What every structural and civil engineer should know about "seismic isolation solutions"

Your bridge, building or other structure is to be protected against earthquakes by means of seismic isolation – but what solutions are available?

Key requirements

Seismic isolators

Seismic isolators are specially designed structural bearings which, like most bearings, form the required connections between a structure’s superstructure and its substructures – thereby typically transmitting weight forces while also resisting other forces and accommodating movements and rotations as required by the structure’s design.

However, seismic isolation bearings are additionally designed to perform in a very specific way during an earthquake, protecting the main structure and its users. For optimal performance, a seismic isolator should offer the following benefits:

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Isolation of the superstructure from violent, potentially damaging ground oscillations – thus drastically reducing shear and bending stresses in the structural components.

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Enabling the superstructure to return to its former position after the dynamic event.

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So that the seismic energy is released in a safe, controlled manner, thus also protecting secondary structural elements against unacceptable deformations.

Key types of seismic isolator

Earthquake protection devices

High-Damping Rubber Bearings

High-Damping Rubber Bearings, such as LASTO®HDRB, which are similar to anchored elastomeric bearings with no sliding surfaces but fabricated using special high-damping elastomeric compounds which provide high resistance to horizontal (shear) deformation and result in high energy dissipation during seismic movements.

A round High-Damping Rubber Bearing (HDRB) of the LASTO®HDRB type as installed in a concrete structure

1.

Mounting plate

2.

Connectors to transfer horizontal loads

3.

Elastomeric block with horizontal steel reinforcing plates

4.

Mounting plate

Lead Rubber Bearings

Lead Rubber Bearings, such as LASTO®LRB, which are also similar to anchored elastomeric bearings with no sliding surfaces but feature a vertical lead core which increases stiffness and damping (energy dissipation) during seismic events – thus optimising the size of the device and enabling a threshold to be defined between the behaviours expected during events of low and high intensity.

A Lead Rubber Bearing (LRB) of the LASTO®LRB type as fabricated, with anchor plates top and bottom

1.

Mounting plate

2.

Connectors to transfer horizontal loads

3.

Elastomeric block with horizontal steel reinforcing plates

4.

Lead core

5.

Mounting plate

Seismic isolation – decoupling of structures
from ground motions

Curved Surface Sliders

Curved Surface Sliders, such as RESTON®PENDULUM, which have the effect of decoupling the supported structure from ground motions during a seismic event through harmonic pendulum-like relative displacements. As the supported structure becomes horizontally displaced, seismic energy is dissipated thanks to the friction at the isolator’s sliding interface(s) with their special high-performance sliding material. During the oscillations, the curvature of the sliding interface results in a slight (almost imperceptible) lifting of the superstructure. After the earthquake, the same curvature causes the supported structure to return by gravity to its original position.

Cross-section illustration of a Curved Surface Slider seismic isolator of the RESTON®PENDULUM MONO type – with ONE curved sliding surface (on top) to accommodate displacements

Cross-section view of a Curved Surface Slider seismic isolator of the RESTON®PENDULUM DUPLO type – with TWO curved sliding surfaces (top and bottom) to accommodate displacements

Seismic protection strategy

Identifying and implementing the optimal seismic protection strategy

The elastomeric isolators (High-Damping Rubber Bearings and Lead Rubber Bearings) are similar in many respects. For example, LASTO®LRB and LASTO®HDRB seismic isolators are typically suitable for applications involving vertical loads of up to 30,000 kN and horizontal seismic displacements of up to 150% – 200% of the total rubber height of the device. However, the damping performance of up to 30% offered by LASTO®LRB isolators is significantly higher than that offered by LASTO®HDRB isolators (up to approximately 20%).

Curved Surface Sliders, on the other hand, are generally suitable for applications involving substantially higher loads and displacements. RESTON®PENDULUM bearings, for example, can typically be designed to carry loads of up to 150,000 kN and to accommodate horizontal seismic displacements of up to +/- 1000 mm, while also achieving damping factors above 30%.

