How to overcome lack of anchoring length in Reinforced Concrete Beams

[kellez]

HI,

So i have a Reinforced Concrete Structure with beams, columns and slabs.
Columns and shear walls are 25cm thick, therefore you can understand that at locations such as edge beams there is lack of anchoring length for the RC beam reinforcement.
Please see picture for examples of edge beams with lack of anchoring.

Lack of anchoring results in the bars not being able to utilise their full bending resistance capacity.
Whereas the provided reinforcement is adequate for the bending moment in middle the bending resistance of the bars at the edges is considerable reduced due to lack of anchorage.

I have seen many houses being erected in the past year and none of the engineers used any kind of measure to increase anchorage resistance at edge beam locations.
Now that I am actually doing my first structural analysis and design for an RC Frame I have come across this issue and i am just wondering how did the other engineers overcome this?
or could they have not seen it or could they have just ignored it?

 

[jike]

A couple of ideas for lack of reinforcement anchorage:
1) Use smaller bars and more of them (shorter dev. length).
2) Provide more As than As req'd (dev. length x As req'd / As provided).
3) Extend beam past column if possible.
4) At top column, bend outside bars down into top of beam and provide req'd lap with beam hooked top bars. Provide hooked bars for column inside bars and hook beam bottom bars if req'd.
5) Consider using A706 bars welded to anchor plate and lapped with beam bars if req'd.
6) A haunch will sometimes provide additional length req'd for development. Depending on the size, it may significantly increase the bending moments.

Just a few ideas but I am sure there are others........

 

[kellez]

I tried using more smaller bars but it quickly becomes impractical (congested) due to the small thickness of the beams (25cm).

Therefore I decided to follow another approach

1. I changed the supports of every edge/corner beam (where there is anchorage issues) from fixed to pinned and carry out the analysis again.
In some cases I only changed the support at only one side of the beam, since the other side had no issue due to the continuity of the beam
2. I then carried out the design of these beams and the anchorage problem was solved, the depth of the beam was enough to provide the required anchorage length.
3. I also took into consideration the clause EC2 9.2.1.2(1) which states that even when using pinned supports, the supports should be designed for a bending moment
arising from partial fixity of at least 􏰁b1 of the maximum bending moment in the span. whereas b1 = 0.15.

Do you think there could be an issue with this approach?

 

[kellez]

Can someone confirm if my approach to lack of anchorage length is reasonable, summarised in post above?