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seismic suspended ceilings g173 pd v1.docx Created in April 2015

Seismic Suspended Ceilings

Introduction

Despite Australia’s seemingly low seismic risk, being in the middle of one of the earth’s larger tectonic plates, we have been subjected to 17 earthquakes registering 6 or more on the Richter Scale in the last 80 years. There have been six major earthquakes recorded in South Australia;

1897 Beachport M6.5

1902 Warooka M6.0

1954 Adelaide (Darlington) M5.5

1986 Marryat Creek M6.0

2012 & 2013 Ernabella M5.7 Seismologists advise that based on local geology earthquakes of up to Richter magnitude M7.5 can occur in South Australia however earthquakes of such a magnitude are very rare. Experience from around the world shows that failure of ceilings as a result of an earthquake can have a significant effect on life safety and economic loss, particularly where ceilings also support services. The National Construction Code requires that ceilings be designed to resist seismic loads calculated using Section 8 of AS 1170.4 - 2007 Structural design actions Part 4: Earthquake actions in Australia. The standard requires that ceilings be designed to resist earthquake forces except where they are located in domestic structures less than 8.5m tall and “Importance Level One” structures. The Standard is also applicable to walls, partitions and other non-structural elements. The aim of this Guidenote is to make designers, contractors and installers aware of the information available on seismic design of ceilings and the requirement to:

Design, specify and install ceilings to resist seismic forces in accordance with Section 8 of AS 1170.4 – 2007 and AS/NZS 2785 - 2000 – Suspended ceilings.

Co-ordinate ceiling design and services design where the services impose any load on the ceiling or penetrate the ceiling.

Provide suitable seismic clearances between services and ceiling members.

Document ceilings and partitions for tender such that the contractors, manufacturers and installers clearly understand the seismic design criteria and seismic design requirements and any specific final design details or information to be supplied.

This Guidenote shall be referenced with DG53. The following items are excluded from the scope of this Guidenote:

Existing ceilings, including where refurbishments occur to government buildings that do not involve significant alterations to existing ceilings.

The design of ceilings and partitions in an importance level 4 building as a special study is required to be carried out to ensure they remain serviceable for immediate use following the design event for importance level 2 structures (1 in 500 year earthquake) although many of the principles in this Guidenote will apply.

Design and documentation of the seismic restraint of engineering services. Refer to the DPTI Guidenote G172 and drawings DG51 and DG52.

Seismic restraint of building contents.


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Definitions

Anchor – A manufactured, assembled component for achieving a connection between the base material and the fixture. Also referred to as a ‘fixing’. Typically installed into concrete, steel or similar and used to transfer seismic forces.

Anchorage – The combination of a fixing, a fixture (e.g.: a bracket), and the immediately surrounding base material on which the fixing depends in order to transfer the relevant forces.

Base material – Load bearing structural element, e.g. concrete slabs, hollow core, floor slabs, steel beams, purlin or roof structure. Sometimes referred to as substrate or structure over.

Brace – An element of the restraint system used to transfer seismic force from a component to the supporting structure. Typically braces will consist of two struts at approximately orthogonal angles at 45° to the horizontal with an associated post, fixed at each end. Alternatively a brace can consist of four wires at 45° as ties together with an associated post or other proprietary element.

Building Importance Level – A level assigned to a building based upon the consequences of its failure to a person or the public.

Ceiling hanger or hanger – A suspension component connecting the primary support ceiling channel or T-bar, angle to the soffit over, eg wire, angle.

Domestic structure – Single dwelling or one or more detached dwellings complying with Class 1a or 1b as defined in the National Construction Code.

Fixing points – Positions at which the hangers are required in accordance with the manufacturer’s instructions.

Inter-storey drift – The difference in the horizontal displacement between a floor and the one above or below as a building sways during an earthquake. It is commonly expressed as a percentage of the storey height separating the two adjacent floors.

Partition – Permanent or relocatable internal dividing wall between floor spaces.

Proof tests – tests carried out on site on a sample of installed fixings, to confirm the fixings have been installed correctly and comply with the design requirements.

Progressive collapse – the sequential spread of local damage from an initiating event, from element to element, resulting in the collapse of a number of elements.

