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Steel Column-Base plate – Anchor rods - Pedestal & Pedestal reinforcement

 
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mjnasar
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Joined: 26 Jan 2003
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PostPosted: Sun Oct 03, 2021 6:36 am    Post subject: Steel Column-Base plate – Anchor rods - Pedestal & Pedestal reinforcement Reply with quote

Dear Engineers
Greetings

As per ACI 318 -14 chapter 17.5.2.9 – if the anchor reinforcement encloses the anchor. The design strength of anchor reinforcement shall be permitted to be used as breakout strength instead of concrete break out strength

Can the reinforcement in the pedestal considered as anchor reinforcement.
( Please see typical pedestal sketch attached )


As the above pedestal reinforcement not complying with  figure R17.5.2.9a , R17.5.2.9b(attached)

thanks
Mjnasar



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typical Pedastal.pdf
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Typical pedestal reinforcement

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ACI 318-14_CH17.5.2.docx
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Figures from Ch17.5.2

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vikram.jeet
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PostPosted: Mon Oct 04, 2021 7:13 am    Post subject: Reply with quote

Just a generic view :-
Anchors are subject to axial tension - -  Anchors being embeded into  Concrete  with Vertical reinforcement bars and closely spaced lateral ties - - - Tension is  passed on to concrete through bond - - Concrete in presence of lateral ties will able to transfer tension to vertical reinf.  Thus  splitting in concrete is protected by ties aiding tensile force to transfer to vertical bars.

Each structural element has its role to play ,
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pvgraju
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PostPosted: Mon Oct 04, 2021 11:17 am    Post subject: Steel Column-Base plate – Anchor rods - Pedestal & Pedestal reinforcement Reply with quote

Dear Sir,

There are some limitations such as No6 bars, distance from center line of anchor were provided in the commentary to use anchor reinforcement.

when high shear force is present concrete will tend to break out in shear. But by providing this hair pin anchor bars, by developing those bars by Ld, by ensuring suitable connection between anchor-anchor bar-concrete this shear force causing breakout will be resisted by anchor bars first.

so before concrete reinforcement comes into action. If this reinforcement is not able to absorb the required breakout force by its own strength,bond with other side of concrete then concrete break out strengh to be considered.

Connection between anchor,anchor reinforcement is to be taken care.

Regards,

P.V.Gavarraju.
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vikram.jeet
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PostPosted: Mon Oct 04, 2021 3:18 pm    Post subject: Re: Steel Column-Base plate – Anchor rods - Pedestal & Pedestal reinforcement Reply with quote

Dear Er PV Gavarraju ,
Since not used such hair pin anchor bars , request you to please enlighten . Is this hair pin reinf is in form of horizontal mesh with its bars having downward legs embedded Ld at periphery with Vertical reinf of pedestal.
But same role is played by lateral ties which create no. of  meshes at regular spacing in concrete mass , the difference is that ties are closed around vertical pedestal bars and are distributed in conc mass in many layers depending upon spacing of rings(Ties).


pvgraju wrote:
Dear Sir,

There are some limitations such as No6 bars, distance from center line of anchor were provided in the commentary to use anchor reinforcement.

when high shear force is present concrete will tend to break out in shear. But by providing this hair pin anchor bars, by developing those bars by Ld, by ensuring suitable connection between anchor-anchor bar-concrete this shear force causing breakout will be resisted by anchor bars first.

so before concrete reinforcement comes into action. If this reinforcement is not able to absorb the required breakout force by its own strength,bond with other side of concrete then concrete break out strengh to be considered.

Connection between anchor,anchor reinforcement is to be taken care.

Regards,

P.V.Gavarraju.
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pvgraju
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PostPosted: Tue Oct 05, 2021 5:01 am    Post subject: Steel Column-Base plate – Anchor rods - Pedestal & Pedestal reinforcement Reply with quote

Dear Sir,

I referred to the ACI attachment. It seems as per research these type of bars are recommended as a shear key with some limitations such as 6No bar,max c to c spacing from center line of anchor.

In the attachment two alternatives were recommended.

1. U bar (hairpin) around anchors.These hairpins shall enclose edge reinforcement and shall be placed as close as possible to anchors.(Fig:17.5.2.9a)
2. Another one is embedded into the concrete. (17.5.2.9b)

This Ld shall be development length in tension since it resist shear by tension in bars.

Regards,

P.V.Gavarraju.
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vikram.jeet
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PostPosted: Tue Oct 05, 2021 11:56 am    Post subject: Reply with quote

Thanks Engineer  Gavarraju ji ,  appreciate yr response.
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