Slab edge R.C. consideration

For R.C. design, catiliver span, as moment increased, it requires more reinforcement at the tension side and so is the Tension Lap/ Anchorage Length(TL/AL) of reinforcement increaed from the end until 100%. Under design assumption, full anchorage is required at the critical section of the member. Such that when the design load is 100%, started from the critical section, 100% TL/AL is required, and when it is x%, then x% times TL/AL is required.

Case 1.

For vertical case such as wall,

the load design would often be as follows:

1. wind/ soil~ such that the design Moment would be  w*d/2(Design load)*d*2/3(Lifter arm) or w*d*d/2such that w*d^2/3 or w*d^2/2 at the section with distance 'd" form the top edge,

2. human impact load~ around 1KN at the top.

3.Vehicle impact load~ depends on the expected impact point from the top.

Say the wall is of  300 tk. and 50 cover. 

Then, start from the top just below the cover, the lap length would be 300-50*2=200

which would normally be enought for the design load. 

To fully understan the calculation, the load capacity at distance d below the cover would be

((200+d)/(Lap Length))*Design capacity for full TL/AL.

 

Case 2. and 3 is for the case when there is no support under the edge (Cantilever), and when the slab is constructed on a plane. (We would expect that poiint load or line load would be posed at the edge. So that a full anchorage is required. And, for easier to bend the edge U bar, we may minize the size of edge U bar if the design point or line load is enough. While according to the code (I have not confirmed), the smaller bar can only be one size smaller than the bigger bar. <<(Edited, present not well before***)

When the edge is under support (Regid joint), the TL/AL would be designed for the Moment at the top near supporting member. Which would not be discussed in this chapter

***What is the code principle based upon? Is the principle under the same design criteria?

 How about if I design it as "anchorage" to the slab?