Brace footing installations on concrete
Alert
Brace footing installations on concrete This Alert highlights the precautions that need to be taken when installing brace footings on concrete slabs at an early age.
September 2010 This Alert provides practical advice for builders, formworkers, panel erectors and erection design engineers (designers). It will also be useful for health and safety representatives. The information and advice relates to the design of brace footings (including anchors and concrete) where concrete panel braces are to be fixed to floor slabs or independent pad footings of 150mm or greater thickness. If the concrete footing thickness is less than 150mm thick, other safety factors must be considered by an engineer. There is also a checklist on the reverse which should be used before each concrete pour. It will assist with your health and safety management of the site (consider incorporating it into your safe work method statement or site OHS plan).
Background For the last 10 years, to improve construction productivity, builders have started erecting precast concrete wall panels on floor slabs within 24 hours of pouring the slab. Concrete strength at any time is greatly influenced by the age and method of curing. For example, after 24 hours air-cured concrete, without admixtures, may only achieve about 10 per cent of its specified characteristic strength. The anchors used for fixing brace footings consist of a cast-in ferrule into which the brace is later bolted. When anchors are installed in concrete slabs that have not achieved the required strength, they may fail by pulling out under moderate loads. This may lead to catastrophic failure of the wall panel, resulting in death or serious crush injuries to workers.
Control measures To ensure anchors achieve the required pull-out capacity, the concrete must attain a minimum strength as determined by the designer (based on manufacturer and supplier specifications). The required concrete strength to be achieved at erection must be specified. Unless designated otherwise, the concrete strength of the brace footing should be at least 20MPa at the time of fixing of the bracing. Note: Projects specifically designed and documented by the designer may use a lower strength of concrete for erection of braces.
ALE0130/01/09.10
Where a specific design is undertaken for a brace footing to be fixed into concrete at low strength, the designer in conjunction with the builder, formwork company and panel erector, need to consider the following variables that may reduce safety of the designed brace footing: • how the required minimum concrete strength can be achieved prior to the erection of the panels • concrete curing method to be used onsite • ferrule placement tolerances • dislodgement/misalignment of ferrules during concrete placement. In addition, the designer needs to give consideration to: • ensuring panel braces, fixings and footings are designed to have a minimum capacity of 10kN • ensuring any modifications to ferrules, including the welding of base plates, is done in accordance with an engineer’s design and relevant Australian Standards • designing the ferrule inserts to have a minimum embedment depth of 150mm. Note: Ferrules should also be designed and manufactured to ensure their designed failure mode is via cone failure of the concrete, not via direct pullout. This will usually require some form of enlarged base of the ferrule. The builder, formwork company and panel erector should: • implement and maintain a documented sign-off system by a competent person on all slab and anchor details before each pour (see checklist) • verify the minimum concrete strength required before panel erection has been achieved under site conditions.
Further information WorkSafe Industry Standard – Precast and tilt-up concrete for buildings Australian Standard – AS3850-2003: Tilt-up concrete
Contact details Call on: 1800 136 089 Email: [email protected] For more information on occupational health and safety, go to WorkSafe’s website: worksafe.vic.gov.au
Alert Brace footing installations on concrete
Cast-in ferrule checklist This checklist applies to concrete designed for less than 20MPa compressive strength at the time of precast installation. Project: __________________________________________ Principal/head contractor: ___________________________ Subcontractors responsible: ____________________________________________________________________________ Designing engineer: ________________________________ Designated pour area inspected: ______________________ Yes 1.
Is there a project-specific engineered design in place?
2.
Is cast-in ferrule assembly embedment depth in concrete minimum 150mm?
3.
Is all welding to cast-in ferrules to engineer’s specifications?
4.
Are cast-in ferrules in correct position for propping arrangement?
5(a)
Is cast-in ferrule reinforcement steel configuration to design?
5(b)
Has reinforcement been checked? For example, N12 through-bar, mesh, baseplate etc or combinations (as per drawings)?
HOLD POINT
Above details checked and verified by competent person:
6.
Has concrete testing been conducted?
Sign:
Date:
/
No
N/A
/
Testing laboratory verified minimum concrete strength (as per design) has been achieved: HOLD POINT
Actual MPa achieved: _______________________________________________
7
Has this checklist been made available to all relevant parties (eg HSR, panel erector and formworker)?
HOLD POINT
Principal/Head contractor verified all above details:
Subcontractor sign:
Sign:
Date: /
Date: /
/
/
Note: This checklist recommends hold points when a competent person should verify the actions before proceeding to the next point on the checklist. All items on this checklist should be completed and verified as compliant before precast placement to designated pour area. Subcontractor responsible /authorised representative Name (print): ________________________________________________________________________________________ Signature: ___________________________________________________________________________________________ Disclaimer: This Alert contains information following WorkSafe’s inquires into the incident at the date of this report. The information contained in this report does not necessarily reflect the final outcome of WorkSafe’s action with respect to this incident. WorkSafe does not warrant the information in this report is complete or up-to-date and does not accept any liability to any person for the information in this report or as to its use.
