Carbon Fiber Reinforced Polymer Steel Research Articles

Secondary flexural behaviour of reinforced concrete beams strengthened with special-shaped rivet bonded steel plates and prestressed CFRP bars

Special-shaped rivet and glued steel plate reinforcement is an innovative structural reinforcement technology. A riveted glued steel plate primarily relies on the rivet to transfer shear. Prestressed carbon fibre-reinforced polymer (CFRP) reinforcement is a new technique for strengthening concrete structures. These studies focus on the ‘primary load’, overestimate the ultimate flexural load of the components by neglecting the ‘secondary load’ of the components in real engineering. In this study, the flexural properties of concrete beams strengthened using special-shaped rivet steel plates and CFRP prestressed bars were studied theoretically and experimentally. The cracking load, ultimate load capacity, and strain of the steel plate, steel bar and CFRP bars were recorded during the tests. In addition, the failure mode of the beams was observed, and the effect of secondary stress on the flexural capacity of the beams was analysed. The failure load of the beams strengthened by CFRP prestressed tendons increased by 67.8% and 46.1% for beams with primary and active secondary loads, respectively. The failure load of the special-shaped rivet and glued steel plate strengthened beam increased by 115.7% and 160.5%, for beams with primary and active secondary loads, respectively. Both methods have a strong guiding significance for engineering practice.

Comparison of Fracture Behavior in Single-Edge Notched Beams Reinforced with Steel Bars or CFRP Bars.

To explore and compare the failure modes, deformation behaviors, and load-bearing capacities of single-edge notched (SEN) beams strengthened with carbon fiber-reinforced polymer (CFRP) and steel bars, static and dynamic three-point bending tests on both types of concrete beams have been carried out in this study. During the static tests, the electro-hydraulic servo machine served as a loading device to apply pressure to CFRP beams and reinforced concrete (RC) beams. During the impact experiments, different impact velocities were imparted by adjusting the drop hammer's height. Thus, information regarding crack propagation, energy absorption, and deformation was obtained. The results from the static tests showed that the RC beams predominantly experienced shear failure. In contrast, the CFRP beams primarily exhibited bending-shear failure, attributed to the relatively weaker bond strength between the bars and the concrete. Impact tests were conducted at three different velocities in this study. As the impact velocity increased, both types of concrete beams transitioned from bending failure to bending-shear failure. At the lowest velocity, the difference in energy absorption between beams reinforced with different materials was insignificant during the bending process. However, at the highest velocity, CFRP beams absorbed less energy than RC beams. The study of structures' impact failure modes and their mechanical characteristics offers valuable references for the anti-collision design and protection of structures.

Shear behavior of circular concrete short columns reinforced with GFRP longitudinal bars and CFRP grid stirrups

Although fiber-reinforced polymer (FRP) reinforcements have become popular, the post-pultrusion bending leads to significant deficiency in bent portions of FRP hoops and spirals. This study adopts flexible carbon FRP (CFRP) grids as stirrups, and investigates the shear behavior of circular short columns reinforced with GFRP bars and CFRP grid stirrups. Six specimens with different shear reinforcement ratios, axial load ratios and types of stirrups (CFRP grids and steel hoops) were tested to shear failures. The failure modes, crack and strain developments, and shear load-horizontal displacement responses were presented for discussion. All specimens experienced shear-compression failures, and the critical diagonal crack widths increased approximately linearly with shear loads. The typical shear load-horizontal displacement curve consisted of three branches: a linear elastic branch, a cracking branch with progressive slope deteriorations, and an almost flat failure branch. Increasing CFRP grid stirrup ratio could not only enhance strength and ductility performance, but also alleviate the slope degradations, while increasing axial load ratios could enhance the initial cracking loads, restrain crack propagations, and reduce the lateral displacements. In terms of strength performance, steel hoops could be replaced by CFRP grid stirrups even with smaller stirrup ratio. Additionally, analytical investigations suggested that the effective stresses and strains of CFRP grid stirrups at failure may be lower than code limits.

