Showing papers in "Journal of Composites for Construction in 2009"

Refinement of a design-oriented stress-strain model for FRP-confined concrete

Abstract: This paper presents the results of a recent study conducted to refine the design-oriented stress–strain model originally proposed by Lam and Teng for fiber-reinforced polymer (FRP)-confined concrete under axial compression. More accurate expressions for the ultimate axial strain and the compressive strength are proposed for use in this model. These new expressions are based on results from recent tests conducted by the writers’ group under well-defined conditions and on results from a parametric study using an accurate analysis-oriented stress–strain model for FRP-confined concrete. They allow the effects of confinement stiffness and the jacket strain capacity to be separately reflected and accounts for the effect of confinement stiffness explicitly instead of having it reflected only through the confinement ratio. The new expressions can be easily incorporated into Lam and Teng’s model for more accurate predictions. Based on these new expressions, two modified versions of Lam and Teng’s model are present...

Flexural Behavior of Concrete Beams Reinforced with Hybrid (GFRP and Steel) Bars

Abstract: Reinforcing concrete with a combination of steel and glass fiber-reinforced polymer (GFRP) bars promises favorable strength, serviceability, and durability. To verify its promise and to support design of concrete structures with this hybrid type of reinforcement, we have experimentally and theoretically investigated the load-deflection behavior of concrete beams reinforced with hybrid GFRP and steel bars. Eight beams, including two control beams reinforced with only steel or only GFRP bars, were tested. The amount of reinforcement and the ratio of GFRP to steel were the main parameters investigated. Hybrid GFRP/steel-reinforced concrete beams with normal effective reinforcement ratios exhibited good ductility, serviceability, and load carrying capacity. Comparisons between the experimental results and the predictions from theoretical analysis showed that the models we adopted could adequately predict the load carrying capacity, deflection, and crack width of hybrid GFRP/steel-reinforced concrete beams.

Durability of GFRP Reinforcing Bars Embedded in Moist Concrete

Abstract: This paper presents mechanical, microstructural, and physical characterization of glass fiber-reinforced polymer GFRP bars exposed to concrete environment. GFRP bars were embedded in concrete and exposed to tap water at 23, 40, and 50°C to accelerate the effect of the concrete environment. The measured tensile strengths of the bars before and after exposure were considered as a measure of the durability performance of the specimens and were used for long-term properties prediction based on the Arrhenius theory. In addition, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy were used to characterize the aging effect on the GFRP reinforcing bars. The results showed that the durability of mortar-wrapped GFRP bars and exposed to tap water was less affected by accelerated aging than the bars exposed to simulated pore-water solution. These results confirmed that the concerns about the durability of GFRP bars in concrete, based on simulated laboratory studies in alkaline solutions, do not properly correspond to the actual service life in concrete environments.

Textile-reinforced mortar versus FRP jacketing in seismic retrofitting of RC columns with continuous or lap-spliced deformed bars

Abstract: The effectiveness of a new structural material, namely, textile-reinforced mortar (TRM), was investigated experimentally in this study as a means of confining oldtype reinforced concrete (RC) columns with limited capacity due to bar buckling or due to bond failure at lap splice regions. Comparisons with equal stiffness and strength fiber-reinforced polymer (FRP) jackets allow for the evaluation of the effectiveness of TRM versus FRP. Tests were carried out on nearly full scale nonseismically detailed RC columns subjected to cyclic uniaxial flexure under constant axial load. Ten cantilevertype specimens with either continuous or lap-spliced deformed longitudinal reinforcement at the floor level were constructed and tested. Experimental results indicated that TRM jacketing is quite effective as a means of increasing the cyclic deformation capacity of oldtype RC columns with poor detailing, by delaying bar buckling and by preventing splitting bond failures in columns with lap-spliced bars. Compared with thei...

