Fiber Reinforced Polymer Composite Jackets Research Articles

Comparative behavior under compression of concrete columns repaired by fiber reinforced polymer (FRP) jacketing and ultra high-performance fiber reinforced concrete (UHPFRC)

This paper summarizes the experimental results from a comprehensive research program to study the fundamental stress–strain behavior of damaged concrete repaired by two techniques: increased concrete section and bonding fiber reinforced polymer (FRP). In this work, two types of FRP composite jackets were used, carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer, and two types of concretes were used to repair the damaged concrete by increased concrete section: ordinary concrete and ultra high-performance fiber reinforced concrete (UHPFRC). Fifteen circular columns of concrete (110 × 220) cm3 were initially pre-damaged up to intense cracking, repaired by increased concrete section and by bonding FRP, and tested under uni-axial compression by loading up the damage. The impact of different design parameters, including plain concrete strength, types of composites, and type of concrete used for increasing section, was considered in this study. The strength enhancement and ductility improvement of specimens are discussed. A simple model is presented to predict the compressive strength of repaired damaged concrete columns. A significant strength and an increase in ductility were achieved, particularly when the columns were repaired by increasing section with UHPFRC and by bonding CFRP. These preliminary tests indicate that the use of UHPFRC is an effective technique for rehabilitating damaged concrete columns, highly competitive with the repaired concrete by wrapping specimens with FRP composite jackets.

Case Study of Strategies for Seismic Rehabilitation of Reinforced Concrete Multicolumn Bridge Bents

The paper presents a case study for comparing the seismic rehabilitation of four reinforced concrete multicolumn bridge bents typical of older bridges not designed for current seismic code criteria. The types of intervention included connecting the piles to the pile caps with high-strength prestressing steel bars, widening of an existing strut beam connecting the pile caps, construction of a new reinforced concrete grade beam overlay to connect the pile caps, and carbon fiber reinforced polymer composite jackets for strengthening the columns and cap-beam-column joints. The paper includes the hysteresis curves from in situ experiments in which a lateral quasi-static cyclic load was applied at the cap-beam and comparisons to analytical pushover curves. A comparison of the capacity of the four bents to the demand of several earthquake records including historical and NEHRP design earthquakes is developed. The cost of seismic rehabilitation of the four bridge bents is presented along with the peak maximum lat...

Seismic Retrofit of Brittle and Low Strength RC Columns Using Fiber Reinforced Polymer and Cementitious Composites

The objective of this study is to investigate the seismic performance of reinforced concrete columns constructed with low quality of concrete and insufficient transverse reinforcement before and after retrofitting. Totally twenty nearly full size specimens with rectangular cross-section were tested under constant axial load and reversed cyclic lateral loads. Both longitudinal and transverse reinforcements were plain bars. Ten of the specimens had insufficient lap splice length of longitudinal reinforcement between stories as well. Both pre-damaged and undamaged columns with these deficiencies were retrofitted with FRP (fiber reinforced polymer) composite jackets or prefabricated HPFRCC (high performance fiber reinforced cementitious composite) panels. The test results showed that all reference specimens, which were not retrofitted, failed with a premature loss of performance either due to buckling of longitudinal reinforcement or loss of bond, while retrofitted ones exhibited a significantly superior performance, particularly in terms of ductility. It should be noted that the enhancement in performance was less remarkable for the specimens with inadequate lap splice lengths. An analytical work is also presented for prediction of the behavior of the specimens both for continuous and lap spliced longitudinal reinforcement cases.

Aerospace technology for strengthening of bridges

A fiber-reinforced polymer (FRP) composite jacket was applied to the reinforced concrete pier caps of the Silver Spring Cove Bridge in Rhode Island. Since this highway overpass bordered a nearby marina, the corrosive environment of the Atlantic Ocean played a major role in the degradation of the concrete and reinforcing steel. The pier caps exhibited severe spalling and cracking and were considered for strengthening using FRP technology. An innovative technique known a vacuum-assisted impregnation was utilized to apply the composite to the structure. Commonly referred to as “vacuum bagging” in the aerospace industry, this method is an efficient way of fabricating high quality FRP laminate composite plates. Rarely seen in infrastructure applications, vacuum bagging uses atmospheric pressure to remove air voids within the composite during lay-up and develops a strong bond between FRP layers. As discussed in this paper, this technique was successfully implemented to place an FRP composite jacket on the reinforced concrete pier caps.

Strain-Based Confinement Model for FRP-Confined Concrete

A constitutive strain-based confinement model is developed for circular concrete columns confined with external fiber-reinforced polymer (FRP) composite jackets. The model includes the properties of the concrete microstructure through a series of relationships developed from experimental data and the fundamental stress-strain behavior of concrete. The secant concrete modulus was used in the model and expressed as a function of the secant modulus softening rate. In addition, the ultimate radial strain was related to the FRP composite effectiveness. The distinguishing feature of the model is that it includes the effects of FRP confinement on the concrete microstructure by evaluating the internal concrete damage using the axial, radial, and volumetric strains. The FRP-confined concrete model predicts the axial stress at any level of axial strain accurately for any normalized effective confinement stiffness of the FRP composite jacket as verified in comparisons with experiments.

