Continuous Concrete Beams

[Structures33]

Hey there - In continuous concrete beams where negative moment occurs over the supports, is the r/f in "tension" or simply flexure? I don't know whether to design the splice lengths for deformed bars in tension or just use standard splice lengths like 36*diameter of bar.
What condition does development of deformed wire in tension (ACI 12.2) apply to -- versus development of flexural r/f (ACI 12.10) or even development of negative moment r/f (ACI 12.12)?
Thanks in advance

 

[JedClampett]

I would try to locate the splices where there can't be any tension in the reinforcing, like midspan. What I like to do is to use minimum flexural steel for the top reinforcing and add bars over the supports for any additional moment. They need to be developed beyond where they're no longer needed. Then you only have to splice the minimum flexural reinforcing. And you can use shorter splice lengths for the Class A critieria. Even that's conservative.
If you look at any concrete detailing book (CRSI, ACI), you'll see examples of this.

 

[JAE]

[blue]In continuous concrete beams where negative moment occurs over the supports, is the r/f in "tension" or simply flexure? [/blue]
The top bars over the supports are generally in tension. Reinforcing steel is either in tension or compression - there is no "flexure" condition.

[blue]I don't know whether to design the splice lengths for deformed bars in tension or just use standard splice lengths like 36*diameter of bar.[/blue]
Top bar lengths in beams should follow ACI 12.10, 12.11, and 12.12. Using "X" bar diameters isn't really the correct way to meet ACI. These three sections rely on the basic development lengths for reinforcing bars found in section 12.2.


[blue]What condition does development of deformed wire in tension (ACI 12.2) apply to -- versus development of flexural r/f (ACI 12.10) or even development of negative moment r/f (ACI 12.12)? [/blue]
If you read through 12.10, 12.11 and 12.12, you will find references to l_d which is the development defined in 12.2. As I stated above, these three sections rely on the basic development lengths for reinforcing bars found in section 12.2.

 

[JLNJ]

In addition to flexure at the column, the beam could be a strut which is dragging forces through the connection - either in tension or compression.