Shear strengthening of concrete structures with the use of mineral-based composites

Abstract: Rehabilitation and strengthening of concrete structures have become more common during the last 10–15 years , partly due to a large stock of old structures and partly due to concrete deterioration. Also factors such as lack of understanding and the consequences of chloride attack affect the need for rehabilitation. In addition, more traffic and heavier loads lead to the need for upgrading. Existing externally bonded strengthening systems using fiber-reinforced polymers (FRP) and epoxy as bonding agents have been proven to be a good approach to repair and strengthen concrete structures. However, the use of epoxy bonding agents has some disadvantages in the form of incompatibilities with the base concrete. It is, therefore, of interest to substitute epoxy with systems that have better compatibility properties with the base concrete, for example, cementitious bonding agents. This paper presents a study on reinforced concrete beams strengthened in shear with the use of cementitious bonding agents and carbon f...

Experimental and Computational Studies on High-Strength Concrete Circular Columns Confined by Aramid Fiber-Reinforced Polymer Sheets

Abstract: The aim of this paper is to study the properties of high-strength concrete HSC circular columns confined by aramid fiber-reinforced polymer AFRP sheets under axial compression. A total of 60 specimens were tested, considering the following param- eters: the compressive strength of concrete, the number of AFRP layers, and the form of AFRP wrapping. In addition, an analytical model for predicting the stress-strain curves is proposed based on the experimental results. Meanwhile, a three-dimensional nonlinear finite- element model with a Drucker-Prager plasticity model for the concrete core and an elastic model for the AFRP is developed by using the finite-element code ANSYS. It is demonstrated that the strength and ductility of the columns with continuous AFRP wrapping are increased greatly; whereas the strength of the columns with discontinuous AFRP wrapping is also increased, but the ductility is not always increased notably. The analytical model and the finite-element model are validated against the experimental results.

Normal- and High-Strength Concrete Circular Elements Wrapped with FRP Composites

Abstract: Reinforced concrete columns usually have a minimum amount of transverse steel reinforcement this transverse reinforcement can have non negligible effects on the response of columns retrofitted with fiber-reinforced polymers (FRP). This paper presents a test program that was designed to study the behavior of small- and large-scale normal- and high-strength concrete circular columns confined with transverse steel reinforcement, FRP, and both transverse steel reinforcement and FRP under concentric loading. The effect of the main variables—such as the unconfined concrete strength, the volumetric ratio, the type and the yield strength of the transverse steel reinforcement, the concrete cover, and the number of FRP layers—are studied in this research program. The test results show that the enhancement of the confined concrete strength and strain is more pronounced in specimens with normal-strength concrete. It is also shown that the rupture of the FRP in the specimens with higher volumetric transverse steel rei...

Strengthening of Eccentrically Loaded Reinforced Concrete Columns with Fiber-Reinforced Polymer Wrapping System: Experimental Investigation and Analytical Modeling

Abstract: This paper presents the results of experimental program and analytical modeling for performance evaluation of a fiber-reinforced polymer (FRP) wrapping system to upgrade eccentrically loaded reinforced concrete (RC) columns. A total of 12 RC columns with end corbels were tested. The test specimen had an overall length of 1,200 mm . Each end corbel had a cross section of 250×250 mm and a length of 350 mm . The specimen in the test region was 125×125 mm having a longitudinal steel ratio of 1.9%. Test parameters included confinement condition (no wrapping, full FRP wrapping, and partial FRP wrapping), and eccentricity-to-section height (e∕h) ratio (0.3, 0.43, 0.57, and 0.86). Research findings indicated that the strength gain caused by FRP wrapping decreased as e∕h was increased. Full FRP wrapping resulted in about 37% enhancement in compression strength at a nominal e∕h of 0.3, whereas only 3% strength gain was recorded at a nominal e∕h of 0.86. The compression strengths of the partially wrapped columns wer...

