ld required not enogh for 300mm footing thick

[istruct1980]

Hello, how do you justify this problem where in the minimum development length, ld required for tension is greater than what was provided. the footing is 300mm thick and im using 16mm.

the minimum requried ld should be 300mm as stated by most structural codes, for 300mm thick footing it will be lesser since ld provided will be 300mm thick minus concrete cover . however there is this client/owner who is very meticulous and wants to make sure of this provision.

is it safe to technically say that you don't really need full development of the bar on that area? since i designed that one with much bars than what is required by flexure (im taking about the bending moment load envelope which includes DL LL EQ)

 

[Agent666]

where in the minimum development length, ld required for tension is less than what was provided.

If the calculated Ld is less than what was provided, this satisfies the code. So not sure I understand your or your clients exact concerns?

 

[KootK]

Do you actually need tension resistance in the rebar? Often you dont. I'd start by sharing the loads that you expect the wall to transmit to the footing.

 

[Strucyou]

Agreed with KootK. Shear strength of the bar should govern instead of tension. Nevertheless ACI recommends checking the bar for a minimum tension of 44 kN for integrity (ACI 318M-11 sec 16.5.1.3(b) - (for precast construction only),I would suggest checking the anchorage capacity of the bar for this minimum pull out force, the length should probably be justified - good luck!

 

[istruct1980]

@Agent666 Thanks. I edit my thread i actually mean the other way around, required development length is greater than what was provided.

 

[Agent666]

My understanding is the minimum (300mm in your case as you state) is based on a transition between the underlying criteria for failure being based on a bond criteria for development/yielding of the reinforcement, vs a concrete breakout based mechanism occurring for a hooked bar (tearing out a chunk of concrete vs yielding of the reinforcement basically).

As such, for reinforcement the minimum is the minimum unless there is any specifics in your code for reducing it further due to confinement, placement of bars within the bend region, or providing more reinforcement than required, etc. But often there is a lower cutoff provided which should be satisfied no matter what, otherwise you risk a non-ductile failure mode as noted above.

If the bars are in compression and you require those bars for contributing as compression reinforcement to the strength, then you also need to satisfy the compression development rules as well I guess, and take the most onerous for detailing purposes.

Often as they note to get full development you may need to increase the depth of the member and the anchorage to achieve this.

 

[BridgeSmith]

If you can't meet the embedment for development for hooks in tension, first determine if you need the full tension capacity of the bar. If not, try using the reduction in ldh for As required / As provided. If it still doesn't pass, try using smaller bars at a closer spacing. If you're close, but still not meeting the required embedment, you can increase the concrete strength. If you still can't meet the required development, you'll have to increase the thickness of the concrete.

 

[MIStructE_IRE]

Is this column also required to act as a vertical tie (theoretically in pure tension) to address robustness/disproportionate collapse requirements?