Post – A structural member of a brace, essentially being near vertical resisting tension and compression, fixed at the top into the underside of the structure and fixed to the ceiling framing at the bottom.

Purlin – A horizontal or near horizontal structural member usually of light gauge steel material in a roof supporting roof sheeting or similar. Purlins are supported by the principal rafters and/or the building walls, steel beams etc.

Seismic Mass – The mass of an object which, under acceleration caused by an earthquake, induces seismic force on that object.

Significant ceiling alteration (in an existing building as part of a refurbishment) – Where more than 50% of the ceiling structure is removed and reinstated as part of refurbishment works in a room the whole room shall comply with this Guidenote.

Site hazard factor (Z) – A factor corresponding to a return period of 475 years calculated by dividing the appropriate peak ground velocity in millimetres per second by 750. The peak ground velocity being chosen as the ground motion value considered to be the best predictor of damage. A hazard factor Z=0.1 corresponds to a peak ground velocity (PGV) of 75mm/sec.

Structural soffit – The underside of the structure from which the ceiling system is suspended.

Strut – A member to resist compression and tension forces.

Tie – A member to resist tension forces only.


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AS/NZS 2785:2000 Suspended ceilings – Design and installation

The current version of AS/NZS 2785 Suspended ceilings – Design and installation issued in 2000 makes specific reference to earthquake loads and compliance with the Australian Earthquake Code, AS1170.4. In Section 3.3, Ultimate Limit State, the code states that the earthquake mass of the ceiling shall take into consideration the following: a. The mass of the ceiling tile and grid system. b. Partitions connected to the underside of the ceiling. c. Recessed or surface-mounted luminaires. d. Services such as air-conditioning registers. e. Insulation. f. A distributed service load of not less than 3kg/m2 AS/NZS 2785 requires that both horizontal and vertical actions be considered and that ceiling systems be designed to resist earthquake loads without:

i. Actions causing suspension components to dislodge. ii. Impact of the ceiling with the building structure, services or non-structural components,

with allowance made for inter-storey drift of the structure; and, iii. Causing tiles of significant weight to dislodge over occupied spaces and egress paths.

Note: Significant weight is considered to be over 1.5kg to 2.0kg depending on the type and location of the tiles.

Why ceilings fail in an earthquake

There are many reasons why suspended ceilings have failed in earthquakes in the past, these include:

A differential in movement between walls on opposite sides of the room during an earthquake which tears the ceiling elements apart at their connections or causes the ceiling to lose support at the walls.

A differential in movement between columns within a room and the ceiling.

A differential in movement between services that penetrate the ceiling and the ceiling.

Movement of services in the ceiling plenum which damage ceiling hangers such that support is lost.

Large horizontal loads induced in the ceiling during an earthquake causing buckling of ceiling members in compression and failure of connections in tension.

Local failures leading to progressive collapse. The design principles to overcome these causes of ceiling failure are therefore:

Positively fix the ceiling to two adjacent walls only and provide sliding connections to the other two walls with enough of a gap to accommodate the expected differential movement during an earthquake.

Alternatively keep the ceiling independent of all perimeter walls by bracing it back to the structure above and providing sliding connections to all walls with enough of a gap to accommodate the expected differential movement during an earthquake.

Limit the sizes of ceilings or spacing between braces such that the horizontal forces induced in ceiling members during an earthquake does not cause them to buckle or break their connections.

Where services penetrate ceilings they shall be either: o Positively fixed to the ceiling grid and their load accounted for in the ceiling design both

vertically (dead load) and horizontally (seismic load), or; o Supported independently of the ceiling, both vertically and horizontally, and provided

with a perimeter clearance to the ceiling to accommodate the expected differential movement during an earthquake.


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Where partitions rely on ceilings for horizontal bracing the load they induce in a ceiling is considered in the ceiling’s seismic design.

Where partitions provide horizontal (seismic) support for ceilings they are appropriately designed and installed to resist such loads and allow for the required fixings between the wall and ceiling.

