PSI - Issue 84

Biruk Yenehun Lemlem et al. / Procedia Structural Integrity 84 (2026) 1255–1263

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slightly higher values of 19% and 18%, respectively. Comparing the two reinforcement configurations reveals that relative capacity increases range from 29% to 91% depending on the STM model. STM A shows the greatest relative improvement (91%), though STM AB maintains the highest absolute capacity in both the reference (397 kN) and increased reinforcement (510 kN) cases. The dominant failure mechanisms differ between the reference and increased reinforcement cases, as summarized in Table 2. For the reference reinforcement case, failure is primarily governed by yielding of steel ties in most models. However, STM AB shows a mixed failure mode involving both reinforcement yielding and crushing of node N1, indicating that the combined load path induces higher compressive stresses in localized nodal regions. In the case of increased reinforcement, all STM configurations exhibit combined failure mechanisms involving both reinforcement yielding and concrete crushing in nodes or struts. This shift demonstrates that as reinforcement quantities increase, concrete capacity becomes more critical. These failure mode transitions are consistent with experimental observation reported by Desnerck et al. (2016) and analytical investigation reported by Luyten et al. (2024).

Figure 6 Reference case STMs capacity and load distributions

Figure 7 Increased rebar case STMs capacity and load distributions

Table 2 STMs failure mechanisms

STM A STM B STM AB

STM C

Reference case Increased rebar case

T2

T5

T5/N1 T5/N1

T2

T1/N1

T5/C4

T2/N5

5. Conclusion 5.1. Main Conclusions

1. Among the four STMs analyzed (A, B, AB, and C), STM AB consistently exhibited the highest lower-bound capacity, effectively mobilizing both diagonal bars and vertical stirrups. The strategically positioned node N6 further enhanced load transfer efficiency. For all cases studied, STM AB provided a conservative yet realistic estimate of structural resistance, confirming its suitability as the preferred model for capacity assessment. 2. Analytical equations were established to determine half-joint capacity using STM within a probabilistic framework, and these calculations were efficiently automated in MATLAB. The proposed approach enabled reliable capacity prediction and facilitated rapid evaluation across varying geometries, reinforcement configurations, loading conditions, and material properties. 3. The mean capacities predicted by the probabilistic STM approach showed good agreement with results from both Luyten et al. (2024) and Desnerck et al. (2016), validating the probabilistic methodology and its ability to capture uncertainties in material properties, loading, and model bias. 5.2. Further Developments Future research should focus on time-variant reliability analysis incorporating material degradation to enable service life predictions. The MATLAB-based framework can be extended to include multi-STM superposition techniques and