Reinforced Polymer Research Articles

Walikukun fiber as lightweight polymer reinforcement: physical, chemical, mechanical, thermal, and morphological properties

Walikukun fiber as lightweight polymer reinforcement: physical, chemical, mechanical, thermal, and morphological properties

PHYSICO-MECHANICAL PROPERTIES OF POLYMER MATRIX COMPOSITE MATERIAL REINFORCED WITH CARBONIZED CASSAVA BACK PEEL AND IRON FILLINGS

The use of natural particles as reinforcement in polymers has been a growing research area. This study aims to explore the use of cassava back peel (CCBP) and iron-fillings (IF), as reinforcement material in epoxy resin-based composite. Composite plates were prepared for the casting of the epoxy resin reinforced with CCBP and IF composites using a hand lay-up technique. The percentage compositions by weight of the CCBP varied between 0%-10 %, while that of IF was kept constant (5%). The physico-mechanical behaviours of CCBP-reinforced epoxy polymer composites were studied using ASTM standards. The density of the epoxy resin was improved by the reinforcements. The maximum density obtained was 1270 kg/cm3 for 5%CCBP epoxy composite. The percentage of water absorption improved by the addition of the filler with 5%IF10CCBP epoxy hybrid composite recording 30% water absorption. Conversely, the ultimate tensile strength (UTS) and breaking strength (BS) varied with the addition of the filler materials. 5%CCBP epoxy composite recorded 41.26 MPa for both UTS and BS. Meanwhile, percentage elongation decreased with the addition of the fillers showing that the composites became less ductile. The HBN of epoxy was improved with the addition of fillers. The composites can be applied to automobile dashboards.

Enhancing decellularized vascular scaffolds with PVDF and PCL reinforcement: a fused deposition modeling approach

BackgroundDecellularized xenogenic scaffolds represent a promising substrate for tissue-engineered vascular prostheses, particularly those with smaller diameters (<6 mm). Despite their benefits, a notable limitation presents itself during decellularization, namely, the diminished mechanical strength that introduces the risk of aneurysmal dilations in the early post-implantation period. This study introduces a strategy for modification the mechanical properties of these biological scaffolds through the forming of an external polymeric reinforcement via thermal extrusion.MethodsThe study utilized scaffolds fabricated from bovine internal mammary arteries through decellularization and preservation. The scaffolds were divided into subgroups and reinforced with polymeric helices made of Polyvinylidene fluoride (PVDF) and Polycaprolactone (PCL), n = 5 for each. An experimental setup for external reinforcement coating was designed. Computed microtomography was employed to obtain accurate 3D models of the scaffolds. Mechanical properties were evaluated through in vitro uniaxial tension tests (Z50, Zwick/Roell, Germany), compliance evaluation and numerical simulations (Abaqus/CAE, Dassault Systemes, France) to investigate the effect of external reinforcement on aneurysm growth.ResultsUsing a double-layer helix for the reinforcement significantly enhanced the radial tensile strength of the scaffolds, increasing it up to 2.26 times. Yet, the comparison of vessel's compliance between two reinforced and the Control scaffolds within the physiological pressures range did not reveal any significant differences. Numerical simulation of aneurysm growth showed that thin-walled regions of the Control scaffold developed aneurysmal-type protrusions, bulging up to 0.7 mm, with a substantial degradation of mechanical properties. In contrast, both PVDF and PCL reinforced scaffolds did not exhibit significant property degradation, with deformations ranging 0.1–0.13 mm depending on the model, and a maximum decrease in the modulus of elasticity of 23%.ConclusionThe results of the study demonstrated that the external polymer helical reinforcement of decellularized scaffolds via thermal extrusion enables a controlled modification of mechanical properties, notably enhancing radial strength while maintaining sufficient compliance within the physiological pressure range. A series of in vitro tests demonstrated the consistency and potential of this approach for decellularized xenogenic scaffolds, a concept that had not been explored before.

