Depressed Girder/ Girders of varrying top and soffit level

[mylife2014]

I have been searching for a references or codes that explains limits and things to consider regarding depressed girder/beam design(or a beam with varying level of top and soffit somewhere in the beam span - I am confused what really is the right term for this, please see my attached image which is a representation of the beam profile that i mean)

Hope anyone can help me in this matter.

Thank you in advance.

 

[AELLC]

They are called stepped beams, and you need to be more specific - is this a steel or a concrete beam, or an open web girder, etc?

 

[mylife2014]

Thanks AELLC. Its a concrete beam..cast in place.

 

[dhengr]

Mylife2014:
Is that depressed beam cast in place against soil, and called a footing or a grade beam? Why not explain a bit more about your problem, with some pertinent design info., if you really want serious help? Why is the bottom sloped and the top surface stepped?

 

[mylife2014]

Hi Mr. Dhengr,
Its a suspended beam, on the amenity level of the tower....I would like to use that kind of beam profile for those area with tree pits...i just dont have any references as of now on the consideratiosn and limits according to code and theoritical basis...

 

[CELinOttawa]

AELLC is correct, you need to provide more information, however:

- If this is a slab supported by steel, then use moment frame type connection in the steel to make the connection: Welded stiffeners and end caps.

- If the concrete must make the transition as a self-supporting (or intra-span) condition, you need to provide stirrups in the transition zone to force the flexural (both tension and compression) forces to make the corner and handle the discontinuity. There is a good discussion on an old thread I was involved with under my old handle "YoungStructural". See:

http://www.eng-tips.com/viewthread.cfm?qid=231262

 

[ztengguy]

Can you design for the smaller depth, and add the weight into the calc. Might be easiest depending on span, load, etc.

 

[mylife2014]

CelinOtawa:

As I have mentioned, it is suspended concrete beam...in addition to this, it will support also a cast in place concrete slab...it will be at the 5th floor of the tower which is an amenity deck(having tree pits from 300mm to 1200mm depression from the floor level to contain the soil).

Thank you for the link you shared but still i need more specific discussion/references. Because in this case,the beam is a main frame element while stairs is not a main frame element wherein you can actually just isolate the design for it and load the forces on the frame element where it rest. So i am just curious if there is a code/books/articles that specifies the limits of depression and the parameters to be considered in the design.

 

[CELinOttawa]

The geometry and the physics are the same as for a staircase...

Show that you have the Strength, Stiffness, and Stability required. Make the details simple and constructible. What further reference could you need?

 

[AELLC]

CE

I think what are seeing more and more in this forum are young inexperienced engineers having to design major structure without mentoring or help in-office.

I went thru that myself at one company in particular.

It is understandable because what we do falls down, hard, when we goof. The mech engrs do not have such an unnerving consequence to their goofs, etc

 

[CELinOttawa]

Alright AELLC, I'll be nice.... Try this reference (if you can stomach something from overseas)

http://caenz.squarespace.com/s/Precast_Concrete.pdf

Some of the discussion is directly applicable, and on p. 34 there is a corbel detail that could do you with minor changes.

 

[AELLC]

@ CEL,

LOL, that is too hi-tech for me. At least it is written in English. But I don't understand the logic of Metric units for structural engineering and construction. They should only be used for chemistry.

We never make decimal location mistakes with English units anymore ever since calculators and computers, so we don't need Metric.

 

[CELinOttawa]

AELLC;

As a Canadian, I was forced to learn and apply both.

I absolutely detest having to design in turtle shells, thumbs and horse hair weights.

I'll take metric any day, and so will 99% of the Engineers on this planet. The English abandoning the IMPERIAL system should be enough of a hint for anyone to take... Those people still weigh themselves in stones!

No. Just no.... And let's agree to disagree before my head explodes or all the respect I've been building for you drains out my ears.

 

[AELLC]

LOL I was just kidding - there are pros and cons of both, too numerous/boring to discuss here - better in Pat's Pub.