Design Responsibility

On DPTI projects the Lead Professional Services Contractor, typically an Architect, has overall responsibility for the design, specification, inspection and reporting at hold points on ceilings in their projects and must ensure that the requirements of AS/NZS 2785:2000 and AS1170.2:2007 are met. The Lead Professional Services Contractor is expected to co-ordinate and obtain relevant input from their team members to support them in fulfilling this responsibility. This does not relieve the General Building Contractor or the ceiling installer of their responsibilities under the contract, AS/NZS 2785:2000 or the National Construction Code. Table 1: Design responsibilities – design documentation

Item Lead Professional

Services Contractor

Structural Engineer Services Engineers

Suspended ceilings

Primary responsibility for overall coordination and final documentation.

Support responsibility for providing seismic design and advice and final design of the fixings and bracing. This will likely include obtaining detailed advice from ceiling suppliers.

Support responsibility for design of service locations, spacing and support within the ceiling plenum given seismic design constraints advised by others.

Methodology

The following steps will be carried out by a combination of the architect, structural engineer, and services engineer as required. The design team will determine amongst themselves which consultants are responsible for which items. Typically the architect will specify the type of ceiling and details, the structural engineer will specify the seismic requirements and loads and carry out the design of the bracing and fixings including the layout of the braces and the services engineer will coordinate services with the architect and structural engineer. The suggested steps to specify and document the requirements for a seismic ceiling to comply with AS/NZS 2785:2000 and AS1170.4:2007 are as follows: 1. Establish the building importance level. 2. Determine if a seismic ceiling is required. If it is not required then no further action is

necessary, if a seismic ceiling is required then continue. 3. Establish the hazard factor (Z). 4. Establish the site sub-soil class. Where a dynamic analysis of the structure is carried out

by the structural engineer, provide the effective floor acceleration afloor at each floor in two orthogonal directions together with advice on the component importance factor Ic to be adopted for the ceilings.

5. Determine the ceiling type, manufacturer and direction of the ceiling main rails or T-bar and secondary framing.

6. Determine the partition support conditions and hence whether the partitions will be used to brace ceilings or will rely upon the ceiling for bracing.

7. Determine the vertical mass of the ceiling.


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8. Check the vertical capacity of the system using the manufacturer’s technical information or obtain their advice directly.

9. Determine the seismic mass of the ceiling. 10. Determine whether the ceiling system is best horizontally braced for seismic loads by a

fixed/sliding perimeter solution or braced solution using the manufacturer’s technical information or obtain their advice directly.

11. Where a braced solution is required determine the bracing detail and maximum bracing spacing.

12. Co-ordinate ceiling bracing locations with service engineers. Ductwork, cable trays, pipework, electrical conduits and the like must be independently supported and braced separately from the ceiling system.

13. Co-ordinate service clearances to ceiling members and partitions with service engineers. 14. Determine if any special details are required where partition walls brace ceilings. Changes

in the ceiling plane by more than 150 mm must have positive bracing. 15. Document all of the above in the project tender documents including where the

contractor/ceiling sub –contractor is to provide written evidence that their ceiling system will comply with the requirements of this Guidenote, the tender documentation and Section 8 of AS 1170.4 – 2007.

1. Establish the building importance level and earthquake annual probability of exceedance

Establish the importance level of the building using the definitions given in Table B1.2a of the National Construction Code (NCC). A discussion should take place with the project team and the importance level be confirmed with the Lead Agency as being appropriate for their intended use of the building. Table 2: Combination of tables B1.2a and B1.2b from the National Construction Code.

Imp

ort

an

ce

Le

vel

Building Type Examples of building types

Earthquake

Annual probability of exceedance

1

Buildings or structures presenting a low degree of hazard to life and other property in the case of failure.

Farm buildings. Isolated minor storage facilities. Minor temporary facilities.

1:250 years

2 Buildings or structures not included in Importance Levels 1,3,4

Low rise residential construction. Buildings and facilities below the limits set for Importance Level 3.

1:500 years

3

Buildings or structures that are designed to contain a large number of people.

