Expert: Arshad Khan - 3/29/2008

Question
QUESTION: Dear Sir,
WE are in our final year B.Tech Civil...
We are doing a project i.e Analysis and Design of 3 storey Resedential Building.
We completed the Analysis Using Staad pro2007...
Now the problem we are facing is we dont have any Mentor..
So please help us
1.What is the loading that we are suppose to give ??
2.Should we model the whole structure or Just on plane as typical..
3.The Supports are to be fixed ??
4.And How do we group the Various Members based on what criteria ??


ANSWER: Hi Syed,

This is a difficult subject to mentor over this forum, but here are some answers:

1. Loading is self weight plus live loading of 3.5 KN/m2
2. You can do either
3. Yes, if you have good foundations- say on rock.
4. Grouping is not necessary- but is usually done for the same sized members.

If you go to the Research Engineers website, you will find a lot of usefull information there, and also example modelling/analysis.



---------- FOLLOW-UP ----------

QUESTION: Sir fi the foundations are not on rock should we design the footing for also the Bending moment ??

Also Sir we have tried both the ways of modelling..the results we got were way different...So pls help in this regard why is it so different and which one is correct ??
Also sir can we use the load reduction for multistorey ??

Can you also pls guide me on how do i apply to become the fellow of civil engineers UK ??

Thanks alot

ANSWER: Syed,

Yes, footing needs to be designed for bending moment, whether on not it is on rock- if column is designed pinned, it will still put moments into the base and the soil reaction will cause moments in the base.

I do not know which 2 ways you did the analysis, so cannot comment. Just ensure that the loading distribution is correct.

You can use load live load reduction if the building is more than 5 storeys- just confirm that according to your local code.

For info on how to apply for membership, visit www.ice.org.uk

---------- FOLLOW-UP ----------

QUESTION: Sir thanks for all the great advice...I tell you i got more help from you then
from my Head of Department.thanks alot.
Sir i have one more doubt,
when modeling the only one floor and and columns with far ends pinjointed,
can you pls tell me how will I find the column loads and moments..??
and please tell me also the procedure when I have chamfered columns, i.e.
when I two beams meeting at an angle and the I provide a Column at the
junction, the column is not circular not rectangle not also trapezium in
section.. the section is as if two rectangles have intersected at ann
angle..Please give me a guide line how to design it.
LAstly sir will you please advice me some good books which have example
designed structures ??
Thanks and salam

Answer
Hi Syed,

Syed, when you do sub-frame anaysis, the total column loads have to be added separately by hand or Excel spreadsheet, so that each floors laoding is transmitted down. Sub-frame analysis is only applicable where lateral stability is provided by shear walls or bracing, so the moments in the columns at each floor can be taken from your sub-frame analysis. This method of analysis is not valid for sway frames- for that you need to model all the floors.

Regarding your odd-shaped column, one way you can do is to analyse it as a circular column that has a diameter that fits within your two intersecting rectangles- then just put additional vertical rebar and links for the protruding 8 number corners. Or you can use a software like PROKON, which you can design any shape of column- you can download a trial version from the website www.prokon.com

One book that has good design examples is by REYNOLDS- see link below:

http://www.amazon.co.uk/Reinforced-Concrete-Designers-Handbook-Reynolds/dp/04191