Compressive Behavior of Concrete Confined by Various Types of FRP Composite Jackets

This paper summarizes the experimental results from a comprehensive research program to study the fundamental stress-strain behavior of concrete confined by various types of fiber reinforced polymer (FRP) composite jackets. More than 200 concrete stub columns with 9 types of FRP composite jackets were tested under axial compression. The impact of different design parameters including plain concrete unconfined strength, types of composites as well as jacket thickness were considered in this study. The strength enhancement and ductility improvement of specimens confined with FRP composite jackets are discussed. In addition, a new stress-strain model to predict the behavior of axial members jacketed with FRP composites is presented. Comparisons between the analytical results using the proposed model and test results are also presented.

Variable Strain Ductility Ratio for Fiber-Reinforced Polymer-Confined Concrete

The encasement of concrete in fiber-reinforced polymer (FRP) composite jackets can significantly increase the compressive strength and strain ductility of concrete columns and the structural system of which the columns are a part, be it a building or a bridge. Because of the approximate bilinear compressive behavior of FRP-confined concrete, analysis and design of FRP-confined concrete members requires an accurate estimate of the performance enhancement due to the confinement provided by FRP composite jackets. An analytical model is presented for predicting the bilinear compressive behavior of concrete confined with either bonded or nonbonded FRP composite jackets. This article describes the basis of the model, which is a variable plastic strain ductility ratio. The variable plastic strain ductility ratio defines the increase in plastic compressive strain relative to the increase in the plastic compressive strength of the FRP-confined concrete, which is a function of the hoop stiffness of the confining FRP composite jacket, the plastic dilation rate, and the type of bond between the FRP composite and concrete.

Stress-Strain Model for Fiber-Reinforced Polymer-Confined Concrete

The design of fiber-reinforced polymer (FRP)-confined concrete members requires accurate evaluation of the performance enhancement due to the confinement provided by FRP composite jackets. A strain ductility-based model is developed for predicting the compressive behavior of normal strength concrete confined with FRP composite jackets. The model is applicable to both bonded and nonbonded FRP-confined concrete and can be separated into two components: a strain-softening component, which accounts for unrestrained internal crack propagation in the concrete core, and a strain-hardening component, which accounts for strength increase due to confinement provided by the FRP composite jacket. A variable strain ductility ratio described in a companion paper is used to develop the proposed stress-strain model. Equilibrium and strain compatibility are used to obtain the ultimate compressive strength and strain of FRP-confined concrete as a function of the confining stiffness and ultimate strain of the FRP jacket.

In-Situ Verification of Rehabilitation and Repair of Reinforced Concrete Bridge Bents under Simulated Seismic Loads

Three in-situ tests were performed on two bents of a reinforced concrete (RC) bridge under quasi-static cyclic loads. The bridge was built in 1963 and did not possess the necessary reinforcement details for ductile performance. The tests included an as-built bent, a bent rehabilitated with carbon fiber reinforced polymer (FRP) composite jackets, and a damaged bent repaired with epoxy injection and carbon FRP composite jackets. Two new concepts of strengthening bridge bents with FRP composites were implemented in this study. The first involves shear strengthening and confinement of a beam cap-column joint through an FRP composite “ankle-wrap.” The second is an FRP composite “U-strap” to improve the anchorage of column longitudinal steel reinforcement extending into the joint. FRP composite jackets were also implemented in the columns and beam cap. An additional rehabilitation measure was that of anchorage of the piles to the pile cap using epoxied high strength steel bars. The performance of the bent in the as-built condition and that of the rehabilitated and repaired bents is described in terms of strength, stiffness, displacement ductility, and energy dissipation.

Compressive Behavior of Concrete Confined by Carbon Fiber Composite Jackets

This paper describes axial compression test results of 27 concrete cylinders confined by carbon fiber reinforced polymer composite jackets. The experimental parameters include plain concrete compressive strength and the thickness of the composite jacket. It is found that the carbon fiber composite jacketing can significantly increase the compressive strength and ductility of concrete. The test results indicate that concrete strength and confinement modulus, defined as the ratio of transverse confinement stress and transverse strain, are the most influential factors affecting the stress-strain behavior of confined concrete. The failure of the confined concrete was dominated by the rupture of the jacket at an average strain much smaller than the ultimate strain obtained from tension tests of flat coupons. In order to describe the main mechanical features of the confined concrete, a simple bilinear stress-strain model is suggested based on the theory of elasticity and minimum number of empirical equations determined from the tests. The simple model is shown to compare well with test results from previous studies by other researchers.