No 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.

The objective of the research is to improve the structural behavior of reinforced concrete (RC) T–beams by applying various techniques of external pre-stressing tendons, thus enhancing the load-carrying capacities and raising the resistance to applied forces. Seven identical RC T–beams were subjected to four-point loading to study the influence of the deviator number, tension mechanism, and tendon profile on flexural behavior. Of these, one beam was an original specimen without any tendons. The other six beams were strengthened with external tendons: two identical specimens with straight–line tendons but with a different number of inner deviators; two identical specimens with V–shaped tendons but with a different tension direction; and finally, two identical specimens with U–shaped tendons but with a different tension direction. The results and discussion were achieved using finite element (FE) software, ANSYS WORKBENCH. The results from all specimens were listed and analyzed for the failure mechanism, load-carrying capacity, deflection, and ductility. According to the FE results, external tendons greatly enhance the load-carrying and stiffness of RC beams. In addition, strengthening beams with external pre-stressing techniques can delay the early cracking load, yield load, and ultimate load by approximately 250%, 570%, and 30%, respectively, when compared to an unstrengthened beam. Moreover, the straight-line tendon with inner deviators was obtained to be the most effective technique for simple beams.

Post tensioned "PT "floors are one of the most widely used systems for building construction all over the world. Such systems have too many behavior, construction and economic benefits over other systems used for relativitely long span floor system . In Egypt, the use of PT systems still has market and economic constraints related to practice and leading to very limited use of such superior system. This paper aims at investigating in-depth the different merits of PT systems considering behavior, design, construction and economic issues. In addition a numerical study for comparison of the costs with the RC flat slab constructio which is the most commonly used system in the Egyptian market. Economic span of PT systems and the saving in concrete, rebar costs as balanced to the additional PT strands, ducts and accessoriness's are investigated. Results indicated the advantages of using PT floor systems especially for relatively large spans and multistory construction where time plays an important role. Spans more than 8.3 meters, PT sy proved to be more economic according to the Egyptitian market practice. This economic span becomes slightly less in case of more live loads.

The use of nanomaterials improves the performance of reinforced concrete (RC) beams in terms of cracking load, failure load, and deflection. To further evaluate this improvement, the behavior of RC beams subjected to cyclic loading has to be experimentally investigated. In the present study, the effect of adding nanomaterials to RC beams was studied experimentally under monotonic and cyclic loadings. Eight RC beams with the dimensions of 2200 mm × 350 mm × 120 mm were prepared and divided into two groups. Both groups were tested under three-point bending, but one group was tested monotonously whereas the other group was tested cyclically. Each group consisted of four beams. The first beam in each group was tested without adding any nanomaterials. Nanotitanium, nanoaluminum, and nanosilica were added to the concrete mixes of the remaining three to replace 1% of the cement content. The performances of the tested beams were compared in terms of load-deflection curves, failure mode, cracking load, failure load, bending stiffness, toughness, and residual strength ratio (RSR). The results from both monotonic and cyclic loadings indicated better performances when nanotitanium was used.