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What design standards exist for the design of ballast against uplift forces, and what factor of safety against uplift do these design standards promulgate? I am familiar with a typical FS of roughly 1.5 against sliding forces due to active soil pressure for the design of many types of structures (including cantilevered retaining walls and gravity dams), but I am not aware of any such standard FS against uplift.

It is possible- perhaps likely- that the safety factor can vary depending on the nature of the loading. Specifically I have in mind uplift due to wind. But other forms of applied uplift may include: buoyant forces, dynamic/static pressure applied by some other fluid (e.g., water, etc.), and load transference forces (perhaps in a machine where ballast is used to counteract forces applied to some arm/member).

The way I have done this in the past is to use standard load combination equations in design codes. For example, the ASCE 7 2010 load combinations for design of the limit state considering wind uplift* are as follows**:

  1. ASD: $~~~~~~~~~~~~~~~~0.6D+1.0W_{working~stress/service~state}^{***}$
  2. Strength design: $0.9D+1.67W_{working~stress/service~state}^{***}$

However, the problem with this approach is twofold.

First, using these load combinations directly leads two different, inconsistent effective factors of safety:

  1. $Effective~FS_{ASD~Method} = 1.0/0.6 = 1.67$
  2. $Effective~FS_{Strength~Method} = 1.67/0.9 = 1.85$

Secondly, the intention of a design code such as ASCE 7 is to provide guidance for the load side of the design equation. The resistance side of the design equation is usually left to the various engineering groups/societies who publish standards for different materials used to resist loads, e.g. the American Concrete Institute (ACI), or the American Institute of Steel Construction (AISC). These groups provide standard factors of safety (ASD design) and resistance factors (LRFD design). However as far as I am aware, there is no American Institute of Ballast.

Also note that for this question I am not considering uplift due to seismic forces, because seismic events occur in the form of a spectral acceleration which results in a force, and that force gets higher as the mass of the ballast increases. Therefore ballast is not effective on its own in preventing uplift due to seismic acceleration (though in some cases it may be effective in restraining lateral seismic acceleration via friction).


* Note that in ASCE 7 2010/IBC 2012 forward, wind loads are factored loads (factored up by 1.6); prior to 2010, wind loads were working stress and the ASD load factor was 1.0 (LRFD load factor of 1.6).

**The actual ASCE 7 load combinations utilize the ASCE 7 2010, factored wind uplift load, i.e.:

$~~~~$7. ASD: $~~~~~~~~~~~~~~~~0.6D+0.6W_{ASCE~7~2010}$

$~~~~$6. Strength design: $0.9D+1.0W_{ASCE~7~2010}$

*** Due to the above notes, $W_{working~stress/service~state}=0.6W_{ASCE~7~2010}$.

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  • $\begingroup$ I wonder whether you have examined Eurocodes for a similar idea. Wrist American standards may be sufficient, another sweet of building codes may actually provide the answers. British Standard codes are likewise insufficient on their own and are now superseded by Euro codes. $\endgroup$ – Rhodie Sep 2 '18 at 12:35
  • $\begingroup$ @Rhodie I haven't. Where are these codes available? $\endgroup$ – Rick supports Monica Sep 3 '18 at 17:07
  • $\begingroup$ en.m.wikipedia.org/wiki/Eurocodes $\endgroup$ – Rhodie Sep 4 '18 at 18:46
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    $\begingroup$ Probably the best resource will be available from UK Institution of Civil Engineering at www.ice.org.uk $\endgroup$ – Rhodie Sep 5 '18 at 0:42
  • $\begingroup$ According to BS EN 1990:2002+A1:2005 ballast design is specified on page 9. You don't specify what kind of ballast you're dealing with. Is it concrete blocks in sea defences, stone gabions, rail ballast, steel lift ballast using water... we don't know. $\endgroup$ – Rhodie Jan 8 '19 at 5:05
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It is possible- perhaps likely- that the safety factor can vary depending on the nature of the loading. Specifically I have in mind uplift due to wind. But other forms of applied uplift may include: buoyant forces, dynamic/static pressure applied by some other fluid (e.g., water, etc.), and load transference forces (perhaps in a machine where ballast is used to counteract forces applied to some arm/member).

A machine where ballast can be used to counteract forces is simpler than you think - it happens frequently in tank / pressure vessel design. The liquid inside the tank is a ballasting force that could counteract a wide variety of loads:

  1. Vacuum pressure inside the vessel causing caving in a flat bottom
  2. External flooding for buoyancy causing the bottom to cave in
  3. External flooding for buoyancy causing the vessel to float
  4. Wind forces from a wind event

The ultra conservative ASME (specifically ASME RTP-1 - I have not verified for other sections of ASME code) will not allow the liquid inside to be used to counteract any of these forces. However, they will allow the maximum allowable strain to be doubled during these events.

ASTM D3982 will allow the liquid inside to counteract the first loading for tanks with a vacuum loading less than .217 psi - or 6" of liquid.

In practice however, before a hurricane reaches land everyone fills their storage tanks before evacuating, regardless of how well they were designed.

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