###### Abstract  
This study aims to strengthen the flexural behavior of structural elements with external pre-stressing tendons, thereby improving their load-carrying capacity and increasing their resistance against the external load. Different techniques were used to apply external pre-stressed strengthening to RC beams and RC frames. Seven identical RC frames were analyzed: an original sample without an external tendon, two strengthened samples with external tendons at the positive bending zone, two strengthened samples with external tendons at the beam-column connection zone, a strengthened sample with external straight line tendons along the beam and, finally, a strengthened sample with external U-shape tendons along the beam of the frame. The analysis and the results were obtained using ANSYS WORKBENCH finite element (FE) program. Comparisons were performed between these techniques to determine which technique is better for strengthening. The failure mode, vertical deflection, column stress, load-carrying capacity, and ductility of the samples were listed and analyzed under four-point vertical loading. The results show that using external tendons significantly increases the load capacity and the stiffness of structural frames. Moreover, the tendon in the beam zone is more effective than the tendon in the column zone. s +
Footnote †: journal: Applied Sciences  
* Easy inspection and replacement of the tendon corrosion protection. * Friction losses are significantly reduced because external tendons are linked to the structure only at the deviation and anchorage zones. * The possibility of controlling and adjusting the tendon forces. * There is no weakening of the compression area due to ducts, so a minimum web thickness is achievable. Many studies have discussed external pre-stressing in different structures. [PERSON] et al. [1] enriched the experimental study of the external pre-stressing of RC members. They strengthened seven identical RC T-beams with external pre-stressing tendons in the laboratory and tested them under vertical loading. This study discussed experimentally the effect of the number of deviators, the tension method (direction), and the tendon profile on the flexural behavior of RC T-beams by making different cases for studying. [PERSON] et al. [14] investigated how to retrofit RC frames against progressive collapse using pre-stressing tendons. They examined the effect of the external pre-stressing tendons along slab girders on the progressive collapse performance of six- and twenty-story RC model frames when the first story loses its inner column suddenly under static and dynamic loads. The results showed that the initial tension and cross-sectional area of the tendons exerted a positive influence on the retrofitting of the structures under static and dynamic conditions. [PERSON] et al. [15] showed that external post-tensioning can increase the load capacity of a single-bay frame by 30%. Subsequently, [PERSON] et al. [16] studied the effect of post-tensioned cables on the strengthening of steel frames in order to raise their efficiency to all types of external loads. The effects of different techniques of external post-tensioning on simple frames, double bay frames, and double story frames were the subjects of this study. The profile and the location of the pre-stressed cable were used to differentiate between these techniques. The results of this paper showed that every frame featured a certain technique that could improve the load-carrying capacity of this frame. Finally, the authors concluded that the pre-stressed tendons could enrich the load-carrying capacity by about 35%or more according, to the pre-stressing force and the eccentricity of the tendon. This technique is more economical compared to other methods of strengthening, as described by [PERSON]. [17].