PSI - Issue 64

Ali Alraie et al. / Procedia Structural Integrity 64 (2024) 1943–1950 Ali Alraie, Saverio Spadea, Vasant Matsagar/ Structural Integrity Procedia 00 (2019) 000–000

1948

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strength. The reason behind reducing the post-tensioning force from 80% (NJF rope) to 30% (steel strand) is to account for the normal strength of concrete (35.5 MPa) and the small cross-section considered in this investigation and reduce the jacking stress because such high-strength steel strands are usually used with high-strength concrete and bigger cross-sections. The comparison between the load-deflection response of the steel-post-tensioned and NJF-post-tensioned beams is shown in Fig. 3(b). It can be seen from Fig. 3(b) that the post-tensioned beam with a high-strength steel strand has achieved 91.9 kN load-carrying capacity with 31.1% improvement over the control beam as compared to a 14.3% improvement in the case of NJF ropes. The highest load-carrying capacity of the steel post-tensioned beam is attributed to the significant difference in tensile strength between the high-strength steel strand and the NJF ropes; however, the non-corrodible merit offered by the NJF ropes may compensate for the relatively low strength achieved and attracts its usage in place of steel strands. To further benefit from using NJF ropes, the steel reinforcement was replaced with basalt fibre-reinforced polymer (BFRP) bars. The beam section became free of steel and, hence, corrosion-resistant. The BFRP bars used in this investigation have a 10 mm diameter, 966.7 MPa ultimate tensile strength, and 48.68 GPa elastic modulus. Fig. 3(b) shows the comparison between the load-deflection responses of all the cases, i.e., reinforced concrete beam with steel reinforcement (control beam), NJF rope-post-tensioned beam with steel reinforcement, high-strength steel post-tensioned beam with steel reinforcement, and NJF rope-post-tensioned beam with BFRP reinforcement. It can be seen from Fig. 3(b) that the beam reinforced with BFRP bars and post-tensioned with NJF ropes has achieved a relatively high load-carrying capacity of 84.2 kN with 20.1% improvement over the control beam; however, the deflection experienced by this beam is significant like the case of all other FRP composites. The low elastic modulus of BFRP, as compared to steel, leads to a large deflection of the beam upon cracking and makes the design governed by serviceability rather than strength. As mentioned previously, the highest load-carrying capacity with acceptable deflection was found corresponding to the steel-post-tensioned beam with steel reinforcement; however, because the beam, in this case, is prone to corrosion, the NJF rope-post-tensioned beam with steel reinforcement is found to be the most promising combination amongst all.

(a) (b) Fig. 3. (a) Effect of jute-post-tensioning on flexural behaviour; (b) comparison of all studied cases.

2.3. Experimental Work and Observations The experimental campaign includes investigations on the flexural performance of beams by conducting the four point bending test on reinforced concrete beams post-tensioned with one rope from natural jute fibre (NJF) of 14 mm diameter. The beams were reinforced with steel rebars and provided with ducts inside to accommodate the post tensioning NJF ropes. The jute rope was inserted inside the beam, fixed with anchors at one end, and tensioned using a hydraulic piston at the other end of the beam. The rope, which is a compressible material, was wrapped with cotton fabric at the anchor zone for better gripping to prevent the slippage of the rope inside the anchor. The rope was post tensioned by 6.8 kN, which is 80% of the ultimate tensile strength of the jute rope (55.4 MPa). The post-tensioning equipment consisted of wedge-type anchors, a hydraulic piston, and a hollow load cell for measuring the applied post-tensioning force. After using the post-tensioning force, the four-point bending test was conducted up to the