Buildings and facilities where more than 300 people can congregate in one area. A primary school, secondary school or day care facility with a capacity greater than 250. Colleges or adult education facilities with a capacity greater than 500. Health care facilities with a capacity of 50 or more

1: 1000 years


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Imp

ort

an

ce

Le

vel

Building Type Examples of building types

Earthquake

Annual probability of exceedance

residents but not having surgery or emergency treatment facilities. Jails and detention facilities. Any occupancy with an occupant load greater than 5000. Power generating facilities, water treatment and wastewater treatment facilities, any other public facilities not included in Importance level 4.

4

Buildings or structures that are essential to post disaster recovery or associated with hazardous facilities.

Buildings and facilities designated as essential facilities or having special post disaster functions. Medical emergency or surgery facilities. Emergency service facilities: fire, rescue, police station and emergency vehicle garages. Utilities required as backup for buildings and facilities of Importance Level 4. Designated emergency shelters, centres and ancillary facilities. Buildings and facilities containing hazardous materials capable of causing hazardous conditions that extend beyond property boundaries.

1:1500 years

2. Determine if a seismic ceiling is required.

Having determined the Importance Level of the building now determine if a seismic ceiling is required on the project. It is anticipated that seismic ceilings will need to be installed on almost all projects managed by DPTI. Table 3: Seismic ceilings required

Building Description Seismic ceiling required?

Domestic dwellings with height < 8.5m No

Domestic dwellings with height > 8.5m (Class 1a or 1b)

Yes

Importance Level 1 buildings No

Importance Level 2 and 3 buildings Yes

Importance Level 4 buildings

Yes – with a special study required to be carried out to ensure the ceiling remains serviceable such

that the building is suitable for immediate use following a 1 in 500 year earthquake.


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3. Establish the hazard factor (Z)

The hazard factor (Z) is taken from Table 3.2 of AS1170.4-2007 or the hazard maps.

Table 4: Hazard factor (Z)

Location Z

Adelaide, Port Lincoln, Port Pirie, Mount Gambier 0.1

Port Augusta 0.11

4. Establish the site soil class

The Geotechnical or Structural Engineer will need to provide advice on the appropriate site soil class for the project.

Table 5: Site Sub-soil Class

Class Description

Ae Strong rock

Be Rock

Ce Shallow soil

De Deep or soft soil

Ee Very soft soil

5. Determine the ceiling type and manufacturer

The ceiling type and manufacturer will be chosen to suit the project. For ceilings supported from purlins or trusses the ceiling layout should be designed with the main rails perpendicular to the purlins or trusses. Bulkheads shall be attached and braced to the structural soffit, independent of the ceiling, unless specifically designed otherwise. Bulkheads shall be designed for seismic loads as well as their own load.

6. Determine the partition support conditions

Determine how partitions will be stabilised on the project. In particular will the wall head track fix to the structural soffit, be braced back to roof members or structural soffit or be fixed to a ceiling member. In general it is expected that permanent partitions will run between the floors and not depend on the ceiling for support. Low height partitions are to be designed not to be braced by the ceiling where possible.

7&8. Vertical ceiling mass calculation and capacity check

Determine the vertical mass of the ceiling in consultation with the project team including the mass of the:

Ceiling tile and grid system.

Recessed or surface mounted luminaires supported by the ceiling.

Services such as air-conditioning cushion head boxes supported by the ceiling.

Insulation.


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Using the manufacturers technical information check the allowable vertical load for the proposed ceiling system and grid arrangement. Always observe the manufacturers limitations on their systems unless advised otherwise in writing. Note that some manufacturers state in their product literature that:

Their suspension system is designed to carry the weight of the ceiling only and that additional loads are not to be placed upon or carried by the suspension system without reference to the manufacturer.

Extra hangers are to be provided for light fittings, air conditioning units etc. that are supported by the grid system.

All light fittings shall be supported on the main runner. Co-ordinate with the project team to ensure that the vertical ceiling mass limitations and manufacturer’s recommendations are observed which in some cases may mean supporting services independently of the ceiling. Refer to the DPTI Guidenote G172 and drawings G51 and G52 for further information on supporting light fittings.

9&10. Horizontal (seismic) ceiling mass calculation and bracing design

Determine the seismic mass of the ceiling including:

Partitions connected to the underside of the ceiling for their stability.

The mass of the ceiling tile and grid system.

The mass of recessed or surface mounted luminaires.

The mass of services such as air-conditioning registers.

