Carbon Fiber Reinforced Polymer Strengthening Research Articles

CFRP Strengthening and Rehabilitation of Inner Corroded Steel Pipelines under External Pressure

The objective of this study was to investigate the performance of pipelines repaired with carbon-fibre-reinforced polymer (CFRP) under external pressure. The repaired pipeline experienced defects in terms of thinning of its local inner wall. The three-dimensional finite element method was used to analyse the collapse pressure of repaired pipes with internal corrosion defects. The traction–separation law and interlaminar damage criterion were applied to simulate the collapse process of repaired pipes. The results show that the collapse pressure of the composite-repaired pipe increased and the CFRP significantly reduced the strain in the defect region. It was observed that the ovality of the corrosion defect region was reduced and that the repair effectiveness mainly depended on the length, thickness, and interlayer cohesion.

Column structure strengthening with FRP (Fiber Reinforced Polymer) due to story addition

This study focuses on strengthening scheme of an existing structure with added story. The addition of a new story increases gravitational loading, which affects the seismic and wind responses of the structure and, as a consequence, the loading combination. To ensure the structure’s capacity requirement, the strengthening scheme uses CFRP (Carbon Fiber Reinforced Polymer). In order to adequately define the structure's performance, a series of structural analyses were performed. The structure's state before and after story addition, subsequently the state after CFRP strengthening, were evaluated. It is demonstrated that the additional story to the structure causes an exceedance in internal forces; however, the strengthening with CFRP is sufficient to withstand these forces, proving that the strengthening scheme is effective and beneficial.

Effectiveness and Efficiency of Externally Bonded CFRP Sheets for Shear Strengthening of RC Beam-Column Joints.

To develop feasible carbon fiber reinforced polymer (CFRP) retrofit schemes for the shear strengthening of real three-dimensional reinforced concrete (RC) beam-column joints, a series of parameters in relation to the contributions of the CFRP sheets externally bonded to joint panels was numerically investigated in this study. The parameters include CFRP reinforcement ratio, CFRP layout, transverse beam-to-joint panel width ratio, transverse beam-to-joint panel height ratio, location of transverse beam, and number of transverse beams. Strengthening efficiency, a new dimensionless index, was introduced to evaluate the residual effect of a CFRP-strengthening system weakened by the presence of transverse beams in comparison with the increase in joint shear capacity in relation to the one-way counterpart. The results obtained from 44 nonlinear finite element models, which were calibrated against experimental observations, confirmed the effectiveness of the CFRP strengthening technique with regard to the relatively wide ranges of the parameters. The significant differences among the roles of the parameters were revealed, and the reasons behind the differences were analyzed. Furthermore, the shear mechanism of the CFRP-retrofitted joint panels was discussed with the proposed strut-and-tie model.

Fatigue behavior of notched steel beams strengthened by a prestressed CFRP plate subjected to wetting/drying cycles

Prestressed carbon fiber reinforced polymer (CFRP) strengthening is effective in suppressing crack propagation of steel beams. However, the fatigue behavior of notched steel beams with prestressed CFRP under a hygrothermal environment is not fully understood. Generally, notch machining on the steel beam is an ordinary method to simulate a fatigue defect for laboratory tests. In this study, the interfacial energy release rate at the notch location was first derived for strengthened steel beams. The theoretical results show that the interfacial energy release rate can be significantly reduced by prestressed CFRP strengthening, contributing to improving the interfacial fatigue performance. In addition, notched steel beams strengthened by prestressed CFRP (with a prestress level of 25% of tensile strength of CFRP plate) were exposed to wetting/drying cycles (WDCs) and then tested under fatigue loading. The experimental results show that prestressed CFRP strengthening increases the fatigue resistance of interfacial debonding initiation and failure 3.47 times and 7.83 times, respectively, which agrees with the tendency revealed by the theoretical results. In contrast, WDC exposure reduced the fatigue lives of interfacial debonding initiation and failure by 34.6% and 27.2%, respectively. An S – N curve based on the maximum principal interfacial stress at the notch location was proposed to predict the tendency of fatigue life of debonding initiation for strengthened steel beams. Moreover, the tendency prediction for fatigue life of interfacial debonding development for the strengthened steel beams with/without WDC exposure was developed based on Paris’ law. • Theoretically reveals that the prestressed CFRP reduces the interfacial energy release rate. • Prestressed CFRP strengthening significantly improves interfacial fatigue life. • Hygrothermal exposure leads to a significant reduction of interfacial fatigue life.

