Shear transfer through construction joint

[MIK]

Assalamu Alaikum

I have some confusion about shear transfer through construction joints in rafts

1) Can we use flexural reinforcement at the top and bottom of the raft for transferring shear through the construction joint?

2) If yes than how will be the mechanism?

3) How can we use flexure reinforcement for both flexure and shear action in the context of shear transfer through construction joints? 

Thanks

[Ayesha]

Shear transfer at construction joint happens through a combination of bearing and shear strength of key where provided. Flexural reinforcement has no role. See also, 

 

Edited January 1, 2021 by Ayesha

[MIK]

Thanks @Ayesha for your prompt reply.

According to ACI-318-19 section 22.9 

 

This section is also applicable to construction joints, as highlighted in the above snaps from ACI-318-19. I was asking about Avf in the above equation 22.9.4.2 which is the area of reinforcement crossing the assumed shear plan (in our case interface between old and new concrete). Provided flexural reinforcement is raft is also perpendicular to the assumed shear plane (interface between two concrete pours)

The same problem is discussed in the link below

https://www.eng-tips.com/viewthread.cfm?qid=477681

[Ayesha]

You can use the recommendations in the paper that allow use of axial compression and rebar perpendicular to crack surface to be accounted.  If I were you, I would just use the conventional method described in the paper and ignore any contribution due to rebar (see snapshot for the method/ equation). 
 Also, I have difference of opinion for your case. I checked the topic at Eng-Tips as the question is explained in much More detail than here (I would suggest you edit your question above and include additional details). The location you have chosen is under compression as directly under columns. You shouldn’t be worried about shear or moment there. 

[MIK]

Please share the relevant paper which you have referred in your last reply.

35 minutes ago, Ayesha said:

 Also, I have difference of opinion for your case. I checked the topic at Eng-Tips as the question is explained in much More detail than here (I would suggest you edit your question above and include additional details). 

The topic at Eng-Tips refers to the same issue which is posted by one of my friend, working on the same issue.

Actually the contractor have provided the construction joint at the wrong location with no shear key arrangement.

So, we are going to investigate the shear transfer through the construction joint.

we are applying shear friction concept for transferring shear forces through the construction joint. But there is no clear explanation available about the use of flexural reinforcement in sher friction equation.

My question was can we use Avf equal to flexural reinforcement in the below equation (6) ?

[Ayesha]

The paper is the one you referred in Eng-Tips.  
Title: SHEAR TRANSFER IN REINFORCED CONCRETE - RECENT RESEARCH
Date: March-April, 1972
Volume: 17
Issue: 2
Page number: 55-75
Author(s): Alan H. Mattock, Neil M. Hawkins

Download Link:
https://www.pci.org/PCI_Docs/Publications/PCI Journal/1972/March-1972/Shear Transfer in Reinforced Concrete - Recent Research.pdf

You can see page 61 of the PDF to see the definition of items in the equation. Another alternate would be to provide epoxy grout to join the two surfaces on either side of the crack. In that way no calculation is required.

 

Edited January 2, 2021 by Ayesha
Fixed typo: Epoxy Grout

[MIK]

Thanks for the paper link

On 1/2/2021 at 11:07 AM, Ayesha said:

Another alternate would be to provide epoxy grout to join the two surfaces on either side of the crack.

ok. it will be good if it can satisfy shear transfer requirements.

[Ayesha]

Of course you can with epoxy grout as bond strength is even high than compressive strength of concrete for most epoxy grouts. You have to check the data sheet. The important thing would be surface prep as aggregate would need to be exposed to half depth and extremely good cleaning. Once you have used epoxy, there is no construction joint at that location. Just remember that.

Edited January 4, 2021 by Ayesha