Conc Code 2001

CICIND

Model Code for Concrete Chimneys

Part A: The Shell Second Edition, Revision 1

Revised and reprinted in loose leaf format August 2001

Copyright CICIND 2001 ISBN 1-902998-13-8

Office of the Secretary 14 The Chestnuts, Beechwood Park, Hemel Hempstead, Herts. HP3 0DZ, UK

Tel: +44 (0)1442 211204 Fax: +44 (0)1442 256155 email: [email protected]

CICIND Model Code for Concrete Chimneys, 2001 page 1

www.cicind.org

CICIND Model Code for Concrete Chimneys, 2001

DISCLAIMER

CICIND documents are presented to the best of the knowledge of its members as guides only.CICIND is not, nor are any of its members, to be held responsible for any failure alleged or proved to be due to adherence to

recommendations, or acceptance of information, published by the association in a Model Code or other publication or in any other way.


Foreword The first edition of the CICIND Model Code for Concrete Chimneys published in October 1984 presented the combined views of acknowledged international experts in the specialist field of concrete chimneys and represented a valiant attempt to combine the best features of the various and disparate national codes. At that time all concrete chimney codes were based on elastic theory and the CICIND Code reflected this to some extent. Subsequently both DIN and ACI made progress in introducing a more consistent limit state approach making it desirable for CICIND to follow suit. This Second Edition is the result.

This Model Code was accepted by the General Assembly of the CICIND Association in April 1998.

This document has been prepared by the CICIND Concrete Committee.This Committee consists of

N. R. Bierrum, Chairman (UK) J. Davenport (UK) C. Gonzalez-Florez (Spain) H. van Koten (Netherlands) A. P. Krichevsky (Ukraine) V. Matej (Czech Republic) P. Noakowski (Germany) B. N. Pritchard (UK) V. Rosetnic (Romania) R. W. Snook (USA) T. N. Subba Rao (India) J. L. Wilson (Australia)

Table of Contents 0 Introduction............................................................2 0.1 General 0.2 Commentary 0.3 Philosophy

1 Scope ......................................................................3

2 Field of Application...............................................3

3 References ............................................................3

4 Notations and Definitions ...................................3 4.1 General 4.2 Notations and Subscripts 4.2.1 Notations 4.2.2 Subscripts 4.2.3 Examples 4.3 Units 4.4 The Sign Rule

5 Basis of Design.....................................................5 5.1 Methods 5.1.1 Limit States 5.1.2 Design Conditions and Values 5.1.3 Load Combinations 5.1.4 Action Effects and Resistances 5.2 Partial Safety Factors 5.2.1 General 5.2.2 Importance Classes 5.2.3 Material Properties 5.2.4 Actions 5.3 Modelling 5.3.1 General 5.3.2 Radial Wind Pressure

6 Material...................................................................6 6.1 Concrete 6.1.1 General 6.1.2 Material Law 6.2 Reinforcement 6.2.1 General 6.2.2 Geometry 6.2.3 Tensile Properties 6.2.4 Steel Grades 6.2.5 Ductility 6.2.6 Material Law

7 Actions ................................................................... 8 7.1 Permanent Load 7.2 Wind 7.2.1 General 7.2.2 Wind Speed 7.2.2.1 Basic Wind Speed 7.2.2.2 Representative Wind Speed 7.2.3 Inline Wind Load 7.2.3.1 Principles 7.2.3.2 Mean Hourly Wind Load 7.2.3.2.1 Main Formula 7.2.3.2.2 Air Density 7.2.3.2.3 Shape Factor 7.2.3.3 Static Equivalent of the Wind Load

due to Gusts 7.2.3.3.1 Main Formula 7.2.3.3.2 Gust Factor 7.2.4 Ovalling 7.2.5 Wind Loads on Ladders and other

Projections 7.2.6 Wind Loads during Construction 7.2.7 Vortex Shedding 7.3 Seismic Action 7.3.1 Design Basis Earthquake 7.3.1.1 Typical Design Response Spectrum 7.3.2 Elastic Response 7.3.2.1 Design Basis 7.3.2.2 Vertical Forces 7.3.3 Seismic Design Actions 7.3.3.1 Importance Factor 7.3.3.2 Structural Response Factor 7.3.4 Seismic Design and Detaling 7.3.4.1 Design Approach 7.3.4.2 General Capacity Design Principles 7.3.4.3 Specific Detailing Requirements for

Capacity Design 7.4 Temperature Effects 7.5 Explosions 7.5.1 External Explosions 7.5.2 Internal Explosions

8 Design Calculations for Ultimate Limit State ........................................................11

8.1 General


8.2 Horizontal Cross-Sections 8.2.1 Definition of the Ultimate Limit State 8.2.2 Design 8.2.2.1 Equations 8.2.2.2 Algorithm 8.2.3 Thermal Effects 8.2.4 Moments of Second Order 8.2.4.1 Material Laws 8.2.4.2 Calculation of the Moments of Second

Order 8.2.4.3 Rotation of the Foundation 8.2.4.4 Approximation of the Moments of

Second Order 8.2.5 Dimensioning Diagrams 8.3 Vertical Cross-Sections 8.3.1 Wind 8.3.2 Temperature 8.4 Openings 8.4.1 General 8.4.2 Virtual Openings 8.4.3 Dimensioning 8.4.3.1 General 8.4.3.2 Tensile Forces above and below an

Opening

8.4.3.3 Bending Moment in Vertical Cross-Sections above and below an Opening

8.5 Local Point Loads

9 Design Calculations for the Serviceability Limit State..............................15

9.1 Cracking 9.2 Deflections in Serviceability Limit

State 9.2.1 Deflection of the Shell 9.2.2 Response to Sun Exposure 9.2.3 Deflections of Support Elements

10 Details of Design................................................16 10.1 Vertical Reinforcement 10.2 Horizontal Reinforcement 10.3 Reinforcement around Openings 10.4 Cover to the Reinforcement 10.5 Minimum Wall Thickness

11 Tolerances ..........................................................17

0 Introduction

0.1 General

The International Symposium on Chimney Design held in Edinburgh in 1973 highlighted common problems in existing industrial concrete chimneys. It also identified significant differences between the requirements of the various national codes covering chimney design. As a result, a committee was founded with the aims of improving the knowledge of chimney design and harmonising the various national chimney standards. This committee took the name ”Comité International des Cheminées Industrielles" (CICIND).

