RC Beam. Are they always considered to be fixed?
RC Beam. Are they always considered to be fixed?
(OP)
Hi, I have a doubt regarding RC beams.
If you are building a rectangular room, which has 4 columns (one in each corner) and 4 beams, how should you proceed with the analysis of the beams?
Should I consider them to be fixed-fixed? My guess is that this is the correct answer, but I'm not 100% sure.
Thanks. =)
If you are building a rectangular room, which has 4 columns (one in each corner) and 4 beams, how should you proceed with the analysis of the beams?
Should I consider them to be fixed-fixed? My guess is that this is the correct answer, but I'm not 100% sure.
Thanks. =)





RE: RC Beam. Are they always considered to be fixed?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: RC Beam. Are they always considered to be fixed?
It is very difficult to completely develop the moment capacity of concrete members around a corner. Most beams at edge columns are assumed to be pinned for design, but with nominal top bars which are usually code required.
RE: RC Beam. Are they always considered to be fixed?
RE: RC Beam. Are they always considered to be fixed?
Today I'd include the columns in the analysis.
ACI 318 allows the designer to assume that the far ends of columns are fixed and implies that the column stiffness should be included in the analysis along with the beam per kikflip's post above.
RE: RC Beam. Are they always considered to be fixed?
Would this change if the construction has two levels? Meaning that the beam is between the first level column and the second level column.
And lastly, in the case JAE commented about. When you have a continuous beam (for example a 4-span section) you consider the connections in the two inner columns to be fixed, and the two connections with the border columns to be pinned?
RE: RC Beam. Are they always considered to be fixed?
RE: RC Beam. Are they always considered to be fixed?
Foundations are usually treated as pinned unless there is a specific measure to ensure fixity.
RE: RC Beam. Are they always considered to be fixed?
My doubt started when I saw that the final design of this rectangular room, had more steel reinforcement in the bottom of the beam. When, if the connections should be considered to be fixed, the reinforcement should be more in the top of the beam were it connects with the column.
RE: RC Beam. Are they always considered to be fixed?
RE: RC Beam. Are they always considered to be fixed?
RE: RC Beam. Are they always considered to be fixed?
I think we need to define "fixed" to answer this.
In some FEM models they may use the terminology "fixed" as in there is moment connection between them. But they are not restrained against rotation!
They are not "fixed" in terms of restrained against rotation.
For a single span fixed at the ends, the end moment would be wl2/12 and span moment wl2/24.
You will never generate this with columns as there will be rotation as several above have said. You have to dertemine the amount of "fixity" depending on the relative stiffness of the columns to tg=he beam!
For a single span with columns, the span moment will still normally be much more than the end support moments due to the totation at the supports.
And you should not be asking a question like this on this site, ask your mentor/supervisor!
RE: RC Beam. Are they always considered to be fixed?
When I referred to the connection as being fixed I meant that they are locked to each other so that the column and beam rotation are the same.
These are absolutely fundamental issues that you need an experienced mentor to help you with.