at the end distance of 1 cm. In terms of failure modes, bearing, shear, and net-tension modes were observed in the CLTs, while Is, IIIs, and IV modes were observed in the lag screws. Full article