Mechanical behaviors of steel-CFRP plate bonded joints after freezing-thawing cycles

The effective bonding between the steel element and carbon fiber reinforced polymer (CFRP) is critical for applying the CFRP to strengthen steel elements. The severe service environment always affects the interfacial bond strength, resulting in a reduction in strengthening efficiency. To research the interfacial bond performance between the steel element and CFRP plate after freezing-thawing environment, this paper conducted studies on the mechanical behaviors of steel-CFRP plate joints. Experiments indicated that the freezing-thawing environment did not influence the failure mode, but decreased the interfacial ultimate capacity of double-shear specimens. The ultimate load is reduced by 14.5% after exposure to 300 freezing-thawing cycles. An approximate bilinear bond-slip relationship is employed for expressing the interfacial bond-slip behavior of all specimens, and the freezing-thawing environment has a negative influence on the bond-slip behavior. By determining the degeneration laws of bond-slip parameters after experiencing freezing-thawing cycles, the bilinear bond-slip model considering freezing-thawing effect was developed. Moreover, the three-dimensional FE modelling was implemented based on the mixed-mode cohesive zone model. The comparisons of the test and FE results show that the FE results are consistent with the test results, and the interfacial damage and debonding process can also be precisely predicted. The numerical modelling also reveals that the asymmetric debonding of the two interfaces can affect the ultimate load, which leads to a higher scatter of test results for the double-shear joint.

Flexural bond behavior and development length of ribbed CFRP bars in UHPFRC

Ribbed carbon fiber reinforced polymer (CFRP) bars in ultra-high-performance fiber reinforced concrete (UHPFRC) are a high-efficiency combination for its sustainable substitute and high strength to weight ratio. This paper aims to investigate the bond stress and development length of ribbed CFRP bar embedded in UHPFRC using the hinged beam test. A total of 12 groups of hinged beam specimens were tested with different parameters, such as bar type (ribbed CFRP, sand coated CFRP, ribbed glass fiber reinforced polymer (GFRP), and steel bar), bonded length (4db, 10db, 20 db, and 40 db), fibers (with and without fibers in ultra-high-performance concrete (UHPC)), and presence of shear reinforcement for assessing the bonding behavior and development length of each bar. Tensile failure occurred in the steel, ribbed GFRP, and ribbed CFRP bars with bonded lengths of 10db, 20db, and 40db, respectively, and pullout failure occurred in sand coated CFRP bars regardless of bonded length. The ultimate load for the bonded length of 10 db was in order of ribbed CFRP, ribbed GFRP, steel, and sand coated CFRP bars. Compared with the bonded length, the bond stress of ribbed CFRP bars is larger than that of the ribbed GFRP and sand coated CFRP bar and these trends became more remarkable as the bonded length increased. There was no difference in the bond stress with presence of the reinforcement cage, and the bond stress increased by 20 % when the fibers were incorporated. The code-based equation for development length of ribbed CFRP bar was found to be underestimated, and ribbed CFRP, sand coated CFRP, ribbed GFRP bar of development length was proposed as 24db, 20db, and 107db.

Influences of the bond-slip on the flexural performance of CFRP plate-strengthened damaged steel beams with intermediate debonding: A numerical study

