This document summarizes a study on the non-linear analysis of a 115m tall reinforced concrete chimney in Turkey that collapsed during an earthquake. The study aims to determine the chimney's displacement and ductility demands through non-linear dynamic analysis using SAP 2000 software. A 3D model of the chimney was created in SAP 2000 based on its design specifications. Time history analysis was performed using ground motion records from the 1999 Kocaeli earthquake. Additionally, 3D pushover analysis was conducted to compare results with the dynamic analysis and evaluate the chimney's inelastic behavior under increasing lateral loads.

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NON-LINEAR ANALYSIS OF REINFORCED CONCRETE
CHIMNEY
Shelly Thomas1
, Dr. Jaya V2
, Manju P M3
1
M.Tech Computer Aided Structural Engineering, SNGCE, Kadayirippu, Ernakulam, India
2
Associate Professor, Geotechnical dept, CET, Trivandrum, India
3
Associate Professor, Civil dept, SNGCE, Kadayirippu, Ernakulam, India
ABSTRACT
A chimney is a structure which provides ventilation for hot gases from industries to the outside atmosphere
which are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly. Tall reinforced
concrete chimney are used in thermal power plant as well as in some important industries as to dispose the pollutant
smoke to the higher elevation without contaminate to atmospheric air. To maintain this, chimneys are constructed as
much as tall. As a result, chimneys are tall slender structures. They have different associated structural problems and
must be treated separately from other form of tower structures. Collapse of this chimney structures would lead to shut
down of whole thermal power plant and important industries. In order to prevent the collapse of the chimney structures,
seismic demands must be determined accurately. So a non-linear dynamic analysis as well as pushover analysis of a
115m high chimney which was collapsed during an earthquake in turkey, is conducted and the response of the chimney is
studied in this paper by using SAP 2000 software. Also study the 3D pushover analysis method by considering 3D
interaction effect in lateral loading pattern of pushover. The results obtained by this 3D pushover analysis will be
compared with the results obtained with those of non-linear dynamic analysis.
Keywords: CICIND, Pushover Analysis, RC Chimney, SAP 2000, Time History Analysis.
1. INTRODUCTION
Tall chimneys are constructed as a result of the large scale development of thermal power plant and industries.
Tall chimneys are commonly used to discharge pollutants in to the atmosphere at higher elevation such that the pollutant
which deemed harmful to the environment is kept within acceptable limits. To reduce the air pollution the chimneys are
now a days constructed as much as tall. That is the height of the chimney has been increasing since the last few decades.
Further due to the availability of advanced construction materials chimneys being made with thinner wall. As a result,
chimneys being tall slender structures, they have different associated structural problems and must be treated separately
from other form of tower structures. Not only the earthquake but also the wind may be critical to the chimney structures
depending up on the zones where the chimney is located. In order to prevent the collapse mechanism of the chimney
structures, seismic as well as the wind demands must be determined accurately. For this reason, many evaluations such as
nonlinear analysis of chimney structures are proposed for the accurate determination of inelastic behaviour and seismic
demands of the chimney. In this paper seismic demand only consider as part of the nonlinear analysis. The nonlinear
analysis such as time history analysis and pushover analysis are considered in this paper. Time history analysis is the
nonlinear dynamic analysis and pushover analysis is the nonlinear static analysis. Nonlinear dynamic analysis is the
benchmark of the seismic analysis of all type of structures. So that, the result obtained from the pushover analysis is
compared with the nonlinear time history analysis.
INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND
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2. CICIND
CICIND (International Committee on Industrial Chimney) was founded in 1973 in Paris. The need for such a
body had been demonstrated at the first International Chimney Symposium, held in Edinburgh earlier that year.
Originally CICIND comprised a small, informal group of engineers who shared an interest in industrial chimneys.
Membership was by invitation. In 1981, the organization was formalized as an Association and expanded to be open to
anyone interested in industrial chimneys. Today, CICIND is a mature, respected association, whose recommendations
and model codes in the field of industrial chimneys are in daily use throughout the world. In 2011 CICIND represents
228 members from nearly 40 countries and is doing active research and development work in many fields in the chimney
technology.
Fig.1: RC Chimney
3. SCOPE AND OBJECTIVES
Determination of the displacement and ductility demands of a chimney structure, which may exhibit inelastic
behaviour during an earthquake as well as wind, is quite important. If these mentioned demands are not estimated
accurately during the design or evaluation phase of the structure, a local or a progressive collapse becomes unavoidable
in a severe earthquake. The evaluation of structures, such as chimney structures with opening at cross section, becomes
more important as they have been seriously damaged or collapsed in the earthquakes due to their special collapse
mechanisms. The seismic evaluation is investigated in this paper by means of non-linear dynamic analysis as well as
push over analysis by using the finite element analysis software SAP 2000. The study was focused on the RC chimney
which is used to dispose of gases from industries to outside atmosphere, which is a seismically vulnerable structure. In
the present study nonlinear analysis of the structure is studied using FEA software SAP 2000. The following are the main
objectives:
• To determine the nonlinear behaviour of chimney structures with and without opening at section utilizing
nonlinear dynamic analysis.
• To validate the result obtained from the nonlinear dynamic analysis using SAP 2000 with the result from
ABACUS software. [6]
• To do the 3-D pushover analysis for various deformation levels.
• To compare the results obtained from the pushover analysis with the results obtained in the non-linear dynamic
analysis.

