Rebar splicing on beams 4

[Penpendrum]

The ACI code gave a provision on structural integrity to perimeter beams is to splice continuous top bars at mid span and splice continuous bottom bars at or near supports. Under gravity loads or in most cases the top bars at mid span and the bottom bars near the supports (in a doubly reinforced beams ) receives compressive stresses. My question is : if I have 3 top bars and the two top bars ( at the sides ) are made continuous , do we need to stagger the splices? if so, what provision in the ACI code allows this? and do we really need to splice (class B tension lap splice) =it exactly at mid-span?

And also at the bottom bars .
If I made 2 bottom bars continuous and I had to splice near the column,do I need to stagger the lap splicing? I have seen a link that it is allowed not to stagger it. but I do not know in what section of the code allows it. here is the link

http://www.condor-rebar.com/news-articles/2011-03-beam-column-joints.html

. I wonder what section of the aci code allows this?

the ACI code clearly states that at non-perimeter at least two bars or at least 1/4 of Area of rebars must be continuous or splice(class B tension lap splice) over the support. Do we really need to interpret this Literally?I mean do we really need to splice it exactly over the support when needed? technically this produces a lot of waste if we should strictly follow this.

Please!! I need clarifications if this statements of the ACI code must be interpreted literally. Please guide me with this provisions.

 

[JAE]

(you didn't specify the specific 318 year - you should)

ACI 318-11 - read the commentary - it states "at or near midspan" and "at or near the support".

 

[Penpendrum]

thanks JAE . it really clarified me. I was reading the old code in the Internet... but one last clarification .. Do we really need to stagger the splices at top bars at or near midspan? and also at the bottom bars? if we do not need to stagger it then is there a provision in the ACI that allows this. or in what cases do we not need to stagger the splices?

 

[JAE]

The latest ACI requires Class B splices for this integrity detailing and Class B splices are typically used in non-staggered situations. You can only use Class A splices with staggered splices.

 

[Penpendrum]

Are you referring to
Section 12.15.2 "class A splices are allowed when :
(a)the area of reinforcement provided is at least twice that required by analysis over the entire length of the splice;and

(b)one-half or less of the total reinforcement is splice within the required lap length.


to clarify things out. I mean to translate it to plain English. does section 12.15.2 (b) mean like you said that we should only use it to stagger lap splices? Please confirm JAE.



BTW thanks a ton JAE.. you are really an expert.

 

[JAE]

Yes - the section that refers to Class A splices (12.15.2) requires that the splices be staggered.

If you are trying to meet the Chapter 7 - Structural Integrity rules then you do not have to stagger those splices since they are Class B splices.

Also - the splice is "at or near" the midspan or column - so you do not have to be exactly at the midspan or centerline of column.

 

[Penpendrum]

BTW in the ACI318-11 code in section 12.11.1 says

"At least one-third the positive moment reinforcement in simple members and one-fourth the positive moment reinforcement in continuous members shall extend along the same face of member into the support. In beams,such reinforcement shall extend into the support at least 6 in."​

and in section 12.11.2

"when a flexural member is part of a primary seismic-load-resisting system, positive moment reinforcement required to be extended into the support by 12.11.1 shall be anchored to develop fy in tension at the face of support."​

JAE ? if I have two bottom bars( continuous beam ), will this prevent me from splicing both bottom bars at the same face of support? because I could not understand the statement in section 12.11.1 that says one-fourth of the bottom reinforcement shall extend along the same face of member into the support. does this section mean that one bar must not be splice and it should be in one piece?

and also if I have 3 bottom bars required at midspan and two bottom bars required at support. and if I splice two bottom bars near the same face of support? do I need to extend the middle bottom bars into the support ?

 

[JAE]

if I have two bottom bars( continuous beam ), will this prevent me from splicing both bottom bars at the same face of support?

No - you can splice both at the support. A Class B splice develops the fy of the bars as long as you don't reduce the splice length using As(required)/As(provided).

does this section mean that one bar must not be splice and it should be in one piece?

No - 12.11.1 is requiring you to extend those bars into the support by 6". In the past, some designers cut off the bottom bars before reaching the support because they thought that the
positive moment had ended (the inflection point) and you no longer needed bottom bars in the negative moment region. ACI is requiring you to extend some of the bottom bars all the way to the support even though you might be in a negative moment region.

 

[Penpendrum]

Hello again JAE. Im sorry I was not using the exact words in my thoughts.

Is this what you mean (see figure A) ? that I should extend one lap splice into the support ( if I have two bottom bars ) at least 6" .?

or is figure B also correct? that I do not need to extend one of the lap splices 6" into the support as long as it is inside the L/5 zone?
if so then can you please tell me the explanation that it does not violate section 12.11.1?

and also are figures C and D also allowed?and which one of these are incorrect?

and also how about Fig E? is the bottom bar correct (non-continuous beam)? please tell me what provisions allows or disallows these kinds of lap splicing?

and I have also notice at section 7.13.2.5 ( for other beams/interior continuous beams ) It did not mention that we could splice the top bars at or near mid-span ( or I just missed something ). Is it okay to assume that we could splice the top bars just like the perimeter/ spandrell beams? and it also says

"In other than perimeter beams, where transverse reinforcement as defined in 7.13.2.3 is provided, there are no additional requirements for longitudinal integrity reinforcement."​

Does this mean that I do not have to extend two bottom bars near the support or L/5 zone?and I also do not need to extend two top bars after L/3? and I only need to comply with 12.11.1?

thanks JAE.

 

[JAE]

I would think that all of the drawings you posted are acceptable. The 6" embed into the support does NOT matter or apply if you are splicing.

The provision of ACI that requires 6" extended into the support is only applicable, in my view, to the bars that are not continuity bars.

 

[smarky0]

Hi,

I was reading thru this thread and I find it quite interesting..

The thing is, I am currently working on detailing rebars on beams, and I read that it is not allowed to do lap splice at a region twice the height of the beam from the face of the column.

So, I'm quite confused why this discussion seems to 'not mind' this?

Please enlighten me.. :0

Thanks!

 

[JAE]

and I read that it is not allowed...

You might show us the code and section where you read this.

Check out Eng-Tips Forum's Policies here:
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[wannabeSE]

JAE
Smark0 may be referring to ACI 318-11 §21.5.2.3(b)for Special Moment Frames.

 

[aterra]

Dears,
Can I use one bar over multiple spans of a continuous beam or should I splice it at each possible splice location, and which article in ACI-318 can help.
appreciate your responses.

 

[hokie66]

Continuous bars in service are preferable to spliced bars. Splicing is only to accommodate available lengths, and to make placement practical.

 

[Penpendrum]

Hello Everyone.. thank you for participating in this thread. I appreciate your curiosity .. please feel free to post all of the questions that have been not clear to you..and to those who have help to answer the questions hokie66,JAE,and wannabeSE thanks for helping us..

BTW JAE and wannabeSE ...im confused .. about the lap splices in the section 21.5.2.3 (b). does this mean that I have to splice the bottom bars not in near or at the support if it is a special moment frame? .. . .

 

[Penpendrum]

hello Smark0.. thanks for opening this up.

 

[KootK]

In a SMF, you need to develop the negative, overstrength, flexural capacity of the beam right next to the columns. Also, as a result of moment reversals, your shear capacity is more dependent on dowel action near the columns than elsewhere. At and near the columns is not a good place to splice your flexural bars in a SMF.

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