Types Of Fiber Reinforced Polymer Research Articles

Seismic performance of exterior RC beam-column junction strengthened with Stainless Steel Wire Mesh (SSWM)

Strengthening of concrete structures is necessary to enhance their performance in terms of serviceability and strength requirements as well as to increase the life span of the structure. In the past, different types of fiber-reinforced polymer (FRP) materials are widely employed for strengthening concrete structures. However, FRP-strengthened structural elements exhibit brittle failure as well as debonding of FRP strips or wraps. Due to debonding of FRP, its tensile strength is not fully utilized. To explore an alternative to FRP, Stainless Steel Wire Mesh (SSWM) is chosen in the present study. SSWM is a locally available material having lower tensile strength compared to FRP but having good bond characteristics with concrete and ductile behavior. The present study mainly focuses on experimental investigations to evaluate the behavior of beam-column junction strengthened using SSWM. In this experimental study, the performance of reinforced concrete beam-column junction is evaluated under cyclic loading. The reduced (one-third) scale test specimen representing an external beam-column junction of a 6-story regular moment resisting frame structure was tested under cyclic loading till its ultimate capacity. Subsequently, the damaged beam-column junction was strengthened using SSWM and its performance was again examined under cyclic loading. Minor cracks developed in the specimen were first filled with grout. Subsequently, epoxy-based adhesive SIKADUR 30 LP epoxy was used for bonding SSWM on the surface of the beam-column junction. The performance of test specimen was evaluated in terms of hysteretic response, displacement ductility, energy dissipation, degradation of stiffness, and failure modes of specimens. Results of experimental investigations show that SSWM effectively contributes to load resistance and enhances ultimate load carrying capacity and ductility of the beam-column junction without brittle or any significant debonding from concrete surface. Therefore, SSWM can be an economical alternative of FRP material for strengthening of concrete structures.

Experimental and Numerical Study on Seismic Performance of PEN FRP-Jacketed Circular RC Columns

This paper presents an experimental study on the seismic behavior of polyethylene naphthalate (PEN) fiber–reinforced polymer (FRP)-jacketed circular reinforced-concrete (RC) columns. A total of seven specimens were tested under constant axial load and cyclic lateral load. The key parameters studied were the thickness (one, two, and three layers) and type (PEN FRP and CFRP) of FRP jacket. Test results indicated that the control column failed by buckling of the longitudinal reinforcement and shortage of ductility, while concrete spalling and bar buckling were effectively inhibited by the application of external FRP jacket. It is also observed that PEN FRP-jacketed specimens had more additional strain capacity compared with CFRP-jacketed specimens at the final condition. The additional strain capacity can serve as a safety reserve for structures and make PEN FRP more suitable for strengthening large or noncircular columns. Furthermore, it is found that 1-ply PEN FRP and 1-ply CFRP had a similar strengthening effect and thus the design of PEN FRP-strengthened column can simply refer to the design method of CFRP-strengthened columns in current codes. Different FRP thickness and types had marginal impact on the hysteretic curves of the specimens, which was attributed to the low axial load ratio (0.15) and high slenderness ratio (5.25) adopted in this paper. Finally, based on a cyclic stress–strain model for longitudinal reinforcement, including buckling effect, developed by the authors in a previous study, the test columns were simulated by the Open System for Earthquake Engineering Simulation (OpenSee)s to achieve an in-depth understanding of the experimental findings and associated strengthening mechanisms. Further parametric analyses showed that considering bar buckling played a significant role in accurately predicting the hysteretic response of FRP-jacketed columns.