Following many years of study, the committee published in 1982 a report entitled "Proposal for a Model Code for the Design of Chimneys". This admirable document contained the committee's model codes for the design of concrete chimneys and their lining systems. Unfortunately the code was not acceptable to the Comité Euro-lnternational du Béton (CEB) because it was not based on limit state analysis. On the other hand the changes resulting from a true limit state code were not at the time acceptable to many chimney experts, so a compromise was sought. This was found in the so-called ‘gliding material law’ which is at the heart of the 1984 CICIND code.

The subsequent publication of two more consistent limit-state codes, namely DIN 1056(1984) and ACI 307-88(1988) left CICIND in an isolated position which was felt to be untenable. Further investigation having shown the conservatism of the First Edition to be somewhat exaggerated, the Second Edition is much more in line with current thought. Nevertheless,

there are still significant differences between European and North American codes which are not going to be reconciled by CEN.

This Second Edition is intended to present the current state of the art of the design of reinforced concrete chimney shells in as simple manner as possible given the complexity of the subject, and to make recommendations on aspects which are not satisfactorily covered by existing national codes.

CICIND will continue to try to improve the understanding of the behaviour of chimneys. Further revisions of this Model Code will therefore be published from time to time.

0.2 Commentary

The Model Code is accompanied by rather extensive commentaries. The Commentaries have the following objectives:

a) Justification of the regulations of the Model Code

b) Simplification of the use of the Model Code

c) Understanding of the meaning of the regulations of the Model Code

d) Documentation of the areas in the Model Code where the present knowledge is sparse so that the regulations are possibly or probably not optimal

The following items are not objectives of the CICIND Commentaries:


e) Change of the meaning of certain regulations of the Model Code where these are falsely expressed or obviously wrong

f) Definition of the meaning of certain regulations of the Model Code where these are badly or ambiguously expressed

g) Expression in a different way of certain regulations of the Model Code which are badly formulated so that they could easily be misinterpreted even by experts.

Since the Commentaries were written simultaneously with the Model Code, any such deficiencies, wherever discovered, were immediately corrected. CICIND asks everybody using or reading the Model Code who discovers deficiencies of type e) f) or g) still left in the Model Code to write to CICIND so that the situation can be improved, either with an amendment to the Model Code - if the situation is serious - or with the next revision.

Certain information from the Model Code is repeated in the Commentaries when this simplifies the presentation of the ideas.

0.3 Philosophy

One of the main objectives of any code for construction is the creation of a model which sufficiently resembles reality. The model should be sufficiently "safe, simple, true", and since e.g. "sufficiently simple" cannot be rationally judged on its own, the predominant objective of this model is to find an optimum compromise between the three properties "safe, simple, true".

The concept "sufficiently safe" was interpreted in the light of economic and social consequences of damage. This normally leads to the adoption of a nominal probability of approximately 10-4 of collapse for the main structure in a 50 years period. If however the economic or social consequences of collapse would be catastrophic it is recommended that this nominal probability be reduced to 10-5.

CICIND has departed from generally accepted principles of reinforced concrete design only when this was necessitated by the specific requirements of chimneys.

1 Scope This Model Code deals with the design of reinforced concrete industrial chimneys above their foundations. It does not deal with architectural aspects or those aspects of reinforced concrete technology which are not peculiar to chimneys, such as generally accepted principles of detailing reinforcement or technology of concrete mix design.

2 Field of Application The Model Code is valid for all chimneys of circular cross-section in reinforced concrete, placed in situ. The Model Code does not deal with prefabricated chimneys, either of reinforced or prestressed concrete.

Other aspects of chimney design, construction and maintenance may be covered by other Model Codes published by CICIND.

It has been assumed in the drafting of the Model Code that the design of reinforced concrete chimneys and their lining systems is entrusted to appropriately qualified structural or civil engineers for whose guidance it has been prepared. It has also been assumed that the execution of the work is carried out by experienced chimney builders under the direction of appropriately qualified supervisors.

3 References Because of the rather extensive ”official" Commentaries to the Model Code, references are not provided in the Model Code itself. References to literature which is useful for an improved understanding of the justification, meaning and consequences of the application of the Model Code are given in the Commentaries.

4 Notations and Definitions

4.1 General

The meaning of the various symbols used is explained extensively in the text of the Model Code. Normally, wherever a symbol is used in a chapter, its meaning is defined within that chapter. Certain repetitions could thus not be avoided. The following list of symbols defines the use of symbols in a general way only. For example, the letter σ means "stresses", and this may mean concrete stresses or steel stresses. The subscript 'c' means concrete, and thus σc means concrete stress, but σc may mean many different concrete stresses, e.g. in horizontal or vertical cross-sections under various load cases.

Further specifications of the type of stress with further subscripts and the like are explained in the body of the Model Code.

4.2 Notations and Subscripts


4.2.1 Notations

The following list shows only the principles by which the notations and their meanings are related. The actual notations are explained in the text of the Model Code after each given formula.

Safety factors γ partial safety factor

Material properties f strength E modulus of elasticity ε strain σ stress

Loading P permanent load W wind T temperature v wind speed w wind force per unit height

Cross-sectional forces M bending moment N normal force e eccentricity

Dimensions h height z height above ground level d diameter t wall thickness ρ ratio of reinforcement area to gross

concrete area c concrete cover A area of cross-section I 2nd moment of area

Deflections k curvature ϕ rotation y deflection w crack width

4.2.2 Subscripts

Materials c for concrete s for steel

States k characteristic value u ultimate limit value s serviceability limit value

Loading W from wind in the direction of the wind

(inline) X from wind due to vortex-shedding

(crosswind) P from permanent load T from temperature E from earthquake 2 from deflection (moment of 2nd order, due

to the action of gravity on the deformed shape)

C from corbel D design value

Kind of Stress c compression t tension

Directions v vertical h horizontal

Locations t at the chimney top b at the chimney base

4.2.3 Examples

Safety factors γcu partial factor of safety for concrete, ultimate

limit state Material properties

fck characteristic strength of concrete Cross-sectional forces

Mw bending moment from wind Dimensions

ρv ratio of vertical reinforcement

4.3 Units

Generally, the units of the Sl system are used.

Examples:

- m (metre) and mm (millimetre) for dimensions

- MN (MegaNewton) and N (Newton) for forces.

- MPa (MegaPascal) for stresses.

- GPa (GigaPascal) for elastic moduli.

