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2014
Department of Civil Engineering
Jorhat Engineering College
DEPARTMENTOFCIVIL ENGINEERING
JORHAT ENGINEERING COLLEGE
JORHAT -785007
REPORT ON
COMPUTATIONAL LABORATORY
Submitted by
Azaz Ahmed
C-13/ME-04
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CHAPTER NO.1
ANSYS
ANSYS is a general purpose finite element modeling package for numerically solving a
variety of mechanical problems.The problems are of structural analysis, heat transfer, fluid
problems, acoustic and electromagnetism.It has two basic levels- Begin level and Processor
level
From the begin level we can enter one of the ANSYS processor. A processor is a collection
of functions and routines to serve specific purposes. The database for any file assignment can
be change from the begin level. The processors most frequently used are: Pre-processor,
Processor, General postprocessor.
The pre-processor contains commands needed to build a model. The processor has the
commands to provide boundary conditions and loads. Once all the information is made
available in the processor, it solves for nodal solutions. The general post-processor has the
command that allows us to list and display results of an analysis. There are other processors
such as time-history processor and design optimization processor which also perform other
additional tasks.
Problem Description
A concrete chimney of height 80 m with the external diameter of the shaft being 4 m at top
and 5 m at bottom is required in a place where the wind intensity is 1.5 kN/m2.Temperature
difference between the inside and outside of the shaft is 75C.
Adopting M-25 grade concrete mix and for reinforcing steel Fe=415 Grade
Process Definition
Chimneys are designed to withstand the following
1) Self weight2) Wind pressure3) Temperature stresses
The wind pressure is calculated as per IS 875 part III, and temperature stresses are given as
differences in temperature value between the inner and outer surfaces of the chimneys. The
wind pressure as calculated using IS 875 part III is 49kN/m2.
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The chimney is modeled in ANSYS as per the description given in the problem with the 3D
finite strain element under Solid-shell element type. In order to analyze the structure with
respect to wind pressure and seismic loads, a linear elastic isotropic structural material
model is taken and to analyze it due temperature difference, an isotropic conductive thermal
material model is chosen. After meshing, the model is solved for statical and modal analysis.
The results are obtained as coloured contour plots of nodal solutions.
Results
Fig.Initial model of chimney for analysis
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Fig.Resultant deformations due wind loads
w
Fig.Resultant stress intensity due wind loads
Table.Modal frequency
Mode No. Frequency Mode No. Frequency
1 0.49164 6 6.9838
2 0.49164 7 7.6181
3 2.6462 8 10.817
4 2.6462 9 13.235
5 6.9838 10 13.235
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Fig.Cross Section of chimney showing distribution of temperature
Fig.Cross Section of chimney showing stress intensity
The maximum displacement due wind load is 0.002276 m at the topmost portion
The maximum stress intensity due to wind load is found to be 64939.9 kN/m2
The maximum stress intensity due temperature difference in surfaces is obtained as 2.97 x
106kN/m2
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To obtain the frequencies and vibration mode shapes solution routines are used which
calculate the required eigen values and eigen vectors and mass matrix to a reduced form. In
the direct integration an unconditionally stable integration scheme is used, which also
operates on the original structure stiffness matrix and mass matrix. This way the program
operation and necessary input data for dynamic analysis is a simple addition to what is
needed for a static analysis.
Problem description
An industrial steel building is to be designed using SAP2000 and analyzed for wind loads,
response spectrum and crane loading. After analysis, the safe performance of the building is
to be ensured by providing or changing frame sections.
Process definition
The industrial building is to be designed consisting of the 3D frame with 2D trusses on the
top interconnected with purlins. Lacings and bracings are provided for increasing the stability
and improving the torsional resistance performance. Section properties of frames can be
defined manually or using auto select feature.
Wind load is defined on the structure as per IS 875 part III with calculated windward and
leeward coefficients and the known dimensions of the structure.
Response Spectrum analysis is done as per IS 1893 part I with a damping coefficient of 0.05.
Crane loading is considered and the whole structure is analyzed for the worst loading case
scenario.
Deformed shape for modal cases and load cases are displayed. Modal analysis data is
interpreted (time period and frequency). Check for structural failure of sections is done and
weak members are identified. Then we allow the software to select a suitable section to so as
to prevent failure and a final design check is done.
