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DESIGN ANALYSIS OF UNBRACED FRAME USING ANSYS
FARHANA BINTI ABDUL HALIM
Thesis submitted in partial fulfillment of the
fe4üifefiient föf the a.VâfdS of the degro of
Bachelor of Civil Engineering
Faculty Of Civil Engineering And Earth Resources
Uniiiersiti Mâiaysiä PähätIg
NOVEMBER 2010
ABSTRACT
Recently, the application of unbraced steel frame in building construction
arises rapidly nowadays, various researches has been carried out to study the behavior
of this type of frame. The tested frame structure was designed using available
recommendation in the existing literature. Finite Element Analysis is devejoped to
stimulate unbraced frame's deflection behavior. The result is compared with the range
of value of several goodness-of-fit measures which are provided from random output
parameter in each response surface set. Polynomial mathematical model generated
using various combination parameters using multiple regression analysis were found
to be statistically significant. Parametric study using response surface methodology
through finite element analysis may form efficient approximation to immediate
deflection. It shows a comparable result and thus, this program is expected applicable.
VI
ABSTRAK
Dewasa mi, aplikasi kerangka tidak dirembat sebagai struktur utama bangunan
semakin pesat membangun dari semasa ke semasa, pelbagai kajian telah dilakukan
bagi mengkaji sifat-sifat kerangkajenis mi. Ujian terhadap struktur kerangka mi telah
diambil dari struktur yang direka bentuk oleh kajian literasi sebelum ini Kaedah
Elemen Unsur Terhingga telah dibangunkan untuk meransang sifat lenturan kerangka
tidak dirembat. Keputusannya akan dibandingkan dengan anggaran nilai dan beberapa
ukuran 'goodness-of-fit' yang mana terhasil dari hasil keluaran parameter yang rawak
di setiap set tindakbalas permukaan. Model matematik polinoniial telah dihasilkan
oleh pelbagai gabungan parameter menggunakan analisis kemerosotan pelbagai yang
dijumpai dan menjadi statistik pelting. Kajian parametrik menggunakan kaedah
tindakbalas permukaan melalui elemen unsure terhingga boleh menghasilkan
pesongan yang hampir benar. mi menunjukkan perbandingan antara hasil keputusan
dan program mi dianggap boleh ditenima guna.
VII
TABLE OF CONTENT
CHAPTER ITEM PAGE
TITLE j
DECLARATION ii
DEDICATION iv
ACKNOWLEDGEMENT v
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENT viii
LIST OF TABLES xiii
LIST OF FIGURES xiv
1 INTRODUCTION 1
1.1 General i 1.2 Problem Statement 2
VIII
Ix
1.3 Objective 3
1.4 Scope Of Work
3
2 LITERATURE REVIEW 4
2.1 Introduction 4
2.2 Frame 5
2.2.1 Braced Frame 5
2.2.2 Steel Frame 6
2.3 Buckling Mode 7
2.3.1 Buckling Mode For Unbraced Frame 7
2.4 Loads On Structure JCS 8
2.4.1 Static Force
9
2.4.2 Wind Loads 9
2.5 Finite Element Analysis 10
2.5.1 History Of Finite Eletñeñt Analysis 11
How Does Finite EJ pAt Analysis Vprk
12
2.5.3 Meshing 13
2.5.4 Advantages Of Finite Element Analysis 14
2.6 Ansys Niametñc Design Language 14
2..l Benefit Of Parametric Design Analysis 15
16
17
18
18
18
19
20
22
22
x
3 METHODOLOGY
3.1 Introduction
3.2 Geometry
3.3 Preprocessing
3.3.1 Introduction
3.3.2 MOklIIij
3.3.3 Define The Element Type
3.3.4 Define Real Constant
3.3.5 Deflti Mäteiiâl P Opthiá
3.3.6 Define Section
3.3.7 Meshing
3.4 Solution
3.4.1 Introduction
3.4.2 Analysis Type
3.4.3 Dèfiiie FeCônstraints
3.4.4 Define Frame Load
3.4.5 Apply The Solution
3.5 Post-Pessing
3.5.1 Introduction
3.5.2 Reaction Forces
3.5.3 M ei Forces Aiid tEesses
16
24
26
2
26
26
27
30
30
30
30
31
A
4
3.5.4 Member Displacement And Rotational 31
RESULT AND ANALYSIS 34
4.1 Introduction 34
4.2 Unbràced Frame Stture 35
4.3 Probabilistic Model Information 36
4.3.1 Random Input Variables 36
4.3.2 Young Modulus 37
4.3.3 Poisson's Ratio 38
4.3.4 Pressure 39
4.3.5 Läd 40
4.3.6 Real Constant 41
4.4 Probabilistic Analysis Summary 42
4.5 Ressiii iii iysis &àiiiT.ài 44
4.6 Probabilistic Analysis Results 46
4.6.1 Sample History Plots 48
5 CONCLUSION AND RECOMMENDATION 49
5.1 Conclusion 50
5.2 Re w. -diradn&ti 51
XII
REFERENCES 52
APPENDIX 54
LIST OF TABLES
NO. TITLE PAGE
3.1 Keypoint data 19
3.2 Real constant data 21
3.3 Section definitions 23
3.4 Line attributes assignments 25
4.1 Random Input Variables Specifications 37
4.2 Specifications for Response Surface Method Analysis 43
