Composite Steel beam cont over support

[coolad2007]

Hi all,

I was wondering if anyone could provide me with a good reference example on design of composite steel beam continuous over support.

Thanks in advance.

 

[ishvaaag]

Composite Structures of Steel and Concrete
Beams, slabs, columns, and frames for buildings
Third Edition
R.P. JOHNSON
Blackwell Publishing 2004
4.6 Example: continuous composite beam

DESIGNERS’ GUIDES TO THE EUROCODES
DESIGNERS’ GUIDE TO EN 1994-1-1 EUROCODE 4: DESIGN OF COMPOSITE STEEL AND CONCRETE STRUCTURES PART 1.1: GENERAL RULES AND RULES FOR BUILDINGS
Example 9.1: two-span continuous composite slab

Elementary Behaviour of Composite Steel and Concrete Structural Members
Deric J. Oehlers
Mark A. Bradford
Butterworth-Heinemann 1999
Chapter 12 Rigid plastic analysis of continuous composite beams
has examples on it.

The reference I am giving today in other composite questions
Structural Steelwork Eurocodes Development of A Trans-national Approach
also has a Chapter 7 on continuous composite beams but lacks example. It however points to probable derivations to floor vibrations checks that can be quite necessary for some cases and opens a new breadth of literature for the question.

 

[JoshPlumSE]

AISC chapter I has some commentary on this subject. I'm no expert, so you should read it yourself. But, my impression from what I remember is the following:

1) Positive moment capacity is based on composite section.
2) Negative moment capacity is based on steel beam only. Though there may be something in there about being able to take advantage of the reinforcement in the slab.
3) Stiffness of the member would be based on a weighted average of the composite section and the steel only section. Based on how much of the beam is in negative bending and how much was in positive bending.

There are probably other, more exact ways of analyzing these beams. But, this method seems straight forward enough that it might actually be useful for us folks without PhD's....

 

[coolad2007]

I have mezz level addition to existing bldg completely independent of the exist frame. This new level framing will have composite deck resting on steel beams. Due to existing frame I have to design some of the beams as cantilever beams and so was wondering if I should just design them as steel beams and ignore the composite action all together. I just can't have pin pin condition for such corner composite beams. Anyways thanks for the input. I would definitely review the references. Thanks for your input.

 

[MrHershey]

Added note: Even if you don't use the concrete or slab reinforcement for strength, probably a good idea to provide extra bars at the cantilever and over the support to limit the amount of cracking in the slab.

 

[JAE]

I'd design the beams alone to support the cantilever and provide steel in the slab to control cracking as has been suggested.

 

[BAretired]

CSA S16-01 Article 17.5.2 Parallel Reinforcement states in part:

Reinforcement parallel to the span of the beam in regions of negative bending moment of the composite beam shall be anchored by embedment in concrete that is in compression.

Taking that clause literally, you cannot anchor the bars in the cantilever in concrete that is in compression. Personally, I would think it would by valid to use the bars within the effective width of the composite beam flange as contributing to the steel beam section.



BA