PSI - Issue 64

Yunus Harmanci et al. / Procedia Structural Integrity 64 (2024) 2067–2074 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Figure 5: Visual comparison of experimental vs. calculated mid-span deflections before unloading and their contribution to the total deflection, with different levels of stress relaxation in the activated SMA strip. Experimental values are mean values of last 6 months before unloading.

During 4-point bending simulations, most recent material values at the time of loading were incorporated. As an example, mean concrete compressive strength was obtained from extracted concrete cores and estimated at 76.6 MPa, a good match to the fib Model Code prediction of 73.2 MPa. Bending response of both beams was accurately captured, effectively capturing yielding and ultimate loads, stiffness and deflections. As a last step, a global sensitivity analysis was conducted, relying on Sobol’ indices of sparse polynomial chaos expansions-based (PCE) metamodels. First order Sobol’ indices indicate the concrete compressive strength as the most influental parameter for output parameters. The SMA area also has a considerable impact, while the effect of concrete Young’s modulus is negligible. Interested readers are directed to (Harmanci, Czaderski, and Shahverdi 2024) for a more detailed explanation of these aspects. 5. Conclusions Long-term structural response of RC beams strengthened with NSM Fe-SMA strips were investigated under sustained loading and 8 years of natural environmental exposure. A cross-section analysis accurately simulated the structural response. Following key conclusions can be deduced from the findings:  Activated FeSMA strips notably affected mid-span deflections, with 41% lower instantaneous deflections during sustained loading and 24% lower long-term deflections compared to non-activated strips.  Despite significant irreversible deflections after long-term exposure and sustained loading, no capacity reduction was observed compared to unexposed beams that were subject to the same loading conditions. This is attributed to the absence of corrosion in both the steel and Fe-SMA reinforcements, and it is likely that any losses due to Fe-SMA relaxation were compensated by the increased strength of concrete.  Structural response of beams were well-reproduced by the cross-section analysis, demonstrating that long term effects such as concrete creeping and SMA relaxation can be integrated within the conventional formulation to accurately predict structural response.  Sensitivity analysis revealed that concrete compressive strength predominantly influenced ultimate load, mid-span deflection, and Fe-SMA strain, while concrete Young’s modulus had a negligible effect.