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Fig.The nodal diagram of the building
Results
Case I: Wind Loading
Table: Wind load data
Load
Pattern Angle WW Cp LW Cp
Wind
Speed
Terrain
Category
Structure
Class k1 k3
Wind1 0 0.4 0.7 50 1 A 1 1
Fig.Contour plot showing deformations in the structure due to winds loads
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Fig.Stress Max. due to wind loading
Case 2: Modal Analysis
Fig.Deformation of building in the first mode ofvibration
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Table: Modal periods and frequencies
Mode Time period (seconds) Frequency
1 0.076731 13.033
2 0.056331 17.7523 0.054245 18.435
Case 3: Response spectrum analysis
Fig.Base reactions due under the defined response spectrum
Table: Maximum base reactions
OutputCase GlobalFX GlobalFY GlobalFZ GlobalMX GlobalMY GlobalMZ
Text kN kN kN kN-m kN-m kN-m
RS 211.322 15.094 4.779 97.3153 1042.9072 1563.5221
Case 4: Crane loading of 100 kN
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Table: Modal participation factors
Period UX UY UZ RX RY RZ
Moda
l
Mass
ModalStiffnes
s
Sec kN-m kN-m kN-m kN-m kN-m kN-m
kN-
m-s2 kN-m
0.4018
0
-
10.725
5
0.35338
7
0.40783
1 -2.203903 -8.45929
-
34.67
1 1 244.53035
0.23592 -0.0121
1.028688 -9.99417
57.791388
59.75187
-
2.8177 1 709.27869
Fig.Identification of flexural failures obtained by design check
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Fig.The design sections are further altered manually to obtain least failure condition of
sections
CHAPTER NO. 3
ETABS
ETABS is a sophisticated, yet easy to use, special purpose analysis and design program
developed specifically for building systems. ETABS features an intuitive and powerful
graphical interface coupled with unmatched modelling, analytical, and design procedures, all
integrated using a common database. Although quick and easy for simple structures, ETABS
can also handle the largest and most complex building models, including a wide range of
geometrical nonlinear behaviours, making it the tool of choice for structural engineers in the
building industry The accuracy of analytical modelling of complex Wall Systems has always
been of concern to the Structural Engineer. The computer models of these systems are usually
idealized as line elements instead of continuum elements. Single walls are modelled as
cantilevers and walls with openings are modelled as pier and spandrel systems. For simple
systems, where lines of stiffness can be defined, these models can give a reasonable result.
However, it has always been recognized that a continuum model based upon the finite
element method is more appropriate and desirable.
Nevertheless this option has been impractical for the Structural Engineer to use in practice
primarily because such models have traditionally been costly to create, but more importantly,
they do not produce information that is directly useable by the Structural Engineer. However,
new developments in ETABS using object based modeling of simple and complex wall
systems, in an integrated single interface environment, has made it very practical for
Structural Engineers to use finite element models routinely in their practice
Problem Description
A simple 3-D building is to be analysed and designed using ETABS.
Process definition
First we have to select an in-built model of the desired structure. Or we can select only a grid
pattern and draw the nodes and elements required for the structure. After completion of the
model, we need to define all the section properties of the elements. We can either select the
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section property of the element (beam, column etc) manually or the software auto-selects for
itself. We then assign live load of 1.5kN on the roof and analysing the model we obtain the
deformed shape for modal case or load case (dead and live). Concrete design for the frame is
executed and minimum reinforcements for beams and columns are obtained. Area of shear
reinforcements required is also displayed. We can also go further for detailing in case of an
earthquake resistant buildings.
Results:-
Fig: planFig: front elevation
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Fig: reinforcement area
Fig: mode 1Fig: mode 2
Fig: mode 3
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Fig: shear reinforcements
Fig: dead load deformation
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Inference
With the help of ETABS we can analyze more sophisticated structures like steel deck,
staggered truss, flat slabs, flat slab with perimeter beams, waffle slabs, two-way or ribbed
slabs. The disadvantage of ETABS that we have inferred is that no reinforcement can be
provided manually for area sections (shell type). But the disadvantage is outweighed by the
fact that ductile detailing can be done here.
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CHAPTER NO. 4
COMPARISON BETWEEN SAP2000 AND ETABS
Table: Relative comparison of SAP2000 and ETABS
Sl no. SAP2000 ETABS
1 Primarily used for gravity analysis and
design
Mostly utilized for handling large scale
seismic or wind projects including those
that involve Non-linear modeling
2 This tool is often utilised for smaller
structures or portions of a larger
structure
It allows more simplified modelling of
the entire structures, enabling the
designer to focus on macroscopic
performance target
3 It can also be used for wind analysis and
for more simplified design procedures.
However it will take more data post-
processing to retrieve the desired results
for storey drift, storey shear, base shearetc.
It is well equipped to handle simplified
lateral procedures, push-over analysis,
response spectrum analysis and response
history analysis
4 It lacks some of the simplicity that
ETABS has, such as discretizing the
structure into macroscopic elements
It has a more user-friendly interface
5 In SAP proper detailing cannot be done Detailing can be done
6 Since it is basically used for gravity
analysis design of walls are not
considered
Since it is used for seismic analysis
predefined walls are available on its
interface and can be designed.