American Journal of Environmental Engineering and Science 2014; 1(5): 99-103

Published online November 30, 2014 (http://www.openscienceonline.com/journal/ajees)

Thermal actions and insolation effects in free standing steel industrial chimneys

Bernard Wichtowski, Janusz Hołowaty

Faculty of Civil Engineering and Architecture, West Pomeranian University of Technology Szczecin, Szczecin, Poland

Email address

Janusz.Holowaty@zut.edu.pl (J. Hołowaty)

To cite this article Bernard Wichtowski, Janusz Hołowaty. Thermal Actions and Insolation Effects in Free Standing Steel Industrial Chimneys. American

Journal of Environmental Engineering and Science. Vol. 1, No. 5, 2014, pp. 99-103.

Abstract

The technical conditions of service limit for steel structures are defined in standards and codes of practice. Horizontal

displacement of the top of a chimney is usually described as a sum of the static wind displacement, the execution displacement

and the ground deformation displacement. Thermal stresses and deformations are very important in concrete chimneys. In

steel chimneys, usually with thin plates, according to customary standards, the problem of differential thermal stress need not

be accounted for. If the temperature of chimney shaft is higher than 700C, it is advised to implement reduced values of basic

properties of structural steel. For chimneys with guys, if the average temperature is higher than 500C, the influence of thermal

effects on internal forces should be taken into account. Differential thermal effects in steel structure can cause corrosion and

misleading temporal displacements. In the paper, the insolation effects are presented in free standing steel chimneys. The

results of measured temperature and displacements are shown and discussed. The heat transmission caused by operation and

solar radiation influence the horizontal displacements of steel chimneys. Because of thermal movement, the execution

tolerances are usually very difficult to achieve. The thermal effects caused by solar radiation should be taken into account

while designing steel chimneys.

Keywords

Steel Chimney, Thermal Action, Insolation Effects

1. Introduction

Temperature changes for chimney surfaces, in its sections

and differences in the structure temperature compared to its

assembly temperature, denoted as thermal actions causes

additional stresses, deformations and displacements of

structures. The issue of thermal stresses, arising from

differences in temperature between the internal and outer

surface of a chimney has a crucial significance in reinforced

concrete chimneys. As to steel chimneys with small thickness

of structural shell, this problem can be neglected according to

existing national standards and international guides [1], but it

is noted that the effect of heat from the sun can deflect tall

steel chimneys. Now thermal action in chimneys from

climatic effects, shade air temperature and solar radiation are

provided by EN 1991-1-5 [2]. The requirements for steel

chimneys are dealt with Eurocode 3 [3] and for free-standing

steel chimney in EN 13084 [4, 5]. If the temperature of

chimney structural elements exceeds 70oC then, it is necessary

to take basic mechanical properties of steel in relation to

temperature [5]. In guyed chimneys, the temperature effects

on the structure internal forces shall be taken into account if

the average shaft temperature is higher than 50oC [6].

Under the impact of differential thermal actions, steel

structures may be subject to accelerated corrosion or

temporary thermal movements, avoiding of that can lead to

false results. The geometric imperfections from the nominal

ones occur at all stages of steelwork fabrication and at a

construction site while erection and execution, they are

inevitable. The basic limits for geometrical tolerances of the

individual members are determined in corresponding codes of

practice. With reference to structural steelworks building

structures, the requirements were dealt with in national

standards. Now they are in European Standards EN 1090-2 [7]

and EN 1993-3-2 [3].

American Journal of Environmental Engineering and Science 2014; 1(5): 99-103 100

This paper presents the effect of thermal actions caused by

solar radiation on the horizontal deflection in free standing

steel industrial chimneys. An analysis of the results of

measured in situ displacements of a chimney which was

designed by one of the authors and executed at his supervision

gave rise to this paper.

2. Stiffness Requirement for

Free-Standing Chimneys

The serviceability limit state for a chimney shall be verified

pursuant to the recommendation of The Code of Practice or

standards for steel structures, usually in the term of limits for

horizontal deflection [8]:

f

H

mδ ≤ (1)

where

δ total horizontal deflection at the top of a chimney,

H height of the chimney above the uppermost foundation,

mf constant, is equal to 75 or 100 for single wall or double

wall chimneys.