Insulation.

Using the manufacturers' seismic technical information check whether:

A perimeter fixed/free solution is suitable.

A bracing solution is required.

If a bracing solution is required or preferred the number or spacing of braces needed for the brace type chosen and room being considered.

11&12. Determine the bracing details and locations

The spacing of bracing may need to be reduced, for example:

Where services obstruct the preferred bracing locations.

Where supporting structure does not align with the preferred bracing locations. Co-ordinate with the project team to ensure that the seismic ceiling mass limitations and manufacturer’s recommendations are observed which in many cases may mean supporting services independently of the ceiling.

13. Co-ordinate Service Clearances

Providing a separation between services and ceilings or services and partitions is an important consideration in ensuring ceilings are not damaged in an earthquake. Such service clearances need to be allowed for in the service design and shown on the tender drawings. The following minimum clearances are recommended.


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Table 6: Minimum clearances

Condition being considered Minimum clearance

Horizontal Vertical

Unrestrained component to unrestrained component 250mm 50mm

Unrestrained component to restrained component 150mm 50mm

Restrained component to restrained component 50mm 50mm

Penetration through structure such as partition or floor 50mm 50mm

Unrestrained services passing through the ceiling 25mm 25mm

Sprinkler heads with flexible droppers nil nil

Note: Ceiling hangers and braces are considered to be restrained components for the purpose of this table, hence 150mm horizontal clearance is required between ceiling hangers and unrestrained services.

14. Partition Wall Design

Where ceilings have a “fixed” connection to the perimeter walls ensure that:

The partition members can withstand the seismic load applied by the ceiling.

The fixings, connections and/or bracing of the partition members can accommodate the required seismic loads.

Where required by the manufacturer the perimeter partition is nogged continuously at ceiling level.

Where ceilings are independent of the partitions ensure that the partitions are braced and /or fixed to resist their own induced seismic loads including the use of movement heads to allow for interstory sway.

15. Drawings and Documentation

The following must be provided in the suspended ceiling documentation on DPTI projects;

Building Importance Level

Site Hazard Factor (Z)

Site sub-soil class

The effective floor acceleration afloor at each floor in two orthogonal directions in accordance with Clause 8.2 of AS 1170.4 – 2007 where available

The seismic mass of the ceilings

The component importance factor Ic to be adopted for the ceilings.

The method of seismic bracing of the ceiling (perimeter fixing or bracing).

If the ceiling is to be restrained on two adjacent sides this needs to be nominated on the ceiling plans.

The location of any seismic ceiling gaps.

Edge and internal spacing of bracing if it is required and notional location.

The detail of bracing if it is required including all fixings.

The locations of the hangers and their fixings.

Whether shop drawings are required of the ceilings. Where recessed luminaires are to be used they shall be shown on the reflected ceiling plans together with an indication as to whether they are supported by the ceiling, their approximate weight and the manufacturer’s reference. Refer also to the DPTI drawing “Seismic Details for Suspended Ceilings”.


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Inspection

Inspection requirements for ceilings are set out in the DPTI NATSPEC ceiling specification section, Schedule 5 of the standard DPTI contract documents and the DPTI Guidenote - Construction Site Visits.

Project teams are reminded of the need to inspect ceiling construction and in particular ceiling framing prior to the installation of ceiling tiles or panels and to forward a site inspection report to DPTI.

An inspection of ceiling framing prior to installation of tiles or panels shall include checking for compliance with the manufacturers’ recommendations and in particular:

Spacing of support hangers – typically 1200mm maximum but reduced around the perimeter to 200mm – 600mm typically.

Angle of hanger support – no more than 15 degrees from vertical;

Fixing of hangers – screwed to purlin webs, never hooked over purlin lips, never pop riveted, never shot fired into concrete.

Ductwork, cable trays, pipework and electrical conduits and the like must be independently supported from the ceiling system and not braced from the ceiling system.

Fixing of bracing – the top of the bracing is to be fixed to purlin webs or roof members with adequate lateral restraint and capable of supporting the load. For fixings into concrete use appropriate rated fixings. The bottom of the bracing is to be fixed to the ceiling framing using appropriate screw fixings.

