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CHAPTER I
INTRODUCTION
1.1 Self Balancing Testing Frame-400KN
Steel structures and steel truss is mostly used in civil engineering to withstand the load
in bridges and factory roof etc. The design calculations are based on readily available
data that has been provided in the steel tables and graphs. But once the truss is
fabricated there was no way to actually test its reliability. The testing of component was
also not possible till universal testing frame technique came into existence. This
frame provides facility to check the performance of truss up to a load of 400kN. It also
provides facility to analysis the various components at 1:1 scale, thus facilitates the
designers to satisfy their calculation in accordance with the requirement of actual
location.
1.2 Versatile Design
This Universal Testing Frame consist of double frame which provides more stability
to the truss modes that is being tested moreover the intermediate space to test the
specimen that all longer in dimension than the frame itself.
1.3 Easy Assembly & Erection
This Universal Testing Frame is collapsible and it can be dismantled and erected
wherever required. Therefore it can be transported to any place easily.
1.4 Manufactured by local material
The materials used in the universal testing frame are generally available in local
market and need no import or special specification. Therefore it is economical. Theerection and assembly etc. does not require very special skill. It can be easily done with
the help of skilled persons those are easily available at factory sites. The erection is also
possible with the help of chain pulley blocks.
The foundation needed for the universal testing frame is also very simple due to fact
that there are not point load on the foundation directly. We get a distributed load
through the frame. Therefore it facilitates the testing procedures immediately after its
assembly without demanding any complicated fabrication.
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1.5 Facility of Direct Analysis
This system provides almost similar conditions that are expected on the place of
erection of the truss so we can analysis the model for the following structural elements
present in the structure.(i) Tension element in the member
(ii) Compression element in the member
(iii) Flexural element in the member
(iv) Tortional element in the member.
1.6 It is portable too
It can be easily shifted or carried along from site to site. Thus we can easily use it for
consultancy and commercial purpose. In this manner this frame can be used for
modifying the existing truss or structure because we can easily make a model on site
and put it under the test to satisfy the requirement. It will save lot of time, money and
manpower.
1.7 Need of Loading Frame
Though there are various methods of design of structure available which fulfill the
above criteria yet there is need of some practical knowledge that how a component of a
structure behave under the application of load. One can easily identified the end
reaction of beam or trusses or the forces acting on the two when subjected to certainexternal forces. But it is difficult to imagine the actual behaviour of a structural
component due to application of load. Thus this load bearing frame prove to be an
important tool to enhance the version of a structural designer towards the structural
behaviour of a member because of external forces applied over it.
For example, if a truck runs into a bridge composed of plate girders it would probably
bend the steel plate a little however a similar accident could cause the breaking of a
members in truss which may even lead to the failure of truss. Thus the above can be
easily computed with help of a load bearing frame. The truss of suitable scale may bemanufacture & with the help of the loading frame by providing loading one can check
the failure mode of a structure. This also play an important role in order to understand
the behaviour of structural material & their properties under certain loading conditions.
It can be used to check the different physical properties of a various structure such as
plate girder, trusses, beams, box type girder, column beams, gantry girders etc.
This universal testing frame is specially designed for large components in 1:1 scale.
The design with its double frame & intermediate space permits specimens longer than
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the size of frame opening to be investigated. In this way the possible uses of testing
frame are almost unlimited. The frame components are manufactured from ISMC 400.
The corners of frame are formed by joints rigid to bending each in fastened together
with a high strength bolts. The testing frame is delivered in pre-assembled modules; it is
assembled on site and placed on four adjustable vibration damping bearing. The
hydraulic ram system are available as accessories are on rollers and can be positioned
as require within frame. The various experiments that can be performed using this
frame are bending, loading, compression experiments on large girders beams, trusses
and other components from the area of civil engineering work. This could be used for a
Test force in central position maximum 300 kN and test force off centered 2x200 kN.
