Base Isolation and Damage Resistant Technologies for Improved Seismic Performance of Buildings

The Introduction provides an overview of modern performance-based design concepts and their relevance to damage-resistant structures. It highlights the importance of specifying and documenting these concepts in design standards such as NZS 1170 Part 5, and suggests the need for an introductory document to facilitate their understanding and implementation. The text emphasizes the potential of displacement-oriented design philosophies to reduce structural and non-structural damage in future earthquakes and advocates for providing practitioners with an open choice between Displacement-Based and Force-Based design methods, provided that seismic performance and building displacements are adequately addressed.

Base isolation is a structural technique used to protect buildings from earthquakes by placing them on a layer of flexible material that absorbs and dissipates energy from seismic waves. This helps to reduce the amount of shaking that is transmitted to the building, making it less likely to be damaged or destroyed. Base isolation has been successfully used on numerous buildings in New Zealand and around the world, including the Christchurch Women's Hospital and the Te Papa Museum in Wellington.

Lead-rubber bearings are a common type of base isolation device. These bearings are made of a rubber core sandwiched between two steel plates. The rubber core is designed to deform in response to seismic waves, which dissipates energy and reduces the amount of shaking that is transmitted to the building. Lead-rubber bearings are also self-centering, which means that they will return the building to its original position after an earthquake.

The document discusses the reasons behind the excessive damage to modern buildings in the Christchurch earthquakes. It highlights the shortcomings of the current design methods and the need for performance-based seismic engineering (PBSE) to ensure that future buildings are more resistant to earthquakes.

The document explores various damage-resistant structures, including ductile structures, base-isolated structures, and steel structures with supplemental damping devices. It explains how these structures can absorb and dissipate seismic energy, reducing damage during earthquakes.

PBSE is introduced as a design philosophy that links expected or desired performance levels with levels of seismic hazard. It aims to ensure that buildings perform as intended under different earthquake scenarios, minimizing damage and protecting occupants and contents.

The document emphasizes the importance of protecting floors and other structural components from damage. It discusses various techniques for avoiding damage to floors, such as using precast concrete frames and hollow core floor units, and ensuring proper diaphragm action.

The document presents several innovative structural systems that have been developed to improve seismic performance. These systems include precast concrete frames with post-tensioned connections, steel structures with sliding hinge joints, and rocking walls with replaceable fuses.

The document concludes by emphasizing the need for a shift towards displacement-oriented design philosophies in PBSE. It advocates for the adoption of new innovative design methods that prioritize reducing structural and non-structural damage in future earthquakes.

It is not possible to design and build structures that are damage-resistant under all earthquakes, so the term should be used with care. In the context of this document, it simply means that there should be less damage than in existing construction during design level earthquake excitation. A structure which satisfies this criteria should also be available for occupation soon after the very large shaking associated with the Maximum Considered Earthquake (MCE) event.

This document is about damage resistant structures in New Zealand after the earthquake. Damage resistant structures can be designed to absorb energy in other parts of the structure, so that the building rocks back and forth in a major earthquake, returning to an undamaged position after the shaking. This combines ductility to reduce the design forces with little or no residual damage.

Base isolation will reduce damage in a major earthquake, by reducing the response of the building by partially isolating it from the shaking ground. This is done by placing the building on base-isolation units such as the lead-rubber bearings under Christchurch Women’s Hospital, also used at Te Papa, and Parliament Buildings in Wellington.

Structural control devices will reduce damage in a major earthquake, by partially isolating the structure from the shaking ground. This is done by placing the building on structural control devices such as the viscoelastic dampers used in the Sky Tower in Auckland.

Hybrid systems will combine the benefits of multiple techniques to reduce damage in a major earthquake. For example, a building could be designed with a base isolation system to reduce the overall response of the building, and with structural control devices to further reduce the damage to the structure.

There are a number of different ways to reduce damage to buildings in a major earthquake. The most effective approach will depend on the specific building and site conditions. However, all of these techniques can be used to improve the seismic performance of buildings and to reduce the risk of damage.

Damage-resistant structures can also be designed to absorb energy in other parts of the structure, so that the building rocks back and forth in a major earthquake, returning to an undamaged position after the shaking. This combines ductility to reduce the design forces with little or no residual damage. New Zealand engineers are contributing to international developments in this field, including the recently completed reinforced concrete Endoscopy building at Southern Cross Hospital in Christchurch, TePuni Village steel building at Victoria University in Wellington, and the new NMIT timber building in Nelson. Experimental research at the University of Canterbury has supported these developments, which will allow new damage-resistant buildings at no more cost than conventional building designs.

Base isolation will reduce damage in a major earthquake, by reducing the response of the building by partially isolating it from the shaking ground. This is done by placing the building on base-isolation units such as the lead-rubber bearings under Christchurch Women’s Hospital, also used at Te Papa, and Parliament Buildings in Wellington. These devices allow an economical building to be built on an expensive foundation, with the total cost being only a little more than conventional design.

structural systems. Ductile structures are able to withstand several cycles of severe loading, with materials stressed in the inelastic range, without losing structural integrity. This design philosophy, referred to as ‚capacity design‛, was developed in the 1960s and 1970s by Professors Bob Park and Tom Paulay at the University of Canterbury.