**4.2. Solution with fluid dynamic dissipation devices (Sol. 1)**

The solution respects all the restraints desired by the client. It is not necessary to intervene by reinforcing the piers, the gaps on the abutments are assured (displacements less than 15 cm), the bearing system of the current situation even in the transient phase (during works) is assured and the structure is totally verified. Implementing this solution requires rather high imple‐ mentation costs. In fact, it is necessary to remodel the top of each pier by widening the top to allow the housing of the contrast structures of the dissipating devices. Another relevant cost can be ascribed to the assembly of the same dissipating devices.

From a global point of view (not strictly engineering), this is the best solution as it allows a check of the stresses acting on the substructures, regardless of the intensity of the seismic event, at the expense of the displacement of the devices. The devices are provided by law with a safety margin to be able to tackle greater displacements compared to those for which they have been designed. Therefore, it is necessary to implement the joint gaps with a consistent safety margin in order to avoid hammering between the deck and the abutment structures.

## **4.3. Solution with curve sliding isolators (Sol. 2)**

The solution with the sliders is the most efficient, in regards to the stresses on the substructures and for the displacements during the seismic stage. But it does feature some issues in regards to the management of the bearing system during assembly, given that the actual fixed points of the deck are removed. During operation, although, for horizontal loads, due to vehicular traffic (braking) and to wind, the minimum friction allows to develop a breakaway torque (*F*0) greater than the one, to which each support is subject, thermal expansion entails displacement at all the piers. This solution also allows a low implementation cost, since the support inte‐ grated the isolator, which features nearly the same sizes of the existing support.

From an engineering point of view, the solution is efficient and allows to involve in the dissipation process, both the piers (within the allowed capacity) and the devices (owing to the friction developed by the material interposed between the curved surfaces), with a work rate lower than the one required by the solution with only the dampers. Since the sliders is at the same time an isolator, the solution, moreover, allows enhancing the total response of the structure, defining a new oscillation period, independent from the deck mass but depending on the curvature of the devices. With reference to the modal analysis with the project spectrum, the structure undergoes a smaller seismic acceleration at the base, due to an increase in the period.

As far as realisation is concerned, the solution shortens the supply period (same type of device on all the piers), simplifies the launching operations for implementation, as the new devices feature sizes and space requirements similar to the existing supports. Yet, the type of support is not suitable for this specific viaduct, featuring a central point‐shaped bearing. It entails the application of auxiliary temporary restraints, for the management of the transitory stage, which is not easy to implement.

## **4.4. Solution with elastomeric isolators (Sol. 3)**

**4.2. Solution with fluid dynamic dissipation devices (Sol. 1)**

146 Structural Bridge Engineering

can be ascribed to the assembly of the same dissipating devices.

**4.3. Solution with curve sliding isolators (Sol. 2)**

period.

which is not easy to implement.

in order to avoid hammering between the deck and the abutment structures.

grated the isolator, which features nearly the same sizes of the existing support.

The solution respects all the restraints desired by the client. It is not necessary to intervene by reinforcing the piers, the gaps on the abutments are assured (displacements less than 15 cm), the bearing system of the current situation even in the transient phase (during works) is assured and the structure is totally verified. Implementing this solution requires rather high imple‐ mentation costs. In fact, it is necessary to remodel the top of each pier by widening the top to allow the housing of the contrast structures of the dissipating devices. Another relevant cost

From a global point of view (not strictly engineering), this is the best solution as it allows a check of the stresses acting on the substructures, regardless of the intensity of the seismic event, at the expense of the displacement of the devices. The devices are provided by law with a safety margin to be able to tackle greater displacements compared to those for which they have been designed. Therefore, it is necessary to implement the joint gaps with a consistent safety margin

The solution with the sliders is the most efficient, in regards to the stresses on the substructures and for the displacements during the seismic stage. But it does feature some issues in regards to the management of the bearing system during assembly, given that the actual fixed points of the deck are removed. During operation, although, for horizontal loads, due to vehicular traffic (braking) and to wind, the minimum friction allows to develop a breakaway torque (*F*0) greater than the one, to which each support is subject, thermal expansion entails displacement at all the piers. This solution also allows a low implementation cost, since the support inte‐

From an engineering point of view, the solution is efficient and allows to involve in the dissipation process, both the piers (within the allowed capacity) and the devices (owing to the friction developed by the material interposed between the curved surfaces), with a work rate lower than the one required by the solution with only the dampers. Since the sliders is at the same time an isolator, the solution, moreover, allows enhancing the total response of the structure, defining a new oscillation period, independent from the deck mass but depending on the curvature of the devices. With reference to the modal analysis with the project spectrum, the structure undergoes a smaller seismic acceleration at the base, due to an increase in the

As far as realisation is concerned, the solution shortens the supply period (same type of device on all the piers), simplifies the launching operations for implementation, as the new devices feature sizes and space requirements similar to the existing supports. Yet, the type of support is not suitable for this specific viaduct, featuring a central point‐shaped bearing. It entails the application of auxiliary temporary restraints, for the management of the transitory stage, The solution with elastomeric isolators is the less suitable option in this case. Although it allows not intervening on the piers, in regards to the base and heading sections, it involves more displacements than the previous solutions (thus requiring the widening of the gaps on the abutments, thus necessarily interfering with traffic circulation). As Sol. 2, it does not preserve the bearing system of the current situation in the transitory stage as desired by the client.

Yet, this solution has been analysed and compared, since it is one of the most widespread as for this type of intervention, and it is undoubtedly the cheapest.

