Post-Tensioning Steel Rod System for Flexural Strengthening in Damaged Reinforced Concrete (RC) Beams

Abstract

In this study, a post-tensioning method using externally unbonded steel rods was applied to pre-damaged reinforced concrete beams for flexural strengthening. Nine simply-supported beams, three reference beams and six post-tensioned beams, were subjected to three-point bending. The design parameters observed in this study were the amount of tension reinforcements (3-D19, 4-D19, and 2-D22 + 2-D25; “D” indicates the nominal diameter of the rebar) and the diameters of the external rod (φ22 mm and φ28 mm). A V-shaped profile with a deviator at the bottom of the mid-span was applied to the pre-damaged beams, and a post-tensioning force was added to overcome the low load resistance and deflection already incurred in the pre-loading state. The post-tensioning force caused by tightening the nuts at the anchorage corresponded to a strain of 2000 με in the external rods; this value was approximately equal to the strain caused by torque that two adults can apply conveniently. The post-tensioning system increased the load-carrying capacity and flexural stiffness by approximately 40–112% and 28–73%, respectively, when compared with the control beams. However, the external rods did not yield in the post-tensioned beam with larger steel reinforcements and external steel rods. The external rod with the larger diameter increased the flexural strength more effectively.

Application of external prestressing on the rehabilitation of reinforced concrete beams

“…The carbon fiber-reinforced polymer (CFRP) has gained popularity for employment in the repair of restoration material for the deteriorated RC structures [5]. The CFRP material is very stiff thus the distinction between the properties of the CFRP sheets and concrete will not favor the transfer of prestressing from the CFRP sheets to RC structure components [11]. Glass fiber-reinforcement polymer (GFRP) sheets have an elasticity Modulus that is close to that of concrete that is why it was selected in the study.…”

Theoretical Study on the Flexural Behavior of Structural Elements Strengthened with External Pre-Stressing Methods

“…For fire protection, the external tendon is usually covered with a coating, such as metal lath and plaster in the case of systems without ducts. External pre-stressing techniques with steel tendons have been widely used with success to improve existing structures in the United States, Japan, and Switzerland [1][2][3][4][5]. The problem of environmental effects (corrosions, fires, etc.)…”

Shear Behavior of RC Deep Beam Strengthened by V-Shaped External Rods

“…Taking account of the minimum prestressing 40% of the yield strengths of the external rods, Shin, Lee, and Kang proposed analysis and design methods for an EPT beam with a rectangular section at yield and the ultimate stage for both shored and unshored beams [4]. Lee, Shin, and Lee [12] further investigated the damage of EPT beam due to repetitive loading and concluded that the method was effective in controlling crack width and re-establishing the service load deflections of the beams. Many other researchers have focused on the determination of the stress generated in the external rod during the ultimate flexural failure of the strengthened beam [13][14].…”