Strategic use of ultra-high-performance concrete and carbon fiber reinforced polymer reinforcement for end zone design of prestressed girders

The design of end zones to prevent severe cracking is a key requirement toward durable prestressed girders. Traditional approaches employ large amounts of steel reinforcement to attain this requirement, which may result in steel congestion. This paper investigates a hybrid girder concept that uses Ultra-High-Performance Concrete (UHPC) and Carbon Fiber Reinforced Polymer (CFRP) bars to enhance crack control and long-term durability in the end zones of prestressed girders. The objectives of this study are to quantify the UHPC zone lengths needed to restrain end zone cracks, eliminate or reduce the required amount of steel reinforcement, and investigate its replacement with CFRP bars. A finite element modeling (FEM) approach was developed for this purpose and its fidelity was validated with experimental data. The FEM results showed that UHPC zones with lengths below or equal to half of the girder depth can significantly reduce end zone cracking. CFRP bars can be added in the UHPC zones as a conservative measure to crack control, to ensure the long-term corrosion resistance of the girders.

Polymeric reinforcements for cellularized collagen-based vascular wall models: influence of the scaffold architecture on the mechanical and biological properties.

A previously developed cellularized collagen-based vascular wall model showed promising results in mimicking the biological properties of a native vessel but lacked appropriate mechanical properties. In this work, we aim to improve this collagen-based model by reinforcing it using a tubular polymeric (reinforcement) scaffold. The polymeric reinforcements were fabricated exploiting commercial poly (ε-caprolactone) (PCL), a polymer already used to fabricate other FDA-approved and commercially available devices serving medical applications, through 1) solution electrospinning (SES), 2) 3D printing (3DP) and 3) melt electrowriting (MEW). The non-reinforced cellularized collagen-based model was used as a reference (COL). The effect of the scaffold's architecture on the resulting mechanical and biological properties of the reinforced collagen-based model were evaluated. SEM imaging showed the differences in scaffolds' architecture (fiber alignment, fiber diameter and pore size) at both the micro- and the macrolevel. The polymeric scaffold led to significantly improved mechanical properties for the reinforced collagen-based model (initial elastic moduli of 382.05 ± 132.01kPa, 100.59 ± 31.15kPa and 245.78 ± 33.54kPa, respectively for SES, 3DP and MEW at day 7 of maturation) compared to the non-reinforced collagen-based model (16.63 ± 5.69kPa). Moreover, on day 7, the developed collagen gels showed stresses (for strains between 20% and 55%) in the range of [5-15] kPa for COL, [80-350] kPa for SES, [20-70] kPa for 3DP and [100-190] kPa for MEW. In addition to the effect on the resulting mechanical properties, the polymeric tubes' architecture influenced cell behavior, in terms of proliferation and attachment, along with collagen gel compaction and extracellular matrix protein expression. The MEW reinforcement resulted in a collagen gel compaction similar to the COL reference, whereas 3DP and SES led to thinner and longer collagen gels. Overall, it can be concluded that 1) the selected processing technique influences the scaffolds' architecture, which in turn influences the resulting mechanical and biological properties, and 2) the incorporation of a polymeric reinforcement leads to mechanical properties closely matching those of native arteries.

Analysis of the transfer, flexural bond and anchorage lengths of pretensioned FRP reinforcement based on Eurocode

Current design codes in North America have guidelines for assessing the anchorage zone of pretensioned fiber reinforced polymer (FRP) reinforcement. However, there is no comparison of the Eurocode approach with experimental data or suggestions for its application for prestressed FRP reinforcement. Therefore, the main objective of this article is to provide a comparison of available data in the literature on the transfer, flexural bond, and anchorage length of different types of FRP reinforcement with Eurocode and to provide insight on the adaptation of this code. The database of more than 300 and 100 specimens with the results of the transfer and flexural bond lengths is used, respectively. This database is used to derive and propose the parameters that describe the type and surface of pretensioned FRP reinforcement based on the Eurocode approach. Furthermore, the influence of shear reinforcement and the type of pretensioned reinforcement release (gradual and sudden) is taken into account. The Eurocode approach with the coefficients proposed for different FRP reinforcements on average gave the best prediction of the experimental transfer, flexural bond, and anchorage length results compared to the North American design codes for FRP reinforcement and the Eurocode for steel strands.

