Design theory of reinforced concrete beams strengthened with prestressed carbon textile reinforced concrete plates

[Objective] In this paper, we proposed a new method to enhance the flexural performance of reinforced concrete (RC) beams, improve construction efficiency, and reduce the wet work at the reinforcement site. This method involves reinforcing RC beams with prestressed carbon textile reinforced concrete (P-TRC) plates connected to the RC beams using nails. [Methods] The proposal is underpinned by a four-point bending test conducted on P-TRC plates RC beams. The test results led to the development of a calculation formula for the height of the compression zone in beams reinforced with P-TCR plates in different modes, such as cracking, yielding, tensile failure, and compression failure. [Results] These calculations consider the strain hysteresis of the carbon fiber fabric, which is caused by nail bending. Furthermore, the formula to calculate the bending bearing capacity of the reinforced beam's tension zone under different failure modes was obtained from moment balance. This paper also introduces the stress mechanism of the nail as a reinforcing layer. When traditional layer paving methods are used to reinforce the RC beam, the adhesion between the reinforcing layer and the RC beam relies heavily on chemical adhesion, the frictional resistance between the old and new concrete, and the mechanical occlusion force of the joint surface. However, quantifying the shear performance index of the reinforcing layer proves challenging, and it is difficult to guarantee the failure mode of the reinforcing layer. If peeling or detachment occurs in the reinforcement beam, it could easily lead to a failure in the reinforcement effect. Conversely, when a nail is used for reinforcement, the nail bears the shear capacity of the reinforcement layer. The shear bearing capacity of the nail gradually tends to decrease from the pure bending section of the reinforced beam to the bending and shear section of the same. Under the action of the concentrated force couple formed by the load and the support reaction, the nail in the bending shear section undergoes normal tension. This normal tensile force is generated by the frictional force between the nail and the concrete. By controlling the number, size, and shear strength of nails, the shear performance index of the reinforcing layer can be quantified. Consequently, the P-TRC plate only experiences a failure mode of tensile failure. Additionally, this paper proposes a calculation formula for the midspan deflection of the beam reinforced with a P-TRC plate during normal use, considering the elongation of the reinforcement at the bottom of the beam. Moreover, through experimental procedures, a theoretical calculation formula for the maximum midspan deflection of the beam reinforced with P-TRC plates is proposed. [Conclusions] To validate the calculation formula for the bending bearing capacity and deflection of the reinforced beam, the flexural capacity and midspan deflection curve of the normal cross-section of the beam reinforced with P-TRC plates under six different working conditions was calculated and compared with the test value. The results show that the theoretical and experimental values of the beam reinforced with P-TRC plates are consistent. This suggests that the presented calculation method holds significant value as a reference for guiding actual engineering design. © 2024 Tsinghua University. All rights reserved.