expansion joint in foundation retianing wall

[geo321]

hi, I have a retaining wall which has a length of 70 meters. I have introduced expansion joints in the wall at 23 meters.
1 - Is it recommended to have the expansion joint also in the foundation knowing that there isnt any high watertable ?
2 - what is the purpose of putting a dowel bar inside 2 foundations separated by an expansion joint ?

Thank you

 

[msquared48]

To keep the footings aligned vertically, and allow the foundations to move laterally (expansion/contraction) as the smooth dowel bar should be greased.

Mike McCann, PE, SE (WA)

 

[jike]

We usually provide wall contraction joints at 25' oc, wall construction joints at 50' oc (may be substituted for contraction joint) and wall expansion joint at 100' oc. We normally just let foundations crack since they are not visible.

 

[msquared48]

What jike says is true in that being in a near constant heat sink of the surrounding soil mass, the temperature differential will not be as much as the exposed wall.

Mike McCann, PE, SE (WA)

 

[geo321]

So no expansion joint in the foundation even if it is long enough.
Regarding the dowels that generally are placed between 2 foundations, i can think of the rigid pavements. Which other places this kind of detail is placed ?
Thank you for the help

 

[RHTPE]

Mike, Would it not be better to say "To keep the footing segments aligned vertically, and to keep the wall faces in the same plane, yet still allow both to expand & contract longitudinally"?

What I often see are footings continuous under wall expansion joints.

The primary purpose of the expansion (& contraction) joints is to allow the visible portion of the wall to expand & contract without damage. The footing, being below grade, is not subjected to the same temperature variations as the wall and is less likely to experience the same magnitude of thermal movement.


Ralph
Structures Consulting
Northeast USA

 

[geo321]

Thanks ralph. I have never seen these greased dowels except in the rigid pavements. Can you name another application of these dowels ?
Thank you

 

[msquared48]

Ralph: yes...

Mike McCann, PE, SE (WA)

 

[RHTPE]

geo321 - Greased dowels are indeed common for pavement. Dowels sleeved or wrapped to prevent bond at one end are more commonly called for in building & landscape situations. Same principle, different method.


Ralph
Structures Consulting
Northeast USA

 

[IFRs]

I used dowels in a long vertical retaining wall

 

[DETstru]

Sounds like you're hesitant about the greased bars. One detail I've seen and used is to specify only a portion of the typical horizontal steel passes through the control joint. For example, if your typical horizontal steel is #4 @ 12" OC, specify only #4 @ 48" OC continues through the joint. This gives you the out of plane connection while somewhat weakening the wall (along with the reduced section) to induce a crack. I don't have "real" numbers to show effectiveness but I haven't had any trouble with it.

No joints needed in foundations.

 

[molibden]

I've seen our contractors use triangular strips (like for column edges) in walls to induce cracking in somewhat weakened cross-section. Rebar went right through the joint. What is you opinion on that?

 

[hokie66]

Vertical cracking in concrete walls due to restraint by the footing will occur at 3-5 metre intervals, regardless of reinforcing, but more horizontal reinforcement controls the cracks better. The only real reason for joints or crack inducing strips is to make the cracks straignt.

 

[geo321]

Thank you for your input. I appreciate it.
another couple of questions
1 - Walls expansion joint will be filled with a joint filler and sealant. Is a water stop needed along the joint ?
2 - At contraction joints, horizontal reinforcement will be stopped and a sleeved dowel bar will be located. Is this the common practice ?
thanks again

 

[jike]

I believe those beveled, crack inducing strips are called "rustification" strips.

For retaining walls, we would drain the backfill using either 1) a continuous drain tile or 2) weep holes at regular intervals. We would only provide waterstops if we felt it was an appearance problem or it was necessary because it was inside a building basement. Weep holes can sometimes be a safety concern, if it can drain onto a pavement that can then create ice.

 

[geo321]

back to the contraction, I am trying to figure out why there is a need for that contraction joint.
Since the wall is reinforced from both sides (vertical steel to take into account the bending stresses and horizontal for shrinkage/temperature stresses), and expansion joint is introduced every 23 or 30 meters , I believe that the crack which will be developed will be minor and most likely not visible.
I understand that u introduce a contraction joint in a slab on grade or a rigid pavement since these can be unreinforced elements so u need to dissipate the thermal stresses but for a retaining wall reinforced from both sides and separated by expansion joints, I cant figure it out !

 

[jike]

It depends how much horizontal reinforcing you have. Is it sufficient to hold the vertical cracking to acceptable levels? In the US, it is generally cheaper to control the cracking with contraction joints spaced at regular intervals than to provide more steel to resist the cracking.

 

[RHTPE]

Based on my experience and perception, contraction joints will be effective only if they are located such that they coincide with reduced horizontal reinforcing. Typically every other horizontal bar is cut at the contraction joint.



Ralph
Structures Consulting
Northeast USA