Development Length Question

[IreStruEng]

Say we have a short span simply supported RC beam with a point load so large at its midspan that the development length required is the full development length of the reinforcement.

Being a simply supported beam set up in this arrangement it's peak moment will be at midspan and the moment goes to zero at the supports. So at midspan we need a full development length and at the support technically the moment says no development length is needed as the rebar is not in tension anymore.

Is a fully developed bar required to extend into the supports in this scenario?

I'd typically fully develop all of my rebar unless space is an issue.

 

[hetgen]

Yes, extend the full development length beyond the point where it is no longer necessary, and consider the additional tensile reinforcement required for shear.

Rebar curtailment does not need to be an exact procedure; it is advisable to add more anchorage length to offset the approximations made in the analysis.

 

[HTURKAK]

I'd typically fully develop all of my rebar....

Agreed. Consider STM analogy .. Excerpt from Narayanan , RC Structures ..

 

[IreStruEng]

Thanks guys!

 

[cliff234]

Consider hooking the bottom bars or installing headed anchors on the ends of the bars. ACI 318-19 made some significant revisions to the development of headed anchors. Both of these will shorten the development length.

 

[KootK]

and at the support technically the moment says no development length is needed as the rebar is not in tension anymore.

Meh, not really. That would only be true if one assumes no shear cracking in the beam. Once you do assume shear cracking in the beam, you have to contend with a shifted bar tension diagram as shown below.

It is not strictly necessary to develop your bottom bars over supports although it is good practice when space allows. Other options using ACI code include:

1) Partially developing the bars for the tension in the bars at the face of the support based on the shifted diagram. This happens all the time in precast work.

2) Taking the ACI "out" which is terminating the reinforcement in a standard hook that extends beyond the centerline of the supports.

3) If STM design is appropriate, extended nodal zones can be used to make the anchorage requirement less onerous.