Astaldi S.p.A. - Max Bogl GMBH





The bridge is "balanced cantilever girder" type and it is characterized by a central 145m span, with two side symmetric 72.5m spans. The total length of the bridge, including segments at abut­ments supports, is 292.0m. The deck show varying-depth through providing a curved soffit, this characterize the typical parabolic shape of deck girder. The depth of cross section deck varies from maximum value of 10.0m, at pier axis, to minimum value of 2.40m, at mid span and abutments supports. The upper slab is 14.75m wide and transversally inclined at 2.5%, like the road transverse slope. The upper slab show a variable thickness from a minimum of 25 cm, at mid span, to a maximum of 45cm, at two intermediate web supports. The box girder section is characterized by area of the bottom slab of variable thickness near the pier to keep bottom fiber compressions below allowable maximum at this location. The thickness of concrete webs is 30cm for center spans segments and 40cm for closest to pier segments. The deck is characterized by internal tendons, where the post-tension layout is characterized by upper and lower positions. The upper tendons play an important role during construction phases because of their counterbalance action against segments self-weight activation, then reduce vertical deflection of the free cantilever under gravity loads. The upper tendons are symmetric to the pier, with a linear path in the upper slab and short vertical deviation near the tendon end anchorage. The tendon anchorage is located at the end of each segment in both web at top position, where it has been defined a wider thickness zone up to 70cm. The lower tendon, activated at the end of free cantilever con­struction stage, are located along bottom slab with tendon end anchorage located in specific r.c. internal blisters. The lower tendon layout is symmetric to mid central span and located at end of side spans. The bridge deck is supported by two piers and two abutments through teflon-steel pot bearings. At each support there are two pot bearings, one with free sliding condition and one with one-way (longitudinal) degree of freedom. The longitudinal bridge restrain is given by viscous-dampers, that connect the abutments deck segment to the abutment front wall, that show a fixed behavior under static loads and displacement/velocity under dynamic actions to dissipate seismic loads. Under transverse direction the bridge deck is restrained to piers and abutments through one-way pot bearings, for static loads. In case of severe seismic actions the horizontal transverse force are transmitted by r.c. shear keys located at intrados of deck section. Per 1 and 2 are characterized by same shape but different height, respectively 17.40m and 16.15m. The pier has hollow rectangular section with 8.0m transverse and 6.0m longitudinal external dimensions and 60-80cm web thickness. At top pier there is a head capital, of same external dimensions of pier current section but with solid type. At the top of head capital are located two bearing r.c. block that transfer the vertical and horizontal deck reactions. At longitudinal edge of head capital are built two walls 1.25m height and 60cm thick. These part of the pier are useful during balanced cantilever construction stages, where pier table segment has to be fixed against rotation applying temporary supports at top of these walls. Piers base section is connected to r.c. massive rectangular footing, of 11.0mx13.0m dimensions and 2.0m thickness, that is founded to a ring of diaphragm walls able to transfer at deep ground static and seismic forces coming from the superstructure. Both abutments are spill-through type. The choice of this type has been supported because of the relevant height of the back embankment, that reach 8.8m in SP1 and 10.5m in SP2, and the high seismic action that could be developed by a traditional full abutment wall. The abutment structure has a top beam seat of L shape that is connected to the back wall. The beam seat collect both bridge deck vertical and horizontal reactions, through bearing pot and seismic longitudinal devices, and earth backfill pressure of the embankment. The beam seat is supported by a number of shear walls of rectangular section, 1.0m thickness and 4.9m length, aligned with longitudinal deck axis. Each shear wall is founded, trough an intermediate footing r.c. slab, to two deep diaphragm walls that transfer at deep ground static and seismic loading coming from superstructure and earth pressures. The seismic design of the bridge has been assessed through refined analysis. In details it has been assumed that under extreme sei­smic actions (Ultimate Limit State) the bridge develop ductility at the base section of the two piers in transverse direction and dissipate inertia force along longitudinal direction because of viscous-dampers on the abutments. These devices show a non-linear behavior with velocity (this is because the viscous property of the liquid that is inside the device), for this reason the seismic device has a limited maxim force that can be developed, reducing the risk of overloading abutments back walls and deck support.