Effect of corroded reinforcement on capacity of square reinforced concrete columns confined with FRP sheets under eccentric loads

Steel corrosion is one of the primary causes which significantly degrade the load-carrying capacity and FRP (fibre reinforced polymer) strengthening efficiency of FRP-strengthened reinforced concrete columns under eccentric loading. However, this issue has not been studied comprehensively and systematically in the literature. Particularly, there has been no study on the strengthening efficiency of basalt FRP (BFRP) which is becoming popular due to its excellent performance and affordable price. This study experimentally investigates the effect of corrosion level of reinforcement by mass (0%, 15% and 30%), relative eccentricity (e/h = 0.125 and 0.375), type of FRP (CFRP and BFRP) and FRP thickness (1 or 3 layers) on the load-carrying capacity and deformation of corroded-reinforcement reinforced concrete (RC) columns. The experimental results showed that steel corrosion reduced the load-carrying capacity of the unstrengthened RC columns up to 23% and this degradation increased with the corrosion level. Both CFRP and BFRP have proven excellent strengthening efficiency since the capacity of the FRP-strengthened corroded-reinforcement RC columns increased up to 47%. Particularly, the strengthening efficiency of BFRP sheets was slightly lower than that of CFRP sheets (<7%). On the other hand, the increase of the relative eccentricity from e/h = 0.125 to e/h = 0.375 reduced the strengthening efficiency of FRP. In addition, a semi-empirical model was proposed to predict the capacity of corroded-reinforcement RC columns strengthened with FRP under eccentric loading. The predictions match well with the experimental results with a small coefficient of variation.

Axial compressive behavior of basalt and carbon FRP-confined coal gangue concrete

Coal gangue concrete (CGC), in which fine and coarse aggregates are completely replaced by coal gangue aggregates, has been limited to non-structural applications owing to its brittle structure, lower strength and stiffness. Nevertheless, the disadvantages of CGC can be minimized by external confinement of fiber-reinforced polymer (FRP) jacket. A total of 39 cylindrical specimens were studied under a monotonic axial compression test to understand the compressive behavior of FRP-confined CGC, considering the CGC strength, FRP layer number, basalt FRP (BFRP) and carbon FRP (CFRP) type as variables. The failure modes, stress–strain relationship, and dilation properties were analyzed in detail. The results indicate that the strength of the BFRP/CFRP-confined CGC was improved by 16.9%–145.8%, and the axial ultimate strain was 4.787–8.812 times that of the plain CGC. The stress–strain curve of the BFRP/CFRP-confined specimen exhibited a bilinear response, where the second portion showed a descending shape under weak confinement and an ascending branch under strong confinement, mainly depending on the FRP confining ratio. Additionally, the axial strain of the confined CGC is larger than that of the confined normal concrete when given the same lateral strain. Most importantly, the modified discriminative models and ultimate strength and strain models for BFRP/CFRP-confined CGC were proposed, providing a theoretical basis for its application in mines.

Seismic Retrofit of Nonuniformly Corroded Coastal Bridge Piers with FRP and Engineered Cementitious Composite Overlays

Coastal bridge piers are prone to corrosion attack owing to their exposure to marine environments, particularly in the splash and tidal zone, which is rich in chloride, oxygen, and moisture. Severe corrosion in this area results in the transfer of plastic hinges and evidently impairs the structural performance under seismic loading. Previous seismic retrofitting typically focused on the area of the pier end with the greatest bending moment. However, the location of the splash and tidal zone varies with the change in season and is generally not in the pier end. This study investigated for the first time the seismic retrofit of such piers using fiber-reinforced polymer (FRP) and engineered cementitious composite (ECC), where the middle part of the pier subjected to NaCl solution corrosion was simulated as the splash and tidal zone. Reversed cyclic loading tests of nine bridge piers with various corrosion rates, FRP types, and retrofit areas were performed. The seismic behaviors in terms of failure mode, crack pattern, load-carrying capacity, ductility, energy dissipation capacity, and stiffness degradation were compared and discussed. The experimental results of mildly corroded specimens indicated that seismic retrofitting with combined FRP and ECC significantly improved the seismic performance of bridge piers. The retrofitted specimen exhibited an even higher ductility and energy dissipation capacity than the noncorroded specimen. For severely corroded piers, the plastic hinge was transferred from the pier end to the corroded area and then transferred back to the pier end after retrofitting. The seismic performance of the specimens retrofitted from the corroded area to the foundation was better than that of the piers retrofitted only in the corroded area.