Regulation and prediction of the dielectric constant and interfacial binding energy of surface modified hexagonal boron nitride/polyphenylene oxide@cyanate ester resin

AbstractParticulate‐filled materials with superior mechanical properties and wave permeability have received extensive research attention in the military industry. To elucidate the role of reinforcement in polymers, γ‐Aminopropyltriethoxysilane (APTES) is used to modify hexagonal boron nitride (h‐BN) nanoparticles, which are then filled into polyphenylene oxide@bisphenol A dicyanate ester composite, exhibiting a 1.46‐fold increase in flexural strength and a dielectric constant of 2.66 at 12 GHz. Finite element analysis is employed to design composite material models, successfully predicting the dielectric properties of composites at different frequencies and reinforcement filling levels. The change in the interface energy induced by the silane coupling agent is quantitatively calculated by molecular dynamics simulation, demonstrating that the modified nanoparticles are conducive to improving the flexural strength. Overall, the predicted dielectric and mechanical properties of composites can be utilized to screen for composites that possess excellent dielectric and mechanical properties, thereby greatly improving efficiency.Highlights A hexagonal boron nitride/polyphenylene oxide@cyanate ester is prepared. Finite element analysis is employed to predict the dielectric properties. The interface energy is calculated by molecular dynamics simulation. The resin has superior mechanical and dielectric properties.

Durability of GFRP and BFRP reinforcing bars in simulated seawater sea sand calcium sulfoaluminate cement concrete pore solution

Thanks to the much smaller carbon footprint of calcium sulfoaluminate cement (SAC) concrete and the corrosion resistance of fiber reinforced polymer (FRP) reinforcement, FRP-reinforced SAC concrete can possibly replace conventional reinforced concrete in some cases. In this study, for the first time, the durability of glass FRP (GFRP) and basalt FRP (BFRP) bars, made with epoxy resin, is investigated in simulated pore solutions of concretes made with (a) SAC and fresh water, (b) SAC and seawater and sea sand. The bars were immersed in each solution and kept at constant temperature of 30 °C, 45 °C and 60 °C for up to 180 days. Bar samples were tested for their retained tensile strength and physiochemical degradation after 30, 60, 90, and 180 days of immersion. Scanning electron microscopy (SEM), X-ray dispersive spectroscopy (EDS), and Fourier transform infrared (FTIR) spectroscopy were used to identify the underlying damage mechanisms. Results show that solution (b) is less harmful to BFRP than solution (a), while the opposite is true in the case of GFRP. Both solutions caused the dissolution of the epoxy resin and the leaching of the Fe in the basalt fiber. Overall, GFRP exhibited higher durability than BFRP. Based on image analysis, the deteriorated zone within the bar cross-section is not a uniform ring, but its area correlates with the loss of tensile strength. Inspired by the Avrami-Erofe'ev Equation and the Eyring's Transition State Theory, a novel time-temperature-dependent FRP bar degradation model is proposed. The proposed model shows close agreement between the predicted and measured tensile strengths.

Sonochemical synthesis of lignin nanoparticles and their applications in poly (vinyl) alcohol composites

Lignin is a common and abundant byproduct of the pulp and paper industry and is generally burned to produce steam. Opportunities exist to acquire greater value from lignin by leveraging the properties of this highly conjugated biomacromolecule for applications in UV absorption and polymer reinforcement. These applications can be commercialized by producing value-added lignin nanoparticles (LNPs) using a scalable sonochemical process. In the present research, monodisperse LNPs have been synthesized by subjecting aqueous dispersions of alkali lignin to acoustic irradiation. The resulting particle size distribution and colloidal stability, as determined by dynamic light scattering, transmission electron microscopy and zeta potential analysis, of LNPs can be adjusted by varying the solution pH and ultrasonication energy. As-synthesized LNPs with a mean diameter of 204 nm were incorporated into poly (vinyl) alcohol (PVA) to prepare thin and flexible nanocomposite films using a simple solvent casting method. The addition of 2.5 wt% LNP increased the material's Sun Protection Factor up to 26 compared to 0 for neat PVA, while maintaining light transmission above 75 % in the visible spectra. In addition, the tensile strength and elastic modulus of the PVA nanocomposites improved by 47 % and 36 %, respectively. The presence of LNP also enhanced the thermal stability of the materials. Significantly, the proposed sonochemical process may be generally applicable to the synthesis of a range of naturally-derived LNPs for a variety of value-added applications.