Flexural behaviour of prestressed reinforced concrete beams strengthened with carbon plate

This paper presents the effect of carbon plate length on the deflection and ultimate moment of resistance of a prestressed flexural member. Numerical and experimental results are also included. Three typical failure modes were observed in the experimental programme: bending failure, end shear failure and peeling off of the carbon plate. The geometry of the beam was chosen so that three typical failure modes occurred when different carbon plate lengths were applied. The experimental results show that for the selected geometry of the prestressed concrete beam, the ultimate moment capacity of carbon-fibre-reinforced polymer (CFRP) strengthened beams is up to 3.66 times that of beams without CFRP reinforcement. However, the stiffness can be increased by as much as 52% using CFRP. Non-linear analyses of pre-tensioned beams, with and without CFRP strengthening, were compared with respect to the ultimate limit state. The experimental test results and numerical calculations showed very good agreement in terms of the yield load and ultimate load.

Effect of the Cyclic Crack Opening-Closure during Epoxy-Curing Period of a CFRP Strengthening System Bonded on Concrete Substrate

This article investigates the potential detrimental effects of cyclic load during the installation of externally bonded (EB) carbon fiber-reinforced polymer (CFRP) on a damaged reinforced concrete (RC) structure. Four RC specimens were tested in three point bending to study the consequences of crack cyclic opening-closure during epoxy-curing period. A first RC specimen (without bonded CFRP) was loaded monotonically up to failure to serve as undamaged control sample. The three other specimens were pre-cracked before being subjected to a fatigue loading procedure to simulate service condition of a damaged RC structure. Two of the three pre-cracked specimens were strengthened by EB CFRP. One specimen was repaired before the fatigue test while the other one was repaired during the fatigue test. Finally, remaining capacities of all three pre-cracked specimens were measured through monotonic bending tests until failure. It was found that, although bonding of CFRP reinforcement during cyclic load can induce some interesting features with regard to serviceability, cyclic crack opening and closing alters the cure process of epoxy located below the initial crack and decreases the effectiveness of the strengthening at ultimate state. Extended experimental studies are then needed to assess reliable safety factor for the design of repairing operations in which the bridge has to be maintained in service during CFRP installation.

A parametric study on the behavior of RC and FRC deep beams with and without CFRP strengthening using ANSYS

Deep beams are common elements in concrete structures such as bridges, water tanks, etc. Deep beams were designed by using the strut-and-tie model (STM) method without any web reinforcement using ACI 318-14 with a shear span to depth ratio (a/d =1). RC deep beams show brittle failure by crushing of struts under applied load. Fiber reinforced concrete (FRC) is a better alternative for the reinforced concrete beam without web reinforcement as it contains fibers such as a ramid, steel, etc. The fibers used were steel fibers of 1% volume, and aspect ratio of 60. The use of carbon fiberreinforced polymer (CFRP) for strengthening the deep beams is utilized and a comparison between reinforced concrete(RC) and fiber-reinforced concrete (FRC) deep beams with and without CFRP strengthening is carried out using (Analysis of Systems) ANSYS 18.1. The mid-span deflections were significantly decreased and improved shear strength was observed in CFRP strengthened deep beams and FRC deep beam in comparison of RC deep beam. The ultimate loads for a maximum deflection value were compared in all the deep beams and RC frame with embedded carbonfiber reinforced polymer (RC-CFRP), fiber reinforced concrete carbon-fiber reinforced polymer(FRC-CFRP) and FRC deep beams showed 29.4%, 42.47% and 32.05% improvement, respectively, when compared with the RC deep beam. A total of 43.4% decrease in deflection and 74% decrease in shear stress was observed in FRC deep beam. The deflection and stress values in strengthened beams were comparatively lesser. In this study, deflection was observed to decrease by 74.4% and 82%, and shear stress decreased by 92% and 93.5% in the strengthened RC and FRC deep beam, respectively, compared to the deep beam RC model. It is suggested that strengthened FRC is a better alternative to RC deep beams.