Evaluation of a climbing drum laminate peel test to determine the interlaminar mode I fracture toughness of thin CFRP laminates—Comparison with the standard mode I DCB test and a mandrel laminate peel test proposed by ESIS TC4

A recently proposed mandrel laminate peel (MLP) test for quantification of delamination propagation in Fiber-Reinforced Polymer (FRP) composites is compared with a climbing drum laminate peel (CDLP) test, and the standard quasi-static Mode I fracture test with Double Cantilever Beam (DCB) specimens. MLP and CDLP both are applicable to thin laminates, for which the Mode I DCB test is not suitable. MLP and CDLP, however, do not yield delamination initiation values. Delamination propagation resistances from the three tests performed with different types of FRP, one partly and one fully cured epoxy laminate, and one thermoplastic laminate, all with unidirectional fiber lay-up agree within about 20%. Reduction of the diameter of the climbing drum (100 mm for the standard climbing drum peel test for adhesives) indicates a minimum diameter on the order of 50 mm for the CDLP test. Additional tests with selected laminates investigated potential effects of specimen width. It is concluded that FRP laminate specimens 20 mm wide and 180 mm long are sufficient for consistent results from CDLP and MLP tests. The CDLP test yielded less scatter (around 10%), i.e., better repeatability than the MLP (round 13%) and the Mode I DCB test (around 17%). Hence, the CDLP test is considered advantageous for industrial application, also due to the simplicity of the test set-up and of the data analysis.

Flexural Response of Concrete Beams Reinforced with Steel and Fiber Reinforced Polymers

This paper numerically investigates the flexural response of concrete beams reinforced with steel and four types of Fiber-Reinforced Polymers (FRP), i.e., Carbon FRP (CFRP), Glass FRP (GFRP), Aramid FRP (AFRP), and Basalt FRP (BFRP). The flexural responses of forty beams with two boundary conditions (simply supported and over-hanging beams) were determined using ABAQUS. Subsequently, the finite element models were validated using experimental results. Eventually, the impact of the reinforcement ratios ranging between 0.15% and 0.60% on the flexural capacity, crack pattern, and fracture energy were investigated for all beams. The results revealed that, for the low reinforcement ratios, the flexural performance of CFRP significantly surpassed that of steel and other FRP types. As the reinforcement ratio reached 0.60%, the steel bars exhibited the best flexural performance.

Reinforced Concrete Beams Strengthened with Externally Bonded Hybrid FRP Sheets

Fiber Reinforced Polymer (FRP) is commonly used in structural repair and strengthening due to its high tensile strength, non-corrosive and lightweight. On the other side FRP is relatively brittle compared to steel. This study used hybrid FRP consisting of GFRP and CFRP, by combining two type of FRP with different characteristic it is to be expected that the more brittle FRP will fail first followed by the more elastic one, therefore creating a sequential failure. However CFRP have a higher tensile strength in comparison to GFRP, therefore it’s necessary to reduce its tensile strength by reducing its volume. This study is divided into two topics, hybrid FRP tensile strength test and beam flexural test. For the hybrid FRP tensile strength test, a total of three variation of hybrid FRP will be compared (GC30, GC40, and GC50). The variation that shown a sequential failure behaviour, will then be applied to a reinforced concrete beam and tested under monotonic point load device. The test result shown that sequential failure occur on GC30 and GC40. However GC40 had a higher ultimate load at 24.86 kN. For the beam flexural test, there will be two variation, i.e. control beam (CB) and beam strengthened with hybrid FRP (BGC). When compared, BGC had a 40.0% increase in yield strength and 55.43% increase for ultimate load.

FAI: Fast, accurate, and intelligent approach and prediction tool for flexural capacity of FRP-RC beams based on super-learner machine learning model

