Min rebar in mass concrete 1

Hi all!

In a mass concrete pier subjected to little bending what %age of min erbar is given? The calculated requirement is < 0.008% !! (to tension side for avoiding cracks). It is right as per calculations but seems very thin in practice. What should be done? please advise.

Thanks in advance,
rebar

 

[shgizmo]

rebarDoubt
To provide you with what you need shed some light on your inquiry, Do you mean slab placed on grade or elevated pier supported by abbutments, walls.. or rigid block foundation or short column pedestals.

 

[Ginger]

There are two approaches;

1. Accept that concrete does have a small degree of tensile capacity (generally around 10% of the compressive capacity) and see if this is sufficient to carry the tensile loads generated under flexure. Note that many design codes do not recognise this tensile capacity in the concrete.

2. Adopt the code allowance for minimum rebar density (in UK the minimum is 0.13% (BS 8110).

Regards Andy Machon

 

[jeg]

BS8110 specifies minimum requirements for columns:
1 - min % of vertical bars is calculated from
100*area steel in compression/area concrete in compression = 0.4
2 - diam of links not less than 6mm and spacing not greater than 12 imes diam of thesmallest vert bar

Check out the codes in your area. They will certainly specify a min and max requirement.

 

[lutein]

ACI Specifies 1% minimum reinf. ratio for Column in compression.

However, if you are dealing with short concrete piers surrounded by soil on top of footing or drilled shaft or pile caps (so called pedestals), please refer to ACI318-99, Section 22.8, if the Height-to-Width ratio is satisfied, then it can be designed as structural plain concrete members in which very minimal or no reinf. is &quot;required&quot;.

**hPlease also read Section R22.2 for temp., shrinkage, and creep effects. I would provide at least 0.5% if the criteria in Section 22.8 is satisfied. (0.5% was recommended by CRSI for Drilled Shaft)

 

[Ginger]

OOPS !!

Jeg is correct. 0.13% is minimum As for beams SORRY !!!!!!
Andy Machon

 

[shymad]

minimum reinforcement required is .8% as per minimum design requirements.i don't think u have any others factors.u can go with .8% which satisfies your requirement.