Experimental and Analytical Behavior of Carbon Fiber-Based Rods as Flexural Reinforcement

This paper presents the results of an experimental and analytical comparison of a study on the flexural behavior of concrete beams reinforced with sandblasted carbon fiber-based composite rods. Twelve beams, including three control beams reinforced with steel, were tested for strength, deformation, and failure characteristics. Analytical comparisons included the generation of the theoretical strength and moment curvature relations. Experimental data from pullout tests indicated that bonding of sandblasted rods is not a major concern. However, excessive deformation in achieving the predicted moment capacity could be a limiting factor in the design of these beams.     

Dynamic Analysis of Truss‐Beam System

As the manned exploration of space continues, many complex structural components are being developed to construct the orbital platforms that will be used to house communication hardware, personnel, and manufacturing complexes. These components are extremely flexible and complex in their behavior. There is a need for a simple method for determining the dynamic characteristics of these space structures with a minimum of effort. A mathematical model of one of these structural elements, an articulating truss beam, has been developed to predict its dynamic response. Assumptions of the force interaction between the beam elements and the joints have been made for using this model. Algorithms are provided to determine the flexibility matrix of the truss beam for use in the equation of motion. The natural frequencies obtained from using this method are compared with those obtained by the finite element method. An experimental procedure is planned to validate the results from the theoretical method.     

Concrete Beams Exposed to Live Loading during Carbon Fiber Reinforced Polymer Strengthening

The need for structural rehabilitation of concrete structures all over the world is well known. Extensive amounts of research have been carried out and are ongoing in this field. Most of the laboratory research has been undertaken on structural elements without live load during the strengthening process. Normally owners of structures want to continue their activity or service during strengthening. Full-scale applications have shown that this is possible, but there is a lack of understanding as to how cyclic loads are distributed during strengthening; for example, traffic loads affect the final strengthening result. This paper presents laboratory tests on concrete beams strengthened with carbon fiber-reinforced polymer laminates and near-surface mounted reinforcement. The beams were subjected to a cyclic load during setting of the adhesive, and after additional hardening were then loaded by deformation control up to failure.     

Control of Corrosion-Induced Damage in Reinforced Concrete Beams Using Carbon Fiber-Reinforced Polymer Laminates

This paper presents the results of an experimental study conducted to investigate the effect of carbon fiber-reinforced polymer (CFRP) confinement on the cracking damage induced by impressed current-accelerated corrosion of reinforced concrete beams. The beams were 254?mm deep by 152?mm wide by 3,200?mm long. Two different corrosion configurations, namely uniform and shear-span corrosion, were investigated in eight specimens at three different degrees of corrosion (5, 10, and 15% theoretical mass loss). Uniform corrosion along the whole length of the beams (3,000?mm) and shear-span corrosion (900?mm from each beam end) were considered. The different degrees of corrosion were induced using an accelerated corrosion technique with an impressed current. Based on the results, it was concluded that CFRP laminate confinement reduces corrosion expansion by up to 70% and slows the rate of corrosion through decreasing the corrosion mass loss by up to 35%.     

Large Deflection Stability of Slender Beam-Columns with Semirigid Connections: Elastica Approach

The large-deflection elastic analysis of slender beam-columns of symmetrical cross sections with semirigid connections under end loads (forces and moments) including the effects of out-of-plumbness is developed in a classical manner. The classical theory of the “Elastica” and the corresponding elliptical functions are utilized in the proposed method which can be used in the large-deflection stability analysis of slender beam-columns with rigid, semirigid, and simple connections under any combination of end loads (conservative and nonconservative). The proposed method consisting of a closed-form solution of the Elastica can also be utilized in the large deflection analysis of beam-columns whose connections suffer from flexural degradation or, on the contrary, flexural stiffening. The main limitation of the Elastica is that only flexural strains are considered (the effects of axial and shear strains are neglected). Therefore results from the proposed method are theoretically exact from small to very large curvatures and transverse and longitudinal displacements for plane beam-columns under bending actions. The large-deflection analysis of a beam-column with flexible connections at both ends becomes a complex problem requiring the simultaneous solution of at least two highly nonlinear equations with elliptical integrals. The solution of this problem becomes even more complex when the end connections are nonlinear or the direction of the applied end load changes (like “follower” loads). The validity and effectiveness of the proposed method and equations are verified against available solutions of very large deflection elastic analysis of beam-columns. Four comprehensive examples are included for verification and easy reference.     