Fiber-reinforced polymer (FRP) composites have recently been considered in the field of structural engineering as one of the best alternatives to conventional steel reinforcement due to their high tensile strength, lightweight, cost-effectiveness, and superior corrosion resistance. However, the variation in FRP physical and mechanical characteristics among the different FRP types and manufacturers makes it difficult to predict the strength of FRP-reinforced concrete (RC) members. For that reason, an efficient prediction tool was developed for a fast, accurate, and intelligent (FAI) prediction of the flexural capacity of FRP-RC beams based on the result of an optimized super-learner machine learning (ML) model. A database of the experimental results on the flexural strength of FRP-RC beams was compiled and randomly split into 80% training and 20% test sets. Six factors were considered in the model; namely, width and effective depth of the beam, concrete compressive strength, FRP flexural reinforcement ratio, FRP modulus of elasticity, and FRP ultimate tensile strength. Grid search is combined with a 10-fold cross-validation to optimize the hyperparameters of the ML models. The prediction capability of the proposed super-learner ML model was benchmarked against boosting- and tree-based ML models, such as classification and regression trees, adaptive boosting, gradient boosted decision trees, and extreme gradient boosting. Moreover, a comparison with the existing code and guideline equations showed that the proposed super-learner ML model provided the most desirable prediction of the flexural capacity of FRP-RC beams.

Performance of damaged concrete stub columns strengthened with post-tensioned CFRP under freezing-thawing environment

Reinforced concrete structure with directly bonded fiber reinforced polymer (FRP) on the surface showed obvious stress hysteresis under load, which caused that the strengthening materials cannot be fully utilized. The strengthening system formed by carbon fiber reinforced polymer (CFRP) and shrinkage compensating self-consolidating concrete (ESCC) applied posttensioning stress to the external CFRP shell as a stay-in-place strengthening method, which eliminated stress hysteresis and exerted the restraint effect immediately after being loaded. This paper explored whether this method can be applied to concrete compression members damaged by freeze–thaw environment and its effect. Experimental variables include the number of freezing-thawing cycles, FRP shell plies and types of strengthening concrete. The experimental results showed that the damage of concrete under freezing-thawing environment was an incremental process: the dynamic elastic modulus loss rate and the mass loss rate of specimens damaged by 50 freeze–thaw cycles were 5.9% and 0.4%, respectively. When the freezing-thawing cycles reached 125, the dynamic elastic modulus loss of concrete compression members reached 24.8% and the mass loss rate was 5.3%. Compared with concrete compression specimens after 125 freeze–thaw cycles, the load capacity of specimens strengthened with single-ply and double-ply CFRP were increased by 63.1% and 114.1% respectively, which fully compensated the damage caused by freeze–thaw cycles. It was indicated that when single-ply CFRP was used for strengthening, ordinary self-consolidating concrete specimens exhibited higher hoop strain and less loss of ultimate load capacity than ESCC. When two-ply CFRP was used for strengthening, concrete compression members strengthened with ESCC showed higher strength and less loss of ultimate load-bearing capacity than specimens strengthened with ordinary self-consolidating concrete (SCC). With the increase of freezing-thawing cycles, the normalized inflection stress, intercept stress as well as ductility coefficient of strengthened specimens showed decreasing trend. The theoretical value of normalized peak stress and corrected strain were in good agreement with experimental value and it shows that the maximum error were 10.74% and 24.88%, respectively

Experimental and theoretical investigation of FRP-steel composite plate under cyclic tensile loading

As the basic element of fiber-reinforced polymer (FRP) strengthened steel structures, FRP-steel composite plate (FSP) is a type of superior composite plate that combines the advantages of steel and FRP. This study combines different types of FRP and steel plates to develop an FSP element. Cyclic tensile tests are conducted to investigate the hysteretic behavior of the FSP, and the yield strength, peak strength, initial stiffness, post-yield stiffness, and residual deformation are analyzed. The experimental results indicate that the stress–strain curves of the FSP are bilinear prior to the fracture of the FRP, and the FSP exhibits a more stable post-yield stiffness and smaller residual deformation than a steel plate, which endows structures with better repairability after an earthquake. A finite element model (FEM) is established to investigate the mechanical behavior and failure process and is validated using experimental results. In addition, a theoretical model based on the composite material superposition theory is proposed and verified to simulate the stress–strain restoring force curves of FSP under cyclic tensile loading. The FEM and theoretical models can guide the practical design of FRP strengthened steel structures.