4.3 Specifications for the Design of Experiment Levels 44
4.4 Listing of the Results for Solution Set 45
4.5 Goodness-Of-Fit Measure 48
XII,
NO TITLE
2.1 Critical buckling mode for an unbraced frame
2.2 Typical types of loading condition
2.3 Finite Element Analysis on Slabs,
Beams and Columns
2.4 Mesh diagram on 2D model
3.1 Frame structure
3.2 Library of element type
3.3 Real constant for BEAM3
3.4 Beam tools
3.5 Line attributes
3.6 Apply U, ROT on keypoint
3.7 Apply pressure on beams selection window
3.8 ANSYS workspace window after the top
of the frame is selected for application
of a distributed load
3.9 Apply pressure on beams window
PAGE
7
8
11
13
17
20
21
23
25
27
28
29
29
LIST OF FIGURES
xiv
xv
3.10 Reaction solution window 31
3.11 List nodal solution window 32
3.12 Nodal solution table 33
4.1 Unbraced Frame Structure 35
4.2 PDF & CDF of Input Random Variable EX 38
4.2 PDF & CDF of Input Random Variable PRXY1 39
4.3 PDF & CDF of Input Random Variable PRES 1 40
4.4 PDF & CDF of Input Random Variable FX1 41
4.5 PDF & CDF of Input Random Variable RI 42
4.6 Sampled Values for Output Parameter
Maximum Deflection 49
4.7 Sampled Values for Output Parameter
Maximum VonMises Strain so
4.8 Sampled Values for Output Parameter
Maximum VonMises Stress 50
CHAPTER 1
INTRODUCTION
1.1 General
Recently, the need for structural rehabilitation of civil infrastructures all over
the world is well known and a great amount of research is going on this field. Every
time new technology will develop which are changes in the contributing factors to
structure such as increase in load requirement, corrosion deterioration to exposure to
aggressive environments, changes in functionality, potential damaged caused by
mechanical and environmental effects, increase in material strength and durability,
etc.
Many different methods are suitable for repair and strengthening, such as
additional reinforcement cover by concrete, external steel plate bonding, using of steel
material, etc. Nowadays, steel frame system with beams and columns is become the
conventional building structure in construction world. Structural design and structural
2
analysis are both of the criteria needed to create a structure that safely accomplish its
function in order to produce structures in a stability condition. In civil engineering
field, steel is widely used in building construction. Its popularity may be due to the
various sizes and the shape of steel sections to be used for various type of structures
such as small and the simple buildings as well as complicated infrastructures
construction. Generally, steel frame not is only design to sustain vertical loads but
also able to resist lateral loads.
In this research, Finite Element Method (FEM) models were used to stimulate
the behavior of the steel frame structure's ability using ANSYS 12.1 program. The
ANSYS was founded in 1970, develops and globally markets engineering simulation
software and technologies widely used by engineers and designers across a broad
spectrum of industries like civil and mechanical engineering. This program is capable
of predicting deflection and stress in concrete concepts and also includes model's
constitutive laws for concrete material, based on smeared crack concepts and for high
strength composite materials.
1.2 Problem Statement
Columns and beams which are in parts of frame structure are also known as
main components in building which have their own capability to support the load
from roof, floors and transfer it to lower level and foundation. Because of that, frame
structures must be designed well with appropriate calculation to make sure it can
support the loads so that it is safe for long period of time. In order to make the
calculation more easily but still in good design method of the structure, therefore
ANSYS Parametric Design Language is use to generate a new equation for
calculating the design of steel frame. The new equation is derived from parameters
which are depends on loads, length of span, Poisonn's ratio, pressure on structure and
so on. Therefore, this is the necessary of this research.
3
1.3 Objective
The objectives of this research are following:
• To present software analysis with analytical results.
• Generate a new equation for frame structure by proving the parameters
in ANSYS Parametric Design Language (APDL) using ANSYS
program.
