Torsional behavior of RC beams strengthened with PBO-FRCM composite

Externally bonded fiber reinforced cementitious matrix (FRCM) composites have been investigated recently as an alternative to fiber reinforced polymer (FRP) composites to overcome certain shortcomings such as the inability to install on wet surfaces or in low temperatures, low fire resistance, low glass transition temperature, low reversibility, and lack of vapor permeability. This study includes an inclusive investigation of the torsional behavior of RC beams strengthened with externally bonded polyparaphenylene benzo-bisoxazole (PBO)-FRCM composite material. A comprehensive review and discussion of the previous experimental, analytical, and numerically-simulated torsional behavior of RC beams strengthened with FRP composite was introduced to gain a better understanding of their behavior. Then, an experimental campaign was conducted that included 11 solid rectangular RC beams, one without strengthening and 10 that were externally strengthened with PBO-FRCM composite. The effect of different parameters such as number of wrapped sides, the continuity of composite layer, number of composite layers, and fiber orientation on the torsional behavior in terms of strength, rotational ductility, and failure mode was investigated. Finite element and analytical models of the PBO-FRCM-strengthened beams were developed and verified with the experimental results. The contribution of the composite to the torsional strength was estimated based on the measured strain using design provisions for FRP-strengthened beams to examine the applicability of these provisions to the FRCM composite system. Furthermore, a comparison with other composite systems was conducted to compare the efficiency of the PBO-FRCM composite system on increasing the torsional strength of RC beams --Abstract, page iv

Shear strengthening of concrete members with TRM jackets: Effect of shear span-to-depth ratio, material and amount of external reinforcement

An experimental work on reinforced concrete (RC) rectangular beams strengthened in shear with textile reinforced mortar (TRM) jackets is presented in this paper, with focus on the following investigated parameters: (a) the amount of external TRM reinforcement ratio, ρf, by means of using different number of textile layers and different types of textile fibre materials (carbon, glass, basalt); (b) the textile geometry, and (c) the shear span-to-depth ratio, a/d. In total, 22 tests were conducted on simply supported rectangular RC beams under (three-point bending) monotonic loading. The experimental results revealed that: (1) TRM is very effective when the failure is attributed to debonding of the TRM jacket from the concrete substrate; (2) the trend of effective strains for carbon, glass and basalt TRM jackets is descending for increasing values of the TRM reinforcement ratio, ρf, when failure is associated to debonding of the jacket; (3) the effect of textile geometry is significant only for low values of ρf, resulting in variances in the capacity enhancement and the failure modes, and (4) the shear span-to-depth ratio has practically no effect to the failure mode nor to the TRM jacket contribution to the total shear resistance of the RC beams

Torsional Strengthening of Reinforced Concrete Beams with Externally Bonded Composites: A State of the Art Review

The use of externally bonded (EB) fiber reinforced composites to strengthen reinforced concrete (RC) structures has been explored extensively in recent decades. While many studies have been conducted on the flexural, shear, and axial strengthening of RC members, far fewer studies have been conducted on torsional strengthening. Thus, the knowledge on the behavior of RC members strengthened in torsion with EB composites is rather limited. The aim of this paper was to present a comprehensive review and evaluation of torsional strengthening of RC beams using EB composites. A detailed survey of the literature was conducted, and a database of experimental tests was developed. The database includes beams reinforced with EB fiber reinforced polymer (FRP) and EB fiber reinforced cementitious matrix (FRCM) composites. The effectiveness of the strengthening system was examined in terms of geometrical and mechanical characteristics of the RC beam, composite type, and composite wrapping configuration. Different modes of failure of the strengthened beams were also discussed. Additionally, analytical and numerical methods developed to predict the torsional response of RC beams strengthened with EB composites were summarized and discussed. Finally, design provisions were examined based on the knowledge gained from this study

A Study of the Effect of Fiber Orientation on the Torsional Behavior of RC Beams Strengthened with PBO-FRCM Composite