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Fig.2: Elevation of Chimney
4. STRUCTURAL MODEL
The reinforced concrete chimney considered here for the analysis is a collapsed one which was located in
tuparas refinery, Turkey. The stack was 115m high and was distinguished by a large rectangular opening for the flue duct
at the 1/3rd
height of the chimney from the base. There is a large rectangular opening of size 3.7m X 4.95m at 30.5m
from the base. The chimney had bottom out side diameter of 10.3m and top outside diameter of 6.6m. The thickness of
the chimney is also varying along the height, 0.45m at the base and 0.2m at the top of the chimney. The elevation of
chimney as shown in fig.2. The chimney structure is model in SAP 2000 software as shown in fig.3. Shell element of
0.2m thick is used to model the chimney. Material properties defined as M30 grade of concrete and Fe415 grade of steel.
The elastic modulus considered is 33.5 GPa as per the codal provision. The Poisson’s ratio and density considered are
0.15 and 25 kN/m3
respectively.
Fig.3: SAP 2000 3D Model

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Fig.4: Rectangular Opening of Chimney Model
5. TIME HISTORY ANALYSIS
Time history analysis considering all the modes of the structure is assumed to give more accurate results when
compared to other linear analysis procedures. This includes the step by step numerical time integration of equation of
motion by expressing the relationship between the displacement and its time derivatives-velocity and acceleration. The
Kocaeli earthquakes were chosen for the analysis. Time histories in all three directions were available for these
earthquakes shown in fig.5. The chosen accelerogram is Kocaeli, August 17th, 1999, Turkey - YARIMCA, horizontal
component YPT060, magnitude of 7.51, duration 10 s, peak ground acceleration (PGA) 0.3055g.
Fig.5: Time History Motion Record in Three Dierctions
6. PUSHOVER ANALYSIS
The NSP procedure normally called Pushover Analysis is a technique in which a computer model of a structure
is subjected to a predetermined lateral load pattern, which approximately represents the relative inertia forces generated
at locations of substantial mass. The intensity of the load is increased, i.e. the structure is ‘pushed’, and the sequence of
cracks, yielding, plastic hinge formations, and the load at which failure of the various structural components occurs is
recorded as function of the increasing lateral load. This incremental process continues until a predetermined displacement
limit. In general, linear procedures are applicable when the structure is expected to remain nearly elastic for the level of
ground motion or when the design results in nearly uniform distribution of nonlinear response throughout the structure.
As the performance objective of the structure implies greater inelastic demands, the uncertainty with linear procedures
increases to a point that requires a high level of conservatism in demand assumptions and acceptability criteria to avoid
unintended performance. Therefore, procedures incorporating inelastic analysis can reduce the uncertainty and
conservatism. This approach is also known as "pushover" analysis. A pattern of forces is applied to a structural model
that includes non-linear properties (such as steel yield), and the total force is plotted against a reference displacement to
define a capacity curve. This can then be combined with a demand curve (typically in the form of an acceleration-