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Brace footing installations on concrete This Alert highlights the precautions that need to be taken when installing brace footings on concrete slabs at an early age.
September 2010 This Alert provides practical advice for builders, formworkers, panel erectors and erection design engineers (designers). It will also be useful for health and safety representatives. The information and advice relates to the design of brace footings (including anchors and concrete) where concrete panel braces are to be fixed to floor slabs or independent pad footings of 150mm or greater thickness. If the concrete footing thickness is less than 150mm thick, other safety factors must be considered by an engineer. There is also a checklist on the reverse which should be used before each concrete pour. It will assist with your health and safety management of the site (consider incorporating it into your safe work method statement or site OHS plan).
Background For the last 10 years, to improve construction productivity, builders have started erecting precast concrete wall panels on floor slabs within 24 hours of pouring the slab. Concrete strength at any time is greatly influenced by the age and method of curing. For example, after 24 hours air-cured concrete, without admixtures, may only achieve about 10 per cent of its specified characteristic strength. The anchors used for fixing brace footings consist of a cast-in ferrule into which the brace is later bolted. When anchors are installed in concrete slabs that have not achieved the required strength, they may fail by pulling out under moderate loads. This may lead to catastrophic failure of the wall panel, resulting in death or serious crush injuries to workers.
Control measures To ensure anchors achieve the required pull-out capacity, the concrete must attain a minimum strength as determined by the designer (based on manufacturer and supplier specifications). The required concrete strength to be achieved at erection must be specified. Unless designated otherwise, the concrete strength of the brace footing should be at least 20MPa at the time of fixing of the bracing. Note: Projects specifically designed and documented by the designer may use a lower strength of concrete for erection of braces.
ALE0130/01/09.10
Where a specific design is undertaken for a brace footing to be fixed into concrete at low strength, the designer in conjunction with the builder, formwork company and panel erector, need to consider the following variables that may reduce safety of the designed brace footing: • how the required minimum concrete strength can be achieved prior to the erection of the panels • concrete curing method to be used onsite • ferrule placement tolerances • dislodgement/misalignment of ferrules during concrete placement. In addition, the designer needs to give consideration to: • ensuring panel braces, fixings and footings are designed to have a minimum capacity of 10kN • ensuring any modifications to ferrules, including the welding of base plates, is done in accordance with an engineer’s design and relevant Australian Standards • designing the ferrule inserts to have a minimum embedment depth of 150mm. Note: Ferrules should also be designed and manufactured to ensure their designed failure mode is via cone failure of the concrete, not via direct pullout. This will usually require some form of enlarged base of the ferrule. The builder, formwork company and panel erector should: • implement and maintain a documented sign-off system by a competent person on all slab and anchor details before each pour (see checklist) • verify the minimum concrete strength required before panel erection has been achieved under site conditions.
Further information WorkSafe Industry Standard – Precast and tilt-up concrete for buildings Australian Standard – AS3850-2003: Tilt-up concrete
Contact details Call on: 1800 136 089 Email: [email protected] For more information on occupational health and safety, go to WorkSafe’s website: worksafe.vic.gov.au
Alert Brace footing installations on concrete
Cast-in ferrule checklist This checklist applies to concrete designed for less than 20MPa compressive strength at the time of precast installation. Project: __________________________________________ Principal/head contractor: ___________________________ Subcontractors responsible: ____________________________________________________________________________ Designing engineer: ________________________________ Designated pour area inspected: ______________________ Yes 1.
Is there a project-specific engineered design in place?
2.
Is cast-in ferrule assembly embedment depth in concrete minimum 150mm?
3.
Is all welding to cast-in ferrules to engineer’s specifications?
4.
Are cast-in ferrules in correct position for propping arrangement?
5(a)
Is cast-in ferrule reinforcement steel configuration to design?
5(b)
Has reinforcement been checked? For example, N12 through-bar, mesh, baseplate etc or combinations (as per drawings)?
HOLD POINT
Above details checked and verified by competent person:
6.
Has concrete testing been conducted?
Sign:
Date:
/
No
N/A
/
Testing laboratory verified minimum concrete strength (as per design) has been achieved: HOLD POINT
Actual MPa achieved: _______________________________________________
7
Has this checklist been made available to all relevant parties (eg HSR, panel erector and formworker)?
HOLD POINT
Principal/Head contractor verified all above details:
Subcontractor sign:
Sign:
Date: /
Date: /
/
/
Note: This checklist recommends hold points when a competent person should verify the actions before proceeding to the next point on the checklist. All items on this checklist should be completed and verified as compliant before precast placement to designated pour area. Subcontractor responsible /authorised representative Name (print): ________________________________________________________________________________________ Signature: ___________________________________________________________________________________________ Disclaimer: This Alert contains information following WorkSafe’s inquires into the incident at the date of this report. The information contained in this report does not necessarily reflect the final outcome of WorkSafe’s action with respect to this incident. WorkSafe does not warrant the information in this report is complete or up-to-date and does not accept any liability to any person for the information in this report or as to its use.
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