Where Curved Surface Sliders are to be used to support and protect a structure, it must be noted that, if different sizes/designs are used for the same superstructure, then all of them must be designed for the same oscillation period. It should also be noted that Curved Surface Sliders should not be combined with elastomeric isolators due to the slight lifting experienced by the superstructure during the oscillations at the locations of the Curved Surface Sliders – but not at the locations of the elastomeric isolators.

Whatever type of seismic isolator is selected to support a structure, it is generally recommended to verify the performance of the devices as designed and manufactured – by means of seismic testing of randomly-selected specimens at an accredited test facility which can simulate the seismic conditions for which the device was designed.

Such testing is generally conducted regardless of the isolator’s size or specification and of any previous testing of comparable devices – the uniqueness of each application warrants the carrying out of testing for every application.

Identifying and implementing the optimal seismic protection strategy for a particular application – considering the structure’s design, use and location, for example – requires specialist expertise and experience.

Please feel free to contact us when you require a seismic isolation (or any other type of seismic protection) solution for your structure – we will be happy to assist you.

Any questions?

Expert Knowledge

To learn more about earthquake protection, please read our “Expert Knowledge”.

Seismic devices

Find specific information on earthquake protection products.

Project References

Turkey

Agin Bridge

The new Agin Bridge in eastern Turkey is a cable-stayed bridge with steel box deck and steel pylons. It is located on...

Products:

RESTON-PENDULUM MONO PM25.0, TENSA-MODULAR expanison joints type LR5

Installed:

2014

City:

Elazig

Completed:

2015

El Salvador

Casa 159

After the earthquakes that occurred in El Salvador in 1986 and 2001, it was necessary to consider the implementation of seismic response...

Products:

LASTO®LRB Lead Rubber Bearings, RESTON®SLIDER

Features:

Prototype testing Sismalab in Italy

Installed:

2020

City:

San Salvador

Chile

Hospital de las Higueras

The hospital de las Higueras is located in the Biobio Region of Chile, which was one of the most affected areas of...

Products:

LASTO-HDRB high damping rubber bearing

Installation:

2019–2022

City:

Talcahuano

Type:

Hospital

Guatemala

Elemento Building

The Elemento Building in Guatemala City, currently under construction, is a 14-storey structure that will house commercial space, corporate offices and eight...

Products:

LASTO-LRB isolators, RESTON-SLIDER bearings

Installation:

2021

City:

Guatemala City

Type:

Residential building

Mexico

Cibeles Tower

The Cibeles Tower is an office building of modern architecture, located in the Roma Norte neighborhood. Its construction began in 1966 and...

Products:

RESTON®SA shock absorbers

Installed:

2018

City:

Mexico City

Structure:

Multi-story building

Ecuador

Chone Hospital

Due to a severe earthquake of magnitude 7.8 in April 2016, the General Hospital of the city of Chone in western Ecuador...

Products:

RESTON®PENDULUM DUPLO

Installed:

2019

City:

Chone

Structure:

Multi-story building

USA

Transbay Transit Center

The new Transbay Transit Center has replaced the former Transbay Terminal that was built in 1939 in downtown San Francisco. This modern...

Products:

RESTON-PENDULUM Mono bearings, RESTON-SPHERICAL bearings, TENSA-MODULAR expansion joints

Features:

Table hysteretic behavior

Installation:

2016–2018

City:

San Francisco, CA

New Zealand

ANZ Triangle

The three-storey ANZ Centre was constructed on a high-profile site bordering Colombo, Cashel and High Streets in the heart of Christchurch’s Central...

Products:

RESTON-PENDULUM DUPLO seismic isolater bearings

Installed:

2015

City:

Christchurch

Completion:

2016

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Earthquake protection is a commitment – we design solutions that make infrastructures and buildings safer.