• To study the response and behavior of unbraced frame structure
through a series of analysis under different load and dimension case.
1.4 Scope of Work
These researches are mainly focused on the design of steel frame structures by
using British Standard and use the data to generate the new equation by proving the
parameters in ANSYS. In order to achieve the objectives of the researches, there are
few researches scope is necessary to be followed. Study the types of steel design
frames and the characteristics of the structure.
Explore the ANSYS program by learning how to use the programming by
using tutorial from internet. Practicing of tutorials can helps to solve problem when
running the real models. Model of columns are designed using ANSYS parametric
design language (APDL). Finite Element Analysis is using to calculate the parameters
which the parameters must success to get new equation as mention in objectives.
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
In recent years, numbers of studies have been made in designing the unbraced
multi-storey steel frames and the development in this type is still continued until now.
Many researchers try to present the easier and simple way for example comes out with
software such as ANSYS, Visual Basic and so on for determination of the section
sizes which meet the principals and limitations as stated in BS 5950-1:2000.
Apart from that, several methods were introduced to fulfill the criteria which
are Wind-Moment Method and Merchant-Rankine Method. However, the
effectiveness of these methods is still in question because the second order effect due
to sway does not taking into account though sway deflection give the major effect in
5
the construction of frames. It is irrelevant to attempt final design that exceeds the
sway limitation because sway does not affect the frame structure. Therefore, a
simplified method which meets the sway deflection criterion is introduced and the
method is called as Direct Design Method.
This method does not stand alone. A supporting computer program should be
established to help the researchers reducing the difficulty when designing the frame
structure. The new software among students in Malaysia that can be used together to
compared with manual calculation is ANSYS 12.1. The establishment of this
computer program actually can help us to modify the structure's design and more easy
if it does not meet the specification as stated in BS5950-1:2000.
2.2 Frame
Frame is a structure made up from columns and beams that connected to each
others at a joints. It can be classified into two types which are braced frame and
unbraced frame. The behavior of these two frames is different to each other when
subjected to the lateral loadings.
2.2.1 Braced frame
Braced frame is a frame that has been supported by a bracing system to
prevent it from sway when subjected by lateral loading to meet the requirement. The
installation of bracing system had provided more stability to the system because it can
resist the lateral loadings from winds and earthquake or in other words, lateral
loadings did not taken by the column and beam (Schodek, 2004). For this type of
6
frame, it only took vertical loadings from dead load and live load. Figure 2.1 shows
the bracing system used in steel frame construction.
2.2.2 Steel frame
The complexity of analyzing and designing of steel frames have decreased the
use of steel material in building construction. However, many approaches have been
made to study the feasibility of steel frames structure since 1856 by Besemer's
process. Nowadays, many tall building is used the steel frame structure.
Frame structure can be classified into two types, braced and unbraced frames.
Braced frame which consist of bracing system that will provide lateral stability to the
structure, so, it will be resistance to the lateral effect. On the other hand, unbraced
frame does not provided with the bracing system and will easily sway if the lateral
loads act on it.
The lateral loading normally cause by the wind forces or earthquake. When
these lateral forces acting against the structure, it will induce overturning moment and
should be balanced by the internal moment developed by the members. Therefore, the
frames should be design properly to ensure that it will be able to carry both lateral and
vertical loads.
8
2.4 Loads On Structure
There are many types of loading that can affect the behavior of the structures.
When designing a building, those loadings should be taken into consideration because
if it is miscalculate, absolute failure will occur in the structure. Figure below
illustrates and describing the types of loads that must be considered (Atiliana, 2009).
Loads
Static force Dynamic force
Live Dead loads Force due to continuous Impact (eg: ioads(movable) (fixed) settlements, etc. blast)
ckcupazicy Self-weight of Internal forces structure
EJlrironmentaj g' Wind forces L elements
Figure 2.2 Typical types of loading condition
9
2.4.1 Static force
The static forces consist of live load, dead load and forces due to settlement or
thermal effect. These types of load are typically being considered when designing
every structure.
Live loads are forces that act vertically downward onto the structure but it is
not fixed in character. The value can change anytime and movable. Occupancy and
environmental can be described as live loads. Occupancy loads include furniture,
stored material, human or any other similar material.
On the other hand, dead loads are non-movable loads and fixed in behavior.
There are several items that can be marks as dead loads and those are self-weight of
the structure, slab, bricks, mechanical equipment or any other building.
2.4.2 Wind loads
This type of loading is one of the most important characteristic especially for
multi-storey buildings because it can cause sway to the structure. As the wind move, it
will deflect or stop when something blocking its path. This phenomenon will cause
the kinematic energy transform into potential energy. This potential energy is called
force that induced horizontally onto the structure. Therefore, high-rise building will
be design properly to resist this force.
