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5.5.4.2 Calculation of First-Order Moments Around Mid-Height

The document provides durability requirements for concrete columns under different environmental conditions. It specifies the minimum concrete cover thickness for various levels of reinforcement based on the exposure conditions, including dry, humid, seaside, and chemically aggressive environments. It also lists requirements for maximum water-cement ratios, minimum cement content, and required concrete strength classes corresponding to the exposure conditions.

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Bertin Bakari
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60 views2 pages

5.5.4.2 Calculation of First-Order Moments Around Mid-Height

The document provides durability requirements for concrete columns under different environmental conditions. It specifies the minimum concrete cover thickness for various levels of reinforcement based on the exposure conditions, including dry, humid, seaside, and chemically aggressive environments. It also lists requirements for maximum water-cement ratios, minimum cement content, and required concrete strength classes corresponding to the exposure conditions.

Uploaded by

Bertin Bakari
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Table 5.

23 Durability requirements for columns


Conditions for exposure Nominal cover to all reinforcement
(for definitions see
Appendix C) mm mm mm mm mm
1. Dry environment 20 20 20 20 20
2. Humid environment
(a) without frost – 30 30 25 25
(b) with frost – – 30 25 25
3. Humid with frost and
de-icing salts – – 35 30 30
4. Seawater environment
(a) without frost – – 35 30 30
(b) with frost – – 35 30 30

The following classes


may occur alone or in
combination with those
above:

5. Aggressive chemical
environment
(a) slightly aggressive – – 30 25 25
(b) moderately – – – – 25
aggressive – – – – 40
(c) highly aggressive*
Maximum free 0.65 0.60 0.55 0.50 0.45
water/cement ratio

Minimum cement 260 280 300† 300 300


content, kg/m3

Concrete class strength C25/30 C30/37 C35/45 C40/50 C45/55


or both
Notes on Table 5.23
1. Cover is expressed in terms of nominal values which have been obtained from the minimum values by
allowing for a negative tolerance of 5mm.
2. The cover in mm to the main reinforcement should not be less than the bar diameter.
*Protective barrier to prevent direct contact with highly aggressive media should be provided.
†280 kg/m3 for exposure classes 2b and 5a.

5.5.4.2 Calculation of first-order moments around mid-height


The first-order moment (Mzi or Myi ) at about mid-height of a braced column should be the
greater of either:

0.6 M2 + 0.4 M1 or 0.4 M2

where M1 is the numerically smaller end moment from first order analysis and M2 is the

IStructE EC2 (Concrete) Design Manual 61


Fig. 5.17 Subframes for column moments – slender columns
numerically larger end moment from first order analysis
Note that algebraically, M1 and M2 will commonly have opposite signs.
5.5.4.3 Calculation of the ultimate deflection
The ultimate deflection in mm is given by

where: fyk = characteristic strength of the reinforcement in N/mm2


le = effective length of the column in direction considered
d = effective depth of section in direction considered
The above value for e2 may be reduced by multiplying by the factor K, which is obtained
iteratively, given by:
N N
K #
N N
where: Nu = ‘squash’ load of column = 0.567 fckAc + 0.87As fyk
Nbal = balanced load i.e. the axial load that when applied to a section maximizes
the ultimate moment capacity. For a symmetrically reinforced section,
Nbal = 0.267 fckAc.
Alternatively, K may conservatively be taken as 1.

62 IStructE EC2 (Concrete) Design Manual

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