Another importance of this frame is for educational purpose. We know that a structuralmember subjected to compressive forces along its axis is termed as a compression
member. The behaviour of compression member differ based on their length, short &
stocky columns can be loaded up to their Yield stress and can attain their squash loads,
provided the element that makeup the cross section are prevented from buckling long
compression members behaves elastically and hence their strength may be predicted by
Eulers formula. Intermediate length compression member fail both by yielding and
buckling and hence their behaviour is inelastic. This can be easily understood with thehelp of the frame by providing the length of various compression members can one can
provide an easy practical example to the student of structural analysis. The buckling
behaviour of column under different end connections can be practically demonstrated to
the students of civil engineers.
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CHAPTER II
LITERATURE REVIEW
2.0 General
Structural design, though reasonably scientific is also a creative process. A structure is a
body composed of several structure elements so assembled that it can setup resistance
against deformation caused due to application of external forces. The various structural
elements that may be present in a structure are
(i) Tension member
(ii) Compression member
(iii) Flexural member(iv) Torsion member
(v) Foundation elements.
The structural analysis deals with the determination of internal stress in these members
as well as the determination of reaction components, when structure is subjected to
external forces. The method of analysis and principle involved in structural analysis do
not normally depend upon the type of material used for various structural components.
Structural design is taken up after the structural analysis has two aspects.(i) Functional Aspect
(ii) Strength Aspect
In the 1st aspect of design, the structure is design in such a way that it fulfills its
intended purpose during its intended lifetime and be adequately safe in terms of
strength, stability and structural integrity.
In the 2nd Aspect, the structure should be strong enough to resist against external forces
to which it is subjected during its entire period of service.In addition to above two aspects of design a structure should be economically viable in
terms of cost of construction and maintenance, aesthetic pleasing & environment
friendly. Safety is paramount importance in any structure and requires that the
possibility of collapse of structure (partial or total) is acceptable low not only under
normal expected loads (service loads) but also less frequent loads (such as due to EQ or
extreme winds) and accidental loads (blast, impact etc.). Collapse due to various
possibilities such as exposure to a load exceeding. The load bearing capacity
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overturning, sliding, buckling, fatigue, fracture etc should be prevented. The
progressive failure should also be minimized. The structure should also perform
satisfactorily under service loads without any discomfort to the user due to excessive
deflection, cracking, vibration etc. The serviceability should be fulfilled.
2.1 Steel
There is a definite need for engineers involved in structural steelwork to acquaint
themselves with some metallurgical aspects of steel. This will help the structural
engineer to understand ductile behaviour of steel under load, welding during fabrication
and erection and other important aspects of steel technology such as corrosion and fire
protection.
2.1.1 The crystal structure and the transformation of iron
Pure iron when heated from room temperature to its melting point undergoes several
crystalline transformations and exhibits two allotropic modifications such as:
(i) Body centered cubic crystal (bcc),
(ii) Face centered cubic crystal (fcc).
When iron changes from one modification to the other, it involves the latent heat of
transformation. If iron is heated steadily, the rise in temperature would be interrupted
when the transformation starts from one phase to the other and the temperature remainsconstant until the transformations are completed. The flat portion of the
heating/cooling curve in Fig. 5 exemplifies this. On cooling of molten iron to room
temperature, the transformations are reversed and almost at the same temperature when
heated as shown in Fig. 5. Iron up to a temperature of 910C remains as ferrite or -
iron with bcc crystalline structure. Iron is ferromagnetic at room temperature, its
magnetism decreases with increase in temperature and vanishes at about 768C called
the Curie point. The iron that exists between 768C and 910C is called the -ironwith a bccstructure. However, in the realm of metallurgy, this classification does not
have much significance.
Between 910C and 1400C, iron transforms itself into austeniteor -iron with
face centred cubic (fcc) structure. When temperature is further increased, austenite
reverts itself back to bcc structure, called the -ferrite. Iron becomes molten beyond
1539C. The different phases of iron are summarised in Table 1.
