Seismic action produces loadings on tanks that are potentially damaging. To maximise asset protection it is critical that the correct design approach is utilised as this will underpin the performance of the entire seismic tank system.

The ONGUARD system uses a capacity design approach, where ductile anchors are used, which concentrates damage from seismic loading in one small replaceable component, and provides protection to the tank walls.

How it works

The ONGUARD anchors are welded to the tank around its base and connected to the tank’s foundation. During an earthquake they prevent the tank from overturning by holding it down whilst dissipating seismic energy through yielding of the anchors.

Unlike traditional tank anchorages that only work in a one-pull, tension manner, ONGUARD anchors provide controlled yielding in both tension and compression throughout cycling earthquake accelerations. This gives excellent energy dissipation, produces a more stable tank response and provides additional resilience to withstand earthquakes that are larger than the design case. Each ONGUARD application is carefully and specifically designed by ONGUARD engineers specifically for the seismic hazard at your location and so that all other elements of the tank system have sufficient strength to remain undamaged.

The energy dissipating element within each ONGUARD anchor acts as a seismic fuse. Once the fuse has done its job it can be inspected and if needed quickly, easily and cheaply replaced using everyday tools and with no specialist skills or experience. Full earthquake readiness is reinstated with minimal fuss.

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Design Approach

Experience has shown that a holistic design approach is required, which considers the tank, anchors, foundation slab, and catwalks, to ensure efficient seismic performance. ONGUARD can provide tank fabricators with design solutions for anchors and tank wall thicknesses. In addition, ONGUARD can also provide design requirements for the foundation slab and catwalks and can work with your foundation and catwalk designers to achieve the desired outcome.

How ONGUARD is designed

New Zealand

United States

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Existing tanks with traditional anchorages pose a greater threat to your operations than new tanks fitted with the ONGUARD system. For many older tanks that may not have been designed to meet modern design codes, this threat is greater still.

Using gathered information such as tank geometry, material thicknesses and foundation construction, ONGUARD engineers are able to calculate the earthquake strength of an existing tank system and quantify the level of risk it poses. They can then specify a customised ONGUARD system to replace the tank’s existing anchorage system. The new ONGUARD anchors protect the remainder of the system from damage by introducing much-needed ductility and resilience, delivering improved earthquake resistance and performance.

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OG Pro Anchor Technical Information

OG PRO anchor range:
Anchor Design Strength Application (Tank Volume)*
  kN kips kiloliters gallons
OG PRO 23 23 5.1 2 - 40 800 - 10,000
OG PRO 33 33 7.5 5 - 60 1,500 - 15,000
OG PRO 51 51 11.5 40 - 100 10,000 - 25,000
OG PRO 81 81 18.2 75 - 150 20,000 - 40,000
OG PRO 117 117 26.3 110 - 300 30,000 - 80,000
OG PRO 172 172 38.7 180 - 800 50,000 - 200,000
OG PRO MAX 295 66.3 100 - 800+ 25,000 - 200,000+

* The most appropriate anchor will depend on the height-radius ratio of the tank and the available slab thickness

OG PRO anchor components: 
Component Specification
Pin AS/NZS 2637.1:2010 - grade300*
Filler Ultra-high molecular weight polyethylene
Cap ASTMA276/479 304L Stainless Steel
Casing ASTMA276/479 304L Stainless Steel 
Coupler 300mpa minimum yield
Epoxy anchors Grade 8.8 galvanised threaded rod with Hilti HIT-HY200 or HIT-RE500SD

* Prior to fabrication, mill and test certificates for each batch is checked for suitability and quality control 

OG PRO anchor testing:

OG PRO anchors have been tested under quasi-static cyclic loading to verify their performance. Prototype testing was completed in accordance FEMA461 (2007) using a displacement-controlled loading protocol. 

Prototype test Yield strength in tension (kN) Maximum tension (kN) Cycle displacement
on which 20% strength
degradation occurs in
compression (mm)
Last cycle displacement
completed prior to
fracture (mm)
OG PRO 33-1 41 62 11.0 15.5
OG PRO 55-1 62 95 15.5 21.7
OG PRO 51-2 65 95 15.5 21.7
OG PRO 81-1 102 152 21.7 21.7
OG PRO 81-2 99 152 21.7 21.7
OG PRO 117-1 158 225 15.5 21.7
OG PRO 117-2 150 222 n/a 7.9
OG PRO 172-1 212 326 30.3 30.3
OG PRO 172-2 209 324 30.3 30.3
OG PRO 172-3 214 324 21.7 21.7
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