column bars splices - position ?

[BauTomTom]

Hi struct.engs

I would like to ask something about the position of the column bars splicing. Does the upper bars really need to start at the floor level or can the splicing be also done in the 1/3 of the column height?

See attached sketch

and the left, ref bar

we discussed it already one, if it is also possible to cover with long bars directly two floors instead of only one. So then the bars will be instead of 3500mm 7000mm. By such thick bars it shouldn't be really a problem I guess as well



BauTomTom

 

[ishvaaag]

You can do splices at midheight between floors if that is your first question; in fact that is recommended where the moment is lesser there under seismic action (or lateral loads in general); that may not be the case for first leveles above ground or some levels more depending on the structure.

Respect if you can have your main (thick) rebars through some floor, you as well can. You need in every case ascertain that moment transfer of the floor or its beams is properly managed; that must mean detailed observation of the hypotheses and then that the floor or beams' rebars themselves are bent to overlap with the column rebar instead than passing horizontally through the column; this obviously introduces new requirements of attention and design; for those cases in that such kind of overlap with the rebar in the column is required, it is normally understood that the required overlap of each bar is in accord with its own diameter.

 

[rowingengineer]

I try to detail my column reo to span three floors to reduce laps if I can. I normally lap at hte bottom just because of the wieght issue.

ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION.”

 

[ishvaaag]

It must also be said that as long the joints are properly proportioned one may not need to enter on the detail with the beam-floor's rebar overlapping the column's rebar. A reasonable strut and tie study of the joint may readily show if such is the case.

 

[BauTomTom]

-- to ishvaag --
Splicing in “midheight between floors” even recommended? Ok then am glad. Ok it is true that you want to have them not spliced in the areas of maximum forces. This makes also sensse. Only that you see usually the splicing right in the bottom (floor level) ok it is also more practical and easier to handle.

For taking the rebars through two floors what is the recommended height (max length) for such column bars?

Only one thing I don’t understand. What you mean with “…instead than passing horizontally through the column…” The beams are actually never connected “into” the column by using L-shape bars. They actually really just go through the column. Hhmm…


--- tp rowingenieur ---
Three floors? So you column bars maid be even 9m long? Can you really still handle it on the site?
About which diameter are you talking here in such an case?
Ok this weight issue and start at the floor makes senses

 

[BauTomTom]

-- to ishvaag --
Splicing in “midheight between floors” even recommended? Ok then am glad. Ok it is true that you want to have them not spliced in the areas of maximum forces. This makes also sensse. Only that you see usually the splicing right in the bottom (floor level) ok it is also more practical and easier to handle.

For taking the rebars through two floors what is the recommended height (max length) for such column bars?

Only one thing I don’t understand. What you mean with “…instead than passing horizontally through the column…” The beams are actually never connected “into” the column by using L-shape bars. They actually really just go through the column. Hhmm…


--- to rowingenieur ---
Three floors? So you column bars maid be even 9m long? Can you really still handle it on the site?
About which diameter are you talking here in such an case?
Ok this weight issue and start at the floor makes senses

 

[rowingengineer]

I like stock lengths of bar, so 12m to 9m is good for me (don't know ft (US)lengths). Generally these cages are welded to enable handling and give them some stiffness. When scoping these projects you will need to check the crane plans as you don't want to swing these columns, these need to be craned into position. Size of bar in metric size would be 16, 20 or 24, laps are important as these need to provide the cantilever ability to the column.

ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION.”

 

[ishvaaag]

Certainly BauTomTom. They are almost never bent unto the columns. However the likelihood of there being such need augments with the big diameter bars that simply could disengage, say, at an edge out of short splice unto the column. If both reinforcements are ok but splice is not you may end not having a proper moment transfer at the joint. As a general rule it is better not to surpass 20 mm diameter in rebar of ordinary buildings. It is very much true that codes are pushing for more and more steel and also that there are many structures, different from ordinary buildings, that need the bigger rebar section. Proper care may avoid some mishap.

In the inner columns, proper splicing is also required; there are always things to look at in structures. For example, you might, even if it is unlikely, to have bottom rebar highly in compression and, cut inside the column you might end having something not able to take such rebar compression unto the concrete, or corresponding spliced rebar to the other side. Precisely because of it being an uncommon situation it also will be a condition rarely checked.

I am sure there is some text out there describing the multiplicity of cases of special problems at reinforced concrete joints, even if I don't remember now one. But it would be good to remind. Er... I had one 1 meter from me, it is easy to forget ...

Design of Beam-Column Joints for Seismic Resistance
ACI SP-123

or some another on detailing concrete, maybe

ACI SP-66 04 Detailing Manual

http://books.google.es/books?id=K07...&resnum=7&ved=0CFAQ6AEwBg#v=onepage&q&f=false

Another nice find

http://www.sefindia.org/rangarajan/usefularticles-2/CRSI_Detailing.pdf

 

[BauTomTom]

--- to rowingenieer ---
12 m even? And the contractors are not complaining that the reinforcement is difficult to handle?
I thing to take the bars through two floors should be good enough so basically in my case rebar length of around 7m

--- to ishvaaag ---
Sorry, but somehow I don’t get really what you mean?
“….They are almost never bent unto the columns…..” ?

Just to confirm that I got you all right. So the splicing can be really done in the middle height of the column? And is actually even recommended?
Please have a look on the attached sketch. So this is the perfect column reinforcement?
Why is it then actually never done this way?

 

[ishvaaag]

Almost never in ordinary buildings with moderate spans, and rebar under 20 mm diameter would be a more proper statement. You may, however, for some moment transfer issue; or to hang some load, either for normal use, or after joint disruption.

Respect the recommended position at midheight, it only appears in our codes (namely NCSE-94) as a device of ensured strength -ductility for that matter at the most solicited points under lateral loads, thought to be joints.

http://www.saralx.es/normativa/01 EDIFICACION/07 ordenar/RD 2543 1994 NCSE 94.pdf

See fig 4.9 of such code where the central part of columns was reserved in the high ductility columns for the longitudinal rebar splice in columns.

The standing seismic code is NCSE-02, in which such "high ductility column" detail has dissappeared; but we only expect earthquakes say up to 0.2g and maybe that has made the better support characteristics of splices at floor level stand.

Follows NCSE-02

http://www.fomento.gob.es/NR/rdonlyres/053727ED-0350-4280-8784-C8F4CC34655F/4491/norma1.pdf

 

[rowingengineer]

Horses for courses, I wouldn't do this on every project, but for most of my high story builders this is a preferred option for a drop panel building, if you have beam ect, it may not be the best solution. The real advantage is that while it may take you a little while longer to setup, once completed, you can complete 3-4 floors at a rapid pace.

ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION.”