Wave Propagation and Mode Localization in Simply Supported Multispan Beams with Couplers on Supports

The influences of couplers on wave propagation and mode localization in simply supported multispan beams with couplers consisting of lumped rotational stiffness and mass on supports are studied. A transfer matrix equation governing the vibrational wave propagation in the simply supported multispan beams with couplers is newly derived and simplified. The eigenvalue of the simplified transfer matrix shows that the larger stiffness or the larger mass of the coupler makes the internal coupling between spans weaker and so it makes the system more sensitive to mode localization. As the wave frequency or the eigenvalues of the system increases, the mass effect is increased while the stiffness effect is decreased. In a case considering the large stiffness and mass at the same time, there is a region with relatively wider passbands and narrower stop bands having small attenuation rates and the normal modes in it become delocalized ones. As an example structure, a simply supported two span beam with a coupler at the midspan is considered.     

Recurrent Single Delaminated Beam Model for Vibration Analysis of Multidelaminated Beams

Free vibration analysis of a through-width multidelaminated beam is performed in the present study. Multiple delaminations are assumed to spread from the top through the thickness direction of the beam. The natural frequencies of the multidelaminated beams are obtained from a recurrent single delaminated beam (RSDB) model, which is the subsingle delaminated beam from the top surface of a global beam. Each frequency equation for the RSDB with unknown boundary conditions is obtained through continuity conditions. Then this result is updated to the next one. With these sequential operations, the final frequency equation of the multidelaminated beams is obtained for both end boundary conditions of the global beam. The numerical results for the beams are compared with those of finite element analysis to give the reliance on the proposed model and to investigate the effects of the shape, number, and size of multidelaminations on the natural frequency. It was shown that the variations in the natural frequency for the multidelaminated beams were significantly affected by the delamination length.     

Environmental Fatigue and Static Behavior of RC Beams Strengthened with Carbon-Fiber-Reinforced Polymer

Many countries around the world have tremendous needs to repair and strengthen their transportation infrastructure. Almost everywhere, traffic loads have reached levels largely exceeding design expectations. Northern countries also experience severe winter conditions that are combined with an extensive use of deicing salts and accelerate structural deterioration. In Canada, the extent of deterioration has prompted many authorities, including the federal and provincial governments, to investigate the potential use of fiber-reinforced polymer products to extend the life of their existing structures. However, it is widely recognized that the large-scale implementation of these products is often impaired by the lack of data on their durability. This paper presents an experimental project undertaken in order to assess the durability of reinforced concrete beams externally strengthened with two types of carbon-fiber-reinforced polymer (CFRP). The beams were first exposed to either wet-dry cycles or continuous immersion in water and then were loaded in fatigue. Finally, they were tested quasi-statically under four-point bending up to failure. The test results presented here provide some insights on the potential long-term performance of CFRP-strengthened beams exposed to severe environmental conditions.     

Concrete Contribution to the Shear Resistance of Fiber Reinforced Polymer Reinforced Concrete Members

Seven beams were tested in bending to determine the concrete contribution to their shear resistance. The beams had similar dimensions and concrete strength and were reinforced with carbon fiber reinforced polymer bars for flexure without transverse reinforcement. They were designed to fail in shear rather than flexure. The test variables were the shear span to depth ratio, varying from 1.82 to 4.5, and the flexural reinforcement ratio, varying from 1.1 to 3.88 times the balanced strain ratio. The test results are analyzed and compared with the corresponding predicted values using the American Concrete Institute, the Canadian Standard, and the Japan Society of Civil Engineers (JSCF) fiber reinforced polymer design recommendations. Based on these results and previous experimental data, it is shown that the ACI recommendations are extremely conservative whereas the Canadian and JSCE recommendations, albeit still conservative, are in closer agreement with the experimental data. Overall the Canadian Standard’s predictions are in better agreement with experimental data than the JSCE predictions.     

Analysis of Test Specimens for Cohesive Near-Bond Failure of Fiber-Reinforced Polymer-Plated Concrete

The failure mechanisms of reinforced concrete (RC) members change due to the application of externally bonded fiber-reinforced polymer reinforcement. Although an extensive literature is available describing the failure mechanisms of poststrengthened flexural systems, brittle failure modes caused by bond failure, such as midspan debonding and end peeling, need to be further investigated in order to identify and quantify the fracture processes that result in bond failure. Simplified experimental tests have been designed to idealize the bond between the laminate and the RC member. However, it is unclear how the simplified test results can be related to the actual flexural debonding failures. This paper investigates and compares two bond failure tests: a simplified test (or simple shear test) and a recently proposed shear/normal test. After discussing the characteristics of both tests and how they relate to the midspan debonding and end peeling failures, the shear/normal test is studied in more detail using a nonlinear finite-element fracture mechanics program. The program accounts for cohesive localized and distributed concrete crack damage and is capable of describing the geometrical discontinuities that induce different brittle failure mechanisms. The numerical results compare well with available experimental data and help explain the crack formation and propagation pattern up to specimen failure. Parametric studies are presented to elucidate the influence of different material parameters on the failure mechanisms.