Study on the Impact Resistance of FRP Pasted onto a Blastproof Partition Wall under Out-of-Plane Repeated Impact Load

A blastproof partition wall in civil air defense engineering is easily subjected to out-of-plane impact loads, such as object impacts, and structural collapse in peacetime. In this study, the pendulum impact test was carried out for the first time on six blastproof partition walls pasted with fiber-reinforced polymer (FRP). Using a method combining finite element simulation and experimental research, the influence of parameters such as the FRP type, layer number and width, and pendulum impact number on the impact resistance of the wall was systematically studied. The test results show that pasting FRP on the back of the blastproof partition wall can significantly improve the impact resistance and reduce the damage degree of the concrete. The impact recovery coefficient increased from 0.33 to 0.57, but with the increase in the number of impacts, large-rupture-strain FRP (LRS-FRP) can give full play to the advantages of a large tensile fracture strain and cooperate with the wall to deform, and the selection of FRP with a large tensile fracture strain is the key to resisting multiple impact loads. Finally, the experimental basis and an economical and reliable protection method are provided for the study of improving the impact resistance of the blastproof partition wall.

Axial Compression Behavior of FRP Confined Laminated Timber Columns under Cyclic Loadings

Fiber reinforced polymer (FRP) has been proved to be effective to improve the structural strength and ductility for column structures. An experimental study was conducted to investigate the compressive performance of FRP confined glued-laminated timber (GLT) and cross-laminated timber (CLT) columns. A total of 60 column specimens of two dimensions in height using different FRP types, FRP thickness, and laminate types were tested under cyclic axial compression loads. This study focuses on the compressive capacity and ductility of the new FRP composited timber structure. For this purpose, a loading protocol was designed, including a force-dependent pre-load and an amplitude-increasing displacement-dependent cyclic compression load. The results showed that the ultimate compression load of specimens was considerably promoted by the FRP sheets. Wrapping FRP sheets led to an average improvement of 29% and 24% for the FRP confined CLT and GLT specimens, respectively, compared to the initial stiffness of unreinforced specimens. Using the FRP sheets, the energy dissipation capacity of CLT and GLT specimens was increased by 358% and 266%, respectively. In general, GLT specimens had a higher energy dissipation rate compared to the CLT specimens, while CLT specimens showed a better potential for sustained energy consumption if confined with sufficient FRP sheets.

An Analysis of the Transfer Lengths of Different Types of Prestressed Fiber-Reinforced Polymer Reinforcement.

The main aim of this paper is to provide a broader analysis of the transfer lengths of different types of fiber-reinforced polymers (FRPs) and to provide corrections to the existing theoretical models. Therefore, this paper presents a description of the main factors that influence the transfer lengths of different types of FRPs based on experimental results found in the literature. A database of more than 300 specimens was compiled with the results of the transfer lengths of different FRPs and the main influencing parameters. The analysis of the database results showed that the transfer length of the carbon fiber composite cable (CFCC) strands depends on the type of prestressed reinforcement release. Therefore, in this article, the new coefficient αt = 2.4 is proposed for the transfer length of suddenly released CFCC strands. Additionally, the transfer length of the aramid fiber reinforced polymer (AFRP) depends on its surface conditions. Therefore, new coefficients αt = 1.5 and αt = 4.0 are also proposed for the transfer lengths of smooth braided and sanded and rough AFRP bars, respectively. Furthermore, the proposed coefficients αt = 2.6, αt = 1.9, and αt = 4.8 found in the literature were validated with the analysis of a larger database of the transfer lengths of glass fiber-reinforced polymer (GFRP) bars, carbon fiber-reinforced polymer (CFRP) bars, and gradually released CFCC strands, respectively. Moreover, the main existing theoretical models are presented, and the comparison of theoretical and experimental transfer length results is discussed. However, the low number of specimens prestressed with basalt fiber-reinforced polymer (BFRP) bars prevented the deeper analysis of the results. the analysis of the transfer length and the proposed new values of the coefficient αt provides possibilities for adapting it to design codes for engineering applications and performing additional research that fills the missing gaps in the field.

