T&R Seismic Calculator - Baffle Ceilings
Because every building is different, there is no standard seismic restraint solution to address site, location, form and function. The scope of seismic restraint and related engineering work that will be required will not be known until the ceiling design is completed. The T&R Seismic System will provide a solution for buildings with an Importance Level of 3 and below. A suitably qualified Chartered Professional Engineer will be required for Importance Levels 4 & 5. It is imperative that mechanical services, sprinkler systems, electrical and suspended ceiling design are all co-ordinated at appropriate stages.
While full compliance with seismic requirements will add cost, it will limit damage, reduce repair costs and reduce the time to re-occupy post event. Furthermore it is now a legislative requirement for Code of Compliance Certificates and Health and Safety Laws. The new laws, affect those who are upstream from the workplace (for example designers, engineers, manufacturers, suppliers or installers). Specifically they have a duty to ensure, so far as is reasonably practicable, that the work they do or the things they provide to the workplace don't create health and safety risks.
This guide allows a designer to calculate required bracing for suspended baffle ceilings. The calculations are based on conservative assumptions. Reduced seismic bracing designs for individual sites may be possible if a suitably qualified Chartered Professional Engineer carries out a site-specific design. This guide should not be used as a calculation template for a PS-1; specific seismic design should be carried out for these cases.
This guide has been prepared by JSK Consulting Engineers for T&R Interior Systems with the usual care and thoroughness of the consulting profession. Interpretation and application of this guide is outside the control of the engineer and therefore is the users' responsibility. This guide does not constitute a producer statement or engineer's certification, and is not for use with trafficable ceilings or ceilings which support partition walls or any other service load.
Allowance for relative motion between the ceiling and structure must be provided by floating edges. Back bracing to the above structure will be used as the primary load path to structure, therefore all edges must be floating. Floating edges must also be provided around rigid or separately braced items that pass through the ceiling. The amount of clearance should be checked by an engineer on a case-by-case basis.
See the assumptions and limitations notes.
Consult a structural engineer for the expected earthquake deflections of the structure.
© The T&R Seismic System has been developed in conjunction with JSK Consulting Engineers and T&R Interior Systems.
It remains the intellectual property of T&R Interior Systems and may not be used with other products.
Step One - Limit State Type
Determine the type of design for the installation.
Is the suspended ceiling and/or elements which directly interact with the ceiling required to be returned to an operational state within an acceptably short time frame in order for the structure to be occupied?
As per the suppliment to NZS 1170.5, this category can apply to ceilings which interact with fire suppression systems, emergency lighting installations and other parts.
Note that this applies for all parts and components that are essential for a building to be occupied. These would include; fire protection systems, critical plumbing systems, electrical systems and lifts. For all structures these will be elements required to be returned to an operational state within an acceptably short time frame (hours or days rather than weeks) in order for the structure to be reoccupied.
For example reinstatement of lightweight fallen tiles may be considered a viable option within the time frame indicated to allow reoccupation of a office but may be unsuitable for an operating theatre
Does the suspended ceiling, when considered as a whole, weigh more than 7.5kg?
For the ceiling to not be considered ULS design it must weigh less than 7.5kg
Is the suspended ceiling installation at a height of 3m or greater?
For the ceiling to not be considered ULS design, it must be installed at a height less than 3m
Would collapse of the suspended ceiling block emergency egress routes?
Could fallen ceiling tiles block emergency egress routes?
Does the ceiling comply with all of the assumptions and limitations?
Obtain site specific design advice from an appropriately qualified engineer
Your Limit State Type is
As there are two limit states which apply to the ceiling in this instance, the most stringent state which results in the shortest allowable lengths will apply.
Step Two - Suspended Baffle Ceiling Weight
Calculate the total seismic weight based on the ceiling and service weights.
