CONSTRUCTION JOINT @ COLUMN FACE
CONSTRUCTION JOINT @ COLUMN FACE
(OP)
I am working on a conventionally reinforced slab that is under construction.
Contractor has requested to locate the construction joint at the face of column, which is not desirable structurally.
I was wondering if you have any experience locating the construction joint at the face of columns?
There are a list of items I could think off that might impact the design:
1. punching shear at the column. Since the shear face is now at the face of column, so the columns are no longer an interior columns - Is this correct?
2. Maximum negative moment at column could be overcome by adding more temperature steel.
Did I miss anything?
I would appreciate your valuable input based on your experience on this.
Thank you very much in advance.
Contractor has requested to locate the construction joint at the face of column, which is not desirable structurally.
I was wondering if you have any experience locating the construction joint at the face of columns?
There are a list of items I could think off that might impact the design:
1. punching shear at the column. Since the shear face is now at the face of column, so the columns are no longer an interior columns - Is this correct?
2. Maximum negative moment at column could be overcome by adding more temperature steel.
Did I miss anything?
I would appreciate your valuable input based on your experience on this.
Thank you very much in advance.






RE: CONSTRUCTION JOINT @ COLUMN FACE
one detail that we have done in the past is to inset the slab into the column face by 2" (or 1 1/2" to avoid rebar conflict. You could, I guess, go even deeper with the joint. This creates a keyed type joint where the shear on a plane converts to bearing on the concrete key.
The key would/could be the full depth of the slab.
But I would still be reluctant to do this unless there...was...just...no...other...way.
RE: CONSTRUCTION JOINT @ COLUMN FACE
Generally, I do not allow a construction joint at the face of a column. You want the construction joint in a zone of low shear.
RE: CONSTRUCTION JOINT @ COLUMN FACE
RE: CONSTRUCTION JOINT @ COLUMN FACE
RE: CONSTRUCTION JOINT @ COLUMN FACE
RE: CONSTRUCTION JOINT @ COLUMN FACE
RE: CONSTRUCTION JOINT @ COLUMN FACE
We would definitely engineer the joint with sufficient reinforcing.
The thing that gets me is ACI 318 Section 6.4 that says "Contruction joint shall be located at 1/3..." and does not allow any engineering analysis to overwrite this.
RE: CONSTRUCTION JOINT @ COLUMN FACE
RE: CONSTRUCTION JOINT @ COLUMN FACE
If you are backed into a corner (situation to avoid in the future, especially if coming from a contractor) be sure to follow thru to the tee, and don't skimp. Pure shear-friction steel for the interface (times 3?) and roughen all surfaces immediately comes to mind.
RE: CONSTRUCTION JOINT @ COLUMN FACE
RE: CONSTRUCTION JOINT @ COLUMN FACE
With flexural behavior, you essentially have your primary stresses perpendicular to the vertical face; thus, the joint doesn't really affect the transfer of orthogonal stresses through the joint. On the tension side, the concrete isn't doing much of anything and the rebar simply continues on through. On the compression side its simply concrete on concrete in direct bearing so again there's no significant affect.
For shear, however, the vertical joint aligns more with the vertical component of the shear and you must depend upon the roughness of the interface and any rebar that crosses the joint to resist the ability of one side slipping with respect to the other.
Placing the joint at the point of inflection (zero moment) doesn't provide you with any significant advantages. Keeping it in the middle third maintains a low shear magnitude at the joint.
RE: CONSTRUCTION JOINT @ COLUMN FACE
Although in theory the shear at mid span on a uniformly loaded beam is zero, in reality this is often not the case. A simple beam with uniform load on half the span will generate a shear at the mid-span equal to 1/4 of the end shear on a fully loaded beam. We, therefore, think it is always prudent to require a key of 1/3 the depth of the beam at the construction joint.
RE: CONSTRUCTION JOINT @ COLUMN FACE
Just as an update - We have decided to engineer the joint at the face of column, because it will help expedite the construction and save the owner at least 1 month of construction time by doing this, due to formwork-shoring process.
What we have done is to check on several items:
1. Shear friction transfer along the slab. By obtaining the shear at the joint location from FEM program, we designed additional shear friction bars at the mid depth of slab.
2. Punching shear at column - Recheck them and add whatever required shear over column head.
3. Apply bonding agent with continuous key along the joint.
RE: CONSTRUCTION JOINT @ COLUMN FACE