Finite Element Simulation of FRP-Strengthened Thin RC Slabs

This study aims to investigate the flexural behavior of high-strength thin slabs externally strengthened with fiber-reinforced polymer (FRP) laminates through a numerical simulation. A three-dimensional (3D) finite element (FE) model is created to simulate the response of strengthened reinforced concrete (RC) slabs under a four-point bending test. The numerical model results in terms of load-deflection behavior, and ultimate loads are verified using previously published experimental data in the literature. The numerical results show a good agreement with the experimental results. The FE model is then employed in a parametric study to inspect the effect of concrete compressive strength on the performance of RC thin slabs strengthened with different FRP types, namely carbon fiber-reinforced polymers (CFRP), polyethylene terephthalate fiber-reinforced polymers (PET-FRP), basalt fiber-reinforced polymers (BFRP) and glass fiber-reinforced polymers (GFRP). The results showed that the highest strength enhancement was obtained by the slab that was strengthened by CFRP sheets. Slabs that were strengthened with other types of FRP sheets showed an almost similar flexural capacity. The effect of concrete compressive strength on the flexural behavior of the strengthened slabs was moderate, with the highest effect being a 15% increase in the ultimate load between two consecutive values of compressive strength, occurring in the CFRP-strengthened slabs. It can thus be concluded that the developed FE model could be used as a platform to predict the behavior of reinforced concrete slabs when strengthened with different types of FRP composites. It can also be concluded that the modulus of elasticity of the composite plays a major role in determining the flexural capacity of the strengthened slabs.

Size effect on compressive behavior of FRP-confined engineered cementitious composites (ECC)

• A first-ever experimental study on the size effect of GFRP- and LRS FRP-confined ECC columns was conducted. • The influences of specimen size, FRP confinement level, and FRP type were examined. • A new size-dependent ultimate stress model of FRP-confined ECC was established. The reliable design of the high-performance column made of fiber reinforced polymer (FRP)-confined engineered cementitious composites (ECC) necessitates a clear understanding of the size effect under axial compression. This paper presents the compressive behaviors of glass FRP (GFRP) and large rupture strain (LRS) polyethylene terephthalate (PET) FRP-confined ECC columns. The specimen size, confinement level, and FRP type were the variables. Five diameters of 100, 200, 300, 400, and 500 mm were designed to cover a wide size range. Results showed that both the compressive strength and ductility of ECC were substantially improved with FRP confinement. Compared with GFRP-confined ECC, PET FRP-confined ECC exhibited higher ductility. The key stresses, namely initial peak stress, post-peak ravine stress, and ultimate stress decreased with increasing specimen size. Nevertheless, the specimen size had a marginal influence on the key strains and dilation behavior. After evaluating the existing size-dependent ultimate strength models of FRP-confined concrete, a new expression for predicting the ultimate strength of FRP-confined ECC was introduced, which was shown to fit well with the test results.

Compressive behavior degradation of FRP-confined RC columns exposed to a chlorine environment

Fiber-reinforced polymer (FRP) has been recognized as a promising method for strengthening reinforced concrete (RC) structures under a chlorine environment; however, it cannot prevent steel reinforcements from chloride-induced corrosion. Thus, the main objectives of this study were to (1) investigate the corrosion-induced performance degradation in FRP-confined RC columns under axial compression; (2) quantity the reduction of FRP rupture strain in FRP-confined RC columns subjected to a chlorine environment; and (3) propose a formula to estimate the load carrying capacity of FRP-confined RC columns considering the corrosion ratio. Twenty-eight columns with different FRP types (carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP)) and different layers of FRP (0, 1, 2, and 3) were conditioned under an accelerated corrosion process to obtain various corrosion ratios (0%, 5%, 10%, and 20%) and then tested under axial compression. The results showed that steel corrosion degraded the compressive response of FRP-confined RC columns, especially their deformation capacity. GFRP-confined RC columns generally had a better deformation capacity and were less vulnerable to steel corrosion than were CFRP-confined RC columns. Based on these test results, predictive equations for estimating the rupture strain of FRP were proposed as a function of corrosion ratio, which was introduced to modify an existing strength model of concrete confined with both FRP and steel stirrups. Finally, the ultimate load of FRP-confined RC columns with or without corrosion was predicted based on the modified concrete strength model.