Slender Steel Columns Strengthened Using High-Modulus CFRP Plates for Buckling Control

Abstract: This paper presents the results of an experimental investigation into the behavior of slender steel columns strengthened using high-modulus (313 GPa) , carbon fiber-reinforced polymer (CFRP) plates. Eighteen slender hollow structural section square column specimens, 44×44×3.2 mm , were concentrically loaded to failure. The effectiveness of CFRP was evaluated for different slenderness ratios (kL∕r) , namely, 46, 70, and 93. The maximum increases in ultimate load ranged from 6 to 71% and axial stiffness ranged from 10 to 17%, respectively, depending on kL∕r . As kL∕r reduced, the effectiveness of CFRP plates also reduced, and failure mode changed from CFRP plate crushing after occurrence of overall buckling, to debonding prior to, or just at, buckling. A simplified analytical model is proposed to predict the ultimate axial load of FRP-strengthened slender steel columns, based on the ANSI/AISC 360-05 provisions, which were modified to account for the transformed section properties and a failure criteria of F...

Strengthening of Brick Masonry Arches with Externally Bonded Steel Reinforced Composites

Abstract: The objective of this study is to investigate the efficiency of an innovative technique for strengthening masonry arches, based on the use of high strength steel cords embedded in either an epoxy (steel reinforced polymer) or mortar matrix (steel reinforced grout). Ten prototypes of brickwork arches strengthened by composite laminates were tested under a monotonic vertical load applied at the quarter-span. Load tests were performed to compare the behavior up to collapse of strengthened masonry arches; the influence of the types of reinforcement (steel and carbon fibers) and matrices (epoxy and cementitious), as well as location of the strengthening layer (intrados, extrados, and both) and the presence of anchorage systems has been investigated. The experimental results highlight the enhanced strength of the arches reinforced with steel cords, as well as the role of the mechanical anchoring with regard to the resulting final strength.

Tensile Behavior of FRP Anchors in Concrete

Abstract: Strengthening of concrete structures using fiber-reinforced polymer (FRP) systems has become a widely accepted technology in the construction industry over the past decade. Externally bonded FRP sheets are proven to be a feasible alternative to traditional methods for strengthening and stiffening deficient reinforced or prestressed concrete members. However, the delamination of FRP sheets from the concrete surface poses major concerns, as it usually leads to a brittle member failure. This paper reports on the development of FRP anchors to overcome delamination problems encountered in surface bonded FRP sheets. An experimental investigation was conducted on the performance of carbon FRP anchors that were embedded in normal- and high-strength concrete test specimens. A total of 81 anchors were tested under monotonic uniaxial loading. Test parameters included the length, diameter, and angle of inclination of the anchors and the compressive strength of the concrete. The experimental results indicate that FRP ...

FRP Confinement of Square Masonry Columns

Abstract: The problem of masonry columns subjected to structural deficiency under axial load was studied and reported in this paper. The results of an extensive experimental campaign are presented in order to show the behavior of columns built with clay or with calcareous blocks, commonly found in southern Italy, especially in historical buildings. Rectangular masonry columns were tested for a total of 33 specimens; uniaxial compression tests were conducted on columns taking into account the influence of several variables: different strengthening schemes (internal and/or external confinement), curvature radius of the corners, amount of fiber-reinforced polymer (FRP) reinforcement, cross-section aspect ratio, and material of masonry blocks. Materials characterization was preliminarily carried out including a mechanical test on plain masonry. For all cases the experimental results evidenced a significant increase in load carrying capacity and ductility after FRP strengthening, which identified the columns as ductile ...

Experimental and Parametric Study of Circular Short Columns Confined with CFRP Composites

Abstract: This paper presents an experimental and nonlinear finite-element analysis (NLFEA) results of circular short reinforced concrete (RC) columns confined externally with carbon fiber-reinforced polymers (CFRP) subjected to pure axial loading. The experimental program involves the fabrication and testing of 55 specimens wrapped with different number and configuration of CFRP sheet layers in the transverse and longitudinal directions. In addition, the columns were modeled using NLFEA. After reasonable validation of NLFEA with the experimental test results of companion columns and available technical literature results, NLFEA was expanded to provide a parametric study of 96 columns that correlates the ultimate axial stress of CFRP-confined RC columns to unconfined strength of concrete ( fco ) , the volumetric ratio of CFRP ( ρf ) , and the size effect. Results indicated that the ultimate capacity and ductility increase with the increase in volumetric ratio of CFRP ( ρf ) and unconfined strength of concrete ( fco...

