PSI - Issue 62

Carlo Pettorruso et al. / Procedia Structural Integrity 62 (2024) 677–684 Carlo Pettorruso/ Structural Integrity Procedia 00 (2019) 000 – 000

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response spectrum the as-built acceleration of the substructure is defined a sub (T sub ). In order to compare this quantity to the target acceleration, a sub is scaled with respect to the effective mass, and the “equivalent substructure acceleration” is introduced: a ES = (a sub m sub )/m eff (8) Comparing the “equivalent substructure acceleration” to the target acceleration highlights in terms of spectral acceleration the relationship between the seismic demand of the substructure and the pier resistance. From this comparison the second condition for the feasibility of seismic isolation follows: a ES < a target (9) If a ES is less than the a target , the pier has enough strength to resist the inertial forces associated to its own mass, otherwise the isolation is not feasible. The two conditions expressed by Equations (6) and (9) define the suitability domain in terms of spectral accelerations, with the first requirement providing the upper limit and the second requirement the lower limit. This domain can by expressed as: a ES < a target < a as-built (10) In Fig. 4 the procedure for the assessment of suitability of seismic isolation is graphically represented in the case of positive outcome.

Fig. 4. Representation of the assessment of suitability

Analysing the existing structure in the two primary directions, longitudinal and transversal, with reference to the development of the bridge, to achieve the suitability of the bridge for seismic isolation it is necessary that the first condition is met in at least direction, and the second condition is satisfied in both directions. If the bridge has a regular plan, with spans of uniform length and piers characterized by similar geometry and materials, it is sufficient to perform the procedure for a single elementary unit of the bridge. Otherwise, it must be repeated for each section characterized by the same typologies of pier and span. 3. Parametric study The procedure is applied to a case study bridge with simply supported spans, where the deck and pier sections are the same, but the pier height and seismic scenario change. The deck consists of 3 V-beams, Figure 5, 35 m long and 12 m wide. The deck accommodates two traffic lanes. Table 1 shows the loads related to the structure's self-weight (G1), non-structural permanent loads (G21, G22) and 20% of traffic loads according to current regulations.