PSI - Issue 78

Dario De Domenico et al. / Procedia Structural Integrity 78 (2026) 65–72

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Fig. 2: Geometry and layout of the steel blocks placed on the beam to generate the additional bending moment required for achieving a 50%-50% dead-to-live load ratio (dimensions in cm).

2.2. Effect of transverse diaphragms, inspection holes and prestressing configurations The PC beam under consideration is meant to represent a typical bridge girder within a real grillage system. As such, it does not carry the full load applied to the bridge deck, but rather a fraction of it, depending on the degree of mutual collaboration among adjacent girders. This load distribution is influenced by the presence of transverse diaphragms, which provide structural interconnection. From an analytical perspective, the role of the transverse diaphragm in redistributing loads transversely can be idealized using a point spring located at mid-span of the primary girder. The stiffness coefficient of this spring must be calibrated to reflect the portion of load that is redistributed from the examined girder to neighboring ones. Based on a simplified Albenga-Courbon method applied to a four-girder bridge deck, approximately 30% of the total applied load is transferred to the adjacent girders. Accordingly, for an idealized case involving a unit point load applied at mid-span, the reaction force provided by the diaphragm (modeled as a spring) to redistribute 30% of the load corresponds to 0.3. This reaction causes a deflection denoted as 1 , which has been used to compute the required spring stiffness . Under laboratory conditions, the behavior of the point spring with stiffness can be physically replicated using a transverse steel beam positioned across the main girder at mid-span. The required flexural stiffness — and thus the specific cross-section — of this steel beam, which spans a length 2.0 m and is simply supported at both ends, can be derived from compatibility conditions. Specifically, the mid-span deflection of the transverse beam under a point load equal to 0.3 must match the deflection 1 of the idealized point spring in the analytical model; the condition = 1 suggests using an IPE 80 steel section as a suitable profile to reproduce the desired stiffness. To ensure proper contact between the transverse steel beam and the PC girder at mid-span, a set of adjustable threaded bars was included in the design to fine-tune the vertical positioning of the steel profile. Four series of beams — each composed of three specimens — were produced with varying configurations of inspection holes and prestressing systems (bonded and unbonded strands). The inspection holes are located on the beam soffit and consist of two recesses per beam (at a center-to-center distance of 23 cm), each measuring 3 cm in length, 30 cm in depth, and 6.5 cm in height. During casting, these cavities were filled with polystyrene, which can be easily removed to permit strand cutting during testing, thereby simulating artificial damage to the prestressing