Free Vibrations of Pultruded FRP Elements: Mechanical Characterization, Analysis, and Applications

Abstract: The research shows the results of experimental tests to establish the dynamic parameters of fiber-reinforced polymer (FRP) structural elements in the free vibration field. The tests and the analysis consider the simply supported configuration of pultruded elements characterized by glass fiber reinforcement, glass fiber-reinforced polymer (GFRP) and the thermosetting vinylester matrix subjected to flexural, transversal, and torsional vibrations. Comparison between the experimental results and numerical analysis and the finite element method is also presented. The dynamic response of GFRP structural elements is compared with the behavior of steel and aluminum elements. The results show a good performance, especially in the case of open cross-sectional profiles, considering the advantages deriving from the ratio between the dead load and total load of fiber reinforced composite material. Finally, the use of pultruded GFRP elements for new-built decks is investigated to detect possible resonance phenomena due...

Effect of Transverse Steel on the Response of RC Beams Strengthened in Shear by FRP: Experimental Study

Abstract: The present paper shows and discusses some of the results obtained within an experimental investigation carried out on 15 reinforced concrete (RC) beams strengthened in shear by externally bonded fiber-reinforced plastics (FRP) sheets. The aim of the study is to analyze the influence that the geometrical percentage of transverse steel reinforcement could have on the FRP resisting action. In particular, the objectives of the experimental campaign are to explore the possible interaction between FRP and steel transverse reinforcement resisting actions, analyzing the deformation behavior of the shear resisting system (FRP, transverse steel, and concrete) and the modes of failure of the strengthened and not strengthened beams. The results of the tests in terms of shear capacity are compared to the design formulations provided by the American Concrete Institute and the National Research Council of Italy code-format recommendations.

Behavior of RC Beams Shear Strengthened with Bonded or Unbonded FRP Wraps

Abstract: Reinforced concrete (RC) beams shear-strengthened with fiber-reinforced polymer (FRP) fully wrapped around the member usually fail due to rupture of FRP, commonly preceded by gradual debonding of the FRP from the beam sides. To gain a better understanding of the shear resistance mechanism of such beams, particularly the interaction between the FRP, concrete, and internal steel stirrups, nine beams were tested in the present study: three as control specimens, three with bonded FRP full wraps, and three with FRP full wraps left unbonded to the beam sides. The use of unbonded wraps was aimed at a reliable estimation of the FRP contribution to shear resistance of the beam and how bonding affects this contribution. The test results show that the unbonded FRP wraps have a slightly higher shear strength contribution than the bonded FRP wraps, and that for both types of FRP wraps, the strain distributions along the critical shear crack are close to parabolic at the ultimate state. FRP rupture of the strengthened ...

Nonlinear Analyses of Tuff Masonry Walls Strengthened with Cementitious Matrix-Grid Composites

Abstract: Previous experimental studies, conducted by some of the authors, on in-plane response of tuff masonry walls strengthened with an innovative cementitious matrix composite grid (CMG) system confirmed that the CMG system could satisfy basic design requirements such as compatibility with the tuff masonry support (i.e., in terms of good bond properties), reversibility of the intervention and strengthening effectiveness. However, very large scatter was found in the experimental outcomes. Micromodeling and some parametric analyses were adopted to understand the contribution of basic material (mortar, tuff blocks and CMG strengthening) and the effect of the workmanship defects on the structural behavior of a natural stone wall. In order to conduct the analyses, finite-element method models of the elements have been compared to experimental data and they were found to be in good agreement with the test data. Significant improvements of strength and in the postpeak response were achieved installing different layouts of the CMG system. However the strengthening intervention had a negligible influence on the initial stiffness of the walls and this means that it has a reduced impact on the behavior of the existing structure.

