computational laboratory report

8/12/2019 Computational laboratory report

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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.

computational laboratory report

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