Shrinkage of Facing Concrete on Sheet Pile Wall

[HighPanda]

I have to design concrete facing (cast in-situ) on sheet pile wall. If the concrete is 150 mm (about 6”) thick and there are “shear studs – actually just some bars welded to sheet piles” to make two sections (concrete + steel sheet pile) as a composite section.

The tricky bit is I am asked to check the effects of the concrete shrinkage. If I think the sheet pile as a steel bridge, by turning the sheet pile by 90 degrees, with a layer of concrete topping (i.e. the concrete facing). And I also assumed the embedded end of sheet pile is fixed by soil so that one end of the bridge is fixed by a pinned joint. At another end, the structure is free to move (i.e. nothing is over the head of the sheet pile wall). According to the method normally used (say, the procedures introduced in Bridge Deck Behaviour, E C Hambly -> Work out concrete shrinkage force, apply the force as an internal restrained force over the entire length of the structure and then apply release forces at end composite sections), it appears that there is not much stress induced by the concrete shrinkage because the thickness of the sheet pile wall is just 12mm and the different between concrete section and composite sections is not huge). Am I Right?

 

[civilperson]

Yes, that is why reinforced concrete and composite construction works so well.

 

[hokie66]

You may have misinterpreted the request to check the effects of shrinkage. It is inconsequential in the vertical direction, but in the horizontal direction, the concrete facing is heavily restrained by the sheet piling, thus you can expect vertical cracking. Another thing you should allow for is variation in the thickness of the concrete, as sheet piling is rarely driven to tight planar tolerances

 

[PEinc]

The sheet pile wall should have some available "slack" or movement in its interlocked joints which may help relieve the expansion/shrinkage along the sheet piling. The sheet pile wall is not really a continuous steel structure due to its interlocks. At approximately every 1.5 to 2 feet, every single sheet pile has a joint which is not perfectly tight.

 

[HighPanda]

Could you guys please give me some clues on the calculation of tensile force induced by concrete shrinkage?

 

[hokie66]

Shrinkage in itself does not cause tension in concrete. It is restraint which causes tension when the concrete shrinks. Suffice it to say that concrete is very weak in tension, and if controlling the width of cracks is important, it has to be done with reinforcing. The greater quantity of reinforcing, the better crack control. And for a given quantity of reinforcing, using smaller bars gives better control than large bars.