Hybrid hemp/glass fiber reinforced high-temperature shape memory photopolymer with mechanical and flame-retardant analysis

Cultivated natural fibers have a huge possibility for green and sustainable reinforcement for polymers, but their limited load-bearing ability and flammability prevent them from wide applications in composites. According to the beam theory, normal stress is the maximum at the outermost layers but zero at the mid-plane under bending (with (non)linear strain distribution). Shear stress is the maximum at the mid-plane but manageable for most polymers. Accordingly, a laminated composite made of hybrid fiber-reinforced shape memory photopolymer was developed, incorporating strong synthetic glass fibers over a weak core of natural hemp fibers. Even with a significant proportion of natural hemp fibers, the mechanical properties of the hybrid composites were close to those reinforced solely with glass fibers. The composites exhibited good shape memory properties, with at least 52% shape fixity ratio and 71% shape recovery ratio, and 24 MPa recovery stress. After 40 s burning, a hybrid composite still maintained 83.53% of its load carrying capacity. Therefore, in addition to largely maintaining the load carrying capacity through the hybrid reinforcement design, the use of shape memory photopolymer endowed a couple of new functionalities to the composites: the plastically deformed laminated composite beam can largely return to its original shape due to the shape memory effect of the polymer matrix, and the flame retardancy of the polymer matrix makes the flammable hemp fiber survive the fire hazard. The findings of this study present exciting prospects for utilizing low-strength and flammable natural fibers in multifunctional load-bearing composites that possess both flame retardancy and shape memory properties.

Effect of temperature on epoxy resin deterioration for fibre-reinforced polymer reinforcement in simulated concrete pore solutions

Fibre-reinforced polymer (FRP) tendons have excellent mechanical properties and corrosion resistance and are widely used in concrete structures; however, corrosion deterioration of FRP tendons is a serious problem in a highly alkaline concrete environment owing to the hygrothermal ageing effect of the resin. Accordingly, this study investigated the macro and micro properties evolution of epoxy resin in a simulated concrete pore solution at different temperatures. The results showed that the resin properties deteriorated significantly under long-term hygrothermal immersion. However, short-term high-temperature soaking caused some of the resin to undergo post-curing, improving its properties.

The Isolation and Characterization of Cellulose Nano crystals from Baobab Pod Fibres using Acid Hydrolysis

In this research, cellulose nanocrystals were isolated from locally grown baobab pod fibres. Fibres were treated chemically using NaOH and then hydrolysed using Nitric acid. The effect of NaOH treatment and acid hydrolysis on surface morphology, crystallinity, and thermal properties of fibres were investigated using Fourier Transform Infrared (FTIR), Scanning electron microscopy/Energy dispersive X-ray spectroscopy (SEM/EDS), X-ray Diffraction(XRD) and Thermogravimetric analysis (TGA/DTA). From the results evaluated, cellulose content of 17.9 % was recorded after NaOH treatment and 25.3 % was recorded after acid hydrolysis, the crystallite size was found to be 3.003 nm and thermal stability of the fibre was enhanced after chemical treatment and acid hydrolysis. Based on the results obtained, it shows that nanocellulose hydrolyzed from baobab pod fibres has excellent properties for use as polymer reinforcement and for other engineering applications.

Investigation of single and multicell honeycomb reinforced shape memory polymer composites: Shape optimization and experimental characterization

Honeycomb materials as reinforcements for shape memory polymers have been considered for their commercial availability, ease of geometric tailoring, and high in-plane stiffnesses. The design optimization of these honeycomb cells remains an open field of research, with many approaches taken in formulating the structural optimization problems. This investigation focuses on implementing a shape variable parametrization of the honeycomb to study the possible value of both cell asymmetry and spatially varying cell geometries in multicell networks. A unit cell finite element model framework was developed to predict the in-plane elastic properties of these composites, and two design objectives were selected to be optimized. Pareto fronts were estimated for multiple loading cases and cell wall material models, and experimental results were collected for model validation. The optimization results find that these composites can achieve a large range of performances, with maximum moduli as high as 17.2 GPa. Large asymmetry is found in the optimized cell geometries, and relationships are identified between loading cases and for different wall materials. Furthermore, the experimental results validate the finite element model predictions, with relative errors as low as 20% for the predicted maximum modulus and 2% for the modulus ratio.

