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[ajayapc]

Dear Sir,
While designing a RCC frame structure (with soft first story), whether STAAD designs ground floor columns as per 1893-2002 provisions i.e. ground floor columns and beams shall be designed for 2.5 times SF and BM, or we have to rerun the program for satisfying above clause.

Thanks
AJAY C

[binaya shahi]

I am also facing problem in modelling soft story building.

In staad pro wall is not generally modelled as structural element. Only the wall load is provided over beams.

So, if you too are also modelling your building as I explained above staad pro won't design for soft story.

There are two ways you can analyze soft story.

1. you model the walls with the properties of brick masonry(if you are using brick masonry)

or instead of wall use equivalent braces.

and perform dynamic analysis.

( I don't know how to do this as I don't know how to model brick wall with proper properties or braces with pertinent properties equivalent to the walls)

2. increase the base shear and moments in beam and column by factor of 2.5 for soft story and design the soft story columns and beams separately.


I tried to do it in etabs by increasing the earthquake load by 2.5, but it didn't increased the base shear by the factor of 2.5.

To increase the base shear by the factor of 2.5 I had to increase the earthquake load by the factor of 6.

This resulted in increase in reinforcement of the columns by more than 5 times. In normal analysis the reinforcement for one of the column was 1200 sq mm. whereas for the soft story analysis it was 6200 sq mm.

I have doubt whether I should use (2.5 times earthquake load that resulted in not much increase in base shear) or (6 times earthquake load that resulted in 2.5 times base shear)

I suggest you to multiply EQ loads in your load combinations by 2.5.
And check if the base shear has increased by 2.5 times or not.
keep on increasing the multiplication factor for EQ load until you achieve 2.5 times base shear.

Also check if moments is columns and beams have increased by 2.5 times or not.
I found that: on multiplying Eq load by 6, the base shear in my model increased by 2.5 times and moment in columns increased by nearly 3 times.

Let me know, what result you get in staad pro?
If you find better method to design soft story, please inform me.