Reduction of Development Length ok?
Reduction of Development Length ok?
(OP)
I have got a question about concrete development length, and whether I can reduce the development length if the tension in my steel is less than the maximum tension that my steel reinforcement can take. Reference is ACI 318-05
Section 15.6.2 - "Calculated tension or compression in reinforcement at each section shall be developed on each
side of that section by embedment length, hook (tnesion only) or mechanical device, or a combination thereof.
Say the tension in my steel bar is only 37% of the full tensile capacity of the bar. Is it right to say that my
development length for that particular bar can only be 37%, esp. if I have no space to develop my length further?
Thanks.
Section 15.6.2 - "Calculated tension or compression in reinforcement at each section shall be developed on each
side of that section by embedment length, hook (tnesion only) or mechanical device, or a combination thereof.
Say the tension in my steel bar is only 37% of the full tensile capacity of the bar. Is it right to say that my
development length for that particular bar can only be 37%, esp. if I have no space to develop my length further?
Thanks.






RE: Reduction of Development Length ok?
If your analysis shows that you have twice as much steel as is necessary for your ultimate loads, then you can cut the development length in half, with certain limitations.
RE: Reduction of Development Length ok?
RE: Reduction of Development Length ok?
RE: Reduction of Development Length ok?
RE: Reduction of Development Length ok?
The ratio is the same thing - unless the required area of steel is governed by something other than strength.
With concrete you are dealing with factored loads, not allowable loads. So technically you don't have an "allowable" capacity of the steel.
RE: Reduction of Development Length ok?
Here's an example, using a spread sheet I have, I found that for a demand of 50 k-ft (with abritary dims)...
I need 1.4in^2 of steel. So if I provided 2.8 in^2 I could reduce my Ld by 1/2 (according to ACI 12.2.5).
However, if I calculate the capacity with 2.8 in^2 it is 87.5 kip-ft...So if you ratioed capacities by EIT's method you could only reduce Ld by by 43%.
RE: Reduction of Development Length ok?
So, it still comes back to the question of do we take the ratio to the required steel versus provided steel, or actual tensile capacity of steel versus factor capacity of steel? Or do we do both, and just go with the one that is more conservative.
Thanks for all the feedback and discussion topics, everyone.
RE: Reduction of Development Length ok?
As(required) / As(provided) as the reduction coefficient.
This is based upon, historically, the stress in the bars as the older codes used to use circumferential contact area on the bar surface as the measure of development.
NS4U, your example appears to be relating bending moment in a beam. This is not the way to look at it. The ratio of bending moments is based on moment capacity which is based on depth, beam configuration, concrete compressive stress, etc.
ACI does not recognize reductions in development length based on moment. Only based on area of steel (thus the As ratio).
RE: Reduction of Development Length ok?
RE: Reduction of Development Length ok?
RE: Reduction of Development Length ok?
RE: Reduction of Development Length ok?
RE: Reduction of Development Length ok?
But there is also a clause which allows you to calculate the length of anchorage required for a specified force in the bars. A modification factor is then used to calculate the length of tension/compression lap required (there is also a minimum length beyond which the lap cannot be reduce).
Is there anything like this in the US codes.