Where other units are used, they are explained in the text.

4.4 The Sign Rule


Strengths are defined as positive values.

Forces, stresses and strains from compression are negative.

Forces, stresses and strains from tension are positive.


5 Basis of Design

5.1 Methods

5.1.1 Limit States

The structural performance of the chimney shell in whole or part is described with reference to specified limit states which separate desired states from undesired states. The limit states are divided into two categories:

- the ultimate limit states which concern the maximum load carrying capacity.

- the serviceability limit states which concern the normal use.

The exceedance of a limit state may be reversible or irreversible. In the irreversible case the damage associated with the exceedance will remain until the structure has been repaired. In the reversible case the damage or malfunction will remain only while the cause of the exceedance is present.

Ultimate limit states include:

- overturning of the structure.

- attainment of the maximum resistance capacity of sections.

The exceedance of an ultimate limit state is always irreversible and the first occurrence causes failure. For simplicity some states prior to structural collapse may be considered ultimate limit states.

Serviceability limit states include:

- local damage including excessive cracking which may reduce the durability of the structure or affect the appearance of structural elements.

- unacceptable deformations which affect the efficacy or appearance of structural or non-structural elements.

In the cases of permanent local damage the exceedance of a serviceability limit state is irreversible and the first occurrence constitutes failure.

In other cases the exceedance of a serviceability limit state may be reversible but non-compliance occurs:

a) on the first occasion if no exceedance is acceptable

b) if the duration of the undesirable state is longer than specified.

5.1.2 Design Conditions and Values

The calculation model for each limit state should consider a specific set of basic variables representing physical quantities which characterise actions, material properties and geometrical quantities.

Given the random nature of variables the purpose of design calculations is to keep the probability of failure below an acceptable value. The present Model Code aims to achieve this by the method of partial factors in which influences of uncertainties and variabilities arising from different causes are separated by means of design values assigned to basic variables.

The design values of actions FD are obtained from

FD = γf Fr (5.1)

where Fr are the representative values of actions and γf are the partial factors for actions. The representative values of actions are specified with reference to a prescribed probability of being exceeded.

The design values of material properties fD are obtained from

fd = η fk / γm (5.2)

where fk are the characteristic values of material properties, γm are the partial factors for materials and η are supplementary factors.

For concrete and steel the characteristic strengths are the 5% lower fractiles of the statistical strength distributions of the supplied materials . The supplementary factors η account for uncertainties in the calculation models.

In the general form the design condition should also include design values of geometrical quantities, a serviceability limit where appropriate, and a factor by which the importance of the structure and the consequences of failure are taken into account.

Table 5.1 Load Combinations and Partial Safety FactorsUltimate Limit States Serviceability Limit States

horizontal sections verticalsections

action symbol inlinewind

cross-wind

earthquake wind wind earthquake

crackwidth

Permanent G 1.0 1.0 1.0 -- 1.0 1.0 --wind normal W 1.61) 1.23) -- 1.4 1.3 -- --

wind hurricane W 1.82) 1.23) -- 1.6 1.3 -- --crosswind X -- 1.2 -- -- -- -- --

temp. gas4) Tg 1.0 1.0 1.0 1.0 1.0 1.0 1.0temp. ambient 4) Ta 1.0 1.0 1.0 1.0 1.0 1.0 1.0

Earthquake E -- -- 1.45 -- -- 1.0 --1) 1.8 for importance class 22) 2.0 for importance class 23) To be applied to alongwind effects accompanying vortex shedding.4) Thermal effects appear in the calculation models as temperature differences between the inner and outer faces of the shell5) An importance factor usually greater than unity is incorporated in the design value of the seismic action (see 7.3)


Model uncertainties may also have to be represented.

5.1.3 Load Combinations

A load combination is an assemblage of the design values of a set of different actions considered simultaneously in the verification for a given limit state.

5.1.4 Action Effects and Resistances

In many cases the basic variables and the factors which describe the uncertainties in the calculation models can be separated into groups so that some groups give action effects S and others give resistances R.

In the simplest case the ultimate limit state design condition can be written as

RD ≥ SD (5.3)

where RD and SD are derived from the design values of the variables introduced in (5.1) and (5.2) above.

For the serviceability limit states the design condition is of the type

SD ≤ C (5.4)

whereby an action effect is compared to a serviceability requirement.

5.2 Partial Safety Factors

5.2.1 General

The numerical values of the partial safety factors have been calibrated using a probabilistic method with the aim of achieving predictable levels of safety.

See Commentary no. 1 for a discussion of the safety concept in this model code and the numerical values of the partial safety factors.

5.2.2 Importance Classes

Two importance classes are recognised. Class 2 comprises those cases where collapse would result in a large number of deaths or consequential costs exceeding 100 times the cost of construction. All others fall into Class 1. The corresponding failure probabilities in 50 years are 10-5 for Class 2 and 10-4 for Class 1.

The importance class should be specified by the owner.

5.2.3 Material Properties

The design strength of concrete in compression shall be

fcu = η fck / γcu (5.5)

with η = 0.85 and γcu = 1.5, where fck is the characteristic strength of concrete cylinders as defined in Eurocode 2 or ACI 318.

The design values of other concrete properties such as tensile strength or modulus of elasticity are given in the relevant sections of the text.

The design strength of the reinforcement shall be

fsu = fsk / γsu (5.6)

taking γsu = 1.15 in both compression and tension

It is assumed that if construction tolerances remain within the limits specified in section 11 the material factors also account for the variability of geometrical quantities.

5.2.4 Actions

The actions, symbolically Sd, to be considered in the investigation of the limit states shall be obtained from the combinations described in Table 5.1. It is assumed that the partial safety factors in Table 5.1 also account for modelling uncertainties.

For each limit state the load combinations concerned are to be found in the corresponding columns in the table. As an example the actions effect for the ultimate limit state in horizontal cross-sections is found under “Inline Wind” to be

Sd = 1.0G + 1.6W + 1.0TG + 1.0TA

In hurricane wind zones 1.6W in this expression is to be replaced by 1.8W.

The factor of safety against overturning due to unfactored actions shall be not less that 1.5.

The partial safety factor for the design of lining supports and corbels shall be 1.4

5.3 Modelling

5.3.1 General

The loading patterns and usual proportions of concrete chimney shells allow beam theory to be used in analysis. For overall horizontal forces and gravity the shell is modelled as a cantilever fixed at foundation level. Local discontinuities such as openings shall be considered in the evaluation of sectional properties.