The interfacial intermediate debonding between the steel beam and CFRP (carbon-fiber-reinforced polymer) is a considerable issue for a CFRP plate-strengthened damaged steel beam. The interfacial bond-slip property determines the interfacial debonding and thus affects the strengthening efficiency. To comprehend the influence laws of the bond-slip behavior, this study conducted a finite element (FE) modelling to assess the strengthening efficiency of the damaged steel beam using CFRP plates. The triangular and trapezoidal cohesive zone models were considered in parametric investigations. The comparisons of FE and experimental results verify the developed FE models. The FE modelling shows that the interfacial fracture energy is the most important bond-slip parameter affecting the flexural strengthening efficiency, relative to the maximum bond stress, elastic and plastic slips. The flexural capacity, ultimate deflection, and debonding load of the damaged steel beam are significantly increased with an increase in the interfacial fracture energy. However, changing the maximum bond stress, elastic slip or plastic slip only produce a minor influence under the same interfacial fracture energy. The selection of the adhesive type is critical for strengthening the damaged steel beam using CFRP plates. In this study, the debonding load, flexural capacity, and ultimate deflection are increased by 75.0%, 51.0%, and 131.1%, respectively, when Araldite-2015 adhesive with the trapezoidal bond-slip model is used instead of Sikadur-30 adhesive with the triangular bond-slip model. Moreover, the debonding load and flexural capacity are hardly increased but the ductility can be considerably improved with an increasing CFRP plate length.

Durability of the liquid rubber‐modified CFRP‐steel interface under freeze–thaw cycles

AbstractAn experimental investigation was carried out to evaluate the feasibility of using a liquid rubber‐modified epoxy resin to improve the bonding durability between steel and carbon fiber‐reinforced polymer (CFRP) plates in a freeze–thaw environment. Forty‐eight CFRP‐steel double strap joints were prepared, with a focus on two key factors: the number of freeze–thaw cycles (0, 50, 100, and 200 cycles) and the amount of liquid rubber in the adhesive (0%, 5%, 10%, and 15% by mass). The bond properties encompassing the damage mode, the ultimate capacity, and the bond–slip response of the CFRP‐steel joints were examined, respectively. The study revealed that the ultimate capacity of the joints decreased as the freeze–thaw cycles increased. The ultimate capacity retention rate for unmodified joints, after undergoing 200 freeze–thaw cycles, was approximately 84.9%, while for the modified joints, it ranged from 90.5% to 96.4%. Furthermore, the impact of the freeze–thaw cycles and liquid rubber content on the key bond indicators in terms of the maximum shear stress τmax, initial slip S1, maximum slip Sf, and fracture energy Gf were ascertained, leading to the establishment of the bond–slip degradation relationship of the liquid rubber modified CFRP‐steel interface under freeze–thaw environment.Highlights The effects of the liquid rubber content and freeze–thaw cycles on the mechanical properties of the epoxy resin‐based adhesive were determined. The influences of both the liquid rubber content and freeze–thaw cycles on the CFRP‐steel interface were analyzed. The bond–slip degradation relationships of the liquid rubber‐modified CFRP–steel interface under freeze–thaw cycles were developed.

Experimental investigation on the friction behavior of CFRP plate in contact with sandblasted steel plate

The coefficient of static friction (COSF) between the steel plate and carbon fiber-reinforced polymer (CFRP) plate is a significant impact parameter for the design of mechanical anchors. In this study, the friction behavior and wear mechanism between the sandblasted steel plate and CFRP plate with different surface treatment methods under various normal pressures and anchor lengths were investigated through the planar clamping anchor. In order to improve the surface roughness level, the surface of CFRP plate was treated by galling or sand coating. The results indicate that the COSF of the galling surface ranged of 0.28–0.30 corresponding to various parameters, while that of the sand coating surface changed between 0.27 and 0.35. Although the COSF could be obviously enhanced by the surface sand coating, the discreteness of COSF was large and the relaxation of bolt preload was severe. Moreover, the COSF presented a decreasing trend when the normal pressure exceeded 33 MPa, whereas that kept almost constant with the increase of anchor length. The failure mode changed from slip failure to incomplete or complete burst failure with increasing normal pressure and anchor length. The friction failure process of CFRP plate was dominated by ploughing and wear, which caused changes of the tensile load and bolt preload at different stages. The research in this paper contributes to providing guidance for the design of mechanical clamping anchors, especially for the clamping anchor with constant or variable curvature waveform.

