topic Re: Column reinforcement changes when cover changes in Robot Structural Analysis Forum

Column reinforcement changes when cover changes

Μηχανικος — Mon, 20 Jul 2015 09:22:27 GMT

Hello everyone, i am using robot provided reinforcment to design a column.

Initially the provided reinforcement calculated by Robot is 8Φ20 = 2513mm2 (with cover = 40mm)

Then the provided reinforcement calculated by Robot is 12Φ20 = 3769mm2 (with cover = 30mm)

so why when i decrease my cover, the area of steel reinforcement increases?

Re: Column reinforcement changes when cover changes

Artur.Kosakowski — Tue, 21 Jul 2015 10:24:27 GMT

Could you send the file with both these columns please? Thank you.

Re: Column reinforcement changes when cover changes

Μηχανικος — Tue, 21 Jul 2015 20:53:07 GMT

Below are the links for both columns.

http://www.mediafire.com/view/t44c48dlyqie822/1._Design_Response_Spectrum_-_Column_Design.rtd

http://www.mediafire.com/view/af2f5ctbieg16i0/1._Design_Response_Spectrum_-_Column_Design_2.rtd

These are exactly the same file except that in one i changed the cover distance within the Rc design module provided reinforcement

Analysis -> calculation options -> General -> Cover -> c >= 30 or 20mm

when i use c >= 30 the actual cover in the calculation is 40mm

when i use c >= 20 the actual cover in the calculation is 30mm

Re: Column reinforcement changes when cover changes

Artur.Kosakowski — Thu, 23 Jul 2015 12:19:32 GMT

For 20 mm cover EC in 5.4.3.2.11 b imposes limits on main rebars tied by stirrups spacing as 20 cm (for 3 bars at at the side that would be 20.3 cm). For 30 mm cover the spacing is smaller that this code limit.

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Re: Column reinforcement changes when cover changes

Μηχανικος — Fri, 24 Jul 2015 07:36:52 GMT

Hi there is no such section (5.4.3.2.11 b) in EN 1992-1-1:2004

Re: Column reinforcement changes when cover changes

Μηχανικος — Fri, 24 Jul 2015 08:24:17 GMT

Hi there is no such section (5.4.3.2.11 b) in EN 1992-1-1:2004

Even if this is the case i dont think this is what is happening in my case. also i dont understand for which spacing limit you are referring to?

ok so when my cover is 40mm (30mm cover + 10mm deviation) i get 8 bars of 20mm diameter

and clear spacing between main bars is [500 - (2 x 40mm cover) + (2 x 10mm links) + (3 x 20mm main bars)]/2 = 170 mm

clear spacing between main bars is = 170mm

when i decrease the cover to 30mm i get 12 bars of 20mm.

and clear spacing between main bars is [500 - (2 x 30mm cover) + (2 x 10mm links) + (4 x 20mm main bars)]/3 = 113.33mm

clear spacing between main bars is = 113.33mm

what i am saying here is that if you decrease the cover and keep the same amount of main bars then the spacing between bars increases so why is Robot adding more bars?

Re: Column reinforcement changes when cover changes

Artur.Kosakowski — Fri, 24 Jul 2015 09:48:56 GMT

You can find the paragraph 5.4.3.2.11 b in EN 1998-1:2004 (EC8, not EC2) which is used as you included seismic in your design:

The distance is understood as axial spacing rather than clear space between bars.

When cover is 40mm (30mm cover + 10mm deviation) and you get 8 bars of 20mm diameter, distance between axes of those bars = [500 - (2 x 40mm cover) -(2 x 6mm links) - (2 x 20mm main bars)/2]/2= 194 mm

This spacing is correct (194mm <200mm).

When you decrease the cover to 30mm and get 12 bars of 20mm, spacing between axes of main bars is [500 - (2 x 30mm cover) - (2 x 6mm links) - (2 x 20mm main bars)/2]/3 = 136mm

For 8 bars fi 20mm you would have [500 - (2 x 30mm cover) - (2 x 6mm links) - (2 x 20mm main bars)/2]/2 = 204mm which would be above the limit (>200mm)

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Re: Column reinforcement changes when cover changes

Μηχανικος — Fri, 24 Jul 2015 10:10:04 GMT

ohhhh i see, you are great, thank you for all your help, really appreciate this.