Ultrasensitive Catechol Detection via Core-Shell Nanofibers: Effect of Type of Conducting Polymer and MWCNT Reinforcement

The detection of phenols is one of the main research directions due to impact of phenols on human life. Herein, novel biosensing matrices based on pristine and composite (including MWCNTs) electrospun nanofibers coated with conducting polymers (poly(3,4-ethylenedioxythiphene (PEDOT) or polypyrrole (PPy)) were employed for immobilization of Tyrosinase enzyme and further evaluated for phenol detection. The current study is meant to provide a comparison between the two conducting polymers in terms of electron transfer and biocompatibility with the chosen enzyme, as resulted from analytical characterization of the biosensor and analysis of Michaelis-Menten behaviour. The developed biosensors (Pt/PAN(-MWCNTs)/PEDOT NFs/PPO and Pt/PAN(-MWCNTs)/PPy NFs/PPO) displayed high sensitivity values of 6846.83 and 10364 μA mM−1.cm−2 within linear ranges of 5.0 − 1.0 × 10−5 and 5.0 − 1.0 × 10−7 M, with limit of detection values in the nanomolar range (1.14 and 4.04 × 10−7 M) depending on the polymer employed (PEDOT and PPy, respectively). Given the nanostructured conducting matrix based on the synergistic effect between MWCNTs and CPs and the principle of detection employed, the analytical parameters of the current study are competent in catechol detection. In addition, the platform screened possible interferences allowing accurate detection of trace amounts of phenolics in spiked water samples.

Influence of seawater and sea sand on early-age performance and cracking sensitivity of concrete

Due to resource constraints, there has been a growing demand for alternative sources of water and sand in construction engineering. Recent advancements in technology, such as the use of fiber-reinforced polymers (FRP) reinforcement or impressed current cathodic protection-structural strengthening (ICCP-SS), have enabled the utilization of seawater and sea sand, garnering significant research attention. The study investigated various aspects of four types of early-age concrete based on the temperature stress testing machine (TSTM) method, including fresh properties, basic mechanical properties, hydration temperature history, restraint stress, autogenous shrinkage, creep, and cracking sensitivity. The results showed that seawater significantly increased the early tensile strength of concrete, while sea sand had the opposite effect. Compared with ordinary concrete, seawater and sea sand increased the early autogenous shrinkage of concrete, and the impact of seawater was more significant. For the early creep of concrete, seawater and sea sand reduced the maximum compressive creep of concrete, and the effect of sea sand was more remarkable. Seawater increased the tensile creep of concrete, while sea sand decreased the tensile creep of concrete. The comprehensive evaluation index indicates that seawater and sea sand have no significant effect on concrete's cracking sensitivity. This research may serve as a valuable reference for the use of seawater and sea sand in concrete.

Three-dimensional reliability stability analysis of earth-rock dam slopes reinforced with permeable polymer

Polymer is a new repair and reinforcement material for earth-rock dams developed in recent years. Models are developed where spatial variability is incorporated into the analytical framework to evaluate the stability and reliability of reinforced three-dimensional dam slopes. The Karhunen-Loeve (K-L) expansion method is employed to generate three-dimensional random fields. The simplified Bishop method and Monte Carlo method are used to calculate the safety factors and failure probabilities of the dam slopes. With the implementation of polymer grouting reinforcement, the safety factors are improved and the failure probabilities are reduced. The reinforcement effect will be affected by the amount of polymer dosing, dam slope characteristics, and polymer grouting parameters. The impact of various longitudinal autocorrelation distances on reliability is influenced by the length of the dam slope itself. An increase of the safety factor by approximately 37% can be achieved through a polymer dosing of around 3%. Nevertheless, with the elevation of dam slope height and slope ratio, the effectiveness of polymer reinforcement is diminished.

Deformation-dependent electrical resistivity of fiber-reinforced nanocomposites: A concentric cylindrical model approach

Fiber-reinforced composites have seen growing demands and widespread use in a variety of fields, including aviation, civil engineering, and the automobile industry. Fiber-reinforced composites must be monitored by nondestructive methods because of their tendency to have complicated and often visually undetectable failure mechanisms. Incorporating self-sensing capabilities into composites through nanofiller modification to leverage the piezoresistive effect is one approach for monitoring these materials. In this method, electrical resistivity is a function of mechanical strains, allowing for intrinsic self-sensing. To date, predictive modeling efforts in this field have mostly concentrated on microscale piezoresistivity. Research on modeling resistivity changes in macroscale fiber–matrix material systems has been limited, and even less research has been conducted to evaluate the impact of continuous fiber reinforcement. To bridge this gap, an analytical model that predicts changes in the resistivity of a material system with nanofiller-modified polymer and continuous fiber reinforcement is proposed. The cornerstone of this strategy is the establishment of an electrical concentric cylindrical model. We begin by defining our domain, which consists of concentric cylinders representing a continuous reinforcing fiber surrounded by a nanofiller-modified matrix. Next, the system is homogenized such that we can predict the change in the axial and transverse resistivity of the concentric cylinders. It is envisaged that the results herein presented will serve as a stepping stone towards the creation of a laminate theory of piezoresistivity.