Seismic Retrofit of Diagonal Tension Members in Steel Deck-Truss Bridges Using CFRP Sheets

This study entailed axial cyclic loading tests conducted on full-scale diagonal tension members of steel deck-truss bridges to evaluate the effects of seismic retrofitting methods using carbon fiber–reinforced polymer (CFRP) sheets. The loading tests were performed on CFRP-retrofitted specimens with varying anchoring lengths of the CFRP sheets. The results indicated that the proposed retrofitting methods, which employed the intermediate-modulus CFRP type (390–450 GPa) and polyurea putty (a ductile adhesive), delayed the plastic buckling of the flanges and substantially increased the load-carrying capacities, stiffnesses, and ductility capacities of the retrofitted diagonal tension members. Additionally, the polyurea putty effectively suppressed the peeling failure of the CFRP sheets. It maintained the cross-sectional integrity between the steel members and CFRP sheets even after the plastic buckling of the flanges and rupture failure of the CFRP sheets. Further, finite-element analyses accurately reproduced the loading test results by considering the nonlinear bond-slip performance of polyurea putty, anisotropic characteristics of the CFRP sheets, and cyclic plasticity properties of steel.

Flexural strengthening of damaged steel beams with prestressed CFRP plates using a novel prestressing system

This study developed a novel prestressing system of the carbon fiber reinforced polymer (CFRP) plate to strengthen damaged steel beams, which reduced the operation space at the tensioning end, thereby extending the application range of prestressing system. Flexural tests were conducted to verify this system and investigate the effects of the adhesive layer, prestressing level, and CFRP plate area on the strengthening efficiency, and subsequently, a parametric analysis was carried out using finite element modeling to obtain more influencing rules of the unbonded CFRP plate-strengthened steel beams. The results indicated that satisfactory strengthening efficiency could be achieved by the novel prestressing system. The adhesive layer significantly affected the strain distributions of the steel–CFRP composite section, whereas it had a very slight effect on the flexural behavior of the steel beams, and the bonded and unbonded CFRP plates had a similar strengthening efficiency. Nonprestressed CFRP plate exhibited limited improvement in the flexural capacity and stiffness of the damaged steel beams under the normal service state; in contrast, the prestressed CFRP significantly increased the flexural behavior of the beams in the elastic and elastic–plastic stages owing to the high strength utilization of the CFRP plate. In addition, as the prestressing level increased, strengthening efficiency increased. Solely increasing the area or elastic modulus of the CFRP plate improved the strengthening efficiency slightly, whereas applying a prestress simultaneously clearly increases the strengthening efficiency. The strengthening efficiency increases with artificial notch depth.

Flexural Performance and End Debonding Prediction of NSM Carbon FRP-Strengthened Reinforced Concrete Beams under Different Service Temperatures

This paper aims to evaluate the influence of relatively high service temperatures (near or beyond the glass transition temperature (Tg) of epoxy adhesive) on the flexural performance and end debonding phenomenon in near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened, reinforced concrete (RC) beams. To this end, an experimental program consisting of 24 beams (divided into four groups) was performed, where different parameters was combined (i.e., service temperature, steel reinforcement ratio, CFRP ratio, and concrete compressive strength). In addition, the effect of the testing temperature on the end debonding phenomenon was investigated with an analytical procedure according to fib Bulletin 90, and the predictions were compared to experimental results. Taking specimens tested at 20 °C as a reference, no considerable change was observed in the ultimate load of the specimens tested below 60 °C (being in the range of epoxy Tg), and all specimens failed by FRP rupture. On the other hand, the increase in testing temperature up to 70 and 85 °C was followed by a decrease in the capacity of the strengthened beams and a change in failure mode, moving from FRP rupture to end debonding and concrete crushing. The analytical procedure successfully predicted the occurrence of premature end debonding failure and demonstrated that the effect of temperature on the mechanical properties of materials can be a key factor when predicting the premature end debonding in a NSM joint.