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displacement response spectrum (ADRS)). This essentially reduces the problem to a single degree of freedom (SDOF)
system. Nonlinear static procedures use equivalent SDOF structural models and represent seismic ground motion with
response spectra. Story drifts and component actions are related subsequently to the global demand parameter by the
pushover or capacity curves that are the basis of the non-linear static procedures.
6.1 Lateral Load Patterns
In order to perform a pushover analysis for a MDOF system, a pattern of increasing lateral forces needs to be
applied to the mass points of the system. The purpose of this is to represent all forces which are produced when the
system is subjected to earthquake excitation. By incrementally applying this pattern up to and into the inelastic stage,
progressive yielding of the structural elements can be monitored. During the inelastic stage the system will experience a
loss of stiffness and a change in its vibration period. This can be seen in the force-deformation relationship of the system.
The choice of the load pattern to capture a dynamic phenomenon through a static analysis is of much importance because
it has been recognized, that it can affect the results significantly. It has been agreed that the application of a single load
pattern would not be able to capture the dynamic response of any system due to a seismic event. This is reflected in
FEMA 356 and EC8 which recommend that at least two load patterns should be used in order to envelope the responses.
For pushover analyses the following load patterns have been used:
6.1.1 Equivalent lateral force (ELF) distribution:
2
2
1
.i i
i n
i i
i
b
W h
F V
W h
=
=
∑
Where Wi is the weight of the ‘i’ storey, and hi is the height of the ‘i’ storey, n is the total number of the storeys,
and Vb is the base shear
6.1.2 Triangular distribution
1
.i i
i bn
i i
i
Wh
F V
Wh
=
=
∑
6.1.3 Uniform Load distribution
i i
F W=
Fig.6: Different Lateral Load Pattern Along Height of Chimney

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7. 3D PUSHOVER ANALYSIS
In traditional pushover analysis, only the distribution of forces equivalent to those produced by earthquake
action in one direction is applied to the structure to represent the inertia forces experienced during the earthquake. This
procedure has provided insightful results for symmetric structures [6]
. But for asymmetric structures, pushover analysis
considering two directional earthquake inputs may be more appropriate, since the structure has different dynamic
properties in each direction. There is very little research focusing on improving the pushover analysis by considering 3-D
interaction effects, so the need for developing improved pushover analysis procedures considering 3-D interaction effects
for asymmetric structures is evident. In this study, consider a 3-D pushover analysis [6]
method which is already stated by
Wei Huang and Philip.L.Gould is to extend the traditional 2-D pushover procedure for the analysis of the asymmetric
Tüpras stack. The validity of the proposed method will be assessed by comparing the results with those from an “exact”
3-D step-by-step nonlinear dynamic analysis. The basic procedure is as follows:
Fig.7: 3D Pushover Load Pattern
1. Carry out a 3-D modal analysis using a FE model with the initial geometry and material properties. Obtain the natural
frequencies and fundamental modes for each direction.
2. Now, two types of lateral load patterns may be selected based on the patterns specified in the pushover analysis, one
type is a fundamental mode, usually Mode 1, and the other type may be one of the patterns.
3. For a lateral load pattern other than the fundamental mode patterns, apply the lateral forces to the structure, and
perform the pushover analysis for each direction. Plot the pushover curves in the spectral displacement vs. spectral
acceleration domain (ADRS). The equivalent SDF (single degree of freedom) period for the lateral load pattern in
each direction is then taken as the initial secant for the pushover curve before yielding.
4. For each direction, given the fundamental frequencies for the fundamental modes and equivalent SDF system
frequencies for the other load patterns, locate the corresponding spectral acceleration values from the response
spectrum in each direction.
5. Apply two directional lateral forces for each load pattern to the structure as illustrated in fig.7.
6. For each load pattern, perform the 3-D pushover analysis using the lateral load forces described in Step 5, and plot the
capacity curve for each direction.
7. Compare the capacity curves with the smoothed mean demand curves of the spectra for each direction to obtain the
target displacement of the structure for the various load patterns.
8. Determine the response over the height of the structure using the 3-D pushover analysis results for the selected
patterns at the respective target displacements.
The validity of this method will be assessed by comparing the results with a 3-D nonlinear dynamic analysis of the
stack [6]
8. RESULT AND DISCUSSION
The modal analyses of chimney with and without opening were conducted in the software and the corresponding
time period and mode shapes are obtained as shown in Table 1. Third mode shape of chimney with opening is shown in

