PSI - Issue 78

Dario De Domenico et al. / Procedia Structural Integrity 78 (2026) 65–72 67 compatibility. By applying only the effects of axial force, the resulting ultimate moment is , = 87 kNm, with a reduction in flexural capacity of roughly 40% compared to the bonded configuration.

Fig. 1: Front view and cross section of designed PC beams with straight strands (units in [cm]) along with some photographs during the casting phases in the prestressing plant.

2.1. Determination of superimposed dead load Under typical service conditions for a PC bridge deck, the dead load and live load contribute approximately equally, each accounting for about 50% of the total loading. In the laboratory configuration, the live load is simulated by the force applied through a jack positioned at mid-span of the beam. Given that the average ultimate limit state (ULS) bending moment — computed using the mean concrete strength ) — is , = 150 kNm, and considering that failure occurs due to concrete crushing in compression, the design ULS bending moment at mid span, , can be estimated using the design strength of concrete = / in place of , where is the characteristic concrete compressive strength and is the partial safety factor for concrete (equal to 1.5): , ≈ 1 5 0 = 11 5. 50 45 53 = 85 (1) Starting from the value of , and assuming a partial safety factor of 1.35 for both permanent and traffic live loads in bridge structures, the mid-span bending moment at the Serviceability Limit State (SLS) under the characteristic load combination (European Committee for Standardization, 2002) is , = 63 . To meet the target distribution of 50% dead load and 50% live load, the mid-span bending moment attributed to the dead load should be: = 0.50 × = 31.5 (2) Given the beam’s self -weight of ℎ = 1.875 kN/m , the mid-span bending moment from self-weight is: ℎ = ℎ ⋅ 2 8 = 11.5 (3) As this value is lower than the required moment in Eq. (2) , it is necessary to supplement the beam’s dead load with an additional static load — referred to as "overload" — to generate the complementary mid-span moment: = − ℎ = 20.0 → = 8⋅ 2 = 3.3 (4) To apply this overload in practice, steel blocks were used. These blocks were fabricated by welding together eight steel plates, each 5 cm thick, resulting in a combined block with a width of 40 cm (slightly wider than the beam) and a height of 12 cm. For safety, each plate was designed with 2 cm teeth on either side to prevent lateral movement on the prestressed concrete beam. The blocks were placed side-by-side to cover a 280 cm clear span length on both sides of the beam, as illustrated in Fig. 2.