PSI - Issue 84

Fabio Mazza et al. / Procedia Structural Integrity 84 (2026) 944–951

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of the steel plate (D s ) and that of the elastomer (D e ); thickness of the interior (t s,i ) and exterior (t s,e ) steel shims; thickness of the outer steel plates (t p,e ); number (n e ) and thickness (t i ) of the single layer of elastomer; total thickness (t e ) of the elastomer; primary S 1 and secondary S 2 shape factors; displacement at the CP limit state (d dC ). Table 1. Geometric properties of the HDRBs (units in mm). D s D e t s,i t s,e t p,e n e t i t e S 1 S 2 d dC 680 700 2 23 30 18 5.4 97.2 31.5 7.0 200 The equivalent viscous damping ratio in the horizontal direction is considered equal to   =10%, on the assumption that the substructure remains in a substantially elastic range (behaviour factor, q H =1). The fundamental vibration period of the isolated deck satisfies the condition T ID (=1.44 s) ≥ 3T FB (=0.47 s), T FB being the fundamental vibration period of the fixed bridge without seismic isolation. The effective mass of the isolated deck (m e,ID ) is equal to 88% of the total mass of the bridge (m tot =605 kNs 2 /m). A nominal stiffness ratio α K0 , defined as the ratio between the nominal value of the vertical stiffness (K V0 ) and the analogous value of the horizontal stiffness (K H0 ), equal to 1120 is assumed for all the isolators, considering a volumetric compression modulus of the rubber E b =2000 MPa and a shear modulus G= 0.40 MPa. 3. Fire scenarios The roadway crossing below the central span of the bridge represents a type D urban flow road (DM6792, 2001), with two lanes per direction separated by a median strip and with piers close to the road and without crash barriers. The traffic composition includes different types of vehicles shown in Fig. 3 (de Silva et al., 2025): i.e. V1, semi-trailer with palletized cargo; V2, large passenger bus; V3, car with an internal combustion engine; V4, standard semi-trailer fuel truck full of gasoline; V5, box-type semi-trailer truck that is half full of palletized flammable cargo; V6, motorcycle; V7, electric car.

(a) Elevation.

(b) Plan. Fig. 3. Fire scenarios for the roadway below the central span of the bridge (unit in m).