Papers by Keyword: Strengthening

Abstract: Textile-Reinforced Mortar (TRM) is increasingly used for strengthening reinforced concrete structures, yet the selection of an appropriate finite element modeling strategy remains ambiguous. While simplified smeared models are often employed for their computational efficiency, their accuracy for complex multi-layer TRM applications is not well-established. This study presents a critical evaluation of three distinct modeling approaches in ATENA3D—discrete fiber modeling with perfect bond, a smeared reinforcement model, and discrete modeling with a bond-slip interface—for simulating the flexural behavior of full-scale RC beams strengthened with TRM. Validated against experimental data, the results reveal a stark divergence in predictive capability. The smeared approach severely underestimated the capacity of beams with four TRM plies by up to 48%, demonstrating its fundamental inadequacy for modeling layered composites. In contrast, both discrete modeling approaches accurately captured the structural response, with deviations below 21% for all multi-ply scenarios. It is concluded that discrete modeling is essential for the reliable simulation of multi-ply TRM systems, whereas smeared models are only acceptable for preliminary single-ply analysis. This work provides crucial guidance for researchers and practitioners, steering the numerical analysis of TRM-strengthened members toward more reliable and defensible modeling practices.

Abstract: Fiber Reinforced Polymer (FRP) has been used as one of the repair or strengthening materials for deteriorated concrete structures. However, the elastic properties of FRP materials cause a limitations on the ductility of the reinforced concrete structure. This research focuses on the study of the behavior of reinforced concrete beams strengthened using a hybrid Carbon-Glass Fiber Reinforced Plastic (Hybrid FRP). Hybrid FRP is a combination of two layers of FRP that have different elastic modulus, namely Glass Fiber and Carbon Fiber. The objective of using hybrid composites is to obtain a combined elastic mode behavior from two kind of fibers. Flexural testing of reinforced concrete beams with FRP hybrid reinforcement was carried out to study the flexural behavior and also the effectiveness of strengthening. The test material is a reinforced concrete beam with dimensions of 150 mm x 200 mm x 3300 mm. Two types of beams were prepared, namely control beams (BN) and beams with FRP Hybrid strengthening (BGC). The composition of the FRP hybrid was 100% of Glass fiber and 40% of Carbon fiber to the width of the beam. The test results show that the beam with FRP hybrid strengthening has a moment capacity of 12% higher than the control reinforced concrete beam (BN). The mode of failure of the BN beams was the crushing of the concrete that was initiated by yielding of the steel reinforcement. For BGC beams, failure mode was in the form of debonding of the hybrid FRP layer.

Abstract: This paper presents a study from an ongoing research project on the bond performance of flexural prisms strengthened using carbon-fiber-reinforced polymer (CFRP) laminates. The primary objective is to evaluate the effect of normal-strength concrete (NSC – 30MPa) and high-strength concrete (HSC - 50MPa) on the bond performance of plain concrete prisms notched at the mid-span and strengthened using CFRP laminates. Six of the twelve plain concrete prisms were strengthened using CFRP laminates, while the remaining prisms were unstrengthened to serve as control specimens. After achieving 28 days of curing in standard lab conditions, all prisms were tested under a four-point bending test. The ultimate mid-span deflection, maximum and ultimate strains at the mid-span, strain distribution at different positions along the length of the laminate, and bond/shear stress versus slip were analyzed to evaluate the bond performance of flexural prisms. The average ultimate load-carrying capacities and mid-span deflection of the NSC and HSC groups were 31.33 and 35.02 kN and 0.55 and 1.54 mm, respectively. The average CFRP strain values at the mid-span corresponding to the ultimate load were 5005 and 3544 με for the NSC and HSC groups, respectively. The maximum attained bond-stress values for NSC and HSC groups were 1.71 and 1.42 MPa, respectively. The corresponding values for slip at maximum bond stress are 0.27 and 0.24 mm for the two groups, respectively. It was concluded from the study that the concrete compressive strength has minimal effect on the flexural bond performance of concrete prisms externally bonded with CFRP laminates.

Abstract: The presence of web openings in the shear span significantly impacts the structural behavior of reinforced concrete (RC) beams, affecting both shear capacity and crack propagation. This study explores the feasibility of strengthening web openings in the shear zone of RC beams using iron-based shape memory alloy (Fe-SMA) bars through numerical analysis with ABAQUS software. The investigation considered various web opening shapes; diamond, circular, and square strengthened with pre-stressed Fe-SMA bars. Results showed that web openings notably decrease the ultimate loads of beams by 53%, 44%, and 39% for square, circular, and diamond shapes, respectively. However, pre-stressed Fe-SMA bars enhanced the shear capacity of beams with unstrengthened web openings by approximately 60%, making their behavior comparable to solid beams. The proposed strengthening technique was most effective for diamond web openings, nearly restoring both shear strength and stiffness, while circular openings recovered nearly 90% of shear capacity and square openings about 75%. Additionally, Fe-SMA bars effectively controlled cracking at the corners of the openings. This study highlights the importance of strengthening web openings in RC beams, especially in shear zones, and provides significant insights into enhancing such beams, contributing to safer structural designs. Further laboratory experiments are recommended to validate and extend these numerical findings.