Axial Load-Bending Moment Diagrams of Carbon FRP Wrapped Hollow Core Reinforced Concrete Columns

Abstract: Hollow core reinforced concrete columns are generally preferred in use to decrease the cost and weight/stiffnesss ratio of members, such as bridge columns and piles. With a simplified stress state assumption, strengthening a hollow core reinforced concrete column with fiber-reinforced polymer (FRP) wrapping provides a biaxial confinement to the concrete, which leads to a need of defining the effect of FRP wrapping on the strength and ductility of the hollow core reinforced concrete columns. In this study, two groups of four hollow core reinforced concrete columns ( 205 mm outer diameter, 56 mm hollow core diameter, and 925 mm height) were tested under concentric, eccentric (25 and 50 mm eccentricity) and bending loads to observe the effect of carbon FRP (CFRP) wrapping. All the columns had internal steel reinforcement. Half of the columns had three layers of circumferential CFRP wrapping, whereas the other half had no external confinement. Axial load-bending moment (P–M) diagrams of each group were drawn ...

Fatigue Behavior of RC Beams Strengthened with NSM CFRP Rods

Abstract: This paper presents experimental results of reinforced concrete beams strengthened using near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) reinforcement. A total of nine beam specimens were tested under fatigue loads. In addition, two specimens were tested for monotonic capacity. The beams were 3,500 mm long with a cross section of 254 mm deep by 152 mm wide. Different load ranges were considered in the fatigue tests to construct the fatigue life curves. The test results showed that under monotonic loading, the beam strengthened with NSM CFRP rod exhibited increases of 26 and 50% in the yield and ultimate load over the control beam, respectively. Under cyclic loading, the fatigue life for the strengthened beams was 24% higher than that of the control unstrengthened beams. An analytical model using sectional analysis and strain-life approach was developed to estimate the fatigue life of the specimens at various cyclic load ranges. A good agreement between the experimental results and analyt...

Fatigue of Reinforced Concrete Beams Strengthened with Steel-Reinforced Inorganic Polymers

Abstract: Steel-reinforced polymer (SRP) composite materials are very attractive due to their low weight and high strength. The ease of installation which significantly reduces repair time and expense is another major advantage. One of the main disadvantages of SRP materials is that the matrices used for their fabrication are typically organic and thus they are susceptible to fire. In this study, a newly developed retrofit system is being used. It consists of high strength steel fibers impregnated in a fireproof inorganic matrix. The objective of this study is to examine the effects of this hybrid rehabilitation system on the fatigue performance of strengthened reinforced concrete beams. Sixteen 100 mm×150 mm×1200 mm reinforced concrete beams with enough transverse reinforcement to avoid shear failure were used in this study. Nine beams were strengthened with steel fiber sheets on their tension faces. The results from the present study indicate that the fatigue life of reinforced concrete beams, subjected to the sa...

Shear Failure of Pultruded Fiber-Reinforced Polymer Composites under Axial Compression

Abstract: When structural elements are subjected to compressive loads, the shear forces and stresses induced by second-order effects may lead to shear failure prior to compressive failure. This is particularly likely to occur in the case of pultruded glass fiber-reinforced polymer profiles, which normally exhibit low shear strength in relation to compressive strength. This paper analyzes the effects of initial imperfection, slenderness, shear-to-compressive strength ratio, shear coefficient, and type of shear failure criterion on ultimate load and failure mode (shear or compressive failure). A formulation for predicting ultimate load based on shear failure and second-order deformation is proposed. The results obtained compare well with similar results obtained using other methods and experimental data available in literature. The proposed method is based strictly on mechanics and thus requires no fitting to experimental data.