Perimeter fixing – perimeter brackets fixed where necessary;

Adequate support of ceilings beneath large service ducts or group of closely spaced services – transfer members may be needed. The ceiling system shall not be suspended from any non-structural building services such as ducts.

Support around access hatches – ensure support members are not cut unless additional trimmers and hangers are provided, note the manufacturer’s recommendations around additional trimmers to support openings, ensure the opening will not adversely affect the ceilings performance in an earthquake.

Support of lighting – ensure lighting is fixed into or supported independently as per the intended design, note the manufacturer’s recommendations around additional trimmers and /or hangers to support lighting.

Downlights or other services shall not rely on the ceiling panel for support. They shall be installed in rigid infill, e.g. MDF board, supported on the ceiling grid, or the load shall be transferred back to the ceiling structural components.

Bulkheads shall be attached to the structural soffit, independent of the ceiling, unless specifically designed otherwise.

Wind uplift – provide bracing of ceilings to all external areas and where necessary to internal installations. Provide ceiling clips if required and check hangers are adequate for uplift.

Seismic specific details to check for include:

Seismic brackets to two adjacent walls and sliding joint to the other two walls where specified. Ensure screws are fixed in the correct locations in the brackets as in some systems the screw location is the principle difference between a sliding and fixed connection.

Bracing is located as specified and constructed to the specified bracing detail.

Seismic joint clips are installed on main beam connections where recommended by the manufacturer.

Seismic joint clips are installed on cross tee connections where recommended by the manufacturer.


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Such an inspection does not relieve the General Building Contractor or the ceiling installer of their responsibilities under the contract, AS/NZS 2785:2000 or the National Construction Code. As per Section 4.12 of AS2785:2000 the installer shall ensure that the installation of the ceiling complies with the following before requesting an inspection:

The contract specification.

The manufacturer’s installation specification.

The suspended ceilings standard, AS2785:2000.

The contractor is also to provide written confirmation that the ceilings have been installed in accordance with the drawings and the specification together with certification by the ceiling supplier that the ceiling meets the design requirements including seismic loads. For all fixings provide certified test data by the manufacturer of the fixing to show the design loads that the fixings are capable of carrying the specified or design loads.

Seismic bracing examples

For examples of seismic bracing of ceilings refer to the DPTI drawing “Seismic Details for Suspended Ceilings”. Note that the drawing does not cover all possible bracing options and that the details need to be adapted and expanded upon to suit specific projects by the design team. Refer also to the reference documents below for further information.

References

AS 1170.4:2007 – Structural design actions Part 4: Earthquake actions in Australia

AS/NZS 2785:2000 – Suspended ceilings – Design and installation

Australian Earthquake Engineering Society, AS1170.4: 2007 – Commentary

NZS 4219: 2009 – Seismic performance of engineering systems in buildings

FEMA E-74, January 2011 – Reducing the Risks of Nonstructural Earthquake Damage

FEMA 454, December 2006 – Designing for Earthquakes, A Manual for Architects.

Rondo, May 2014 – Introduction to Rondo Seismic Wall and Ceiling Systems.

Armstrong, March 2013 – Armstrong Seismic Design Guide

Kwikloc Studform – Kwikloc Seismic Ceiling Systems

ASTM E580/M, American Society for Testing and Materials, Standard Practice for Installation of Ceiling Suspension Systems for Acoustical Tile and Lay-in Panels in Areas Subject to Earthquake Ground Motions

USG Australasia, 2012 – Generic Seismic Design for USG Donn Exposed Grid Suspended Ceilings.

Best practice guide – selection and installation of top fixings for suspended ceilings, Association of Interior Specialists and Construction Fixings Association, UK, 2012

Contact

For further information contact: John Callea

Manager Construction Advice Telephone: 08 8226 5315 Email: [email protected]


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Appendix – Photographs of Earthquake Damaged Ceilings

Photo: University of Canterbury, Christchurch New Zealand 2010

Photo: Failure of partitions and ceilings in the 1994 Northridge Earthquake (Photo courtesy of Wiss,Janney, Elstner Associates).

Source: FEMA E-74, January 2011, Reducing the Risks of Non-structural Earthquake Damage

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