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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Subsequently, the previously described CSA was employed not only to simulate the response to 4-point bending loading until failure, but also the long-term behavior during exposure to natural environmental conditions under sustained loading while accounting for time effects. Additionally, sensitivity analysis was conducted to explore the effects of relevant parameters on both long-term and monotonic loading responses. For the long-term calculations, fib Model Code creep and shrinkage models were validated and the evolution of concrete compressive strength was considered from the same guideline. FeSMA stress relaxation was evaluated under three different assumptions, namely no relaxation (not realistic, only for comparison purposes), 10% (as in (Shahverdi et al. 2018) and 15% (typical value for relaxation of prestressing steel). Subsequently, structural response was simulated for the entire duration of sustained loading and exposure for both beams with activated and non-activated strips. The accuracy of the CSA was confirmed, as demonstrated by mid-span deflections in Figure 4.

Figure 4: Measured and calculated mid-span deflections of beams during natural environmental exposure and sustained loading.

As an exploratory investigation, the CSA was used to assess the impact of mechanical loading, load-dependent, and load-independent long-term effects (e.g., creep and shrinkage of concrete, relaxation of FeSMA) on mid-span deflection, as summarized in Table 3 and shown graphically in Figure 5. Initially, only mechanical loading influences deflections, but after the 8-year period, its contribution decreases to roughly 45%. Shrinkage contribution was determined by simulating bending behavior only with self-weight. Creep contribution was calculated based on the stresses resulting after assumed FeSMA relaxation. The remaining deflection was attributed to FeSMA relaxation, which was significant and should not be neglected. The contribution of concrete creep did not significantly differ between the two beams. However, due to lower total deflections in the activated beam, creep had a relatively higher contribution to its total deflection. Table 3: Calculated mid-span deflections immediately after loading (2015) and before unloading (2023), and their respective contribution to the total deflection, assuming different levels of stress relaxation in the activated SMA strip. B8 - no relaxation Contribution to ݑ [mm] / u [%] [mm] / u [%] [mm] / u [%] [mm] / u [%] Loading 4.74 47.73% 4.74 44.18% 4.74 43.13% 6.00 44.41% Creep 4.68 47.13% 4.96 46.23% 5.01 45.59% 5.62 41.60% Shrinkage 0.51 5.14% 0.51 4.75% 0.51 4.64% 1.89 13.99% Relaxation 0.00 0.00% 0.52 4.85% 0.73 6.64% 0.00 0.00% Total 9.93 100.00% 10.73 100.00% 10.99 100.00% 13.51 100.00% B7 - no relaxation B7 - 10% relaxation B7 - 15% relaxation