Table 2.1: Various forms of Iron
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Stable Temp. Range 0C Form of matter Phase Identification symbol
>2740 Gaseous Gas Gas
1539-2740 Liquid Liquid Liquid
1400-1539 Solid bcc -ferrite
910-1400 Solid fcc -austenite
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of steels. More amount of carbon causes problems during the welding process. Wewill see later, how both mechanical strength and ductility of steel could be improvedeven with low carbon content. The iron-carbon equilibrium diagram, which is a plot of
transformation of iron with respect to carbon content and temperature, is shown in Fig.7. This diagram is also called iron-iron carbide diagram. The important metallurgicalterms, used in the diagram, are presented below.
Table 2.2: Metallurgical terms of iron
2.1.3 The Structural Steels or ferrite Pearlite Steels
The iron-iron carbide portion of the phase diagram that is of interest to structural
engineers is shown in Fig. 8. Temp
0C
0.0
200
400
600
800
1000
1200
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
7230C
Austenite ()1147 C
Ferrite
Ferrite + Pearlite
Ferrite +
Austenite +
Weight % of Carbon
Hypo-Eutectoid
Eutectoid
Cementite + Pearlite
Hyper-Eutectoid
ba c d
i
j
k
l
Fig. 2.2: The Eutectoid section of the Iron Iron Carbon phase diagram
The phase diagram is divided into two parts called hypoeutectoid steels (steels with
carbon content to the left of eutectoid point [0.8% carbon]) and hyper eutectoid steels
7
NameMetallurgical
term% Carbon(max)
Crystal
structure
- Iron Ferrite 0.02 bcc
Fe3C Cementite 6.67 -
Ferrite + Cementitelaminar mixture Pearlite 0.80 (overall) -
- Iron Austenite2.0 (depends on
temperature) fcc
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which have carbon content to the right of the eutectoid point. It is seen from the figure
that iron containing very low percentage of carbon (0.002%) called very low carbon
steels will have 100% ferrite microstructure (grains or crystals of ferrite with irregular
boundaries) as shown in Fig. 9(a). Ferrite is soft and ductile with very low mechanical
strength. This microstructure at ambient temperature has a mixture of what is known as
pearlite and ferrite as can be seen in Fig. 8. Hence we see that ordinary structural
steels have a pearlite + ferrite microstructure. However, it is important to note that
steel of 0.20% carbon ends up in pearlite + ferrite microstructure, only when it is cooled
very slowly from higher temperature during manufacture. When the rate of cooling is
faster, the normal pearlite + ferrite microstructure may not form, instead some other
microstructure called bainite or martensite may result.
Fig.2.3: Microstructures of steels
(a) 100% Ferrite in extra low carbon steel, (b) Ferrite+Pearlite,
(c) 100% Pearlite in eutectoid steel, (d) Pearlite+Cementite in hyper-eutectoid steel
(Source: Thelning K.E., Steel and its heat treatment, Butterworths, 1984.)
Table 2.3: Chemical composition of some typical structural steels
Type of steel Designation
IS:
code C S Mn P Si Cr
Carbon
equivalent
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Standardstructural steel
Fe 410A 2062 0.23 .050 1.5 .050 - - SK 0.42
Fe 410B 2062 0.22.
045 1.5.
0450.4 - SK 0.41
Fe 410C 2062 0.20.
040 1.5.
0400.4 - K 0.39
Micro alloyedhigh strength
steel
Fe 440 8500 0.20 .050 1.3 .050.
45 0.40
Fe540 8500 0.20.
045 1.6.
045.
45 0.44
Fe590 8500 0.22.
045 1.8.
045.
45 0.48
K- killed steel SK- Semi Killed steel (Explained in section 6.2)
2.2 Mechanical Properties of Steel
2.2.1 Stress strain behaviour: Tensile test
The stress-strain curve for steel is generally obtained from tensile test on standard
specimens as shown in Fig.14.
P
P
r
t
d
Lc
Area=S0-
L
Fig.2.4: Standard tensile test specimen
The details of the specimen and the method of testing is elaborated in IS: 1608 (1995).
The important parameters are the gauge length Lc and the initial cross section area So.
