PSI - Issue 84

Gian Felice Giaccu et al. / Procedia Structural Integrity 84 (2026) 991–998

996

general trends. Figs. 4a and 5a demonstrate that the linear evaluation of the stress ratio Σ at 50% of the plastic resistance N pl,Rd yields a conservative estimate of concrete stress, making it suitable for Serviceability Limit State assessments. In contrast, Figs. 4b and 5b show that the linear estimate of the stress integral ratio η provides an accurate

approximation of the axial design force N Ed at the Ultimate Limit State. Table 1. Geometrical and structural properties of the investigated composite deck cross-section. Cross sections A s [cm 2 ] A c [cm 2 ] f ck [N/mm 2 ] f cd [N/mm 2 ] ε cu3 [% 0 ] f yk [N/mm 2 ]

f yd [N/mm 2 ]

ε su [%]

ρ m

N pl,Rd

[-]

[kN]

2410 2410 2950 3640 4000

17978 17978 17978 17978 17978

30 55 50 50 50

20.00 36.67 33.33 33.33 33.33

3.50 3.13 3.50 3.50 3.50

355 355 355 355 355

338.10 338.10 338.10 338.10 338.10

7.55 2.27 53840 7.55 1.24 75530 7.55 1.66 73072 7.55 2.05 85470 7.55 2.26 88620

S A /30 S A /55 S B /50 S C /50 S D /50

The discrepancy between the total axial force in the concrete N c,T and the effective axial force N c,eff is only marginally influenced by the simplifications inherent in the linear approximation - especially when compared to results from the nonlinear analysis. This observation holds consistently across all cross-sections analyzed in the study. While the authors previously applied a similar linear modeling approach to assess SLS behavior in a cable-stayed bridge (Giaccu et al. 2022), the present work extends that methodology to nonlinear analysis at ULS, see Fig. 6.

(a)

(b)

(c) (d) Fig. 6. Comparison of the stresses in the concrete slab at section = -0.2, under (a) bending moments ( M = -2830 kNm), (b) compressive forces ( N = -8424 kN) and (c) compression and bending ( M and N ); (d) dimensional interaction curves of the investigated cross-sections assessed according to Eurocode 4, with their effective width B eff . Notably, the results confirm that the diffusion angles of normal stress observed under nonlinear loading remain in close agreement with those reported in established literature, including Byers (1999), AASHTO (1994), and DIN 1075:1981. This finding reinforces the robustness of the proposed methodology and the reliability of stress diffusion assumptions across different limit states.