Finite element, analytical, artificial neural network models for carbon fibre reinforced polymer confined concrete filled steel columns with elliptical cross sections

In the present era of architecture, different cross-sectional shapes of structural concrete elements have been utilized. However, this change in shape has a significant effect on load-carrying capacity. To restore this, the use of column confinements with elliptical sections has gained attention. This paper aim to investigate the effect of elliptical shape sections of confined concrete reinforced with Carbon Fiber Reinforced Polymer (CFRP) and steel tube on axial load-carrying capacity. This study is achieved using following tools Finite Element (FE) in Abaqus and Artificial Neural Networks (ANN) modeling. The study involved a 500-mm-high column with three sets of aspect ratios: 1.0, 1.5, and 2.0. In each aspect ratio, three different layers of CFRP were used, i.e., .167, .334, and .501-mm. Analytical results showed that with the increase in aspect ratio from 1 to 2, there is a decrease in ultimate axial load of about 23.2% on average. In addition, the combined confining pressure of steel tube and CFRP increases with a decrease in dilation angle as the number of CFRP layers increases. The failure mode for the column with a large aspect ratio is local buckling at its mid-height along the minor axis. The result showed a good correlation between FE and experimental results of ultimate stress and strains, with a mean squared error of 2.27 and .001, respectively. Moreover, ANN and analytical models showed a delightful correlation of R2 of .97 for stress models and .88 for strain models, respectively. The elliptical concrete section of the column confined with steel tubes can be adopted for a new architectural type of construction; however, with more than three aspect ratios, the wrapping of the section with CFRP jackets is highly recommended.

An Experimental Study on Shear Performance of Adhesive Interface between Steel Plates and CFRP

CFRP (Carbon Fiber Reinforced Polymer) are widely used in steel structural reinforcement. For steel structures strengthened with CFRP, except the cases the structures have defects before strengthening, the adhesive interface is the weakest part and CFRP debonding is the most common failure mode. In order to investigate the failure mechanism of CFRP strengthened steel structures, this paper presents an experimental study on shear performance of adhesive interface between steel plate and CFRP by twin shear model. Six steel plates strengthened with CFRP are divided into two groups, one has no damage, another has a gap at the mid. The specimens are tested under tensile loadings. The study results show that, the plates with a gap failed for CFRPs debonding, the cracking loading and breaking loading are 14.85kN, and 17.88kN respectively; the strain-loading curves had long linear stages, two strains decrease and other strains of another side increased rapidly at the cracking loading, then they both rose until the plates failed.

Interface slip of steel–concrete composite beams reinforced with CFRP sheet under creep effect

Under the creep action of composite steel and concrete beams reinforced by carbon-fiber-reinforced polymer (CFRP) sheet, the face of the CFRP sheet, steel beam, and concrete slab beam produce relative slip. This slip affects the interface interaction, reduces the bearing capacity and stiffness of the members, and increases the deformation. In this paper, elastic and energy methods are used to analyze the interface forces between steel beams and concrete slabs reinforced by CFRP sheeting under the action of concrete creep. The calculation formulas for interface slip, axial force, and incremental deformation are established. The influence of design parameters on the mechanical properties of the interface is analyzed. Results show that the increments in interface slip, axial force, and deformation are zero on the 28th day. With increasing age, the increments in interface slip, axial force, and deformation gradually increase, and the increase is large in the first 100 days; it basically remains unchanged during the time interval from 100 to 1028 days. When the load increases by 5 N/mm (5 kN), the slip increments increase by approximately 0.004 mm, 0.002 mm, and 0.002 mm. The increments in axial force are approximately 19.4 kN, 15.9 kN, and 16.1 kN. The deformation increments increase by approximately 1.7 mm, 1.1 mm, and 0.6 mm.