Development of multi-fiber approach finite element model for reinforced concrete beam using frp reinforcements under pure torsion

A finite element model using a multi-fiber approach is proposed in this paper for the analysis of reinforced concrete (RC) members using fiber-reinforced polymer (FRP) reinforcements, with a specific focus on the effect of pure torsion. The proposed model is formulated using a displacement-based approach and a kinematic assumption involving a two-node Timoshenko beam. The compatibility and equilibrium between concrete and FRP materials in the membrane elements are formulated based on a discretization of the cross-section into several areas following its stress state and the principle of the Modified Compression Field Theory. The nonlinear responses of RC elements with FRP bars can be predicted using an appropriate constitutive material law with internal equilibrium of transverse reinforcement and concrete. The pure torsional response is implemented using an enhanced formulation of concrete's tensile behavior, which is based on experimental tests on torsion and the characteristics of FRP materials. The good agreement between the numerical results and experimental data confirms the validity of the proposed model

Mechanical Interlocking to Unlock the Reinforcing Potential of Carbon Nanotubes.

Single-walled carbon nanotubes (SWNTs) present extraordinary mechanical properties, with Youngs' modulus>1 TPa and tensile strength>50 GPa; this makes them ideal candidates as fillers for the reinforcement of polymers. However, the performance of SWNTs in this field has fallen behind expectations. This is due to a combination of imperfect individualization of the SWNTs and poor load transfer from the polymer to the SWNTs. Here, we study the reinforcement of polymers of different chemical nature using mechanically interlocked derivatives of single-walled carbon nanotubes (MINTs). We compare the mechanical properties of fibers made of poly (methyl methacrylate) (PMMA) and polysulfone (PSU) and their composites made with pristine SWNTs, MINTs, and the corresponding supramolecular models. With very low loading of MINTs (0.01 % w/w), improvements of more than 100 % on Youngs Modulus and the tensile strength are observed for both the nonpolar aliphatic PMMA and the very polar aromatic PSU polymers, while pristine carbon nanotubes and the supramolecular nanofillers showed smaller reinforcement. These data, together with our previous report on the reinforcement of polystyrene (nonpolar and aromatic), indicate that derivatization of SWNTs as MINTs is a valid general strategy to optimize the interaction between SWNT fillers and the polymer matrix.

Experimental study of novel wrapped CFRP-strengthened CFS-to-sheathing screw connections

Cracking damage of the sheathing wallboards in screw connections is the typical failure mode of cold formed steel (CFS) structures under seismic effects, which limits the shear capacity and weakens the hysteretic performance of CFS structures. To improve the shear performance of CFS-sheathing screw connections, a novel screw connection with carbon fiber reinforced polymer (CFRP) reinforcement is proposed in this paper. Cyclic tests were conducted on a total of 26 sets of screw connections with different configurations and wall sheathings, and the effects on the failure modes and shear performance of the connections with and without CFRP reinforcement were investigated. The strengthening effects of the sheathing material, panel thickness and end distance on the shear properties of the connections were discussed. The results indicated that (1) except for specimens with 15 mm end distance, CFRP reinforcement can effectively avoid brittle cracking failure of the connections, and the failure mode tended to ductile failure of the bearing and pull-through damage. (2) in addition to the stiffness, the shear strength, deformation capacity, ductility and energy dissipation capacity of CFRP-strengthened connections are significantly enhanced. The effect of CFRP on the shear performance improvement of connections sheathed with gypsum board (GWB) and magnesium glass board (MgO) is greater than that of oriented strand board (OSB), and the strengthening effect is not significantly influenced by the board thickness. A toughness evaluation method for CFRP-strengthened connections was proposed, and the design formulae for the shear strength of the CFRP-strengthened screw connections were recommended based on the load resistance factor design (LRFD) method and allowable strength design (ASD) method.