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: The microstructure and mechanical properties of Al-Zn-Mg alloys with low Zn/Mg ratios have been studied.According to various researchers, the major strengthening is due to η-phase and T phase. There are many briefly research on the microstructure and interface of the η-phase types but not briefly information about the T-phase That’s why now our aim to work on T-phase. In actual our aim is to observe the T-phase interface. The MgZn₂ phase (η phase) and its metastable phase (η′ phase) were the most prominent precipitates. Another study revealed various Mg₃₂(Al, Zn)₄₉ phases (T phase) and their metastable phase (T′ phase) in Al-Zn-Mg alloys with low Zn and high Mg content. Al-Zn-Mg alloys with a Zn/Mg ratio of 0.71 were explored for this study. The alloy with a Zn/Mg ratio of 0.71 aged at 473k for 2000 minutes exhibited the highest hardness, according to the observations. The strengthening precipitates in the investigated alloy were totally T′ phase, according to TEM observation.

Abstract: The multi-bolted method is typically used for pultruded GFRP (PGFRP) connections. As the capacity of PGFRP structures is governed by connection strength, many researchers have sought to improve this performance. In a previous study investigating the effectiveness of glass fiber sheets (GFSs) in strengthening multi-bolted connections, debonding failure was observed as a failure mode in various types of GFSs, including 0°/90° and ±45° with 4 and 5 bolts. The present study tested four types of specimens to characterize failure modes when PGFRP is multi-bolted with GFS strengthening. Different failure modes were observed with two different numbers of bolts. Based on the observed failure sequences and previous material properties tested, a calculation equation was proposed. The estimated strength showed good agreement with experimental results. Furthermore, the study highlights some features of the failure load (such as the type of GFS and tensile strength) as recommendations for designing strengthening of PGFRP bolted connections.

Abstract: In recent decades, fiber-reinforced polymer (FRP) is being used more and more to make concrete structures stronger. In this study, nonlinear finite element (FE) analysis was used to model and compare the influence of curvature performance on the behavior of the simply-supported RC curved soffit reinforced girders strengthened with fiber-reinforced polymer plates (CFRP) with a curve height of 5 to 130 mm. In this study, two models with different heights of curve (5 and 130 mm) and references for each model were used. Each model had dimensions that were similar to those of the models used in the program in terms of cross-sectional area and effective span. Simulations were done on the girders to find out how the load moved in relation to the mean range, the failure load, and the failure mode. This was done so that the effect of curvature on the performance of this type of structural element could be understood. The results show that the girder of height of curve is 5 mm more than 130 mm of the analytical ultimate load compared with that experimentally with a difference of only 4.5%, and 4.2% respectively. The load-displacement curves of the experimental tests were accurately simulated with the help of a nonlinear finite element model.

Abstract: Achieving a strong bond between carbon fiber (CF) and recyclable thermoplastic polymer (TP) has always been highly sought after. So far, applying electron beam (EB) irradiation with optimal dose and cathode potential (V_c) has shown success in increasing mechanical properties of interlayered CFRTPs. However, with concern for durability and safety, higher strength is desired. Therefore, EB setting applying electron beam (EB) irradiation with cathode potential (V_c) to 170, 210, 225 or 250 kV was applied to CFRTPA (carbon fiber reinforced thermoplastic polyamide) articles just before shipping. Specimens were 9 CF plies alternating between 10 PA (polyamide) sheets, designated [TPA]₁₀[CF]₉. When optimal EB dose of 43.2 kGy is applied to both finished specimen surfaces after fabrication, experimental results show higher V_c setting of 250 kV can increase impact strength of the [TPA]₁₀[CF]₉ over that at 170 kV. In summary, the 250 kV-EB (250 kV) strengthens [TPA]₁₀[CF]₉ significantly, about 25 to 27% larger than that of 170 kV and zero (untreated). Based on Christenhusz and Reimer equation to calculate penetration depth, D_th of EBI into polymers, increasing V_c to 250 kV increased D_th to more than 2 times that at 170 kV.

Abstract: Concrete structures may become obsolete and be unfit for use to the extent that they need special attendance of repair or strengthening so as to revive them. The weakness in the buildings may be caused by natural disasters like earthquake, floods, changes of use of the buildings in which higher loads more than the design loads, e.g. vertical extension loads, are applied. When the structures are defective they need to be strengthened in order to restore their original structural integrity. Sometimes, the defect or deterioration needs to be scientifically analysed first in order to know the root cause of the problem and apply the right corrective measures. A case study on an eleven stories damaged building in is presented, starting with an investigation on causes of sudden crushing of one column and a strengthening method which embraced a number of techniques such as Land Surveying and non-destructive tests in assessing the building structural integrity. The crushed column and other columns is the ground floor were all strengthened using jacketing method and provision of additional columns at the crushed column. Keywords: Columns, crushing, non-destructive tests, concrete quality, deflection, plumb, jacketing, strengthening