Nonlinear Numerical and Analytical Assessment of the Shear Strength of RC and SFRC Beams Externally Strengthened with CFRP Sheets

This study investigates numerically utilizing nonlinear finite element (ANSYS software) and analytically the shear response of the Reinforced Concrete (RC) beams. Different beams are considered in the current study, such as RC, steel fibre reinforced concrete (SFRC) without web reinforcement, and RC externally reinforced in the shear zone with carbon fibre reinforced polymer (CFRP) sheets. Nonlinear finite element model (FEM) is designed to simulate the performance of the designed beams. The results of FEM are compared to experimental measurements and standard design codes (ACI 440.2R‐17, FIB 14, CNR‐DT200, and ACI 318‐19). According to the experimental approach and nonlinear finite element, the enhancement in the load carrying capacity of SFRC beam due to CFRP strengthening decreases with a volume fraction of steel fibres of 2%. However, the effect of CFRP strengthening on the shear behaviour of RC beams was observed in increased load carrying and ultimate deflection capacities as a result of the CFRP strengthening. The results show that CFRP has a significant contribution to shear strength. At each load increment, the created model accurately reproduced the initial and progressive crack patterns. A comparison of nonlinear finite element and analytical models was conducted using the codes ACI 440.2R‐17, FIB 14, CNR‐DT200, and ACI 318‐19. Numerically, the FEM results showed a high agreement with ACI 440.2R‐17 standard code, with correlation approach to 99%. The comparison experimental load capacity of beams to FEM and ACI 440.2R‐17 shows that the FEM can be significantly used to estimate the shear strength of beams in the X‐Y directions with simulating different scenarios of CFRP and SFRC characteristics. The discrepancy between the nonlinear FEA and the theoretical predictions from the ACI 440.2R‐17 code is less than 1%, from the FIB14 code is less than 2%, from the CNR‐DT200 code is less than 15%, and from the ACI 318‐19 code is less than 30%. The ultimate load capacity evaluated based on ACI 440.2R‐17 code provision shows a good agreement with the experimental data as compared to the others’ code provision. The results of the finite element analysis and analytical models were in good agreement with the experimental results. The most significant advantage of finite element analysis over experimental approaches was that it can aid in the investigation of different output results that cannot be measured experimentally, such as shear stress in the XY direction throughout the beam strengthened in shear with different CFRP properties and steel fibre reinforced concrete (SFRC).

Fatigue Performance of CFRP‐Strengthened Rib‐to‐Diaphragm Welded Details of Orthotropic Steel Decks: Experimental and Numerical Evaluation

Rib‐to‐diaphragm welded details of orthotropic steel decks (OSDs) are susceptible to fatigue cracking. To deal with such cracking problem, a strengthening method using externally bonded carbon fiber‐reinforced polymer (CFRP) plates was investigated by fatigue experiment and numerical evaluation. A full‐scale OSD specimen with two ribs and two diaphragms was tested to evaluate fatigue cracking behavior, as well as the stress before and after strengthening. An experimentally validated numerical model was established to confirm the optimal opportunity for CFRP strengthening. The influence of different CFRP strengthening measures were then discussed on the stress intensity factors at crack tips. It was shown that bonding of CFRP plates can significantly reduce stress of rib‐to‐diaphragm welded details. The best opportunity for CFRP strengthening is selected as the length of crack reaches at 25.00 mm where the amplitude of stress intensity factor is the smallest. The attachment of CFRP plates by bonding on the surface of cracked plates can reduce stress response at cracked region by more than 30%. The length of crack is of no flat growth until the total number of loading cycle after strengthening arrived at 0.8 million. Results of SIFs calculated by numerical model dropes after strengthening with reduction rate more than 35% and 18% at two crack tips and crack midpoint, respectively. Compared to the geometric dimensions of CFRP, the elastic modulus of CFRP and glue layer shows more significant influence on the fatigue performance of Rib‐to‐diaphragm welded details due to their stronger restraint to the propagation of crack peaks. This study provided a technical reference to the design and actual application of CFRP in the strengthening of welded details in OSDs.

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.

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.