The maximum horizontal deflection at the top of a chimney

δ shall be taken as a sum of three components (Fig. 1):

δ = δs + δm + δp (2)

where

δs static deflection in the I design situation caused by

the characteristic wind pressure pk for section without

corrosion allowance,

δm is equal H/300 for initial assembling imperfection,

δp deflection caused by possible deformation of the

ground.

Fig. 1. Constituent components of deflection at the top of a chimney

While assembling the chimney and evaluating its verticality

on a sunny day, additionally the influence of insolation effects

shall be taken into account. Insolation is the heating and rise of

temperature ∆T of one side of the chimney structural shell

caused by solar radiation. It makes the expand of insolated

side relative to the shaded side. That differential expansion

causes deflection of the chimney away from the sun.

Deflection at the top of a chimney caused by solar radiation

action with constant values αT, ∆T and D amounts to:

2

2n T

HT

Dδ α= ∆ (3)

where

αT coefficient of linear thermal expansion for carbon

steel, is equal 12⋅10-6

/°C,

∆T differential temperature between the outer insolated

surface and the shaded one, is equal Tn – Tc,

D external diameter of the chimney.

Different values of deflection at the top of a free-standing

chimney are given in Eurocode 3. According to EN 1993-3-2

[3] these values are:

� maximum value of deflection at the top of a

self-supporting chimney in serviceability limit state is

recommended as δ = H/50,

� the permitted horizontal deviation from the vertical steel

shell is /1000 1 50 /m H Hδ = ⋅ + , where H is in [m].

Fig. 2. Deflection of the top of a cylindrical chimney (a) and conical chimney

(c) caused by insolation and thermal deflection of section ds (b)

Eq. (3) is given only in technical literature and it is not

included in standards [2, 3, 4, 8]. It was obtained for the case

when a flat curve is assumed as the deflection line (Fig. 2).

Using the dependences given on Fig. 2b, the increment of the

rotation angle of sections of an elementary construction cut

out d∆ϕ caused by the thermal deflection can be determined.

Taking into account the increment of length ∆hav, the central

angle ∆ϕ, in radians, is expressed as:

( )T avT H H

D

αϕ ∆ + ∆∆ = (4)

where

av T avH T Hα∆ = ∆ total length increment of the chimney

axis,

0,5avT T∆ = ∆ average temperature increment in the chimney

axis.

Horizontal displacement of the top of a chimney under the

action of solar radiation determined from the dependence (Fig.

2a) is:

101 Bernard Wichtowski and Janusz Hołowaty: Thermal Actions and Insolation Effects in Free Standing Steel Industrial Chimneys

22sin sin

2 2n av

T

Da

T

ϕ ϕδα

∆ ∆= =∆ (5)

where

2 R sin2

av avaϕ∆= length of arc chord in the chimney

axis,

R av avav

H H H

ϕ ϕ+ ∆

= =∆ ∆

arc radius of deformed structure

axis.

Introducing approximate values: ∆Hav = 0 and sin ∆ϕ = ∆ϕ

to the Eq. (5), we shall obtain Eq. (3). In the case of chimney

with a conical shaft (Fig. 2c) we shall determine the deflection

from the general simplified formula (6):

1 1

n ni

n T av j

i ji

hT h

dδ α

= =

= ∆

∑ ∑ (6)

where

hi segments of height on which the variability of

diameters di is averaged.

3. The Insolation Effects on

Temperature Rise in Chimney Shell

While determining the deflection of the chimney, as a result

of a one-sided insolation, according to the Eq. (3) or (5) there

are doubts about the assumed value of differential temperature

∆T on the surfaces of the structure. The ∆T values are not

stated by the Polish chimney standard [8], however, in the case

of potential uneven heating of the structure, the obsolete

Polish standard for masts and towers recommended to assume

a differential temperature ∆T = 15°C and its linear drop. Such

value of temperature difference is stated in the literature [1].

The new European standard EN 13084-1 [4] recommends

to determine the temperature action on the structure according

to EN 1991-1-5 [2]. Old Polish standard for thermal action

gives formulas to calculate the temperature of walls [9]. The

average temperature insolated wall of an open structure is to

be calculated according to the Eq. (7) and for the screened wall

according to the Eq. (8).