Effects of second order shall be taken into account.

The dynamic characteristics of the chimney may be determined by an equivalent discrete system. The number of masses considered shall be sufficient to ensure stability of the results.

5.3.2 Radial Wind Pressure

The effects of radial wind pressure are analysed for unit height rings considered independently of each other except in the neighbourhood of openings.

6 Material

6.1 Concrete

6.1.1 General

The characteristic cylinder strength of the concrete shall be not less than 25 MPa.


6.1.2 Material Law

The stress-strain relationship for determining the resistance capacity of cross-sections is given by (6.1).

002.0

0002.0

0

cu −<ε≤ε−

<ε≤−

ε≤

( )cu

cu

ff25011000

0

−=σε+ε=σ

=σ

(6.1)

where fcu is given by (5.5)

The ultimate strain for concrete, εcu is defined as −0.0030 at the centre of the wall for horizontal sections and −0.0035 at the edge for vertical sections.

−σc

strain

stre

ss

f cu

0.002 ε cu

0 −εc Fig. 6.1: Material law for concrete

6.2 Reinforcement

6.2.1 General

The products to be used as reinforcement are steel bars defined by geometrical, mechanical and technological properties. These properties are generally specified by Product Standards and are usually assured by compliance certification schemes.

6.2.2 Geometry

The geometrical properties are the size and surface characteristics. The nominal cross-sectional area to be considered in design is derived from the nominal diameter of the bar. The difference between actual and nominal area should not exceed the limiting values specified in relevant standards. Ribbed high-bond bars satisfying the projecting rib factors should normally be used for main reinforcement.

6.2.3 Tensile Properties

The characteristic values of

- the yield stress (fsk)

- the tensile strength (ftk)

- the total elongation at maximum load (εuk)

defined on the basis of standard tests are normally used in the definition of steel qualities.

6.2.4 Steel Grades

The steel grade denotes the value of the specified characteristic yield stress in MPa This Model Code does not consider reinforcing steel grades in excess of 500.

6.2.5 Ductility

Two ductility classes are defined for design purposes. These are normal (A) and high (S) as follows:

Class A : (ft / fy)k ≥ 1.08 and euk ≥ 0.05

Class S : (ft / fy)k ≥ 1.15 and euk ≥ 0.15

where (ft / fy)k is the minimum characteristic value of the ratio and εuk is defined in 6.2.3.

In seismic regions high ductility steel should be used for vertical reinforcement.

6.2.6 Material Law

The idealised stress-strain relation to be considered in the determination of the resistance capacity of sections follows from figure 6.2.

for

su

sk

ssu

sk

sssu

sk

fE

f for

EE

f for

γ=σ

γ≥ε

ε=σγ

<ε

An average value of 210 GPa may be used for the modulus of elasticity of steel, Es.


The stress-strain diagram of figure 6.2 is valid for both tension and compression.

For earthquake analysis the limit strain for steel class S may be taken as εsu = 0.04 in sections in which there are no significant openings. Otherwise the limit strain is εsu = 0.01.

Detailed evaluation of sectional properties such as may be required for time-history analysis for earthquake loading or second order analysis shall be conducted in line with generally accepted laws within the strain limits set above. Results of relevant tests may be taken into account where available.

7 Actions

7.1 Permanent Load

Both a maximum and a minimum permanent load must be determined for the calculation of the limit states of horizontal sections and foundations. The maximum permanent load shall include the estimated weight of all permanent structures and structural elements, fittings, insulation, dust loads, clinging ash, present and future coatings, etc.

7.2 Wind

7.2.1 General

The wind load on a chimney depends in the first instance on the magnitude of the wind speeds in the area where the chimney is to be erected and their variation with respect to height. Apart from that, the wind loads in the direction of the wind will be influenced by some or all of the following:

a) the local topography

b) the level of turbulence

c) the presence of nearby structures

d) the air density

e) the drag coefficient (shape factor)

f) the natural frequencies of oscillations of the chimney

g) the amount of structural damping

h) the shapes of the first few modes of vibration

7.2.2 Wind Speed

This section is included primarily for the benefit of engineers designing chimneys to be constructed in locations where local codes of practice do not treat these structures in sufficient detail.

7.2.2.1 Basic Wind Speed

The determination of the effective wind pressure is based on the basic wind speed.

The basic wind speed vb appropriate to the location of the chimney is defined as the mean hourly wind speed at 10 m above ground level in open flat country without obstructions having probability 0.02 of being exceeded in any one year.

The value of the basic wind must be established by meteorological measurement. An indication of values of the basic wind speed for various parts of the world is given in Commentary No. 3.

Where the terrain of the location of the chimney is hilly or built-up, measurements for the determination of vb should be taken as near as possible at a place which is flat and open.

7.2.2.2 Representative Wind Speed

This section deals with the influences on the wind speed due to changes in the terrain elevation or local obstructions. The influence of mountains around the chimney site must be determined by local measurements.

The basis for the determination of the wind loads is the representative wind speed, which equals the basic wind speed corrected by three factors which take into consideration the speed variation over the height of the chimney, the topography of its surroundings and the existence of adjacent objects. These three factors are the height factor k(z), the topographical factor kt, and the interference factor kj.

The representative wind speed is calculated by the following expression:

( ) ( ) itb kkzkvzv = (7.1)

where

v(z) hourly mean wind speed at level z

z height above ground level (m)

vb basic wind speed

k(z) = ks(z/10)α exposure factor

ks scale factor, equal to 1.0 in open flat country

α terrain factor.

kt topographical factor (see Commentary No. 3)

ki interference factor (see Commentary No. 3)

The terrain factor α should normally be taken as 0.14, corresponding to open flat country, unless there is no possibility of all nearby buildings being subsequently demolished. A different value of α may be used if its suitability can be proved, in which case ks and the gust factor G in 7.2.3.3.2 should be modified accordingly with reference to background literature.


The determination of kt and ki, if these are different from 1, is complicated and may require wind tunnel tests. Commentary No. 3 contains suggestions for the determination of these factors.

