PSI - Issue 84

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

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as-built reinforcement layout. For STM A, tie T2 is positioned between the first two stirrups, while tie T3 is located at the fourth stirrup, resulting in the geometry shown in Figure 2. STM B follows a similar nodal positioning procedure but reflects the diagonal reinforcement arrangement, as illustrated in Figure 3. STM AB employs additional geometric optimization through strategic placement of node N6, with the final configuration presented in Figure 4. STM C incorporates the specific tie arrangements prescribed by design guidelines, as shown in Figure 5. 4.2. Predicted Capacity of Reference Case STMs The probabilistic resistance predictions for the half-joint with the reference reinforcement configuration are presented in Figure 6, along with the applied load distribution. The four STM configurations yield substantially different capacity estimates, reflecting their distinct internal load transfer mechanisms. STM A predicts a mean capacity of 179 kN, representing the most conservative estimate and falling significantly below the mean service load of 197 kN. STM B and STM C provide intermediate predictions with mean capacities of 222 kN and 202 kN, respectively, though both remain below the characteristic design load of 300 kN. STM AB predicts a mean capacity of 397 kN, significantly exceeding all other models and surpassing the characteristic design load. This enhanced capacity—80% greater than STM B—demonstrates that the combined load path mechanism mobilizes both diagonal and vertical reinforcement more effectively by engaging multiple reinforcement components simultaneously. The coefficient of variation across all models is approximately 16%, indicating moderate and comparable uncertainty in resistance predictions. The resistance hierarchy (STM AB > STM B > STM C > STM A) reflects the effectiveness of reinforcement utilization in each model, underscoring the critical influence of STM selection on predicted capacity.

Figure 2 STM A

Figure 3 STM B

Figure 4 STM AB

Figure 5 STM C

4.3. Predicted Capacity of Increased Reinforcement Case STMs The probabilistic resistance predictions for the half-joint with increased reinforcement are presented in Figure 7. The increased reinforcement amount significantly improves predicted capacities across all STM models compared to the reference case. STM A, STM B, and STM C predict mean capacities of 343 kN, 332 kN, and 367 kN, respectively. These values are closely grouped and all exceed the characteristic design load of 300 kN. STM AB predicts a mean capacity of 510 kN, maintaining its position as the highest-capacity model and exceeding the service load by more than a factor of two. The coefficients of variation are 16% for STM A and STM B, while STM AB and STM C exhibit