Investigating a Structural Form System for Concrete Girders Using Commercially Available GFRP Sheet-Pile Sections

Abstract: This paper presents a new girder consisting of a trapezoidal pultruded glass fiber-reinforced polymer (GFRP) hat-shaped section commercially available as a sheet pile, but used in this study as a structural form for concrete. It can also offer continuity in the transverse direction through a pin-and-eye connection. Five 610 mm×325 mm and 3,300-mm-long girders were tested in flexure to examine different bond systems, voided and solid concrete cores, and the performance in positive and negative bending. Bond systems were wet adhesive bond to freshly cast concrete, adhesively bonded coarse aggregates, and mechanical shear studs. No slip was observed between concrete and the GFRP section until delamination failure occurred within a thin layer of cement mortar that remained attached to GFRP. The studs failed by pull out from the concrete flange. In general, 47–75% of the full strengths of concrete and GFRP were reached at ultimate bond failure. Wet adhesive bonding was the simplest and quickest to apply, while...

Novel Technique for Inhibiting Buckling of Thin-Walled Steel Structures Using Pultruded Glass FRP Sections

Abstract: The use of composite materials for strengthening the ailing infrastructure has been steadily gaining acceptance and market share. It can even be stated that this strengthening technique has become main stream in some applications such as strengthening concrete structures. The same cannot be said about steel structures; for which research on composite material strengthening is relatively new. Several challenges face strengthening steel structures using composite materials such as the need for high-modulus composites to improve the effectiveness of the strengthening system. This paper explores a new approach for strengthening steel structures by introducing additional stiffness to buckling-prone regions. The proposed technique relies on improving the out-of-plane stiffness of buckling-prone members by bonding pultruded fiber-reinforced polymer (FRP) sections as opposed to the commonly used approach that relies on in-plane FRP contribution. The paper presents results from an experimental investigation where ...

Are Available Models Reliable for Predicting the FRP Contribution to the Shear Resistance of RC Beams

Abstract: In this paper the trustworthiness of the existing theory for predicting the fiber-reinforced plastic contribution to the shear resistance of reinforced concrete beams is discussed. The most well-known shear models for external bonded reinforcement are presented, commented on, and compared with an extensive experimental database. The database contains the results from more than 200 tests performed in different research institutions across the world. The results of the comparison are not very promising and the use of the additional principle in the actual shear design equations should be questioned. The large scatter between the predicted values of different models and experimental results is of real concern bearing in mind that some of the models are used in present design codes.

CFRP-Based Strengthening Technique to Increase the Flexural and Energy Dissipation Capacities of RC Columns

Abstract: A strengthening technique, combining carbon fiber-reinforced polymer (CFRP) laminates and strips of wet layup CFRP sheet, is used to increase both the flexural and energy dissipation capacities of reinforced concrete (RC) columns of square cross section of low to moderate concrete strength class, subjected to constant axial compressive load and increasing lateral cyclic loads. Laminates were applied according to the near surface mounted technique to increase flexural resistance of the columns, while the strips of CFRP sheet were installed according to the externally bonded reinforcement technique to enhance concrete confinement, particularly in the plastic hinge zone where they also offer resistance to the buckling and debonding of the laminates and longitudinal steel bars. The performance of this strengthening technique is assessed in undamaged RC columns and in columns subjected to intense damage. The influence of the concrete strength and percentage of longitudinal steel bars on the strengthening effectiveness is assessed. In the groups of RC columns of 8 MPa concrete compressive strength, this technique provided an increase of about 67% and 46% in terms of column's load carrying capacity, when applied to undamaged and damaged columns, respectively. In terms of energy dissipation capacity, the increase ranged from 40–87% in the undamaged columns, while a significant increase of about 39% was only observed in one of the damaged columns. In the column of moderate concrete compressive strength (29 MPa), the technique was even much more effective, since, when compared to the maximum load and energy dissipation capacity of the corresponding strengthened column of 8 MPa of average compressive strength, it provided increases of 39% and 109%, respectively, showing its appropriateness for RC columns of structures requiring upgrading against seismic events.