7.2.3 Inline Wind Load

7.2.3.1 Principles

The wind load w(z) per unit height at height z is determined by the following expression:

)z(w)z(w)z(w gm += (7.2)

where

wm(z) is the mean hourly wind load per unit height, see formula 7.3

wg(z) is the static equivalent of the wind load per unit height due to gusts, see 7.2.3.3.1

7.2.3.2 Mean Hourly Wind Load

7.2.3.2.1 Main Formula

The mean wind load per unit height is

( ) ( ) ( )zdCzv.zw Dam250 ρ= (7.3)

where

ρa density of air, see 7.2.3.2.2.

v(z) wind speed at height z, see (7.1)

CD shape factor, see 7.2.3.2.3.

d(z) outside diameter of the chimney at height z

7.2.3.2.2 Air Density

The density of air ρa is to be taken as:

ρa = 1.25 kg/ m3

at sea level in temperate climates. Transient variations in the density due to atmospheric changes need not be taken into account.

The air density relevant to a chimney situated at an altitude of h1 (m) can be found from the expression:

8000

h-. 1

a 251=ρ (7.4)

7.2.3.2.3 Shape Factor

The shape factor CD depends on the slenderness of the chimney. For a chimney with circular cross-section, CD is given by the following formula:

25d/h if 7.0C

25d/h5 if 0.5(5)log

(h/d)log0.1C

5 < h/d if 6.0C

D

10

10D

D

≥=

<≤+=

=

(7.5)

where

h height of the top of the shell above ground level

d chimney diameter at 0.75 h

7.2.3.3 Static Equivalent of the Wind Load due to Gusts

7.2.3.3.1 Main Formula

The static equivalent of the wind load due to gusts is assumed to vary linearly with the height. This causes an increase of the bending moment at high levels in the chimney compared with the normal gust-loading method.

The wind load due to gusts can be determined by

( ) ( ) ( )∫−

=h

0m2g dzzzw

hz

h1G3

zw (7.6)

where

G gust factor, see 7.2.3.3.2

h height of the top of the shell above ground level

z height above ground level

wm(z) mean hourly wind load per unit height at height z, see 7.2.3.2.

7.2.3.3.2 Gust Factor

The gust factor is

ζ

++=ES

BigG 21 (7.7)

where

g peak factor: Tlog

.Tlogg

ee

ν+ν=

2

57702

with 2

1

ESB

1

f3600T 1

ζ+

=ν


i turbulence intensity hlog089.0311.0i 10−=

B background turbulence:

880630

2651

..hB

−

+=

E energy density spectrum

83.0

42.02

b

1

21.0

b

1

hv

f3301

hvf

123E

+

=

S size reduction factor

880

980141

17851

.

..

bh

vf

.S

−

+=

ζ damping expressed as a fraction of critical damping. For the calculation of wind loads in the direction of the wind the value ζ = 0.016 should be used.

f1 natural frequency in Hz of the chimney oscillating in its first mode.

h height of shell above ground level in m

vb basic wind speed in m/s, see 7.2.2.1.

T sample period

ν effective cycling rate

7.2.4 Ovalling

The uneven distribution of the wind pressure causes bending moments in vertical cross-sections. These moments are given in section 8.3.1.

7.2.5 Wind Loads on Ladders and other Projections

Where a chimney is provided with external structures such as projecting flues, platforms, ladders etc. due account must be taken of these in establishing the wind load on the chimney. A suitable addition to the wind load on the chimney itself will normally suffice on the assumption that the external structures will not alter the wind flow round the chimney.

If an external ladder is relatively large compared to the diameter, it may increase the shape factor of the whole structure.

7.2.6 Wind Loads during construction

During construction or other temporary condition not exceeding two years in duration, the wind loads may be taken as 80% of those calculated in sections 7.2.3 to 7.2.5.

7.2.7 Vortex Shedding

This is the subject of further investigation. At the present time it is recommended that the tip deflection due to vortex shedding be calculated by the method of ACI 307-95 section 4.2.3. The moments should be calculated from the deflected shape.

7.3 Seismic Action

7.3.1 Design Basis Earthquake

The design basis earthquake is a representative earthquake associated with a return period of 475 years (i.e. 10% chance of exceedence in 50 years).

7.3.1.1 Typical Design Response Spectrum

No single response spectrum can cover all types of earthquake in all parts of the world. Reference must be made to the codes of practice which apply at the site of the chimney. An example of a normalised acceleration response is provided in the commentary.

7.3.2 Elastic Response

7.3.2.1 Design Basis

The elastic response of the chimney is calculated by the response spectrum method using the design basis earthquake.

- Assume uncracked properties.

- Use a response spectrum with 5% critical damping and 50% shape bound probability.

- Include sufficient modes to ensure that at least 90% of the chimney's gravity load is accounted for in the modal analysis.

- The maximum response in each mode does not occur simultaneously since the modes are not exactly in phase. Consequently the overall response of the chimney is found by calculating the square root of the sum of squares of the modal values.

- The value Ec given by equation 8.3 must be used for the calculation of the frequencies.

7.3.2.2 Vertical Forces

The effect of the vertical seismic forces is generally small and may be ignored, because the peak vertical responses are at a very high frequency and do not occur simultaneously with the horizontal accelerations.

7.3.3 Seismic Design Actions

The seismic design actions are obtained from the elastic response by multiplying the actions by an importance factor (γi) and dividing by a structural response factor (R).


7.3.3.1 Importance Factor

The importance factor depends on the importance class of the chimney:

Class 1: γi = 1.0

Class 2: γi = 1.4

7.3.3.2 Structural Response Factor

The structural response factor depends on the level of seismic detailing:

R = 1.0 No specific seismic detailing

R = 2.0 Seismic detailing in accordance with Section 7.3.4 (this implies the use of Capacity Design)

7.3.4 Seismic Design and Detailing

In low seismic regions where the wind loads predominate, design against wind loads provides significant overstrength compared to the seismic actions. In these cases an economical design will be achieved by designing to resist the actions calculated from the elastic response with R = 1.0. By contrast, in high seismic regions it is difficult to develop an efficient design without consideration of ductility and the reduction of seismic actions through the introduction of a structure behaviour or response factor. Significant economies may be achieved by following the approach given below.

7.3.4.1 Design Approach

The design approach described below is based on performance criteria:

(a) design the chimney elastically to resist the earthquake induced loads considered reasonable for a serviceability limit state earthquake event.

(b) design the chimney with sufficient ductility so that the chimney will survive an extreme earthquake event without premature failure and collapse at the structural stability limit state.

