Improving Torsional Behaviour Of Reinforced Concrete Beam Strengthened With Ultra High Performance Fibre Reinforced Concrete

Reinforced concrete members subjected to torsion may fail suddenly due to insufficient transverse steel reinforcing resulting from construction errors, or increased loading due to a change in purpose. Therefore, strengthening and upgrading is the most cost-effective and convenient solution. The proposed techniques to strengthen concrete members such as steel plates, polymers or concrete have important deficiencies in adherence and durability. So, the use of ultra-high performance steel fibre concrete (UHPFC) can effectively resolve these problems. On the other hand, there have been very little studies on the torsional behaviour of reinforced concrete (RC) beams with UHPFC composite. This work aims at studying the strengthening of rectangular beams with or without stirrups using UHPFC with different types of configurations and thicknesses to improve the torsional resistance of RC beams. Thereby, an experimental study has been made through this investigation to understand the behaviour of RC beams with UHPFC under torsion. Moreover, simulation of the experimental beams was studied using finite element analysis. The FE method from the ANSYS program is used. Variables considered in the test program include; influence of UHPFC configuration (full, U-jacked and left-right sides), influence of UHPFC layer thickness (10, 15, 20 and 25 mm), and influence of transverse steel reinforcement. Test results are discussed in this research based on torque-twist behaviour, torque-strain curve, influence of UHPFC on cracking and ultimate torque, crack patterns and mode of failure of each beam. Results show that the UHPFC matrix can generally be used as an effective external torsional reinforcement for RC beams with or without stirrups. The UHPFC contribution to torsional strength is increased when thickness increases, for all cases of strengthened beams. Moreover, the UHPFC material can be cast in a thin layer, while sandblasting of the specimen surface ensures good adhesion of the U-jacket without using any primer, which subsequently prevents premature failure of the structure and a significant increase in torque capacity. Despite the positive effect in increasing the torque capacity, left-right wrappingis not the most efficient and economical scheme for strengthening reinforced concrete using UHPFC. The fully wrapped beams exhibited considerably higher torque capacity and torsional behaviour. Therefore, the cracking and maximum torque capacity of the strengthened beams is dependent on both configuration and volumetric ratios of UHPFC. Meanwhile, the FE results show good agreement with the experimental results. The ratio of experimental values of the cracking torque to the predicted valuesfrom the FE results for all beams hasa mean of 1.059 and standard deviation of 0.089.The ratio of experimental values of the maximum torque to the predicted values from the FE results for the beams has a mean of 1.038 and standard deviation of 0.062.It is worth mentioning, the possibility of increasing the durability of the member by applying the UHPFC matrix, due to the reduced crack openings and to the compactness of the UHPFC matrix. Hence, the use of UHPFC appears to be a good method to enhance the torsional performance of RC beams

Numerical Analysis of Torsional Reinforcement of Concrete Beams in Unconventional by ANSYS Software

In this study, a finite element analysis is conducted to study the behaviour of RC beams with different configurations of transverse reinforcement under torsion. These configurations of stirrups are traditional closed stirrups, circular spiral stirrups, and inclined rectangular spiral stirrups. The numerical torsional load values are compared with the experimental torsional load values from previous research. The numerical analysis determined by the ANSYS software shows a reasonable agreement with the experimental torsional load values. The numerical results demonstrate that the use of continuous rectangular spiral stirrups improved the torsional response compared to using another type of beam stirrup. Thus, numerical results show that continuous spiral stirrups are effective at increasing torsional capacity. It is also noted that the behaviour of these beams with continuous spiral stirrups is better than the behaviour of the beams with traditional stirrups. The beams with helical reinforcement, which are TB2, TB3, and TB4 spiral reinforcements, greatly enhanced the toughness. The equivalent stresses are 13.709, 13.728, 14.72, and 15.894 MPa, while the equivalent elastic strains are 0.00421, 0.00377, 0.00347, and 0.00539 mm/mm for the beams TB2, TB3, and TB4, respectively. The beam TB4 had the highest stress and strain value, so its strength improved its ductility properties. As a result, the stirrups' configurations enabled the detection of beam failure mechanisms by improving torsional behaviour when compared to the beam's traditional stirrups. As a result, this research adds more knowledge to the literature on the most effective spiral stirrups for transverse reinforcement to improve the torsional behaviour of beams. Doi: 10.28991/CEJ-2023-09-01-04 Full Text: PD