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DETAILING OF STIFFENER BARS [SIDE STEEL]

DETAILING OF STIFFENER BARS [SIDE STEEL]

(OP)
Hi,

DETAILING OF STIFFENER BARS (SIDE STEEL)

I am currently detailing continuous beams to the ACI codes.

Previous answers to questions I have asked on this forum have been enormously helpful.

I am trying to find justification to terminate the side steel stiffeners short of the columns; due to limited space within. However I cannot find any justification for this in the codes. I have found that shear links(stirrups) can be stopped 50mm from the columns but
nothing yet for stiffeners.

Please advise.

Cheers

peakpilgrim


RE: DETAILING OF STIFFENER BARS [SIDE STEEL]

"Stiffener bars" is not a term familiar in concrete beams. What do you mean by saying that you are "detailing"? If you are designing the beams, you should have the structural engineering knowledge to answer your question. If you are not an engineer, and rather are detailing the bars, you should ask the engineer if the requirements have not been made clear on the design drawings.

RE: DETAILING OF STIFFENER BARS [SIDE STEEL]

(OP)
Hi


The bars I am referring to are not main structural tension /compression members,which are continued into the column; for
obvious reasons. The 'stiffeners are 12mm bars whích have been specified in the side of the beam to improve torsional resistance.

If continued into the column they will clash with the column steel. I would like to terminate them just short of the column.

I am looking for a reason in the ACI codes to justify this but I have not been able to find any.

As you suggest, terminology is an issue. for instance links are referred to as stirrups etc.

Cheers,

peakpilgrim

RE: DETAILING OF STIFFENER BARS [SIDE STEEL]

Torsion in beams is usually greatest at the ends - the additional longitudinal bars added for torsion (ACI calls them Al) are mostly required at the ends and do need to extend through the support.

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RE: DETAILING OF STIFFENER BARS [SIDE STEEL]

While the longitudinal torsion steel doesn't need to extend through the column, it is my belief that it needs to extend into the column some distance. We usually conceive of concrete beam torsion as a three dimensional network of diagonal compression struts. Those struts need to be anchored over the support by reinforcement in a manner similar to the struts that we envision at the supports for simple shear.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: DETAILING OF STIFFENER BARS [SIDE STEEL]

For end spans, KootK, I think you are correct. A simple embedment length or hook would suffice.
But for interior continuous spans, where you might have Al coming in from both sides, just running the bars through the column for each adjoining span makes the most sense to me.

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RE: DETAILING OF STIFFENER BARS [SIDE STEEL]

I misread your original post JAE and mistakenly thought that you'd recommended not extending the bars through/into the support. My bad. We're on the same page here. Must learn to read gooder.

@OP: If congestion is an issue, I think that one could terminate the longitudinal torsion bars at the faces of the columns and then splice them together with a designated splice bar that passes through the columns. Maybe some nice, generous, non-contact lap splices.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: DETAILING OF STIFFENER BARS [SIDE STEEL]

Out of curiosity, how do your top and bottom beam bars miss the column vertical bars? The longitudinal torsion bars are aligned with the beam outer top and bottom bars aren't they?
If necessary, headed bars can help.

RE: DETAILING OF STIFFENER BARS [SIDE STEEL]

Best practice is to avoid making columns and beams the same width. A beam wider than the column is easy to form and place while avoiding reinforcement conflicts. Bottom bars in beams ride up and over girder bottom bars. Beam bars shift inward to avoid column corner bars.
Distributed reinforcement along side faces (skin reinforcement) should develop beyond the point at which the bar is stressed. There is no specific requirement for continuing skin reinforcement, so the basic rule would apply. This would require development beyond the last stirrup (link.) You may discontinue these bars once developed, but avoid lapping inside the columns unless there is a lot of space. Avoid splices, heads, and hooks inside columns as these make construction more difficult (or impractical.) This reinforcement is principally to reduce width and extension of diagonal ("shear") cracks. (The mechanism is the same as for vertical stirrups, that is restraint of splitting tensile cracking inside compression struts, aka shear cracks.)

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