Construction/Cold joint location in RC Column/walls

[EngrJunaid 43]

AoA all,

Is it mandatory to do column concreting upto the soffit of the beam in a single pour ?

What code says about the construction/cold joint location in column ?

Majority of the contractors are pouring the column concrete upto the soffit of the beam (full height of the column), some contractors leave the column height about 9" to 12" below the beam level and then fill this 9" to 12" column height with the beams & slab concreting. On one site column concreting was stopped at the mid height and the remaining half was filled on the next day.

Thanks

 

 

[waqar saleem 285]

Salam

Dear Junaid!

Cold joints are common and practice is upto soffit, properly roughen the face and apply some chemical at the joint. Leaving column at mid height is not good.

Regards

[EngrJunaid 43]

Thank you Waqar.

I need code reference for this practice.

 

Thanks

[EngrUzair 535]

Here are my two cents:-

1. General guidance regarding placement of construction joints in RC work has been provided in Section 6.4 of ACI 318-08 and its commentary. Some clarity is given in section 6.4.3, where it is stated that "Construction joints shall be so made and located as not to impair the strength of the structure. Provision shall be made for transfer of shear and other forces through construction joints."

For transfer of shear etc through construction joints, reference is made to the ACI Section 11.6.9 that deals with the calculation of shear-friction, at the interface between two concretes cast at different times (beside other situations described in section 11.6.1 of the code).

Moreover, Section 6.4.4 suggests that "Construction joints in floors shall be located within the middle third of spans of slabs, beams, and girders.

2. Regarding construction joints in columns, however, Section 6.4 does not provide guidance clearer  than that in Section 6.4.6 stating that the "Beams, girders, or slabs supported by columns or walls shall not be cast or erected until concrete in the vertical support members is no longer plastic." 

And, the commentary section R6.4.6 explains that "Delay in placing concrete in members supported by columns and walls is necessary to prevent cracking at the interface of the slab and supporting member caused by bleeding and settlement of plastic concrete in the supporting member."

3. The support member (referred in previous paragraph) will generally be a column or a wall. And, in a simplified form, Section 6.4.4 & its commentary are advising us NOT to cast beams & slab monolithically with the wall or column, BUT only after the supporting column (or wall) concrete has hardened,  in order to avoid plastic cracking at the beam-column (or beam-wall) joint.

4. In our normal field practice (within Pakistan as well as abroad), beams & slabs are cast at least one day after casting of columns or supporting walls. This gap of one day (between casting of column & beam concretes) ensures that the column (or wall) concrete poured one day earlier has hardened (is no longer plastic),  thereby avoiding any possibility of plastic cracking (discussed in paragraph 2 above). 

5. Now coming to your queries;

On 26/07/2017 at 6:20 PM, EngrJunaid said:

Is it mandatory to do column concreting upto the soffit of the beam in a single pour ?

In general terms, it is preferable to cast the column in one pour..

However, in compelling circumstances it may be done in more than one pour too, subject to certain conditions.

 

On 26/07/2017 at 6:20 PM, EngrJunaid said:

What code says about the construction/cold joint location in column ?

Already described in initial paragraphs.

 

On 26/07/2017 at 6:20 PM, EngrJunaid said:

Majority of the contractors are pouring the column concrete upto the soffit of the beam (full height of the column

This is the normal & IMHO desirable practice, according to ACI code Section 6.4.6.

 

On 26/07/2017 at 6:20 PM, EngrJunaid said:

some contractors leave the column height about 9" to 12" below the beam level and then fill this 9" to 12" column height with the beams & slab concreting.

IMO, leaving 9" or 12" column depth below the beam soffit is excessive & undesirable. It should not be more than 1" or 2" in any case.

 

On 27/07/2017 at 2:55 PM, EngrJunaid said:

I need code reference for this practice.

IMO, this practice is based on the requirements of ACI 318-08 (also ACI 318-11) Section 6.4.6.

The same requirement is available in ACI 318-14 Section 26.5.7.2 (a) as well.

HTH

Regards.

Edited July 29, 2017 by EngrUzair
Corrected punctuation & grammer

[EngrJunaid 43]

Thanks & Jazakallah  @EngrUzair Sir

[miqureshi77 12]

On 27/07/2017 at 10:52 AM, waqar saleem said:

Salam

Dear Junaid!

Cold joints are common and practice is upto soffit, properly roughen the face and apply some chemical at the joint. Leaving column at mid height is not good.

Regards

For zone 3 4, construction of column should concrete upto mid height. Because joint should be flexible and monolithic in these zone