What exactly is extended drop panel? 2

[struggle66]

Hi all

In PT design, what is extended drop panel? Most designers in here quite often extend the drop panels and called them extended drop panels. When they ran the design in the extended panels direction, they include slab tendons together with the tendons in the extended drop panel. There is no links inside the extended drop panel and they said it is because they run it like a drop panel not like a beam. The tendons in the other direction ran assuming pin at the extended drop panels location. But for me, it looks like one way slab with band beams. There should be links inside the so called extended drop panels and the slab tendons parallel to extended drop panels should not be included in the extended drop panels run. Do you guys experience that before?

Thanks

 

[rapt]

Struggle,

Sounds like band beams to me also. They should not include the slab tendons parallel to the bands in the band design. Some US software companies do this but it is wrong, same as doing average moment design with drop panels and including the tendons in the 'middle strip? away from the drop panels with the depth of the drop panel. Completely stupid. This results in serious under capacity.

Both ACI318 and AS3600 would allow you to design the beam shear for wide flat band beams as you would for a slab, oly requiring ligs if the applied shear is greater then Vc, not .5Vc and not requiring minimum shear as BS8110 and Eurocode would at all cross-sections for a beam. Basically beam shear rules for slabs are used!

 

[rowingengineer]

I would call them band beams as well from the description. Warner & Ragan did some tests on these beams and found an increased shear strength due to slab effects. Maybe they are using these tests?

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[TXStructural]

Maybe designed as a thick slab without ties/stirrups, as opposed to band beams which would probably necessitate stirrups. This removes the extra dead weight of concrete where it is not needed.

 

[struggle66]

Hi all,

Is there any limit for band beam depth and width?

Kindly see whether my understanding is wrong.

For one-way design, all the tendons should be concentrated inside the band designed as a beam.

For two-way design, I should design as a slab with column/middle strips in the both directions.

Thanks

 

[rapt]

Struggle,

You should really be getting this information from your superiors and design codes, not the internet!

Minimum widths to treat shear as slab shear are controlled by your design code. AS3600 requires width greater than twice depth and depth less than 750mm. ACI relates it to depth below the slab and I think the ratio is 4, but you should read it yourself, not rely on hearsay. In an earlier post on this I told you which codes have allowances for this. It is then up to you to follow up and read them and make any decisions on how you apply them.

Maximum width would be about the same as a drop panel, so about .3 of the transverse span. But this all depends on the slab depths and the overall situation, there is no code rule.

In my opinion, you comments on one way and two way design are correct. Any tendon within the effective flange width could be included in the band, but then people start using stupid effective flange widths which makes this difficult. The flange outstand should be no more than about 4 times slab depth either side of the beam, not the full panel width as some try to justify.

 

[struggle66]

Rapt,
Of course I will look into the code as everything in here needs to refer to code.
Thanks for your help.