## Loading combination: Basic question

## Loading combination: Basic question

(OP)

Dear All,

I am currently checking the work done on a project in Singapour (calculation done with UBC 97 and British standards.

The earthquake seismic combinations used are not the classical 1.2 D + 0.5 L + Ex + 0.3 Ey

Instead the design office uses 1.44 D +.55 L + 1.1 Ex

Has somebody see such a combination??

I am very amazed and want to diaprove this formula.

Any idea where this formula comes from?

Thank you in advance for your help.

Alan

I am currently checking the work done on a project in Singapour (calculation done with UBC 97 and British standards.

The earthquake seismic combinations used are not the classical 1.2 D + 0.5 L + Ex + 0.3 Ey

Instead the design office uses 1.44 D +.55 L + 1.1 Ex

Has somebody see such a combination??

I am very amazed and want to diaprove this formula.

Any idea where this formula comes from?

Thank you in advance for your help.

Alan

## RE: Loading combination: Basic question

Perhaps the combination is a British one? I'm in the USA and I've never seen those numbers (1.44, 0.55,etc.)

## RE: Loading combination: Basic question

It's really very weird combinations. !

Seismic load can be applied in the Load combination of British standards as the wind load.

1.4 DL+ 1.4 WL.

1.2*(Dl+LL+WL).

where WL is wind load or seismic load.

Because British standards clear of any method to calculate seismic load.u can use UBC to calculate the base shear force only

but don't use UBC load combination if ur general code is BS.

Ahmed

## RE: Loading combination: Basic question

Now I am totally confused by the paragraph "Exceptions" of section 1612.2.1 of UBC 97.

In this section the basic load combinations 1.2 D + 1 E + 0.5 L are defined.

In the exception it is writen " Factored load combinations multiplied by 1.1 where load combinations include seismic forces"

Does it mean that when I am designing a concrete structure I need to take into accout:

1.32 D + 1.1 E + 0.55 L

If somebody can clarify this exception, I would be very grateful.

Thank you in advance and thank you for the help already given to me. It's very helpful

## RE: Loading combination: Basic question

Yes, for non-seismic load combinations your are directed to section 1902.2 for concrete (per Exception 1)

For seismic combinations you must multiply the two seismic combos in 1612.2.1 by 1.1 for concrete and masonry.

## RE: Loading combination: Basic question

Anyway, thank you so much for your help.

Alan

## RE: Loading combination: Basic question

1.4D + 1.7L

1.05D + 1.3L + 1.3W

and were tied to specific phi factors (strength reduction factors).

The ACI 318 has now revised its load combinations and phi factors to match that of the IBC. When the UBC 97 was published, ACI was still under the older combinations so the UBC had to adjust the Chapter 19 combinations to account for the difference.