Development length, ldh of deformed bars in tensions

[istruct1980]

hello, how do you handle this the of problem wherein your computed development length required exceeds the provided length, say
the wall support thickness is only 150mm or effective depth is only around 120mm, but the required length is 300mm?

 

[BridgeSmith]

1) Use smaller bars at a closer spacing.

2) Increase the cover to (the backside of) the hook (if you're reducing the capacity based on cover.

3) Increase the concrete strength.

If you already have enough cover to avoid the reduction, #1 is the most effective option, since #3 will only give you a modest gain.

 

[TehMightyEngineer]

4) Use headed studs.

5) See if you actually need full development at the edge of the wall (likely you don't).

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[KootK]

1) In my opinion this, fundamentally, is not a development problem. Rather, it's a closing moment joint design problem. The two are subtlety, but importantly, different.

2) I think that most designers, including me, would do the following:

a) Use small diameter bars to the tune of #4 or #5.

b) Design the slab such that it was assumed pinned at the wall to reduce reliance on the corner bars.

c) Consider the corner bars to form a nominal/crack control/shear connection without worrying about development length.

2) In some parts of the world, outside of North America, bars can be considered to be developed around the corner given that attention is paid to selecting a bar diameter which will not overtax the concrete behind the bend. This is one version of path #1.

3) In North America, where we don't develop bars around corners, similar joint design can be accomplished in compliance with ACI 318 by using strut and tie methodology in conjunction with curved bar nodes. This is a second version of #1 but is way too labor intensive for routine work.

4) Closing concrete joints have been tested for efficiency and, frankly, perform rather well. If I cared enough about one of these joints to not do #2, I'd just apply one of the tested efficiency ratings to the joint design. This is a third version of #1.