Swissgrid GIS buildings

Gruner was commissioned by Swissgrid Ltd to conduct a fire resistance assessment of a representative GIS building (gas-insulated substation) with steel construction. The aim of this study was to assess existing structures and develop mandatory guidelines for future facilities.

According to VKF/AEAI guidelines, single-storey buildings have no structural fire protection requirements regarding fire resistance duration. However, since substations are classified as critical infrastructure for Switzerland's power supply, the buildings must withstand a fire event at least until firefighter intervention.

For the selected reference building, several representative fire scenarios were initially developed to identify existing fire loads and their possible arrangements within the facility. Based on these scenarios, the associated fire developments were simulated using numerical models to predict gas temperature distribution in the building during a real fire event.

In a second step, the unprotected steel structure was evaluated for each fire scenario using structural fire design (hot design). The fire design process consists of a numerical thermal analysis to determine structural element temperatures from fire gas temperatures, and a numerical mechanical analysis for the actual verification of load-bearing capacity during fire conditions.

The thermal and mechanical analysis of the examined GIS building demonstrated - considering the applied natural fire scenarios with corresponding fire loads and including additional measures where necessary - that the load-bearing structure maintains sufficient capacity throughout the entire design fire duration.

The analyses were used to develop specifications for future facilities to ensure the required fire resistance until firefighter arrival.

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