Where components are connected to supports that allow them to move independently under seismic action, the design of the restraint system must accommodate relative displacement between the components. This can be achieved by using flexible connections or, in the case of pipe and duct work, configuring the system to accommodate movement without fracture.

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Piping systems

Piping systems should have a flexible connection between piping and anchored equipment, wall or slab penetrations, seismic joints between adjacent buildings and seismic joints in base-isolated buildings. Flexible connections should also be used at anchor points (including possible unintentional anchors, such as external penetrations), pipe junctions and points where the piping makes an abrupt change in direction.

Flexible pipe supports should be used where flexible connections are not possible. The design of the flexible connection or supports depends on the anticipated relative movement, the diameter and material of the pipe and its location.

Vertical pipes must be have sufficient flexibility to allow for the relative horizontal movement between floors or fixing points. Where vertical pipes pass through more than one floor and are located more than 1 m from a column or shear wall , the fixings or pipework configuration must have enough flexibility. This is to allow differential vertical movement between the floors.

Piping across seismic gaps

Where pipes cross structural separations, the design should allow for the relative horizontal movement in two orthogonal directions. The allowance should be either 160 mm for every 4 m rise in height of the structural separation or the building design movement, where known.

Flexible connections.

Simple flexible connections can be designed to withstand severe seismic displacement. (BRANZ)

Where a connection is necessary between two structural systems, it should have adequate flexibility and be as close to the ground as possible. Bellows type expansion joints are usually unsuitable. Offsets, bends, and loops provide the best means of crossing seismic joints.

In all cases, piping that crosses a seismic gap requires a specific design.


Air diffusers and grilles should have positive fixings to the ducting. Ducting between ceiling-mounted grilles and rigidly mounted ducting should be flexible or allow for movement.

Dampers, louvres and diffusers should also be positively attached to the duct with mechanical fasteners. Duct tape is not acceptable.

This video shows the performance of a suspended ducting system being tested on a shake table.

Electrical services

In all cases, cables, conduit and cable trays that cross a structural separation or seismic gap require a specific design.