Fatigue behavior of corroded steel plates strengthened with CFRP plates

This paper presents an experimental study performed to investigate the effectiveness of carbon fiber reinforced polymer (CFRP) plates in extending fatigue life of corroded steel plates. Specimens with five kinds of corrosion damage level, four kinds of strengthening configuration and four kinds of applied fatigue stress amplitude were tested and the primary fatigue behavior indications consist of failure mode, fatigue fractography, fatigue life and crack propagation were analyzed. Results showed that externally patching CFRP plates significantly strengthened the fatigue behavior of corroded steel plates, and even made the fatigue life of corroded steel plates recovered or exceeded that of the un-corroded ones, the fatigue life of the patched specimen which presented the most significant strengthening effectiveness even showed a fatigue life extension of more than 85.3 times with respect to the un-patched corroded steel plate and approximately 2 times over the un-corroded steel plate. Results also indicated that different strengthening configurations appeared to have diversity effect on the fatigue life extension and crack growth retardation of corroded steel plates, end anchorage measures effectively delayed the failure process of CFRP bonding interface and improved the fatigue strengthening effect, increasing CFRP strengthening stiffness or adopting prestressed CFRP plates significantly reduced the crack growth rate and extended the fatigue life of corroded steel plates. The outcome of the tests provided meaningful references and essential data for the reliable application of CFRP strengthening system in the fatigue performance improvement of corroded steel structures.

Experimental Study of the Fatigue Performance of the Bonding Surfaces and Load-Bearing Capacity of a Large-Scale Severely Damaged Hollow Slab Strengthened by CFRP

In recent years, carbon fiber reinforced polymer (CFRP) has been widely used in bridge repair, retrofitting, rehabilitation and strengthening to improve the bearing capacity. Although many studies have been conducted to explore the strengthening efficiencies of CFRP, the test specimens were small and the results were difficult to apply to full-scale bridges. Investigations into the strengthening effects of CFRP on real life structures rely on field load tests (without damaging the structures), making it difficult to understand actual improvements in load carrying capacity and strengthening effect. Moreover, there have been few experimental studies on the fatigue performances of CFRP-strengthened structures, especially on the large-scale structures with real wheel moving loads. In this study, the feasibility and efficiency of CFRP strengthening and repair was investigated on a large-scale, prestressed concrete hollow slab decommissioned from a real-life concrete bridge. The hollow slab was first put through a destructive test to test the ultimate load-bearing capacity. Then, CFRP strips were installed on the surface of the severely damaged slab to repair and strengthen it. Fatigue load test—including the moving load test and single point sinusoidal load—and load-bearing capacity tests were conducted on the CFRP-strengthened hollow slab after the destructive test to evaluate the strengthening performance. This study could help us to understand the actual load-bearing capacities of severe damaged concrete structures strengthened by CFRP, reduce waste, save resources and improve the utilization of our infrastructures.

Flexural behaviour of notched steel beams strengthened with a prestressed CFRP plate subjected to fatigue damage and wetting/drying cycles

Applying a prestressed Carbon Fibre Reinforced Polymer (CFRP) to strengthen deficient steel structures is a favourable approach. However, fatigue loading and hygrothermal exposure can weaken adhesive bonding. A theoretical analysis of the interfacial stress distribution at the notch location was first carried out to explain the mechanism of delay of the interfacial debonding of notched steel beams after prestressed CFRP strengthening. Then, the prestress loss and flexural behaviour of specimens (with a prestress level of 25%) subjected to fatigue damage (FD) and/or wetting/drying cycles (WDCs) with 3.5 wt% NaCl solution were further experimentally investigated. Theoretical results showed that prestressed CFRP strengthening can significantly reduce the interfacial stress at the notch site and delay interfacial debonding. The CFRP prestress loss mainly occurs in the hardening stage of the adhesive layer, and the total prestress loss is less than 2.7% for specimens subjected to WDC exposure, indicating the effectiveness of the end anchorage system. The adhesive microcracks at the notch induced by FD and adhesive bonding degradation caused by WDCs significantly affect the interfacial debonding. In addition, NaCl solution penetration accelerated by microcracks causes further degradation of interfacial bonding. Nevertheless, the end anchorage system showed promising stiffness and load-carrying capacity behaviour for the specimens subjected to FD, WDCs, and the combined effects. The mixed failure mode of CFRP fracture and CFRP extraction from the end anchorage demonstrates that the strength of the CFRP plate was thoroughly utilized for the specimens with prestressed CFRP.

