Plans for conversion or renovation work provide an opportunity to ascertain whether the building's seismic safety needs to be verified. The checks this involves will determine if the building is sufficiently earthquake-resistant or whether seismic safety measures need to be incorporated into the construction work.
Many existing buildings in Switzerland are inadequately protected against earthquakes, compared with today's requirements applicable to new buildings. The main reason for this is a lack of regulations on earthquake mitigation at the time they were built and / or insufficient compliance with the seismic safety requirements concerning construction work. Such buildings could face the risk of collapsing and suffer considerable damage from even a relatively weak earthquake.
Consequently, whenever planning conversion or renovation work, a structural engineer should be brought in early on to check the building's earthquake resistance and recommend or impose any seismic safety measures. The relevant factors here are the type and extent of the planned work, any suspicion of low resistance to earthquakes, the sum of money being invested, the value of the building and its remaining useful life. A check should be performed in good time to ensure that any required measures can be properly incorporated into the planned (re)construction work.
Expert verification based on SIA Fact Sheet 2018 on the examination of existing buildings with regard to earthquakes will ascertain any design faults or structural defects and determine the so-called compliance factor αeff by performing the appropriate calculations. The compliance factor describes the extent to which the inspected building meets seismic safety requirements according to applicable standards on load-bearing structures. A factor of 1.0 indicates full compliance with the respective requirements. To guarantee personal safety, SIA Fact Sheet 2018 stipulates a minimum compliance factor of 0.25 (0.4 for class III buildings like acute care hospitals or fire brigade facilities).
- A compliance factor of < 0.25 (or 0.4 for class III buildings) indicates inadequate earthquake-resistance.
This being the case, measures have to be taken to meet the minimum requirements for existing buildings, which is the case when the compliance factor reaches a value of 0.25 (or 0.4 for class III buildings).
- A compliance factor of between 0.25 (or 0.4 for class III buildings) and 1.0 indicates deficient earthquake-resistance.
Here, further improvements should be made if a cost-benefit analysis demonstrates that the associated measures would represent a proportionate expense. In principle, an attempt should be made to meet the standards applicable to new buildings. Should this be unattainable, at least the furthest-reaching cost-effective measures should be implemented.
- A compliance factor ≥ 1.0 indicates a level of earthquake-resistance that meets current standards.
In this scenario, no action is required because the requirements applicable to new buildings have been fully met.
If earthquake-resistance is deemed inadequate or deficient, appropriate seismic safety measures are to be drawn up and assessed for their cost-effectiveness. The expense associated with potential structural or operational measures will vary widely, depending on the situation in question. Synergies with planned construction will positively impact cost-effectiveness.
FOEN Fact Sheet "Ist unser Gebäude genügend erdbebensicher? Wann eine Überprüfung und eine Verbesserung sinnvoll sind – und warum"
FOEN Report "Seismic Retrofitting of Structures - Strategies and Collection of Examples in Switzerland"