Development Length Calculation with Variable Bar Spacings 1

[Quade999]

Hi Everyone,

When calculating the development length of straight reinforcing bars, it is based off the center to center spacing of bars being developed. If I have a slab where the spacing of bars is variable (i.e. tight spacing near the ends, and wider spacing near the middle), how is the calculation effected? Would I consider it from a standpoint of each individual bar and calculate it based off the distance to the bars beside it, or would I look at the worst case spacing as a whole group? If it was for a beam, I would consider the worst case as there wouldn't be many bars, but since a slab would be very wide I would think it would be acceptable to calculate it based of the bars in the section under consideration (i.e. longer development lengths at the ends with tighter spacing, and shorter development lengths at the middle with wider spacing as shown in my sketch).

Thanks

 

[r13]

C_b = ....one half of the center to center spacing of bars or wires been developed.

 

[Quade999]

So my understanding from that wording is that the development length of each individual bar would vary depending on how close it is to adjacent bars.

 

[KootK]

That's correct although, for small bars and more generous spacings, you quickly max out the gains available via additional spacing. The idea is to control splitting stresses which are exacerbated by nearby bars generating splitting stresses of their own.

 

[r13]

The idea is to control splitting stresses which are exacerbated by nearby bars generating splitting stresses of their own.

Excellent explanation.

 

[dik]

In the first posting, (sn) is what?

Dik

 

[r13]

dik,

According to 318-11,

s = maximum C-C spacing of transverse reinforcement within the development length

n = number of longitudinal bars being developed along the plane of splitting.

I think the equation has changed since 318-14.

 

[dik]

thanks...

Dik