1 2( 0,5 ) In e i

e e

A aA IT T R R k aψ ξ ξ

α α

= + + + +

(7)

1c eT T a ξ= + (8)

where

Te surface temperature for summer,

A coefficient of absorption of solar radiation,

I intensity of total solar radiation,

αe coefficient of taking over the heat by the outer

surface of the wall,

Ri resistance of taking over the heat by the outer

surface,

R thermal resistance of the structural wall,

k heat transfer coefficient,

ψ coefficient of simultaneous air temperature and

solar radiation effects,

a twenty-four hours’ amplitude of external air

temperature,

aI difference between the maximum value and the

average twenty-four hours’ solar radiation,

ξ1 coefficient of amplitude reduction for the value of

twenty-four hours’ wall temperature with double-sided inflow

of heat,

ξ2 as above, with single-sided inflow of heat.

Putting into Eq. (7) and (8), the adopted and calculated

coefficients of values: Te = 27°C; A = 0.6; I = 222 W/m2; αe =

20 W/m2K; Ri = 0.12 m2K/W; R = 0.0002 m

2K/W; k = 5.9

W/m2); ψ = 0.9; a = 8°C; ξ1 = 0.6; aI = 652 W/m

2; ξ2 = 0.2, we

receive the average temperature of the chimney shell – on the

insolated side Tn = 39.6°C and Tc = 31.8°C on the shadowed

side.

To verify the differentiated literature values ∆T = 15°C and

calculated ∆T = 7.8°C, the temperature of chimney shell was

measured in situ as presented in Fig. 3. It was a new, unused

chimney with height of H = 31.80 m and diameter D = 2.50 m.

At the moment of measurement, the chimney had no smoke

inlet connected. The measurements were carried out at the air

temperature of 32°C (and of 36°C in the sun). The temperature

of chimney shell plate was measured twice from a gallery

located at the level of +20.15 m. The temperature was

measured in 32 points, symmetrically placed on the

circumference with the use of a digital thermometer, model

YF-160A (with the resolution of 0.1°C) and a measuring

probe, type TP-04. The maximum value of the temperature on

the insolated side amounted to Tn = 41°C, and the minimum

value on the shadowed side to Tc = 32°C, which means that it

may be assumed that ∆T = (41 – 32) = 9°C.

Fig. 3. Chimney structure and the measured shell temperature

4. Deflections of the Chimney of

Height H = 30 m and Diameter D =

0.815 m

The horizontal deflections of the chimney were determined

by the field measurements during its assembly [11]. The value

of structure deflections were of four components: fabrication

American Journal of Environmental Engineering and Science 2014; 1(5): 99-103 102

and erection imperfections and thermal and elastic deflections.

On sunny and hot days chimney structures are exposed to one

side insolation which causes uneven temperature rise.

Omitting this physical phenomenon may cause an erroneous

interpretation of measured deflections, both as to the absolute

value and the sign and, by the same, a mistaken assessment of

the technical condition of the structure being under survey.

Such an event took place during the assembly of the

chimney presented in Fig. 4. A chimney of 30 m height and

815 mm diameter has a 0.5 m long diffuser. The individual

segments are connected by flange bolted connections with

thirty M30 bolts of class 5.8. At the upper section close to the

outlet of a length of 9.0 m, helical turbulisers of Ø8 mm bars

were installed. The assembling of the chimney was carried out

on a very sunny day with the air temperature of about 37°C in

the sun. A chimney section of 29 m length was assembled

totally at the ground level and lifted with a crane on the lower

segment of 1.0 m height.

The determined elastic deflection at the top of the chimney

with the along-wind direction amounted to δs = 188 mm, and

the deflection caused by possible deformation of the ground

was δp = 14 mm. The measured deflection of the chimney

during the assembling at flanges did not exceed the nominal

standard value δmd = Hp / 300 [3] (broken line on the chart

Fig. 4), where Hp is the level above the base of the measuring

point.

The deflection from vertical of the chimney top was

measured as 76 mm and was lower than the value δmd = H /

300 = 100 mm, according to the Polish standard for chimneys,

but it was larger than the permissible deflection of 30 mm

recommended in the standard requirement for steelworks for

chimneys of height lower than 50 m. The shell deflections

from the straight line in the places of three flange bolted joints

were of a value of 5, 6 and 7 mm and also exceed the

permissible value ±4 mm of requirements.

