Minimum Steel Reinforcement in Concrete and Clear Cover Requirements

7/24/2019 Minimum Steel Reinforcement in Concrete and Clear Cover Requirements

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Minimum Steel Reinforcement in Concrete

and Clear Cover Requirements

The minimum amount of steel reinforcement is defined as that for

which "peak load at first concrete cracking" and "ultimate load

after steel yielding" are equal. In this way, any brittle behavior isavoided as well as any localized failure, if the member is not over-

reinforced.

In other words, there is a reinforcement percentage range, depending

on the size-scale, within which the plastic limit analysis may beapplied with its static and kinematic theorems.

minimum area of reinforcement is required to control the cracking,

which occurs in the concrete due to temperature, shrinkage and creep.

It enables cracking to be uniformly distributed and thereforeminimizes individual crack width.

The following criteria have been used to determine the cross-section

area of temperature or minimum reinforcement required in hydraulic

structures. The percentages indicated are based on the gross cross-sectional area of the concrete to be reinforced. !here the thickness of

the section eceeds fifteen #$%& inches #'() mm&, a thickness of

fifteen #$%& inches #'() mm& should be used in determining thetemperature or minimum reinforcement.

he minimum ratio of required reinforcement is*

FOR SLABS:

f min + ).)) #for f y + ),))) psi&

min + ).))$( #for f y + /),))) psi&

FOR WALLS:

For Vertical Steel

f min + ).))$%



For Horizontal Steel

f min + ).))%

The temperature reinforcement shall not be less than 0 inch at nine 1 inch center to center. ll

concrete stilling basins, glacis and floors and all concrete aprons structures #with slab thickness 2

$% inch & shall be reinforced in the eposed #top& face with 3 inch bars at twelve #$& inch center

to center, both ways, placed three #'& inch clear from concrete face, unless otherwise designed.

4ominal reinforcement of concrete chute blocks, baffle blocks and sills for stilling basins, aprons

and other portion of structures shall consist of 3 inch bars at twelve #$& inch center to center,

both.

Temperature and shrinkage reinforcement should be uniformly distributed alongside faces of

structure elements to control cracking due to temperature changes, creep, and shrinkage.

5epending on the thickness of the structural element, it is preferred that the centre-to-centre

spacing of the primary and secondary reinforcement be equal to or less than ')) mm* however,

in no case should it eceed %) mm. The minimum clear distance between bars should not be

less than $. times the bar diameter or $. times the nominal maimum size of the coarse

aggregate, whichever is greater. This requirement also applies to the clear distance between a

contact lap splice and ad6acent splices and bars.

The minimum thickness of concrete cover over the reinforcement has been determined by

considerations of adequate fire resistance and durability. The cover for the reinforcement to meet

specified period of fire resistance is detailed as follows7



Fire

Resistance

(hours)

Beams slabs

columns

Simply

supported continuous

Simply

supported continuous

).% ) ) ) ) )

$.) ) ) ) ) )

$.% ) ) % ) )

.) ) ') '% % %

'.) /) ) % '% %

.) 8) %) %% % %

9over in ecess of ) mm #$.%8 inch& may require additional measure to reduce risk of spalling.

Cover gainst Spalling

Concrete !lement

Minimum

Concrete Cover

(in) (mm)

:ace in contact with earth ' 8%

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Minimum Steel Reinforcement in Concrete and Clear Cover Requirements