Non-structural systems include all the elements within a building that are not part of the primary gravity or lateral force-resisting structure, but are still required for the building to function.
Broadly, non-structural components can be divided into two categories:
- Engineered systems, such as ducting, electrical distribution, piping, engineering plant and fire suppression systems.
- Architectural elements, such as suspended ceilings, internal partitions and façades.
Non-structural systems within MDH generally present a low risk to life in a large earthquake. However, poorly restrained non-structural systems or components may collapse with a possible risk to life, both inside and outside the building. They can also render the building unusable, leaving the building owner and occupants facing major disruptions.
When carrying out the seismic design of MDH, designers should consider non-structural systems and components to a degree commensurate with the risk they pose to the building and its occupants during a seismic event. Non-structural elements should not be viewed as an isolated system to be added once other design aspects of the buildings, particularly the structure, is complete.
Accommodating earthquake movement
An MDH building designed to the New Zealand seismic loadings standard NZS 1170.5:2004 Structural design actions – Part 5: Earthquake actions – New Zealand should be expected to displace laterally under earthquake actions. All non-structural components connected to adjacent floors need to be able to accommodate this relative displacement. Non-structural components are not always expected to remain functional under these movements, but there should be no risk of them detaching or falling.
Earthquake movement should be expected to influence the following non-structural components of an MDH building. Designers of MDH should ensure the risks these components represent are properly mitigated in the design.
- Exterior claddings:
- curtain wall systems (attached to the building at floor levels)
- prefabricated panels (sometimes fitted between structural frame members or hung off structural elements)
- brick and block veneers (supported at each floor level and fitted between vertical structural elements and the floor above)
- masonry veneers
- framed glazing fixed between floors or columns or fitted as a horizontal band between spandrel panels
- structural frameless glazing systems
- Internal partitions (spanning between floor and soffit above):
- lightweight (drywall on steel or timber framing)
- glazed panels
- heavyweight (concrete masonry)
- Suspended ceilings
- Stairs and ramps (providing access between floors or carpark decks)
- Riser pipes, ventilation ducts, electrical trunking, drainage stacks (running vertically between floors and supported by floors)
- Lifts and escalators
- Externally mounted elements:
- decks, balconies and verandas
- clip-on or adhered cladding elements and finishes (stone and tile veneer)
- sunshades and planters
- Floor-mounted equipment
- Utility connections (water, power, sewerage, telecommunications)
- Shelving and racking.
In addition, if the mass of an individual non-structural component exceeds 20% of the combined mass of the component and the building structure, the component may affect the seismic response of the structure. In this case, the structure should be modelled, including the mass of the component.