Experimental investigation and strength model of RC deep beams externally bonded by CFRP

This paper presents an experimental study on shear strengthening of reinforced concrete (RC) deep beams using externally applied carbon fiber reinforced polymer (CFRP) jackets. A total of 18 RC deep beams were tested using a four-point bending load. The examined parameter included span to depth ratio with or without CFRP strengthening. CFRP strips were applied perpendicular to the probable crack pattern as observed during testing for un-strengthened beams. The properties that is cracking behavior, ultimate strength, deflection, and energy dissipation capacity of beams were evaluated and discussed. The test results showed enhancement in shear strength up to 17% with CFRP. An increase in depth of RC deep beams caused a decrease in the rate of enhancement in shear strength for CFRP strengthened beams as compared to that observed in their counterparts. The experimental test results were compared with the existing design guidelines to assess their application for RC deep beams strengthened with CFRP. A strength equation based on regression analysis was developed to predict the experimental shear strength of RC deep beams strengthened with CFRP. This study showed that the RC deep beams strengthened with CFRP can effectively be used in structural engineering applications with enhanced shear strength and energy absorption capacity.

CFRP strengthening of butt-welded ultra-high strength steels under quasi-static tensile loading

Due to the softening at the heat-affected zone (HAZ) in ultra-high strength steels (UHSS), the mechanical properties can deteriorate depending on the steels’ grade, welding heat input, and its associated cooling rate. Hence, a design based on the properties of the base material (BM) may not be appropriate, and there is a need to retain the lost properties of the weldment. This study presents an effort to strengthen butt-welded UHSSs using ultra-high modulus (UHM) carbon fiber reinforced polymer (CFRP) plates. Although the rehabilitation and strengthening of steel structures using CFRPs have been available during the last two decades, they have not been used to strengthen higher grades of steel such as UHSSs. For this aim, a series of tensile tests were carried out on butt-welded UHSSs strengthened with adhesively bonded UHM CFRP plates on both sides of the weldment. Two welding processes, i.e. the gas metal arc welding (GMAW) and laser welding, were implemented separately to join the plates. Microhardness measurements and tensile tests were carried out for the experimental part, as well as finite element (FE) analysis of the joints. The results were also compared with other available methods, i.e. high-frequency mechanical impact (HFMI) treatment and TIG-dressing (tungsten inert gas) of the weld toe that are commonly used to increase the fatigue life of UHSS joints. It was found that CFRP strengthening can not only retain the lost properties of the weldment but can also increase the joint strength up to 32% compared to the BM, and a considerable 50% higher stiffness. In contrast, the other methods (HFMI and TIG-dressing) had no impact on the tensile characteristics of the weldments.

Activated Ductile CFRP NSMR Strengthening.

Significant strengthening of concrete structures can be obtained when using adhesively-bonded carbon fiber-reinforced polymer (CFRP) systems. Challenges related to such strengthening methods are; however, the brittle concrete delamination failure, reduced warning, and the consequent inefficient use of the CFRP. A novel ductile near-surface mounted reinforcement (NSMR) CFRP strengthening system with a high CFRP utilization is introduced in this paper. It is hypothesized that the tailored ductile enclosure wedge (EW) end anchors, in combination with low E-modulus and high elongation adhesive, can provide significant strengthening and ductility control. Five concrete T-beams were strengthened using the novel system with a CFRP rod activation stress of approximately 980 MPa. The beam responses were compared to identical epoxy-bonded NSMR strengthened and un-strengthened beams. The linear elastic response was identical to the epoxy-bonded NSMR strengthened beam. In addition, the average deflection and yielding regimes were improved by 220% and 300% (average values), respectively, with an ultimate capacity comparable to the epoxy-bonded NSMR strengthened beam. Reproducible and predictable strengthening effect seems obtainable, where a good correlation between the results and applied theory was reached. The brittle failure modes were prevented, where concrete compression failure and frontal overload anchor failure were experienced when failure was initiated.

Performance of the novel C-purlin tubular beams filled with recycled-lightweight concrete strengthened with CFRP sheet

This research investigates the performance of double C-purlin sections used in the concrete-filled steel tube (CFST) beams system. A recycled-lightweight concrete was used as infill material to reduce the newly suggested composite beam's self-weight and cost. Up to 70% of the raw coarse aggregate was replaced with the expanded polystyrene beads and recycled aggregate concrete. Also, the strengthening performance of the suggested CFST beam was investigated using carbon fiber reinforced polymer (CFRP) sheets. A total of seven specimens of concrete-filled C-purlin tubular sections were tested under four-point loads, and additional 12 models were numerically analyzed using finite element software. The conducted failure modes, flexural strength, flexural stiffness, and energy absorption index are presented and discussed. The results confirmed that the recycled-lightweight infill concrete material has a slightly lower influence on the investigated CFST beams' flexural performance than those with normal concrete (less than 10%). Like the conventional CFST beams, the double C-purlin tubular beams filled with recycled-lightweight concrete showed a normal response to the CFRP's strengthening quality. Moreover, the flexural strength capacity and stiffness values obtained from the current analyses are analogous with those theoretically predicted using the existing methods, which achieved mean values of about 0.759 and 1.126, respectively, as average prediction mean values of these methods.