Fatigue failure mechanisms and probabilistic S-N curves for CFRP–steel adhesively bonded joints

In this study, fatigue tests were conducted on a series of carbon fiber reinforced polymer (CFRP)–steel double lap shear joints. The fatigue failure mechanisms were investigated based on the failure modes, load–displacement relationships, and stiffness degradation. Inherent scatter characteristics of the fatigue life were discussed using probabilistic S-N (P-S-N) curves based on four statistical models (ISO 12107, ASTM E739-91, two-parameter Weibull, and Gumber models). The results indicate that the fatigue life decreased dramatically with the increase of the load level, and interface debonding is the primary failure mode of fatigue joints. Stable debonding and accelerated debonding of the bonded interface are initiated when the joint stiffness degrades to approximately 98% and 82–86% of the initial stiffness, respectively. The S-N curve based on the mean bond stress range shows a better fit than that based on the local bond stress. Based on the comprehensive evaluation of the performance of the P-S-N curves, the two-parameter Weibull model is recommended for fatigue life design as it can well-constrain fatigue data without excessive safety redundancy.

Shear behavior of reinforced concrete beams repaired using a hybrid scheme with stainless steel rebars and CFRP sheets

Repairing corroded flexural-deficient reinforced concrete (RC) structures using a hybrid scheme with stainless steel (SS) rebars and carbon-fiber-reinforced polymer (CFRP) sheets revealed excellent structural performance and contributes to lower maintenance costs in the remaining service life of the repaired structure. However, although cutting the bottom arm of stirrups in a hybrid repair method could affect the structural performance of shear-critical RC beams since this effect was not investigated in the past research. In this paper, structural performance of a group of shear-deficient RC beams repaired using the hybrid method is investigated experimentally to examine the effect of cutting the bottom arm of stirrup on the shear capacity of the repaired beams. The test variables included the longitudinal reinforcement types (i.e. carbon and SS), shear reinforcement configurations, and CFRP sheet wrapping schemes. Experimental results demonstrate that cutting the bottom arm of stirrup for replacing the corroded tensile rebar could significantly reduce the shear capacity of the retrofitted beams. Therefore, strengthening using CFRP sheet is needed to restore the shear performance of the retrofitted beams. Test results revealed that complete wrapping of CFRP sheet is effective to overcome the shear deficiency due to cutting the bottom arm of stirrup in the shear-critical RC beams. In addition, the effectiveness of CFRP sheet wrapping schemes on shear performance of SS-RC beams is approximately identical with that of CS-RC beams. Finally, a design methodology to repair the corroded RC bridge using hybrid method is developed and presented based on bending and shear tests.

Numerical and analytical investigation of square timber columns confined with steel and carbon fiber reinforced polymer external jacket

This paper numerically investigated the timber confinement of columns with carbon fiber reinforced polymer (CFRP) and steel tubes under axial compression. An elastic-plastic model with linear hardening, a CFRP hashin damage, and a timber damaged anisotropic elastic-plastic model, respectively, are used to simulate the inelastic behavior of the steel tube, CFRP layers, and timber core. In addition, a comprehensive numerical study was conducted using a wide range of cross-sections, thicknesses, lengths, and the number of CFRP layers developed to varying degrees (0, 45, and 90). To confirm the accuracy of the current FEM model, numerical data is compared to the experimental model’s final strengths, behavior, and failure mechanisms. Additionally, the ultimate strengths of timber-steel and CFRP are compared to various standards and design formulas. The results reveal that columns with thicker steel tubes and more CFRP layers have an average of about 42% and 12% greater load-bearing capacity and ductility. The degree of CFRP affected the load-bearing capacity of timber columns, which increased by around 10% from 45 to 90. In comparison to specimens with equal cross-sections and thickness, shorter specimens with greater cross-sections typically have 40% higher stiffness. According to parameter studies, the AISC 360-16 American standard design approaches can be safely extended to anticipate the ultimate strength of timber-steel columns. Meanwhile, both the ACI-440 and Ilki et al. design formula predictions are the most precise, particularly at 45° with high ultimate strength.