7.3.4.2 General Capacity Design Principles

The design of the chimney should be consistent with the principles of capacity design. The foundation system and the shell in the vicinity of the openings should be designed for overstrength in both flexure and shear so that inelastic flexural behaviour will develop in the ductile regions of the shell and not near the base or in the neighbourhood of significant openings.

7.3.4.3 Specific Detailing Requirements for Capacity Design

a) Deformed reinforcement shall be class 'S', high ductility steel with a fracture strain in excess of 15%.

b) Maximum spacing of circumferential steel shall be 10db (where db = vertical steel diameter) to reduce the possibility of buckling of the vertical steel under severe cyclic loading.

c) Splice lengths for the vertical reinforcement shall be 30% greater than the bond lengths of the bars.

d) The vertical reinforcement should be sufficient to ensure that the ultimate moment capacity of the chimney at any cross section in the lower 80% of the chimney is greater than the nominal cracking strength. For this condition the tensile strength of concrete fcte may be assumed to be fcte = 0.6fck

0.5

e) In the ductile regions the vertical reinforcement ratio should nowhere exceed

ckdtfN

14.0024.0π

−

7.4 Temperature Effects

The effects of temperature differences between the inner and outer faces of the concrete shell should be calculated for the steady state heat flow.

The characteristic value of the flue gas temperature should be determined from the given operational conditions and controls.

The characteristic value of the ambient temperature should be taken as the regional average minimum temperature for the two coolest months of the year.

The thermal characteristics of all materials in the heat flow equations shall be decided by reference to the product specifications.

Temperatures may for simplicity be calculated as for plane walls.

The design provisions which follow assume that in normal operating conditions the temperature drop across the wall will not exceed 60K.

7.5 Explosions

7.5.1 External Explosions

The ability of a chimney to withstand wind and/or earthquake loads will in most cases ensure sufficient resistance to explosions and other high velocity pressure waves with their sources a distance of more than 100 m from the chimney. The provision of guidelines on measures to adopt if explosions can occur in the direct vicinity of a chimney is outside the scope of this Model Code.


7.5.2 Internal Explosions

Internal explosions in a chimney can occur due to the presence of soot or explosive gases in the chimney. Damage is, however, more often caused by explosions in the installations leading to the chimney. Protection of the chimney by explosion panels in these installations may prevent serious damage to the shell and lining.

8 Design Calculations for the Ultimate Limit State

8.1 General

The resistance capacity of any horizontal or vertical section in the shell calculated as specified herein shall exceed the corresponding effect of factored loads. The loading combinations and loading factors are given in Table 5.1.

For each loading combination the design condition (5.3) may be described in bending moment terms only as

maxu MM ≥ (8.0)

In the case of inline wind Mmax is given by

2wwmax MMM +γ=

where M2 is the moment due to deflection in the ultimate limit state (see section 8.2.4).

8.2 Horizontal Cross-Sections

8.2.1 Definition of the Ultimate Limit State

The resistance capacity of the horizontal cross-section is reached when either ultimate strain, ε εcu su or , is

reached anywhere in that section.

8.2.2 Design

8.2.2.1 Equations

The ultimate sectional forces are given by

( )∫π

φρσ+σ=2

0scu drtN (8.1.a)

( )∫π

φρσ+σ=2

0scu dxrtM (8.1.b)

where

Nu ultimate normal force

Mu ultimate bending moment

σc concrete stress at wall centre as a function of strain according to 6.1

σs steel stress at wall centre as a function of strain according to 6.2

function of strain according to 6.2

ρ reinforcement ratio

t wall thickness (zero in openings)

r radius of the centre-line of the wall

x perpendicular distance from the centroid of the elemental area to the diameter perpendicular to the plane of bending

Equations (8.1.a) and (8.1.b) may be integrated numerically assuming that the strain varies linearly across the section. In the absence of openings the strain at position x is given by

( ) ( ) r2/xrctc −ε−ε+ε=ε (8.1.c)

where

εc = maximum compressive strain in the section at the wall centre

εt = maximum tensile strain in the section at the wall centre

8.2.2.2 Algorithm

1. εc and εt are set equal to the limiting values given in 6.1 and 6.2.

2. The corresponding axial force Nb is computed from (8.1.a).

3. If -Nb > -Nu then εt is held constant, otherwise εc is held constant.


4. The depth of the neutral axis is varied by trial and error to satisfy (8.1.a).

5. Mu is computed from (8.1.b)

6. The design variables in equations (8.1) are adjusted until (8.0) is satisfied.

8.2.3 Thermal Effects

The action of temperature and loading from permanent load and wind cannot be directly superposed. The reason is that the moment from temperature depends on the actual stiffness of the cross-section, which decreases with an increase of the loading. Therefore, loading causes the bending moment from temperature to become smaller.

Provided that the temperature drop in the wall is less than 60K (see section 7.4) the thermal effects on the limit strains and on the average stresses may be disregarded.

In cases where the characteristic temperature drop exceeds this limit the strain variation across the wall must be taken into account.

8.2.4 Moments of Second Order

8.2.4.1 Material Laws

For the determination of the moments of 2nd order, the deflections are needed. For the computation of the deflections, the average material properties are used as opposed to the minimum material properties which are used in the calculation of stresses and strains.

For the concrete in the compression zone, the following linear material law shall be used:

εγ

=σcu

cc

E (8.2)

where the modulus of elasticity is

( ) )MPa in (f 8f9500E ck33.0

ckc += (8.3)

In the tension zone, the stiffening effect of the concrete is important.

The effective tensile stress in the reinforcement may be calculated by the following approximate method.

for 0 < ε < ε1 σ = 106ε

( but not exceeding su

skfγ

)

ε1 < ε < ε2 σ = Es(ε + ∆ε)

ε2 < ε < εsu σ = su

skfγ

where

cu

ct

vs

fE

5.0γρ

=ε∆ (8.4)

66.0ckct f3.0f = (8.5)

ε∆=ε 266.01 (8.6)

ε∆−γ

=εsus

sk2 E

f (8.7)

8.2.4.2 Calculation of the Moments of Second Order

Moments of 2nd order are calculated numerically from deflections of the shell as described in Commentary No. 4.

8.2.4.3 Rotation of the Foundation

Rotation of the foundation causes moments of 2nd order in the shell.

