Rebar lap splice transverse reinforcement additional to shear links 9

[Samuee]

Hi buddy
We know transverse reinforcement is required to be provided at the lap zone of rc beam, I would like to know your practice if shear links are already provided for the beam, the area of transverse reinforcement in additional to the shear links area or not

Thanks

 

[r13]

We know transverse reinforcement is required to be provided at the lap zone of rc beam,...

From where you have learnt this requirement? Are you talking about a typical beam-slab condition at the location of splice of beam main reinforcement? If this is the case, no, the transverse reinforcement can't be counted for shear strength of the beam.

 

[Agent666]

I believe you can count any shear reinforcement that's present towards any reduction in lap length or to provide the requirements for confinement of the lapped regions. It isn't additional to the requirement for shear strength.

I.E. The opposite of what r13 is stating if I'm understanding his response correctly?

 

[r13]

I was thinking the transverse reinforcement in the OP's statement is slab reinforcement transverse to the beam. If you are adding more stirrups/shear links, then it shall be counted towards the shear strength of the beam. But I don't think the additional stirrups can be counted on to reduce the splice length for bars enclosed in the stirrups. As the splice length is the length required to transfer tension from one bar to the other, that has nothing to do with shear. Correct me, if I am wrong.

 

[Agent666]

Transverse reinforcement is the shear reinforcement in a RC beam. Most codes would disagree with you on the fact that lap lengths cannot be reduced with sufficient transverse reinforcement.

 

[r13]

Agent,

Where I said it can? I am confused. However, Per ACI, the splice length is less if they can meet the conditions stated below:

— Lap splices of deformed bars and deformed
wire in tension shall be Class B (1.3 l[sub]d[/sub]) splices except that
Class A (1.0 l[sub]d[/sub]) 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
spliced within the required lap length.

Note that both cases have nothing to do with stirrups, nor shear.

 

[Agent666]

But I don't think the additional stirrups can be counted on to reduce the splice length for bars enclosed in the stirrups.

Your words. This statement is wrong.

 

[dik]

@Agent: gave you a LPS just to emphasize the importance of your post... deserved, too.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[r13]

Agent and dik,

So both of you think the stirrups can be counted towards reducing the "splice length"? Please clarify and provide your code provisions that allow it, if you don't mind. Thanks.

 

[r13]

The OP's focus point/question need to be clarified. I might have misunderstood it. But let me be clear on my stance:

- Additional stirrups CAN BE counted towards shear strength of the beam, so the answer will be "YES", it is in addition to the already provided shear links.
- Stirrups CAN NOT be counted on to reduce the splice length of the bars it encloses, there is no such rule in the ACI.

 

[Agent666]

The splice length is a function of the development length. For example in ACI take a look at how this is calculated and you'll find the answer. For example in ACI318-19 look into 25.4.2. development length clauses, in particular the Ktr factor.

Earlier versions of ACI318 had similar reductions. Other international codes all have similar reduction factors to the development lengths and hence splice lengths where there is sufficient confinement of splices.

There are also specific reductions to column splices allowed if you have sufficient confinement (CL 10.7.5.2.1).

r13, probably best to start your own thread in future if you have gaps in your knowledge of codes and principles involved rather than get into sideline conversations in others threads.

To the OP, did you get your answer in amongst that? No need to double count the requirement, all transverse reinforcement contributes.

 

[Agent666]

Regarding your edit r13 to previous.

- Additional stirrups CAN BE counted towards shear strength of the beam, so the answer will be "YES", it is in addition to the already provided shear links.
- Stirrups CAN NOT be counted on to reduce the splice length of the bars it encloses, there is no such rule in the ACI.

See above post, you're mistaken/incorrect/wrong in this instance.

 

[r13]

Below is copied from ACI318-08. I've no access to, nor knowledge on, ACI318-19 though. Please let me know my "gap" in my knowledge on the code.

12.2.4 — The factors used in the expressions for development of deformed bars and deformed wires in tension in 12.2 are as follows:
(a) Where horizontal reinforcement is placed such that more than 12 in. of fresh concrete is cast below the development length or splice, ψt = 1.3. For other situations, ψt = 1.0.
(b) For epoxy-coated bars or wires with cover less than 3db, or clear spacing less than 6db, ψe = 1.5. For all other epoxy-coated bars or wires, ψe = 1.2. For uncoated and zinc-coated (galvanized) reinforcement, ψe = 1.0.
However, the product ψtψe need not be greater than 1.7.
(c) For No. 6 and smaller bars and deformed wires, ψs = 0.8. For No. 7 and larger bars, ψs = 1.0.
(d) Where lightweight concrete is used, λ shall not exceed 0.75 unless fct is specified (see 8.6.1). Where normal weight concrete is used, λ = 1.0.

 

[Agent666]

Hint.... K_tr

Perhaps re-read my reply. Requirements are similar in 2008 and 2019 code.

 

[dik]

Thanks Agent... I wasn't going to reply... it was becomming an engineering Monty Python skit... I think this topic has been resolved... it may be best for the OP if it is dropped unless the OP needs clarification or additional information...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[r13]

I think the confusion here is the phrase "We know transverse reinforcement is required to be provided at the lap zone of rc beam, ...". I don't think it is addressing the development of hooked bars in tension, which allows a 0.8 reduction for the development length L[sub]dh[/sub], but again, it has nothing to do with splice length.

Please let's be courteous towards each other. None of us are perfect, but facts and truth will come after sensible discussions.

 

[rowingengineer]

R13,
The below link is for high strength concrete beam, but does give you some very good perspective on the transverse reo and the effect on the behavior of lapped slices.

https://www.researchgate.net/public...ce_In_High-Strength_Reinforced_Concrete_Beams

The transverse reo in my mind is providing some confinement to the reo, as would shear ligs in a concrete beam, which would increase the bond stress of teh reo, making the laps more efficient.

https://www.mdpi.com/1996-1944/13/17/3701/htm

In seismic zones, often teh concrete codes have minimum requirements around confinement to ensure the bonds of reo do not reduce over the period of an earthquake.

 

[r13]

rowingengineer,

Thanks for the information, I'll look into it. But I am not a researcher, so I don't have the knowledge to judge the "permissibility" of reducing splice length due to confinement of stirrups, or any other transverse reinforcement. At this moment, I am not aware of any proposed change in ACI regarding this matter, I chose to stick to the code for now, which can be very conservative. BTW, as a side note, that the excessive reinforcement clause is also not to be considered for splice length calculation.

Does Euro Code permits reducing splice length due to confinement? I am curios to know.

 

[Agent666]

Does Euro Code permits reducing splice length due to confinement? I am curios to know.

Yes eurocode 2 does consider transverse reinforcement to reduce the development and hence splice length. Most codes consider this in one form or another, some codes only consider for compression or tension, not both.

 

[r13]

Agent,

I think your answer is a welcome news for the OP, who should be use one of the country code using Euro code as the mother code. Unfortunately, ACI does not allow it for tension splice, and I wouldn't argue with it, as it is a conservative practice. Also, I question the wisdom in providing more shear links just to save a little in splice length, unless shear is a concern too.