Strengthening Of Reinforced Concrete Members Research Articles

Torsional behavior of FRP-strengthened reinforced concrete members considering various wrapping configurations: Theoretical analysis and modeling

Reinforced concrete (RC) structural members such as spandrel, flanged and curved beams, slab beams, and bridge girders may be subjected to significant torsional loading. Despite extensive research on the strengthening of RC members, very little is known about the torsional behavior of RC members strengthened with fiber-reinforced polymer (FRP) sheets. Therefore, very limited guidelines apply to the design of externally bonded FRP systems for torsional strengthening, and no design provisions exist for the U-wrapped and 2-sided strengthening systems in torsion. This study aims to contribute to this growing area of research by developing a new analytical model to predict the full torsional response of strengthened RC members with many conventional configurations such as spiral, transverse and longitudinal FRP, continuous and intermittent strips along the beam length, side bonded, and full-wrapped systems. Moreover, this study provided an analytical model accurately predicting the contribution, efficiency, and failure mode of side-bonded strengthening systems. Additionally, the influence of various parameters such as FRP stiffness and transverse steel reinforcement ratio is taken into account in the constitutive law of concrete and internal reinforcement for the first time. The good agreement between the test results of 32 collected FRP-strengthened RC beams from the literature and the theoretical ones, which were predicted through programming proves the validity and accuracy of the presented theory.

Ultimate torsional resistance and failure modes of FRP-strengthened reinforced concrete members: A nonlinear design model

Reinforced concrete (RC) structural members, especially flanged and spandrel beams, bridge girders, curved beams, and eccentrically loaded beams may be subjected to significant torsional loading. Despite extensive research on the strengthening of RC members, far too little attention has been paid to the torsional behavior of RC members strengthened with fiber-reinforced polymer (FRP) sheets. Therefore, a limited number of guidelines specified the design of externally bonded FRP systems in torsion. This study provides an important opportunity to advance the understanding of the torsional behavior of FRP-strengthened members by developing a nonlinear design model predicting the failure mode and ultimate torsional resistance of FRP-strengthened RC members subjected to torsion. Serious discussions and analyses of desired failure modes emerge by defining two balanced conditions between the components, and eight failure regions. The first balanced condition defined between FRP and concrete specifies the failure mode of the member, and the second balanced condition defined between steel and concrete is used for the analysis of steel reinforcement stresses. A clear design approach is proposed in this study to access the desired percentage of the externally applied FRP sheets based on the required torsional strength. Moreover, the ultimate stresses and strains of concrete struts, steel reinforcements, and FRP sheets are derived by incorporating the nonlinear behavior of concrete. To evaluate the validity of the design method, 70 FRP-strengthened specimens are collected from 11 previous studies; then, a comparative analysis is conducted among the experimental results, the estimations of the presented model, and the predictions of the commonly available guidelines for torsional strengthening. The excellent agreement between the test results and the presented model estimations confirms the validity and accuracy of the presented model.

Durability of reinforced concrete beams strengthened by galvanized steel mesh-epoxy systems under harsh environmental conditions

Strengthening and rehabilitation of reinforced concrete (RC) structural elements are being efficiently carried out by fiber-reinforced polymer (FRP) composite materials. However, their long-term durability is still causing concerns for the repairing industry. Recently, the use of steel wire mesh-epoxy systems for strengthening is gaining the attention of researchers and engineers and their long-term durability warrants investigation. This paper presents the results of an extensive experimental study carried out on 60 RC beams strengthened in flexure by medium and high cord density galvanized steel mesh (MSM, HSM). In order to evaluate the durability of these strengthening systems, the RC beams were exposed to direct sunlight and immersed under saline water for 6, 12, and 24 months. The beams were tested under four-point bending till failure after each exposure period. The MSM and HSM strengthened beams showed up to 51 and 62% higher load-carrying capacity than that of the control beams at 28 days, respectively, and up to 82% after two years of sun and saline water exposure. Furthermore, the exposed beams showed significant delay in crack initiation, no pronounced degradation in strength or stiffness, and no delamination of epoxy. On the contrary, there was significant improvement in the strength of the exposed beams, especially that of the MSM. Based on ACI 440.2R-17 Guidelines, environmental reduction factors were proposed for the exposed beams. This study showed that galvanized MSM and HSM laminates could be promising and durable alternative materials for rehabilitation, retrofitting, and strengthening of RC members under harsh climatic conditions of elevated temperature, high salinity, and high humidity.

Computational Method on Axial Tension of Secondary Loaded RC Members Strengthened with Carbon Fiber Reinforced Plastic Sheets

Base on the existing condition that the bearing capacity is insufficient of some aging reinforced concrete (RC) members with axial tension, the formula for calculating the tensile capacity of the RC members strengthened with externally bonded carbon fiber reinforced plastic (CFRP) sheets is deduced and experiments of 8 RC members are conducted to examine the influences of CFRP sheets on the cracking load and ultimate load of the RC members. The calculation formulas agree with the experimental data and give the reference to the practical projects. The study is instructive and useful in strengthening of RC members with externally bonded CFRP sheets under axial tension.

Zero-span tensile model for evaluating cracking behaviour of SHCC for RC flexural strengthening

Strain hardening cementitious composites (SHCCs) have obvious advantages when used to strengthen reinforced concrete (RC) structures – high tensile and compressive strengths, as well as large tensile strain in uniaxial tensile behaviour. However, when used for flexural strengthening of RC members, the ductility of SHCC is reduced and the cracking behaviour of the SHCC strengthening layer varies with different layer thicknesses. In this paper, a zero-span tensile model using a fictitious material is proposed to assess the cracking behaviour of SHCC used for RC flexural strengthening, considering the localised behaviour of the SHCC on the cracked RC substrate member. In the model, the crack in the RC substrate member is represented by an artificial crack formed by two areas of fictitious material. The proposed model can evaluate the cracking behaviour of SHCC layers of varying thickness used for flexural strengthening of RC members.

Behavioral Trends of RC Beams Strengthened with Externally Bonded FRP

The performance of conventionally reinforced concrete (RC) beams strengthened in flexure with externally bonded fiber-reinforced polymers (EB-FRP) was studied by compiling and analyzing an experimental database. A total of 127 specimens from 23 separate studies were included in the database. A profile of specimens in the database is given, followed by an analysis of trends in failure mode, strength gain, and deformability. Failure by debonding of FRP was prevalent among specimens in the database. One-third of the specimens with external reinforcement added showed strength increases of 50% or more in combination with considerable deflection capacity. It was clear from the experimental studies that the procedures followed were most representative of member strengthening rather than repair. Most of the specimens in the database were not subjected to sustained loading or damage causing loss of original capacity before external reinforcement was added. To assess the real potential of using FRP for expedient and economical field repair and strengthening of RC members, it was concluded that future research on the application of FRP to RC members should focus on conditions that are similar to what is observed in the field, including the effects of sustained load during repair/strengthening as well as corrosion- and load-induced damage.