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fig.8. Time period of vibration is reduced when a chimney had an opening and maximum frequency is obtained at the
third mode of chimney with opening which is vulnerable to chimney and it may cause collapse of the structure.
Table.1: Results obtained from Modal analysis
Chimney Modes Time period in (sec) Frequency (cyc/sec)
Without opening
1 0.9953 1.005
2 0.9953 1.005
3 0.1340 7.463
With opening
1 0.5656 1.768
2 0.5503 1.817
3 0.1120 8.929
Fig.8: 3rd
Mode Shape
The non linear dynamic analysis were conduted on the chimney with and without opening in the SAP 2000
software and the obtained results were compared with the result obtained from the same done in the ABACUS software
[6]
. Thus validate the results obtained from the SAP software as shown in Table 2.
Table.2: Deformation of Chimney by Non-linear Dynamic Analysis
Chimney
Deformation from SAP
2000(mm)
Deformation from
ABACUS(mm)
without opening 591 601
with opening 516 525
The 2D and 3D pushover analysis were also conducted to the same material model of chimney with and without
opening in the SAP software. Percentane of error was computed by comparing the results with the results obtained from
the 3D step by step nonlinear dynamic analysis. ELF and triangular distribution show less percentage of error compared
with uniform distribution. The deformation and its percentage of error is tabulated in Table 3. But incase of pushover
analysis over estimate the displacement than that of obtained from the nonlinear dynamic analysis. Non linear dynamic
analysis(NLDA) is the benchmark of the seismic analysis which gives most accurate result. Pushover analysis taken less
time consuming than that of nonlinear dynamic analysis. That’s why it gives immediate reults while nonlinear dynamic
analysis was take more time consuming. The variation of deformation along the height of the chimney with different
pushover lateral load case as shown in graph, fig.9.

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Fig.9: Deformation Along the Height of Chimney for Different Load Pattern
Table.3: Deformation at the Top of Chimney for Different Lateral Load
Displacement in mm error in %
NLDA 516
3D ELF 547 -6
3D Triangle 546 -6
3D Uniform 648 -26
2D ELF 480 7
2D Triangle 472 9
2D Uniform 316 39
Fig.10: Stress Formation in Chimney Shell

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9. CONCLUSION
A chimney structure which provides ventilation for smoke to outside atmosphere. This work presents a
numerical procedure to simulate the non linear analysis of the Reinforced Concrete Chimnney subjected to strong
ground motion. A pushover analysis procedure was done and the results were compared with those from a nonlinear
dynamic analysis. Based on these analyses, some of the conclusions are summarized as follows:
• For the target displacement of the model without the opening, the error from the uniform distribution was the largest
than that of ELF distribution and triangle distribution which are provided somewhat better estimates, while the
uniform distribution underestimated the total response by up to 30%.
• The ELF distribution and triangle distribution gave similar estimates.
• Compared to a 2-D pushover analysis, the new 3-D pushover analysis procedure provides a better estimation for
target displacements.
• For the 3-D pushover analysis on the model with the opening, the failure displacements predicted using different
lateral patterns were in an acceptable range.
• The 3-D nonlinear dynamic analysis results confirmed that the Chimney could not survive the earthquake inputs
under both directions.
This thesis was proposed to examine the influence of chimney under nonlinear analysis such as time history and
pushover analysis considering the seismic effect only. Sometimes wind will be critical to the chimney than that of
seismic effect. The further scope in this thesis work is to conduct wind analysis on chimney and compare with seismic
analysis to find out which is critical to the chimney.
10. ACKNOWLEDGEMENT
The authors would like to thank all the staffs of the civil department of SNGCE and friends for their valuable
suggestions and feedback. We also like to thank all the authors of the papers which we have referred to get a clear idea
regarding our work.
REFERENCES
Journal Papers
[1] M.R.Tabeshpour (2010), “Nonlinear dynamic analysis of chimney like towers”, Asian journal of civil
engineering, Vol.13, No.1 pp 97-112
[2] Wei Huang and Philip.L.Gould (2007), “3-D pushover analysis of a collapsed reinforced concrete chimney”,
Science direct, finite element in analysis and design, Vol.43, pp 879-887.
[3] Jhon.L.Wilson (2002), “Earthquake response of tall reinforced concrete chimneys”, Engineering structures,
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[4] M.G.Shaikh and H.A.M.I.Khan (2010), “Governing loads for design of a tall RC chimney”, IOSR-JMCE, ISSN:
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[11] Chopra, A.K. and Goel, R.K., “A Modal Pushover Analysis Procedure for Estimating Seismic Demands for
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