The rotation Θ of the foundation can be estimated from the following formulae:

- for a shallow circular raft on soil if there is no uplift under the characteristic wind load

3

ft

WW

rE5.1

Mγ=Θ (8.8)

- for a foundation on end bearing piles


p

2pp

WW

Kx

M

∑β

γ=Θ (8.8)

where

Mw wind moment acting on the underside of the foundation

Et dynamic modulus of elasticity of the soil

rf the outer radius of the raft

xp distance of a pile from the axis of rotation

Kp spring constant of an end-bearing pile

bp factor for pile interference

+=

p

pp

sd61

1b

dp pile diameter

sp spacing of the piles

8.2.4.4 Approximation of the Moments of 2nd Order

The moments of 2nd order can be estimated from equation 8.9 (see Commentary No. 4).

( ) ( )4.2

cuc

2

WW2 hz

1hz

4.21IE

Nh100

h14.085MzM

−

+

⋅γ−

γ=

(8.9)

where

Mw bending moment from wind at chimney base

γw wind load factor for ultimate l imit state

h height of chimney

z height of the considered cross-section

M2(z) moment of 2nd order at height z

N normal force at the chimney base

Ec rnodulus of elasticity from equation 8.3

γcu = 1.0 (safety factor for concrete)

l 8/td 3mπ= second moment of area of the

uncracked section at the chimney base ignoring reinforcement

dm mean shell diameter at the chimney base

t notional wall thickness at the chimney base (not the actual wall thickness, but rather the thickness which would be required at the chimney base if there were no openings at the base).

The effect of deflection caused by rotation of the foundation is not considered in equation 8.9.

The more accurate method of section 8.2.4.2 is recommended for final design.

8.2.5 Dimensioning Diagrams

In order to simplify the dimensioning of chimneys, dimensioning diagrams are given in Commentary No. 6.

8.3 Vertical Cross-Sections

8.3.1 Wind

The uneven wind pressure distribution around the circumference of a circular cylinder causes bending moments acting on vertical cross-sections of the shell.

The characteristic bending moment is given by

( ) ( )zd

Czw

k09.0MD

mtWh = (8.10)

where

kt = 2.2 correction factor to convert the mean hourly wind load to the corresponding 5-sec. wind

wm(z) see formula (7.3)

d(z) diameter of chimney at level z

CD shape factor

The moment MWh causes tension at both faces of the shell.

8.3.2 Temperature

The maximum bending moment from the temperature difference is calculated by:

ctT fwM = (8.11)

where w is the section modulus.

The following formula may be used as an approximation to the section modulus in the case of equal reinforcement on each face:

2h

cm

s2

tEE

tc2t6/1w

ρ

−+= (8.12)

where

t wall thickness (m)

c cover to reinforcement

Es modulus of elasticity of steel

Ecm modulus of elasticity of concrete for mean material properties

)8f(850E ckcm +=

ρh ratio of one layer of circumferential reinforcement

fct tensile strength of concrete


(8.13)

Sufficient reinforcement must be provided to satisfy both the following equations

Tuh MM > (8.14a)

whwhuh MM γ> (8.14b)

where Muh is the ultimate moment of resistance of

the section, calculated using the material laws of sections 6.1 and 6.2 with the appropriate material factors.

8.4 Openings

8.4.1 General

The stresses around openings may be calculated with a finite element method or approximated by the method given in 8.4.2.

8.4.2 Virtual Openings

Parts of chimneys where openings occur do not satis fy the basic assumption of Navier in beam theory, namely that plane sections remain plane. This model may still be applied for the dimensioning of horizontal cross-sections if the openings are considered to be enlarged as in figure 8.3 and in addition the following conditions are fulfilled:

a) No virtual opening has a width larger than 1.2 times the inner radius.

b) For each horizontal section with more than one opening, the circumferential distance a between any two adjacent virtual openings with width b1 and b2 must be such that

( )21 bb25.0a +≥

where a, b1, b2 are measured at the mean radius.

c) For the determination of the equilibrium when an opening is in the compression zone, the vertical reinforcement ratio existing within a distance of 0.5 b from the edges of the opening shall be assumed to be 0.005 less than the actual amount.

In the preparation of the dimensioning diagrams in Commentary No. 6, half the vertical steel displaced by the opening has been assumed placed close to the opening on each side. The reduction in lever arm has been taken into account.

8.4.3 Dimensioning

8.4.3.1 General

The ovalling moment due to wind acting over the height of the opening may require additional horizontal reinforcement above and below the opening.

The model of virtual openings will not adequately take care of the flow of forces around the opening. Additional reinforcement may be needed locally. The following two cases are particularly important.

8.4.3.2 Tensile Forces in Vertical Cross-Sections above and below an Opening

The total tensile force in the horizontal direction above and below an opening should be taken to be

γ

ρ+γ

=su

skv

cu

ckt

fftb1.0F (8.15)

where

b clear width of the opening

t wall thickness

ρv ratio of the vertical reinforcement

8.4.3.3 Bending Moment in Vertical Cross-Sections above and below an Opening

In the shell above and below an opening the bending moment given by (8.16) should be assumed to produce tension on the inside of the vertical sections over the width of the opening:

γ

ρ+γ

=su

skv

cu

ck3 ffdt

b002.0m (8.16)

where d is the mean diameter of the shell, other variables as in 8.4.3.2

( )( )t400.1t246.2

8ft2.085.045.0f 66.0ckct +

++−=


8.5 Local Point Loads

Loads transmitted to the shell through separate narrow supports will cause vertical bending and torsion moments in the shell. The vertical bending moment will have its largest values, positive and negative, at the level of the support of:

tr

M6.0mk = (8.17)

where

mk maximum bending moment in the shell per unit length

M moment caused by the eccentricity of the load measured to the centre of the shell

r mean radius of the shell

t shell thickness

Inner and outer reinforcement should be provided in the vertical and the horizontal directions over a minimum length and width of the shell of

tr6.1 (8.18)

See Commentary No. 5 concerning justification of formulae (8.17) and (8.18).

9 Design Calculations for Serviceability Limit State

9.1 Cracking

It is not necessary to check the width of horizontal cracks because the dead weight of the chimney above the section will tend to close any such cracks.

The horizontal reinforcement must prevent unacceptable vertical cracks. The crack width must be limited according to environmental conditions as indicated in table 9.1, even if a protective coating is provided.

Table 9.1 Limit of crack width wk depending on environment

Environmental conditions

Characteristic crack width

aggressive

normal

0.2 mm

0.3 mm

The characteristic crack width determines the bar diameter and spacing.

