I assume you are talking about a pour strip at the perimeter of a Tilt-up concrete wall.  If this is the case, the pour strip is generally used to "stabalize" the base of the wall.  Dowels are generally installed in the panel, these dowels will lap reinforcing bars in the pour strip, which either extend into the slab, or lap bars which extent from the slab into the pour strip.

The idea is that the out-of-plane loads would be transfered to, and resisted by the weight of the floor slab.  Out-of-plane loads may also be resisted by the passive soil pressure of the backfill, however, I have typically seen this ignored.  In-plane loads (if applicable) can also be transfered to the slab, and/or footing, through the pour strip.

The pour strip also provided for constion methods.  Typically the tilt-up panels are cast on the finished slab, then lifted into place.  The pour strip, typically about 4'-0" wide, helps to prevent the panels from chipping the slab as they are set in place.  It also alows a trench to be formed in the soil on each side of the panel so that the base of the panels can be grouted.

I hope this answers your questions.

Murali27,

Pour strips are also used in post-tensioned floor slab cnstruction, again for construction related issues like access for stressing, breaking up large pours, BUT they also serve/attempt to control "restraint to concrete skrinkage" and elastic shortening.

What type of pour strips are you referring?

 

Yes Ingenuity

I am looking for a pour strip used in post-tensioned floor slab construction. How to design basically the pour strip part?
and how to decide on width of pour strip?

Murali27,

1. Most pour strips are about 3 or 4 feet wide x length of the slab. This provides sufficient space to access for PT slab edge stressing 9jack is about 24" long), enough length to lap in mild steel rebar and is not too wide that lots of formwork is required to infill it.

2. Most times the pour strip is simply a reinforced concrete infill as the PT terminates at each side of the pour strip. On some special occasions you may install additional overlapping tendons through the pour strip and into the back of both adjacnet spans if you want P/A prestress through the joint - if this is warranted - then these tendons are stressed AFTER the pour strip is placed and cured.

3. Usually the design of the pour strip is based upon flexural strength as a RC section for the flexural demand required. Then check that you satisfy serviceabbility/crack control requirements as an RC section.

4. You will also check shear but usually a key way is provided and shear seldom governs. But the slabs are often thin here becasue they are sized as PT but the pour strip is RC.

5. If the pour strip is infilled too soon then there will be continued concrete skrinkage and shortening and the joints will tend to open up, so you can provide additional rebar to anticipate this long-term deformation.

We aware thet there has been numerous legal action taken in projects where pour strips that get screwed up. Contractors often hate them because of the delays it causes in construcuton when they may be required to be "open " for 60+ days, and sometimes the engineer does not adequately detail the strip so very nominal rebar get provided, when in actual fact it may require substantially more.

If this is a parking structure in an exterior environment you will need to consider a good joint sealing compound all around the pour strip. Do not forget to place notes regarding no shoring removal to the contractor at the pour strip location if the "cantilever spans" are so large that they will NOT cantilever.


Be conservative, keep it simple, keep it "contractor friendly" and it will keep the legal guys off your back.

HTH




4. The location of the pour strip is best located at about 25% of the span but this will depend on the span lengths etc. If there are short spans in a non-typical bay that is sometime a convenient place to locate them. You need to be aware that often ther eis a mismtch of deflection of the two slab edges, so the infill results in