Investigation on shear behavior of reinforced concrete deep beams without shear reinforcement strengthened with fiber reinforced polymers

Shear failure is an undesirable type of failure in terms of structural safety. Particularly, reinforced concrete (RC) deep beams without shear reinforcement are vulnurable to shear failure. In order to improve the shear behavior of such beams, externally bonded (EB) fiber reinforced polymer (FRP) as a strengthening technique is being applied to the outer part of the beams. However, investigations on the shear behavior of deep beams without shear reinforcement strengthened with FRP materials are insufficient in the literature. Therefore, a comprehensive experimental study was carried out on RC deep beams without shear reinforcements strengthened with fully wrapped FRP strips. The experimental parameters were chosen as the shear span-to-effective depth ratio (av/d), the number of carbon layers, the span length between carbon strips, and the type of FRP. A total of sixteen deep beams, four of which were reference beams, were fabricated and tested under three point bending load until failure. According to the experimental results, the gain percentage both in the shear and deflection capacities of strengthened deep beams increased with the av/d. Additionally, the failure modes and crack patterns of strengthened deep beams were different from those of the reference beams. Moreover, all test parameters affected the ductility behavior of deep beams having av/d of 1.5 and 2 positively. A comparative study was also conducted employing the methods commonly used in the literature and the methods based on the strut and tie model. It was observed that the methods based on strut and tie model provided superior estimates over the models commonly used in the literature.

Vehicular Impact Resistance of FRP-Strengthened RC Bridge Pier

As-built bridge piers are likely to be subjected to vehicular collisions, causing severe damage to the bridge substructure and even resulting in the collapse of the entire bridge. This study aimed to evaluate the effectiveness of fiber-reinforced polymer (FRP) strengthening in enhancing the vehicular impact resistance of as-built bridge piers. A typical local, refined finite-element (FE) model of a simply supported two-span, double-column, reinforced-concrete (RC) bridge was established. The adopted material constitutive models and the FE analytical approaches were then validated through reduced vehicle model lateral impact tests on bare and carbon fiber–reinforced polymer (CFRP)-strengthened RC columns. The effective schemes for FRP strengthening of bridge piers against vehicle impact are discussed from the aspects of fiber orientation, number of layers, and strengthened height as well as by FRP type. Based on the FRP strengthening scheme, 48 vehicle–bridge collision scenarios were designed to evaluate the collapse of bridges with/without FRP-strengthened piers. It was found that (1) external FRP wrapping can effectively enhance vehicular impact-resistance of as-built bridge piers (e.g., reducing the degree of damage and deformation of the impacted pier); (2) for typical bridge piers, the effective strengthening scheme comprised a fiber orientation of 0° in reference to the circumferential direction, a 3-m strengthened height, and four-layer CFRP wrapping; (3) compared with bare bridge piers, FRP-strengthened piers could improve the vehicular impact-resistant safety redundancy of as-built bridges and, to some extent, avoid bridge collapses under truck collisions at high speed. Furthermore, through introducing the dynamic increase factors of concrete strength, reinforcement rebars, and FRP, and considering the nonuniform distributions of the strain rate of FRP-strengthened bridge piers caused by vehicular collision, the dynamic shear capacity of strengthened bridge pier was formulated.

Preliminary Study on the Behaviour of Fibre-Reinforced Polymer Piles in Sandy Soils

Fibre-reinforced polymer (FRP) is a type of composite material used to provide resistance to corrosion when incorporated into piles. However, there is a gap in knowledge in terms of the behaviour of FRP piles under axial or lateral loading in soils. Thus, the aim of this experimental study is to assess the factors that influence the behaviour of FRPs under axial and lateral load in sandy soil. CFRP (carbon-fibre-reinforced polymer) and GFRP (glass-fibre-reinforced polymer) piles were tested in this experiment based on a special pressure chamber. The results show that the surface roughness (Rt), confined pressure (σc), and relative density (Dr) determined the shearing resistance of the soils and subsequently affected the bearing capacity of the FRP piles under an axial load. The flexural stiffness of the FRP piles was determined by the FRP type, pile dimeter, and aging in the environment, which were affected under the lateral load. In addition, an alkaline environment was more aggressive to the FRP piles than those aged in an acidic environment. The numerical modelling results show that the sand types, in terms of the dilation angle and Young’s modulus, also had a great influence on the behaviour. This feature should be considered more carefully in future studies.