PSI - Issue 78

Stefano Bozza et al. / Procedia Structural Integrity 78 (2026) 1213–1220

1218

Fig. 4: Maximum shear forces in load bearing (on the left) and shear keys (on the right).

The mean shear demand exceeds the nominal resistance in almost all load bearings, with the exceptions of those in the pier PI06, which is the tallest pier. The highest shear forces are concentrated in the shortest piers (PI01, PI02, PI08), the lowest ones are found in the tallest piers (PI04, PI05 and PI06), although the second load bearing of the pier PI04 shows forces comparable with bearings in shorter piers (PI03, PI07); this could be associated to dynamic effects related to the mid-span joint between PI04 and PI05. The demand/capacity ratio are higher in unidirectional bearings, ranging from 1.26 to 3.07, while in fixed bearings the ratio varies between 0.76 and 1.61; this can be mainly attributed to the lower transversal resistance of the unidirectional bearings. It is worth noticing that one of the seven analyses induced much larger effects, in particular in the curved deck, so that the mean demand is quite higher than the median demand. The mean shear demand in the shear keys exceeds the nominal resistance of the elements, with demand/capacity ratios up to3.35; the most stressed element is the shear key in the bottom slab, which restrains the differential transverse displacements of the two parts on the deck. As noticed for load bearings, one time history shows much larger forces than the other ones. In order to keep mean shear forces under the nominal capacity of all devices, the set of seven accelerogram records reported in Table 1 should be scaled by a factor 0.18; elements that first exceed the nominal capacity are the load bearings in PI01 and PI08. Since the forces in the numerical model exceed the nominal strength of the devices, their post-elastic behavior should be investigated to properly assess the real behavior of the structure and the actual seismic demand on the piers. 4.2. Joints and load bearings displacements Longitudinal displacements of unidirectional (U) and multidirectional bearings (M), transversal displacements of multidirectional bearings, closure of deck joints (J) and longitudinal displacements in the shear keys (SK) were evaluated and compared to the nominal displacement capacity specified in the design documentation of the bridge. All these results are reported in Fig. 5. The nominal capacity of joint closure was assumed equal to the gap between the abutment rear wall and the deck for the initial and final joint. The gap between the two parts of the deck was instead taken for the mid-span joint, while the capacity of the shear key displacement was assumed equal to the nominal capacity specified in the design documentation of the bridge. Actually, the values of the displacements are underestimated due to the linear behavior assumed for the bearings instead of the actual nonlinear behavior, but provide preliminary results to comprehend the bridge criticalities. The nonlinear behavior of load bearings and shear keys should be investigated in order to better estimate the actual displacements of the structure.