Guide
Seismic isolation: what it is, when it is mandatory and how much it protects
A guide for investors, architects and healthcare managers.
Seismic isolation is a protection system that places special devices, the isolators, between the foundation and the superstructure. Its goal is to significantly reduce the seismic forces that reach the building.
The principle: decoupling the building from the ground
The system is based on dynamic decoupling. A highly flexible, energy-dissipating interface between the superstructure and the foundation lengthens the vibration period of the whole system. With a longer period, the seismic demand on the building, and on everything it contains, drops substantially.
That flexibility must be carefully controlled. If poorly designed, it produces large displacements at the base, requires wider seismic joints and can compromise the system’s ability to return to its original position after the earthquake.
Benefits
- Protection of people, structure and contents. Accelerations reaching the building are reduced, in many cases by 80% or more. Inertial forces drop, as does damage to the structure, to nonstructural elements and to sensitive equipment.
- Operational continuity. An isolated building is designed to remain functional after a severe earthquake. That is why it is the standard for hospitals.
- Investment protection. Less damage means lower repair costs, fewer losses and less downtime.
- Cost-effectiveness relative to risk. The initial added cost is marginal compared with the reduction in structural and economic risk over the building’s service life.
- Freedom of configuration. It allows irregular configurations that the standard prohibits in conventional essential buildings, and makes it possible to reduce or eliminate concrete walls in favor of frames.
When is it mandatory in Peru?
Standard E.031, Seismic Isolation, is mandatory nationwide for buildings with seismic isolation, in accordance with the Peruvian Seismic Design Standard E.030 of the National Building Code (Reglamento Nacional de Edificaciones). New Category A1 buildings, that is, public and private healthcare facilities of the second level of care and above, must incorporate base isolation when located in seismic zones 4 and 3.
Technical decisions that define a good design
- Site study. Tests such as the horizontal-to-vertical spectral ratio (HVSR) method help determine the soil period and potential amplifications.
- Isolation system design. Type, number and properties of isolators and sliders, specified by performance rather than by brand.
- Recentering capability. If lateral stiffness is too low, the building may be left with residual displacements. Flexibility and restoring force must be balanced.
- Seismic joints. An isolated building needs freedom of movement relative to its surroundings, including ramps, stairs and building services.
- Elevators. Their pits and shafts require special details to accommodate the displacement of the isolated structure.
- Testing and installation. The devices are tested before installation and their placement is supervised on site.
Our experience
PRISMA designed some of the first isolated buildings in Peru and, as of 2019, more than 80% of the country’s buildings with modern seismic protection. Recent projects include the new Clínica Internacional tower in San Borja, with 103 devices, and the hospitals in Casma, Recuay, Yungay and Llata.