Shear Strengthening of RC Deep Beams with Symmetrically or Asymmetrically Positioned Square Openings Using CFRP Composites and Steel Protective Frames

In most cases, openings are made in the Web of deep beams for installations to pass through. These members require to be strengthened since the openings reduce load-bearing capacity. This study utilizes carbon fiber-reinforced polymer (CFRP) composites and steel protective frames (SPF) as strengthening configurations in reinforced concrete (RC) deep beams to improve the strength lost due to the square openings. To this end, eleven specimens with 10 × 50 × 120 cm in size were subjected to the three-point monotonic loading. In each beam, one or two square openings of 18 cm in each side are positioned either symmetrically or asymmetrically along the beam before it is strengthened with CFRP composites or SPFs. The strengthening composites were installed using externally bonded reinforcement (EBR) or externally bonded reinforcement on grooves (EBROG) techniques in two wrapped or inclined configurations. The obtained results indicate that specimens retrofitted by the SPF exhibited a superior performance as their loading capacity and energy absorption were enhanced by 115% and 337% in comparison with the reference beam, respectively, while these values for the specimens retrofitted by the EBROG technique were 58% and 182%, respectively, and 42% and 105% for those strengthened with the EBR technique.

A novel seawater and sea sand concrete-filled CFRP-carbon steel composite tube column: Seismic behavior and finite element analysis

The seismic behavior of a novel seawater and sea sand concrete (SSC)-filled carbon fiber-reinforced polymer (CFRP)-carbon steel composite tube (SFSCT) column under combined axial compression and reversed cyclic loadings was studied in this paper. This structure makes use of seawater and sea sand resources, and CFRP was adopted to isolate the corrosion by chloride ions on the steel tube. Tests of eight composite columns were carried out. The test parameters include the axial compression ratio, the number of CFRP layers and the bonding direction. The test results revealed that all of the specimens displayed superb seismic performance with a drift ratio over 4%. The failure of the SFSCT column exhibits a typical compressive-flexural failure mode. Compared with the results of the SSC-filled steel tube columns, the hoop strain of the specimen under additional CFRP confinement is reduced by 1.6 times, and the flexural strength and drift capacity increase by 22% and 17%, respectively. A fiber model was created by finite element analysis, and parametric studies of the main design parameters were performed. The effects of the steel tube and CFRP on the seismic performance were evaluated. Using experiments and finite element analysis, the relationships among the drift capacity, axial compression ratio and confinement level were investigated. A design method for predicting the drift capacity of SFSCT columns was proposed.

Durability of CFRP-Steel Double-Lap Joints under Cyclic Freeze-Thaw/Wet-Dry Conditions.

The usage of carbon fiber–reinforced polymer (CFRP) to strengthen cracked steel structures can effectively improve its bear capacity, so it has been extensively used in recent years. The degradation of interfacial bonding is one of the most important factors affecting the durability of CFRP–steel structures under a freeze–thaw(F–T)/wet–dry (W–D) environment. In this study, epoxy resin adhesive (ERA) dog-bone specimens and CFRP–steel double-lap joints (bonded joints) were prepared. F–T/W–D cycles experiment and tensile tests of the ERA specimens and the bonded joints were also performed. Under F–T/W–D cycles, the main properties of the ERA specimens and the bonded joints were examined. Results indicated that fracture failure occurred in all ERA specimens. The hybrid failure modes of fiber peeling on the surface of CFRP plate and the bonded interface peeling between the CFRP plate and ERA layer primarily occurred in the bonded joints. The failure of both of them can be considered to be brittle, which was unaffected by the F–T/W–D cycles. With increased F–T/W–D cycles, the ultimate load and tensile strength of the ERA specimens initially increased and then decreased, whereas the elastic modulus initially increased and then remained unchanged. The ultimate load of the bonded joints decreased gradually. Based on the relationship between the interfacial bond-slip parameters and the number of F–T/W–D cycles, the bond–slip model of the bonded joints was established. The proposed relationship was validated by comparing with the experimental bond-slip relationships and the predicted relationships under the F–T/W–D cycles.