Brief

The Client requested the design of a seismic retrofitting intervention following a vulnerability assessment conducted on critical components within its facility.

Project challenge

Seismic verification is a mandatory requirement for any operator of an industrial facility. This obligation:

• derives from OPCM No. 3274 of March 20, 2003;
• is reiterated in Legislative Decree 105/15 (Seveso III Directive), which states that the operator of an industrial plant must demonstrate that all plausible accident scenarios have been identified, including those triggered by seismic events. This applies to both lower-tier and upper-tier establishments;
• is methodologically defined in the UNI/TS 11816-1:2021 guidelines, which first require seismic verification of critical plant components—both structural and non-structural (such as tanks, towers, piping systems, and fire protection systems)—in accordance with the current NTC 2018 standards, and subsequently introduce the use of quantitative risk analysis to properly design any mitigation measures and technical/organizational systems aimed at reducing seismic risk.

Following the results of the seismic assessment, some critical elements of the facility were found to be non-compliant with the current NTC 2018 standards. The Client therefore had to decide whether to improve and/or retrofit these components or demonstrate, within the Safety Report, the implementation of appropriate technical and organizational measures to mitigate the risk associated with their potential collapse in the event of an earthquake.

In such situations, identifying the optimal solution is not always straightforward, as it depends on various factors, including the type of required intervention, cost and schedule estimates, the potential need to shut down the plant during works, and/or the implementation of the intervention.

This analysis required a multidisciplinary approach due to the complexity of the context.

Achieved results

With the support of our team of experts, the Client decided to proceed with the seismic retrofitting of the critical elements. This made it possible to objectively exclude from the Safety Report the consequences (and related mitigation measures) associated with highly impactful scenarios, such as the total collapse of the components in question.

The proposed solution, accepted by the Client, involved the introduction of steel bracing elements to reinforce the existing supports (support legs) of spherical tanks.

The design activities were assigned to the Design & Virtual Prototyping team.

The key steps that enabled the design of the seismic retrofitting intervention—following the NaTech seismic risk assessment conducted at the facility—were as follows:

• Structural calculation report, including justification of the selected intervention, design and sizing, and pre- and post-intervention analyses/verifications;
• Materials report;
• Technical drawings and construction details;
• Maintenance plan for the structure.

Furthermore, throughout the design phases, an open and constructive dialogue was maintained with the contractor responsible for the works, in order to identify and minimize any potential issues during the execution phase.

This approach fully met the Client’s requirements, delivering results that required the integration of multiple competencies and areas of expertise, while adhering to the defined schedule.