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

1946

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Fig. 1. Natural jute fibre (NJF) ropes and stress-strain curves of the tested samples.

2.2. Analytical and Numerical Approach The reinforced concrete beam considered in this study has dimensions of 150 mm, 200 mm, and 2000 mm for width, depth, and length, respectively. The centre-to-centre distance while testing in flexure is 1800 mm. The compressive strength of the concrete is 35.5 MPa. The beam is reinforced with two steel bars of 12 mm diameter as tension reinforcements for the control beam (without post-tensioning) and the same reinforcements for the post tensioned beam in addition to one unbonded jute rope of 14 mm diameter for post-tensioning. The steel bars' yield and ultimate tensile strength are 500 MPa and 565 MPa, respectively. The ultimate tensile strength of the jute rope is 55.4 MPa, and the elastic modulus is 754.3 MPa, as mentioned previously. The jute rope is post-tensioned up to 80% of its ultimate tensile strength. The shear reinforcements were made from steel bars of 6 mm diameter with 120 mm centre-to-centre spacing. The longitudinal section and cross-section of the beam are shown in Fig. 2. For evaluating the effect of post-tensioning on the flexural strength of the beam, the flexural analysis was carried out for both cases, i.e., for the beam with and without post-tensioning. The load-carrying capacity was found to be 60.9 kN and 63.8 kN for the control beam (without post-tensioning) and the jute-post-tensioned beam, respectively, and was hence improved by 4.8% owing to the post-tensioning applied through the NJF rope. However, the analysis was extended by using four unbonded NJF ropes for post-tensioning, and the load-carrying capacity was found to be 72.2 kN, with an 18.6% improvement over the control beam. For more reliability, a finite element modelling (FEM) of the NJF rope-post-tensioned RC beam and the control beam was conducted using the commercially available software ABAQUS ® . Concrete was modelled using 8-node linear brick (C3D8R) elements, whereas the steel was modelled using 2-node linear 3-D truss (T3D2) elements, all having six degrees of freedom. The unbonded NJF rope was modelled using its complete geometry as 6-node linear triangular prism (C3D6) elements with six degrees of freedom. Concrete damaged plasticity (CDP) was used to model the concrete, whereas the elastic modulus, Poisson’s ratio, yield strength, and ultimate tensile strength were specified to define the steel material. As mentioned previously, the ultimate tensile strength and elastic modulus of the NJF were determined based on the results of the experimental work. The steel reinforcements were embedded inside the concrete host element. The post-tensioning force was applied in the predefined field as an initial stress of 80% of the ultimate tensile strength of the jute. The displacement-control loading was used in a static step up to failure. The FEM was validated with experimental results of sets of beams tested in the Concrete Structures Laboratory (CSTL) at the Indian Institute of Technology (IIT) Delhi (India), and it was deemed valid for further investigation.