Enter or select the corresponding values in the column on the right and sum all the component weights to get a total seismic weight. This value will be used in the following steps this worksheet.
|Baffle Spacing (m)||
Minimum 0.1m - Maximum 1.0m
Alternatively contact a suitably qualified chartered professional engineer for specific design.
|Baffle Mass (kg/m2)||
|Strongback Mass (kg/m2)||41x21x1.2 PST Channel||
|Services||Luminaires incl. Gridlux (kg/m2)|
|Services Allowance (kg/m2)|
|Total Seismic Weight Sw||
Strongback and hanger rod spacing for M10 Hanger Rod or 41x21x1.2 PST Channel is 1.2m
Note: If Gridlux is to be used as the primary lighting, allow 1 kg per 1200mm unit and 0.5 kg per 600mm unit. An average Gridlux layout would have a 1200mm unit every 5m 2 , resulting in a luminaire allowance of 0.2kg/m 2 . Note that Gridlux is only compatible with the 150x30mm aluminium baffle.
Step Three - Seismic Actions
Calculate seismic force based on seismic zone, height above ground level, and building importance level.
Locate the area for which the suspended ceiling will be installed. Find the Site Specific Zone Factor by locating the line closest to the area of installation, or the shaded area it is within, and tapping it to show the rating.
Anything above IL3 will require a design by an engineer
Ceiling connection height above ground floor
|Seismic Weight Sw|
|Total Seismic Force Sf
Step Four - Selecting Back Bracing
Determine the maximum area of ceiling that each brace can support based on seismic force, brace type and the plenum height.
Maximum Plenum Height (m) Ph
|45° stud length (m)||0.28 m|
|Gridlok Brace Capacity (kg)||
|Brace Arm Size||64x35x0.55mm or 92x35x0.55mm Steel Stud|
|Area per Brace (m2)||Ab|
Note that figures above are based on the Gridlok specifications, (Tracklok - Seismic & Structural partition & Ceiling Bracing Guide NZ Second Edition, February 2018) ensure that when Gridlok is used the installation recommendations and guidelines are followed. Gridlok C-Channel or custom strut brackets (to suit 41x21x1.2mm strut) are to be used.
If further refinements to the back bracing design is required or a greater capacity of back bracing needed contact a suitably qualified chartered professional engineer.
Installation arrangement of Gridlok C-Channel back brace. The brace is constructed of various steel stud compression posts with 2x steel studs at 45 degrees in each direction, depending on the plenum height.
All fasteners into the building structure are sufficient for the loadings imparted from the back bracing, as long as the manufacturers specifications are followed during the installation of the fastener.
For connections into structure which are not detailed in the table please refer to the consult a suitably qualified chartered professional engineer.
Step Five - Back Bracing Layout
The minimum number of braces for a ceiling depends on 2 factors:
- Capacity basis (sufficient braces to transfer the total ceiling load)
- Motion limiting basis (sufficient braces to ensure that the ceiling moves as a single unit)
Minimum number of braces (capacity basis)
|Ceiling Area (m2) Ca||/||Area per brace (m2) Ab||=||Min. # of braces #b|
Maximum brace spacing along a Strongback
|Area per brace (m2) Ab||/||Strongback Brace Spacing (m)||=||Max. Brace Spacing (m) Bs|
The calculated minimum number of braces represents the number of braces required to carry the total ceiling load, with the assumption that ceiling load is evenly shared between braces.
Often the shape of the ceiling means that more than the minimum number of braces are required to adequately control the motion of the ceiling, therefore costing should not be based of the minimum number. Instead an RCP should be annotated with required bracing in accordance with the bracing guidelines below to work out the actual number of braces:
- Bracing should be laid out evenly throughout the ceiling area
- Strongbacks closest to the ceiling edges should be braced
- Thereafter every second strongback must be braced. It is preferable that every strongback is braced
- If a strongback is broken along its length each shall be considered as a separate strongback, and braced accordingly
For complex ceiling shapes it is recommended that advice on the bracing layout is sought from a suitably qualified chartered professional engineer.
Step Six - Determining the Seismic Clearance
Determining a seismic clearance is to ensure there is sufficient clearance to allow parts to move relative to each other during a seismic event.
|Plenum height (m) Ph||X||Interstory drift factor
|=||Required Seismic Clearance (mm) Sc|
For larger plenum heights the required seismic clearance may be impractical, for site specific installations contact a suitably qualified chartered professional engineer.
You Will Need...
- Building Location
- Ceiling Height
- Baffle Type, Size and Spacing
- Luminaire Weight and Spacing
- Reflected Ceiling Plans
- A section showing plenum depths
This design is for T&R Aluminium Baffle Ceiling only and cannot be used with other manufacturer's baffle ceiling products.