Shear behavior of flexural CFRP-strengthened RC beams with crack-induced delamination: Experimental investigation and strength model

This study investigates the shear behavior and debonding characteristics of initially ductile RC beams (failing in flexure when unstrengthened) at the verge of transitioning to a more brittle shear failure upon strengthening using external flexural carbon fiber reinforced polymer (CFRP). Despite the absence of shear CFRP strengthening, various degrees of improvement in the shear capacity were achieved depending on the flexural CFRP amount. However, steeper shear cracks that bypass the stirrups in addition to the nonyielding stirrups results in shear capacities that cannot be reliably predicted using the ACI and other similar codes’ provisions. Instead of adopting capacity models that focus on the shear failure alone or the crack-induced debonding as oneway cause-effect (shear crack-debonding) relationship, a more holistic capacity prediction approach (calibrated with finite element anlaysis) that considers the synergistic effect between the shear failure and the CFRP debonding is provided. Since any enhancement in flexure must be checked against shear, the presented capacity prediction approach could be a more handy means to assess the shear strengthening level needed in such cases where the flexural strengthening is insufficient to achieve the overall structural upgrade sought. The designed beams – i.e. at the verge of changing failure mode with flexural FRP strengthening – and the test program could serve as a bond assessment philosophy in the sense that this upper bound brittle failure mechanism provides more realistic behavior of the crack-induced debonding performance of FRP-strengthened beams. Analytical load–deflection assessment of the tested specimens is also provided.

FRP strengthened SHS beam-column connection under monotonic and large-deformation cyclic loading

Many civil applications use square hollow sections (SHSs) as members in beam-column connections which can be vulnerable under cyclic loading. Cyclic loadings from earthquakes, wind, waves and currents affect onshore and offshore civil infrastructure. In addition, these beam-column connections can become structurally inadequate through incremental service loads, design/fabrication errors and material property degradation over time. Due to this, it will be necessary to strengthen SHS beam-column connections to improve their performance under sustained monotonic and cyclic loadings. This paper treats the performance of SHS beam-column connections strengthened with externally bonded carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP). Experimental investigations have been conducted on the bare, CFRP and GFRP strengthened SHS connections under monotonic and cyclic loading. Results show that under cyclic loading, both CFRP and GFRP strengthened SHS beam-column connections exhibit improved ultimate moment capacity, moment degradation behaviour, secant stiffness, energy dissipation capacity and plastic hinge behaviour compared to their bare counterparts. Under monotonic loading, both types of strengthened connections show higher moment capacity, secant stiffness and ductility. In addition, CFRP strengthening enhances the ultimate strength, while GFRP strengthening enhances the ductility.

Behaviour of thin-walled castellated beams strengthened using CFRP

This paper presents the behavior of Carbon Fibre Reinforced Polymer (CFRP) strengthened Thin-Walled Castellated Beams (TCBs). A detailed experimental study was carried out in two phases viz, 1. Study on effective bonding between steel substrate and CFRP under varying surface preparation scales, 2. Ultimate load behavior of TCBs provided with and without CFRP strengthening. While studying the effect of bonding between steel substrate and CFRP under various surface preparation, the bond strength of specimens prepared with copper-slag blasting was potentially stronger due to the maximum ultimate direct tensile stress of 2.54 N/mm2 in pull-off test. The investigation on ultimate load behavior of TCBs provided with and without CFRP strengthening was carried out experimentally on ten beams under the domination of Shear (SDB), Moment (MDB) and Moment & Shear (MSDB). This strengthening process was more effective in MDBs. Especially the load carrying capacity was increased by 35.38% in plastic section and 42.53% in semi-compact section and significant ductility enhancement observed in MDBs. Simultaneous interaction between shear and bending mode of failure of TCBs were studied.