PSI - Issue 78

Pasquale Bencivenga et al. / Procedia Structural Integrity 78 (2026) 1545–1552

1547

In this regulatory context, it is important to highlight that not all successive codes introduced substantial modifications relative to their predecessors. For instance, the 1945 standards (Ministry of Public Works 1945) brought significant changes primarily in the determination of design actions for bridges, while the approach to structural capacity assessment remained essentially unchanged. Based on an accurate code review, it has been stated that the most relevant regulatory developments were introduced by the following standards: • Royal Decree n.2229 of 16/11/1939 (Ministry of Public Works 1939); • Ministerial Decree of 30/05/1972 (Ministry of Public Works 1972); • Ministerial Decree of 26/03/1980 (Ministry of Public Works 1980); • Ministerial Decree of 09/01/1996 (Ministry of Public Works 1996). According to the first Italian code aforementioned, i.e. Royal Decree of 1939, the allowable compressive stress (σ c,adm ) in r.c. elements must be at least three times less than the compressive cube strength. Specifically, this value can be assessed using the 28-day cube compressive strength after casting (σ r,28 ), according to Equation (1): It is worth noting that the previous formula applies to values of strength greater than 225 kg/cm², while for ordinary ( σ r,28 =12 MPa) and high-strength ( σ r,28 =16 MPa) concretes, the allowable stresses was set to 40 kg/cm² e 50 kg/cm², respectively. Moreover, it included strength limits also for the steel, set at 140 MPa for mild steel and 200 MPa for medium hard or hard steel. Regarding the ratio between the elastic modulus of steel and concrete (E f /E c ), namely homogenization coefficient n, it was indicated as varying from 10 for normal-strength concrete to 8 for high-strength concrete. The first significant changes in the calculation approach were introduced with the Ministerial Decree of 30/05/1972 (Ministry of Public Works 1972), which imposed the use of concrete with compressive strengths not lower than 150 kg/cm², specifically 15, 20, 25, 30, 40 and 50 MPa. Furthermore, the allowable compressive stress was defined according to Equation (2), based on the 28-day characteristic strength R’ bk . As for steel, this regulation introduced the use of improved bond steel bars. It also identifies two types of steel (FeB22 and FeB32) with smooth round bars and three (A38, A41, and FeB44) with improved adherence, specifying for the latter allowable stresses σ s,adm of 220 MPa, 240 MPa and 260 MPa, respectively (Table 1). Referring to the homogenization coefficient n the possibility of using a value equal to 15 was also provided. The technical standard introduced in 1980 (Ministerial Decree of 26/03/1980), compared to the previous one, only permitted the use of a homogenization coefficient equal to 15. No changes were introduced regarding the evaluation of concrete and steel strengths. Regarding steel, four different classes were identified: FeB22k, FeB32k, FeB38k, and FeB44k as summarized in Table 1. The regulation introduced in 1996 (Ministry of Public Works 1996) marked a significant shift in structural design by transitioning from allowable stress methods to limit state design methods. This change focused on ensuring a more reliable approach to the safety and performance of structures. The new standard provided rules for determining allowable stresses and defined limit states for both the materials (e.g., concrete and steel) and the overall structure. Differently from allowable stress design, which limits material stresses under exercise loads, limit state design considers the ultimate strength and serviceability of structures under all possible conditions, including extreme scenarios. This approach uses partial safety factors for both loads and material resistances, ensuring that structures meet safety requirements throughout their lifecycle, consistently with current design approaches. The former two refer to smooth round bars, while the latter two correspond to bars with improved adherence. r,28 9 σ − 2 c,adm σ = + 75 225 kg / cm (1) ' R 150 − bk 2 c,adm σ = + 60 kg / cm 4 (2)