PSI - Issue 84

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

945

1. Introduction Bridge fires resulting from the collision of vehicles, underneath an overpass at low clearance, are fuel-controlled fires, generally very intense and explosive in nature, characterized by a fast-heating rate and very high temperature peaks. However, bridge fire design is not covered in current Italian and European regulations despite the rapid increase of urban ground transportation systems. Specifically, performance levels for different categories of use and fire loads for thermal analysis are not prescribed while significant differences exist between bridge and building fires. It is well known that bridges with steel beams are particularly sensitive to fire-induced damage compared to any other bridge beams, because of their high thermal conductivity and high ratio of the exposed heating surface to cross-sectional area (Zhang et al, 2022). However, bridges with prestressed concrete (PC) double-T beams and isolation at the deck level with elastomeric bearings (e.g. high-damping-rubber bearings, HDRBs) also exhibit higher vulnerability to fire than early bridges with concrete beams. Experimental studies report that concrete spalling and loss of prestress at elevated temperatures have a significant influence on the fire resistance of PC beams with thin webs (Shakya and Kodur, 2016). On the other hand, a sudden reduction of the horizontal and vertical stiffness of HDRBs is observed when temperatures exceed the point at which vulcanization between layers of rubber and interior steel plates occurs (Mazza and Alesina, 2019), with higher temperatures inside the rubber in the proximity of the steel plates confirming that heat transfer in both the radial and vertical direction occurs (Lucon et al., 2022). 2. Bridge structure A simply supported overpass constituted of three spans of equal length supported by two RC abutments and two RC frames with four circular piers with 1 m diameter and 4.45 m height, connected at the top by a pier cap, is assumed as test bridge (Fig. 1). A type F urban road, with two traffic lanes and two rows of parking spaces, is supposed to be located in the densely populated area of Rende (Cosenza, Italy) over a roadway. The deck is made of four precast PC beams, with a double T symmetric cross-section, and a reinforced concrete (RC) slab, with self-supporting precast predalles (Fig. 1b). The seismic isolation of the deck is obtained by inserting twenty-four identical elastomeric bearings (i.e. HDRBs), eight on the top of each pier and four on the top of each abutment (Figs. 1a,b). The design of the composite (PC/RC) deck is carried out in line with the provisions of the current seismic Italian code (NTC18, 2018), considering the Courbon’s method for calculating the distribution of the vertical loads: i.e. distributed dead loads, corresponding to self-weight of PC beam (20.68 kN/m), RC slab (7.5 kN/m 2 ), pavement (2.35 kN/m 2 ) and sidewalk (5 kN/m 2 ); double-axle concentrated (i.e. 300 kN, 200 kN and 100 kN for the notional lanes 1, 2 and 3, respectively) and distributed (i.e. 9 kN/m 2 , 2.5 kN/m 2 and 2.5 kN/m 2 , for the notional lanes 1, 2 and 3, respectively).

(a) Cross-section in the longitudinal direction at a PC beam.

(b) Cross-section in the transversal direction at a frame pier. Fig. 1. Simply supported bridge structure (unit in m).