The loads are applied through the threaded or shouldered ends. The initial gauge length
is taken as 5.65 (So)1/2 in the case of rectangular specimen and it is five times the
diameter in the case of circular specimen. A typical stress-strain curve of the tensile
test coupon is shown in Fig.15 in which a sharp change in yield point followed by
plastic strain is observed. When the specimen undergoes deformation after yielding,
Luders lines or Luders bands are observed on the surface of the specimen as shown in
Fig.16.
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of elasticity can be taken as 205,000 MPa and the tangent modus at the onset of strain
hardening is roughly 1/30th of that value or approximately 6700 MPa.
f
y
fy
0.2% strain
Uniform plastic
Fracture
Non-uniform plastic
Elastic
0.2% proof stress
Fig. 2.7: Stress strain curve for continuously yielding structural steels
2.2.2 Hardness
Hardness is regarded as the resistance of a material to indentations and scratching. This
is generally determined by forcing an indenter on to the surface. The resultant
deformation in steel is both elastic and plastic. There are several methods using which
the hardness of a metal could be found out. They basically differ in the form of the
indenter, which is used on to the surface. They are presented in Table 6.
Table 2.4: Hardness testing methods and their indenters
S.
No.
Hardness Testing
MethodIndenter
(a) Brinell hardness Steel ball
(b) Vickers hardness Square based diamond pyramids of 135 O included angle
(c) Rockwell hardness Diamond core with 120 O included angle
Note: Rockwell hardness testing is not normally used for structural steels.
Table 2.5: Hardness values of some metals
Metal
Brinell Hardness Number
(BHN)
Vickers Hardness Number
(VHN)
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Copper (annealed) 49 53
Brass (annealed) 65 70
Steel 150-190 157-190
2.2.3 Mechanical properties of structural steel
Table 8 summarises some of the important mechanical properties of steel produced in
India. In Table 8, the UTS represent the minimum guaranteed Ultimate Tensile
Strength at which the corresponding steel would fail.
Table 2.6: Mechanical properties of some typical structural steels
Type of
steelDesignation
UTS
(MPa)
Yield strength
(MPa) ElongationGauge
065.5 S
Charpy V -notch values
Joules (min)Thickness (mm)
40
Standardstructura
l steel
Fe 410A 410 250 240 230 23 27
Fe 410B 410 250 240 230 23 27
Fe 410C 410 250 240 230 23 27
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rolling has high strength but very poor ductility. This product needs to be annealed at
650-6800C in the hood annealing furnaces to improve its ductility.
Now-a-days hollow sections are also becoming very popular. Hollow sections i.e.
round; square or rectangular are produced either by seamless rolling process or by
fusion welding or electric resistance welding after cold forming of HRC/CRC into the
desired shape.
2.3 Tension Members
2.3.1 Introduction
Tension members are linear members in which axial forces act so as to elongate
(stretch) the member. A rope, for example, is a tension member. Tension members
carry loads most efficiently, since the entire cross section is subjected to uniformstress. Unlike compression members, they do not fail by buckling.
Stay cables
Stayed bridge
Suspenders
Suspension bridge
(b) Cable Supported Bridges
(a) Roof TrussTie
RafterSuspenders
(c) Suspended
Building
(d) Roof Purlin System
Purlin
Top chord
(e) Braced Frame
X bracings
Fig. 2.8: Tension Members in Structures
Tension members are also encountered as bracings used for the lateral load resistance.
In X type bracings [Fig.1 (e)] the member which is under tension, due to lateral loadacting in one direction, undergoes compressive force, when the direction of the lateral
load is changed and vice versa. Hence, such members may have to be designed to resist
tensile and compressive forces.
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The various factors which govern the failure of tension member are:
(i) The rupture of net section at end connections where tensile stresses are
largest.
(ii) The block shears failure at end connections.
(iii) The yield strength of cross section.
The 1st two failure modes will governs when the members are connected at ends by
bolts where as the yield strength of gross section may be the governing failure mode of
tension members connected by welding at ends. The above criteria can be easily
demonstrated with the help of using Universal testing frame under diff loading
conditions.Thus universal testing frame proves to be an important tool not only for the educational
purpose but it can also figure out the actual behavior of only structural component
underspecified loading condition. These properties of materials to be used for
construction of structure under the different loading conditions.