Repair and rehabilitation of reinforced concrete (RC) structures with different types of external reinforcement has been investigated widely. Fiber reinforced cementitious matrix (FRCM) is a new type of composite system that contains continuous fibers embedded in inorganic matrix. This system has been proven to be effective for strengthening RC members under flexure, shear, and axial loadings. However, studies on the use of FRCM composite for torsional strengthening are very limited. This study investigated experimentally the torsional behavior of solid rectangular RC beams strengthened with externally bonded PBO-FRCM composite in different wrapping configurations. The study focused on the effect of fiber orientation as well as other parameters that influence the torsional strength, torsional moment-twist per unit length response, and mode of failure including fiber continuity and number of composite layers. The strains in the internal and external reinforcement and the longitudinal elongation of the strengthened beams were examined, and a comparison with other types of fiber reinforced composite was also discussed. The 90° fiber orientation (perpendicular to the beam longitudinal axis) was more effective in increasing the torsional strength than the 45° fiber orientation since premature debonding of the fibers occurred at the ends of the 45° strips, which contrasted the potential benefits from optimizing the fiber orientation and led to the underutilization of the composite. The 90° fiber orientation was also more effective than the 0° fiber orientation

Torsional Behavior of RC Beams Strengthened with PBO-FRCM Composite -- An Experimental Study

The use of fiber reinforced cementitious matrix (FRCM) composites has been studied for flexural and shear strengthening of reinforced concrete (RC) members, but currently there are no studies on its use for torsional strengthening. This paper presents the results of an experimental study in which solid rectangular RC beams were externally strengthened with PBO-FRCM composite material in different wrapping configurations to investigate the torsional behavior in terms of strength, rotational ductility, and failure mode. Increases in the cracking torque, torsional strength, and corresponding values of twist were achieved by beams strengthened with a 4-sided wrapping configuration relative to the control (unstrengthened) beam. On the other hand, the 3-sided wrapping configuration was found to be largely ineffective in improving the torsional performance due to excessive fiber slippage. The contribution of the strengthening system to the torsional strength was reasonably predicted (±20%) by the strain measured in the composite fibers. Provisions used to estimate the torsional strength of RC beams with fully-wrapped, externally-bonded fiber reinforced polymer (FRP) composites were found to be applicable to beams strengthened with PBO-FRCM composite

Analytical Study on the Torsional Behavior of Reinforced Concrete Beams Strengthened with FRCM Composite

In this study, an analytical approach was used to predict the full torsional response of RC beams strengthened with externally bonded fiber-reinforced cementitious matrix (FRCM) composite. The analytical model was based on the softened membrane model for torsion (SMMT) modified for fiber-reinforced polymer (FRP)-strengthened beams. As a first attempt, fully wrapped beams with fiber rupture governing the mode of failure were considered in this study. The model was validated by comparing the analytical response to the experimental response of five solid, rectangular RC beams. The model was able to predict values of the cracking and ultimate torsional moment and the corresponding angles of twist per unit length with reasonable accuracy. Also, reasonable agreement was achieved between the experimental and analytical results in terms of the overall response and failure sequence. The results confirm the feasibility of the SMMT model to predict the torsional response of fully wrapped FRCM-strengthened beams with the fiber rupture failure mode. However, additional modifications are required to extend the model to U-wrapped configurations and composite debonding failure modes

Finite Element Study on the Behavior of RC Beams Strengthened with PBO-FRCM Composite under Torsion

This paper describes the results of numerical simulation performed to investigate the torsional behavior of reinforced concrete (RC) beams strengthened with externally bonded fiber reinforced cementitious matrix (FRCM) composite. A nonlinear finite element analysis was performed using LS-DYNA. FE predictions were in reasonable agreement with experimental results of FRCM-strengthened beams under torsional loading in terms of failure mode, torsional strength, and corresponding twist per unit length. A parametric study was also carried out to study the influence of concrete compressive strength and FRCM composite strip width and spacing. Results showed that the torsional strength increases with increasing concrete compressive strength when failure is governed by crushing of the concrete strut. When failure is governed by fiber rupture, the torsional strength was not sensitive to concrete compressive strength. The parametric study also showed that the torsional strength increases with increasing fiber reinforcement ratio, although the increase in torsional strength is not directly proportional to the increase in fiber reinforcement ratio