At the request of the user, after 19 months of the chimney

lifetime, the verticality was measured again and the

deflections measured shown as a full line on the chart (Fig. 4).

It is clear that over the level +13.5 m the measured deflections

exceed significantly the admissible values of deflection δmd.

An example of measured chimney top deflection equal to

152 mm exceeds the value δmd by 52%.

a)

b)

Fig. 4. Chimney structure, H = 30.5 and D = 0.815 m and its deflections Fig. 5. View on ventilation (a) and flue (b) chimneys

Assuming the occurrence of deflection, arising from

substrate deformation δp = 14 mm and assembling deflection

δm = 76 mm, the remaining value of deflection δn = 152 – 76 –

14 = 62 mm was caused by solar radiation. Using the Eq. (3),

the deflection of such a value (62 mm) shall occur at

single-sided insolation, causing an increment in the

temperature ∆T = 9.4°C.

103 Bernard Wichtowski and Janusz Hołowaty: Thermal Actions and Insolation Effects in Free Standing Steel Industrial Chimneys

5. Summary

The analysis of temperatures distribution in two chimneys

(Fig. 5) showed the incorrectness of the conviction that

because of small heat/thermal inertia and good conductivity,

the temperature distribution in steel structures is on principle

constant and have a little effect on structures.

The emission and flow of heat during the technological

processes [1, 4], as well as, one side insolation have a crucial

impact on structure deformation. The impact is generally not

taken into account when drawing up measurement results. An

example of such proceedings is the analysis of assembling

deflections of the discussed 30.0 m high chimneys.

The temperature measured on the insolated and shadowed

surfaces of the ventilation chimney (Fig. 5a) proved a

difference in temperature of ∆T = 9°C. An analogous value ∆T

= 9.4°C was received from the analysis of deflections of flue

chimneys (Fig. 5b). A similar difference in temperature ∆T =

10°C was obtained by the authors during insolation of a

semi-gantry crane and in steel bridges. The 20°C difference in

temperature, assumed sometimes in the literature seems to be

overrated.

The provisions of obsolete Polish standard for mast and

towers, seem to be justified. In the case of unequal insolation

of the structure it recommended to assume the differential

temperatures ∆T = 15°C and its linear drop. This statement

was not repeated in the new edition of chimney standard [8].

In the opinion of the authors a request to insert into the

standard for steel chimneys [3] the requirement that the

insolation action on the steel chimney structures shall be

considered as a constant value of differential temperature ∆T =

10°C.

References

[1] The CICIND Chimney Book. Industrial Chimneys of Concrete or Steel, CICIND, Zurich, 2005.

[2] EN 1991-1-5. Eurocode 1 – Actions on structures – Part 1-5: General actions – Thermal actions, 2005.

[3] EN 1993-3-2. Eurocode 3 – Design of steel structures – Part 3-2: Towers, masts and chimneys – Chimneys, 2006.

[4] EN 13084-1. Free-standing chimneys – Part 1: General requirements, 2007.

[5] EN 13084-7. Free-standing chimneys – Part 7: Product specifications of cylindrical steel fabrications for use in single wall steel chimneys and steel liners, 2005.

[6] EN 1090-2. Execution of steel structures and aluminium structures – Part 2: Technical requirements for the execution of steel structures, 2008.

[7] Wichtowski, B, “Forces in guys according thermal analysis of structural shell of a 40 m high steel chimney”, Przegląd Budowlany, No. 8-9, pp. 32-35 (in Polish), 1994.

[8] PN-93/B-03201. Steel structures. Chimneys. Design rules (in Polish), 1993.

[9] PN-86/B-02015. Actions on building structures. Variable environmental actions. Temperature actions(in Polish), 1986.

[10] PN-B-06200. Building steel structures. Specifications and tests (in Polish), 2002.

[11] Wichtowski, B, Hołowaty J, “Insolation of a free-standing steel chimney. Splar radiation action and effects”, EUROSTEEL 2011, 6th European Conference on Steel and Composite Structures: Research – Design – Construction, Budapest 2011, pp. 825-830.