## IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

## IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

(OP)

Does this sentence mean that whenever the load H resists the primary variable load effect, its load factor "H" shall be changed to 0.9 where the value of H is permanent? And throughout all other equations within this load combination, will the value of H be set to 0?

According to the exception on IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design #2 "Where the effect of H resists the primary variable load effect, a load factor of 0.9 shall be included with H where H is permanent and H shall be set to zero for all other conditions."

For instance, in a tank, you have load combinations such as:

1.4(D +F)(Equation 16-1)

1.2 (D + F) + 1.6(L + H) + 0.5 (Lr or S or R)( Equation 16-2)

1.2(D + F) + 1.6 (Lr or S or R) + 1.6H + (f1L or 0.5 W)(Equation 16-3)

1.2(D + F) + 1.0W + f1L + 1.6H + 0.5 (Lr or S or R) (Equation 16-4)

1.2 (D + F) + 1.0E + f1L + 1.6H + f2S ( Equation 16-5)

0.9D+ 1.0W+ 1.6H(Equation 16-6)

0.9(D + F) + 1.0E+ 1.6H (Equation 16-7)

And given that the pressure of the fluid (F) inside the tank is being resisted by the lateral pressure (H) acting outside the tank. Will the primary load H be set to 0.9H and all other combinations including H be turned to 0 and would the load combinations then be like these?

1.4(D +F)(Equation 16-1)

1.2 (D + F) + 1.6(L) + 0.5 (Lr or S or R)( Equation 16-2)

1.2(D + F) + 1.6 (Lr or S or R) + (f1L or 0.5 W)(Equation 16-3)

1.2(D + F) + 1.0W + f1L + 0.5 (Lr or S or R) (Equation 16-4)

1.2 (D + F) + 1.0E + f1L + f2S ( Equation 16-5)

0.9D+ 1.0W (Equation 16-6)

0.9(D + F) + 1.0E (Equation 16-7)

Thank you in advance for your thoughts with regards to this matter.

According to the exception on IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design #2 "Where the effect of H resists the primary variable load effect, a load factor of 0.9 shall be included with H where H is permanent and H shall be set to zero for all other conditions."

For instance, in a tank, you have load combinations such as:

1.4(D +F)(Equation 16-1)

1.2 (D + F) + 1.6(L + H) + 0.5 (Lr or S or R)( Equation 16-2)

1.2(D + F) + 1.6 (Lr or S or R) + 1.6H + (f1L or 0.5 W)(Equation 16-3)

1.2(D + F) + 1.0W + f1L + 1.6H + 0.5 (Lr or S or R) (Equation 16-4)

1.2 (D + F) + 1.0E + f1L + 1.6H + f2S ( Equation 16-5)

0.9D+ 1.0W+ 1.6H(Equation 16-6)

0.9(D + F) + 1.0E+ 1.6H (Equation 16-7)

And given that the pressure of the fluid (F) inside the tank is being resisted by the lateral pressure (H) acting outside the tank. Will the primary load H be set to 0.9H and all other combinations including H be turned to 0 and would the load combinations then be like these?

1.4(D +F)(Equation 16-1)

1.2 (D + F) + 1.6(L) + 0.5 (Lr or S or R)( Equation 16-2)

1.2(D + F) + 1.6 (Lr or S or R) + (f1L or 0.5 W)(Equation 16-3)

1.2(D + F) + 1.0W + f1L + 0.5 (Lr or S or R) (Equation 16-4)

1.2 (D + F) + 1.0E + f1L + f2S ( Equation 16-5)

0.9D+ 1.0W (Equation 16-6)

0.9(D + F) + 1.0E (Equation 16-7)

Thank you in advance for your thoughts with regards to this matter.

## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

Correct.

Also, it's worth noting that tanks are often leak tested prior to backfilling which will result in the same load case. That said, pretty much all my buried tank designs are controlled by inward soil pressure with no internal fluid pressure. The exterior wall rebar is usually just the minimum reinforcement required.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)

American Concrete Industries

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## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

So when you design tanks and have to consider these load combinations, taking into account that I am using Staad, should I still consider the conditions met on the PCA Rectangular Tank?

i.e.

Condition 1: Soil is absent, fluid is present.

Condition 2: Soil is present, fluid is absent.

Condition 3: Uplift

Condition 4: Earthquake

Thanks

## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

Professional Engineer (ME, NH, MA) Structural Engineer (IL)

American Concrete Industries

https://www.facebook.com/AmericanConcrete/

## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

Thanks.

## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

What kind of tank is it?

Professional Engineer (ME, NH, MA) Structural Engineer (IL)

American Concrete Industries

https://www.facebook.com/AmericanConcrete/

## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

Hi, just read through your reply. It is a multi-cell tank mostly for storing liquid. We are to have an investigation with regards to the structure and most of the process that I am seeing in the internet and from the PCA guidelines use the values of 1.3 1.65 and 1.3. As to checking ACI 350-06, it states that these values are now changed with consideration to the value of fs and the equation I stated before. Well the sanitary coefficients or Sanitary Durability Factor still applies because you still have to multiply it with the Load Combination and such. The one thing I am concerned about though is with regards to the γ, since I am not particularly sure if I would use 1.4 or 1.7. PCA states that using the value of 1.7 as a multiplier i.e. Mu = Sd x 1.7 x F is a much more conservative approach than using the value of 1.4. But as of recent from the ACI 350-06 articles and post and practices state that the use of 1.4 is being considered more.

Sorry for my english, I am quite confuse how to go about with this approach.

Thank you in advance.

## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

Let me know if I misunderstood you.

American Concrete Industries

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## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

Does it mean to say I would use the load factor of 1.7 when considering liquid loads ? I'm confused whether to use the values of 1.7 or 1.6 and since on the Appendix C, it also state that an alternative way determining the load combinations is of the use of values of 1.7 on both F and H.

Thanks,

## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design

American Concrete Industries

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## RE: IBC 2015 1605.2 Load Combinations Using Strength Design or Load and Resistance Factor Design