The maximum bar diameter is given by equation (9.1)

( ) 2s

12.1k

66.0ck

6s /w8f104.0d σ+⋅= (9.1)

where

ds bar diameter in mm.

fck characteristic strength of concrete.

wk characteristic crack width in mm.

σs post-cracking steel stress resulting from bending moment causing cracking.

The ratio ρ2 required on each face to limit the crack width for the chosen bar diameter ds may be found by assuming σ ρs ctf≈ 0 2 2. and rewriting (9.1) in the

form

12.1k

66.0ck

6s

ct2w)8f(104.0

df2.0

+⋅=ρ (9.2)

The minimum ratio ρ on each face is the greater of ρ2 and that required to satisfy section 8.3.2.

The maximum spacing is given by

ρ

π=

t4000d

s2

s (9.3)

where s is the distance between bar centres in mm and t is the shell thickness in metres.

9.2 Deflections in Serviceability Limit State

Figure 8.3: relation of real opening (solid line) to virtual opening (dashed line)


9.2.1 Deflection of the Shell

Deflection of the shell is only important in connection with the effect on the lining. The calculated deflections of the shell in the ultimate limit state may be so large that the lining would be destroyed before the shell reached the ultimate limit state. A reduced load factor for this serviceability limit state is justified because the probability of reaching the ultimate limit state is extremely small and collapse of the lining is much less serious than collapse of the shell,.

Other effects of interactions between the shell and the lining may be of two kinds:

a) Forces caused by direct contact between shell and lining. The determination of the clearances necessary to avoid this is treated in part B of the CICIND Model Code for Concrete Chimneys.

b) Inertia forces induced in the lining by the motion of the shell and, consequently, the lining support. The determination of these forces is treated in parts B and C of the CICIND Model Code for Concrete Chimneys.

The deflections may be computed in the same way as in the determination of the moments of 2nd order in 8.2.4 using the serviceability wind load factor.

9.2.2 Response to Sun Exposure

The top of a chimney will move under sun exposure. This may affect the setting-out of the chimney during construction.

The maximum displacement of the top can, for a cylinder, be estimated from the formula.

d2Th

y T2

maxα∆

= (9.4)

where

∆T difference between the mean temperatures on the sunny and shady sides of the chimney, the mean temperatures varying linearly across the diameter.

αT coefficient of linear thermal expansion of concrete = 10-5 K-1

d mean diameter of a cylindrical chimney

The bending moments due to this movement may be ignored.

9.2.3 Deflections of Support Elements

Deflections of support elements (e.g. supporting platforms) are particularly important in the case of brick linings. A lining section constructed of brickwork is very stiff in respect of vertical deformation of cross-sections. Undue flexibility of the supporting structure may cause extremely high local stresses in the brickwork resulting in large cracks.

10 Details of Design

10.1 Vertical Reinforcement

The minimum ratio ρv of the vertical reinforcement to the gross cross-sectional area should be not less than 0.003 for fsk less than 300 MN/m2 or 0.0025 for fsk greater than 300 MN/m2. Over a height of 0.2 diameters or 2.5 m, whichever is greater, below the top of the shell, this minimum reinforcement should be increased by 50%.

The reinforcement should be distributed in layers towards the inner and the outer face with not less than half the reinforcement in the layer (or layers) towards the outer face. The diameter of vertical reinforcement should not be less than 12 mm and the spacing should not exceed 300 mm. Laps should be staggered so that not more than half the bars are spliced at any cross-section.

10.2 Horizontal Reinforcement

Equal layers of horizontal reinforcement should be provided towards both faces of the shell. The minimum ratio ρh of the horizontal reinforcement on each face to the gross cross-sectional area will usually be determined by the requirement of section 8.3.2 but should in no case be less than 0.001. The bar diameter should be not less than 8 mm. Laps should be staggered so in any three adjacent layers no splice is within 150 mm of another.

The maximum spacing is determined by the requirement of section 9.1 but should not exceed the lesser of the wall thickness or 300 mm or (in seismic areas) 10 times the diameter of the vertical reinforcement. If the shell top is not stiffened by a concrete roof slab this minimum reinforcement ratio should be doubled over a distance of 0.2 diameters or 2.5 m, whichever is greater, below the top of the shell. To ensure that cracking due to early thermal contraction is properly controlled the minimum horizontal reinforcement ratio should also be doubled over a height of 2m above the base.

10.3 Reinforcement around Openings

The minimum vertical reinforcement should be 0.0075 in a distance of half the width of the opening on each side of the opening.

Both horizontal and vertical additional reinforcement at openings should extend beyond the edge of the opening by at least half the width of the opening plus the bond length of the bars.

10.4 Cover to the Reinforcement


The nominal concrete cover to the reinforcement should be 40 mm minimum with tolerances of +20 mm and -10 mm.

10.5 Minimum Wall Thickness

The wall thickness of cast in situ shells should be not less than 200 mm.

In the presence of openings the wall thickness should not be less than 0.04 times the height of the opening unless properly designed buttresses or other means of stiffening are provided, in which case the buttresses are to be ignored when calculating the moment resistance of the horizontal section.

11 Tolerances Tolerances in the concrete work are defined in a statistical way and expressed in terms of

a) the mean inaccuracy m between a specified dimension Ln and the real dimension L measured at several points chosen at random

b) the standard deviation S of the measurements.

The values m and S shall not exceed the appropriate values given in table 11.1.

Table 11.1 Upper limit for absolute value of mean inaccuracy m and standard deviation S

m (m) S(m)

Wall Thickness (m)

t < 0.3 m

t > 0.3 m

0.005

0.002 + 0.01 t

0.01

0.004 + 0.02 t

Shell Diameter(m)

0.05 + 0.01 d 0.05 + 0.01 d

Deviation from

Vertical Axis (m)

h < 50 m

h > 50 m

0.05

0.001 h

0.05

0.001 h

Note 1: The mean value of the wall thickness at one level over a 60 degree arc shall be taken to represent one measurement.

Note 2: This table 11.1 is only valid if the variables are random. In the event of systematic inaccuracies, special investigations are required.

Note 3: The inaccuracies of the vertical axis are determined from conditions of stresses produced by these inaccuracies and the practicability of observing these tolerances. Architectural considerations may lead to closer limits for the inaccuracies of the vertical axis.

Note 4: Locally the centre point of the shell shall not change by more than 25mm per 3m vertically.

Conc Code 2001

Documents

Transcript of Conc Code 2001