Mechanically Fastened FRP-Strengthened Two-Way Concrete Slabs with and without Cutouts

Abstract: The feasibility of strengthening concrete slabs in flexure, with and without cutouts, using the mechanically fastened MF FRP technique is investigated. Two series of large-scale reinforced concrete slabs are tested. The first series is comprised of five slabs without a cutout, and measuring 2,6002,600120 mm; the second series consists of four slabs of the same dimensions with a central cutout measuring 800800 mm. The mechanically fastened system is found to be a valid alternative to the externally bonded system resulting in a rapid, economic, and effective strengthening technique for two-way concrete slabs. The increases in ultimate capacities of the MF FRP-strengthened slabs range between 30 and 70% over those of the unstrengthened specimens. In addition, finite-element modeling of MF FRP-strengthened slabs is introduced in this study. The interfacial behavior between the MF FRPs and the concrete substrate is accounted for by using appropriate interfacial models. Very good agreement is obtained between the test results and the numerical predictions.

Bond Behavior of Near-Surface Mounted FRP Strips Bonded to Modern Clay Brick Masonry Prisms: Influence of Strip Orientation and Compression Perpendicular to the Strip

Abstract: In this paper the results of 18 pull tests performed on clay brick masonry prisms strengthened with near-surface mounted carbon fiber-reinforced polymer (CFRP) strips are presented. The pull tests were designed to add to the existing database and investigate variables significant to masonry construction. FRP was bonded to solid clay brick masonry; FRP aligned both perpendicular and parallel to the bed joint; and in the case of FRP reinforcement aligned parallel to the bed joint, compression applied perpendicular to the strip was used to simulate vertical compression load in masonry walls. Results including bond strength, critical bond length, and the local bond-slip relationship are presented as well as a discussion on the effect of the new variables on these results.

Direct versus Indirect Method for Identifying FRP-to-Concrete Interface Relationships

Abstract: Several proposals have been carried out for modeling a fiber-reinforced-polymer (FRP)-to-concrete interface whose behavior is not completely described by fracture energy value, which could often be derived in closed form. Although the bilinear formulation is one of the most widely accepted relationships, neither standard testing procedures nor well-established calibration and identification techniques are currently available. The present paper mainly deals with the latter aspect and is basically aimed at examining the differences possibly arising from adopting either direct or indirect techniques for identifying the interface relationship. In particular, after an outline of the analytical formulation of both mentioned identification methods, their application is proposed considering a set of experimental results already utilized by other authors in similar studies. Besides the expected superiority of the indirect procedure in identifying the interface relationship, emphasis is placed on the fact that such a procedure is quite unaffected by the possible reduction in the number of experimental data considered in calibrating the interface relationship.

Seismic Performance Assessment of Damage-Controlled FRP-Retrofitted RC Bridge Columns Using Residual Deformations

Abstract: Despite the improved performance of fiber-reinforced plastic (FRP)-retrofitted bridges, residual deformations in the event of an earthquake are inevitable Little consideration is currently given to these deformations when assessing seismic performance Moreover, important structures are currently required not only to have high strength and ductility but also to be usable and repairable after high intensity earthquakes This paper presents a definition of an FRP-RC damage-controllable structure An intensive study of 109 bridge columns, extracted from recent research literature on the inelastic performance of FRP retrofitted columns with lap-splice deficiencies, flexural deficiencies, or shear deficiencies, is used to evaluate the recoverability of such retrofitted columns The residual deformation, as a seismic performance measure, is used to evaluate the performance of 39 FRP-retrofitted RC columns from the available database Based on this evaluation, a requirement for the recoverable and irrecoverable states of FRP-RC bridges is specified Finally, the Seismic Design Specifications of Highway Bridges for RC piers is adapted to predict the residual deformations of FRP-RC columns

Anchor System for Tension Testing of Large Diameter GFRP Bars

Abstract: The scope of this paper is to describe the development of an anchor system for tension testing of unidirectional fiber-reinforced plastic bars of large diameter used as reinforcement in concrete structures. The main objective was to develop a simple, economical, and effective system to permit tensile loading of the bars up to failure in a universal testing machine. In the system suggested, each end of the bar is embedded in a conical polymeric head that fits a conical hole inside the anchoring device. In the experimental tests performed, the bars broke between the anchorages, while the resin heads remained always undamaged. These outcomes strengthen the confidence in the proposed anchor system.