10
2.5 Finite Element Analysis
Finite element analysis (FEA) is consists of computer model of a material or
design that is stressed and analyzed for specific results. It is used in new product design,
and existing product refinement. In other words, FEA is a numerical method to find out
an approximate solution for variables in a problem which is difficult to obtain
analytically. The calculation of potential design changes such as temperature, buckling
and deflection are usually complicated. A numerical method that is able to solve these
engineering problems id the finite element analysis. In case of structural models failure,
FEA may used to help determine the design modifications to meet the new condition.
The concept of the finite element analysis is solving a continuum by a discrete
model. It is done by dividing the problem into small several elements. Each element is in
simple geometry and this is easier to be analyzed than the actual problem or the real
structure. Each element is then applied with known physical laws. The equation which is
formed by each element or parameters then will combined to form a global equation. The
new equation can be used to solve the field variables such as displacement, buckling,
temperature and so on.
12
The aeronautics, automotive, defense, and nuclear industries had started using the
finite element application since early 70's. However, this is limited to expensive
mainframe computer. Zienkiewicz and Cheung is the important person in developing the
finite element technology at that time. But later, Hinton and Crisfield carried out the
finite element into modeling and solution of nonlinear problems (Reddy, 1993).
With the development of the CAE technology, engineering drawing can be
produced. Besides, the analysis can be carried out and also the Finite element modeling
can be done. The finite element becomes more and more important today which can
simplify and solves various types of engineering problems.
2.5.2 How Does Finite Element Analysis Work
FEA uses a complex system of points called nodes which make a grid called
a mesh. This mesh is programmed to contain the material and structural properties
which define how the structure will react to certain loading conditions. Nodes are
assigned at a certain density throughout the material depending on the anticipated
stress levels of a particular area. Regions which will receive large amounts of stress
usually have a higher node density than those which experience little or no stress.
Points of interest may consist of: fracture point of previously tested material, fillets,
corners, complex detail, and high stress areas. The mesh acts like a spider web in that
from each node, there extends a mesh element to each of the adjacent nodes. This web
of vectors is what carries the material properties to the object, creating many elements
(Peter Widas, 1997).
13
Figure 2.4 Mesh diagram on 2D model
The powerful design tool has significantly improved both the standard of
engineering designs and the methodology of the design process in many industrial
applications. The FES has substantially decreased the time to take products from concept
to the production line. It is primarily through improved initial increased accuracy,
enhanced design and better insight into critical design parameters, fewer hardware
prototypes, a faster and less expensive design cycle, increased productivity (Peter
Widas, 1997).
2.5.3 Meshing
The important requirement of the FEM is the need to split the solution domain
(model geometry) into simply shaped subdomains called 'finite elements'. This is a
discretization process commonly called meshing and element are called finite because of
their finite, rather than infinitesimally small size having infinite numbers of degree of
freedom. Thus the continuous model with an infinite number of degrees of freedom
(DOF) is approximately by a discretized FE model with a finite DOF. This allows the
reasonably simple polynomial functions to be used to approximate the field variables in
each element. Meshing the model geometry also discretized the original continuous
15
APDL are can be known as tools to help designers perform parametric analyses in
which simulation software automatically solves for entire ranges of specified variables
and generates displays that enable users to readily spot trends and identify an optimal
design. Parametric analysis can guide the product development process to a design
configuration that can save the time compared if by individual analyses were manual
performed. The period of time to set up is required in APDL which a model can increase
significantly with the complexity of the geometry.
ANSYS Workbench platform is one of the most efficient ways of deal with
geometric parameters which enables parameters of the CAD model to be driven directly
from simulation.
2.6.1 Benefit of parametric design analysis
Parametric analysis is an excellent to get accurate information about the
influence of all parameters on the design objectives, such as system performance with
respect to stress, loading, deflection of structure and other variables. With this
information, the design team can make informed decisions throughout product
development. In addition, the design teams also can response quickly to any
modification due to external constraints for example, manufacturing (Thieffry, 2008).
CHAPTER 3
METHODOLOGY
3.1 Introduction
Nowadays, research undertaken the finite element analysis was proven to be a
successful tool in predicting the behavior of frame structures. From the previous
research, finite element analysis provides only approximate solution and the results
are not fully can be used in real design with reasonable confidence. This is because
there are various ways to perform the finite element process such as meshing of
structure which varied analysis results may be obtained. Therefore, the comparison
between manual calculations and finite element analysis is needed to determine their
efficiency and reability.