(a) (c)
(d) (e)
(b)
Fig. 2.9: Cross Sections of Tension Members
The tension members can have a variety of cross sections. The single angle and double
angle sections [Fig 2(a)] are used in light roof trusses as in industrial buildings. Thetension members in bridge trusses are made of channels or I sections, acting
individually or built-up [Figs. 2(c) and 2(d)]. The circular rods [Fig.2 (d)] are used in
bracings designed to resist loads in tension only. They buckle at very low compression
and are not considered effective. Steel wire ropes [Fig.2 (e)] are used as suspenders in
the cable suspended bridges and as main stays in the cable-stayed bridges.
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2.3.2 Behaviour of Tension Members
Since axially loaded tension members are subjected to uniform tensile stress, their load
deformation behaviour (Fig.3) is similar to the corresponding basic material stress
strain behaviour. Mild steel members (IS: 2062 & IS: 226) exhibit an elastic range (a-
b) ending at yielding (b). This is followed by yield plateau (b-c). In the Yield Plateau
the load remains constant as the elongation increases to nearly ten times the yield strain.
Under further stretching the material shows a smaller increase in tension with
elongation (c-d), compared to the elastic range. This range is referred to as the strain
hardening range. After reaching the ultimate load (d), the loading decreases as the
elongation increases (d-e) until rupture (e). High strength steel tension members do not
exhibit a well-defined yield point and a yield plateau (Fig.3). The 0.2% offset load, T,as shown in Fig. 3 is usually taken as the yield point in such cases.
T
a
b c
de
0.2%
Fig. 2.10: Load Elongation of Tension Members
The important factors to be considered while evaluating the tensile strength are the
reduction in strength due to bolt holes and due to eccentric application of loads through
gusset plates attached to one of the elements. The yield strength of the gross area or the
ultimate strength of the net area may govern the tensile strength. The effect of
connecting the end gusset plate to only one of the elements of the cross section was
empirically accounted for by the reduction in the effectiveness of the outstanding leg,
while calculating the net effective area.
2.4 Compression Members
2.4.1 Introduction
There are many types of compression members, the column being the best known. Top
chords of trusses, bracing members and compression flanges of built up beams and
rolled beams are all examples of compression elements. Columns are usually thought of
as straight vertical members whose lengths are considerably greater than their cross-
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sectional dimensions. An initially straight strut or column, compressed by gradually
increasing equal and opposite axial forces at the ends is considered first. Columns and
struts are termed long or short depending on their proneness to buckling. If the
strut is short, the applied forces will cause a compressive strain, which results in the
shortening of the strut in the direction of the applied forces. Under incremental loading,
this shortening continues until the column "squashes". However, if the strut is long,
similar axial shortening is observed only at the initial stages of incremental loading.
Thereafter, as the applied forces are increased in magnitude, the strut becomes
unstable and develops a deformation in a direction normal to the loading axis. (See
Fig. 1). The strut is in a buckled state.
Buckling behaviour is thus characterized by deformations developed in a direction (orplane) normal to that of the loading that produces it. When the applied loading is
increased, the buckling deformation also increases. Buckling occurs mainly in
members subjected to compressive forces. If the member has high bending stiffness, its
buckling resistance is high. Also, when the member length is increased, the buckling
resistance is decreased. Thus the buckling resistance is high when the member is
stocky (i.e. the member has a high bending stiffness and is short) conversely, the
buckling resistance is low when the member is slender.
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Fig. 2.11: Long column vs short column
17
A short column failsby compression yield
Buckledshape
A long column failsby predominant buckling
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2.4.2 Strength of Compression Members in Practice
The highly idealized straight form assumed for the struts considered so far cannot be
achieved in practice. Members are never perfectly straight; they can never be loaded
exactly at the centroid of the cross section. Deviations from the ideal elastic plastic
behaviour defined by Fig. 5 are encountered due to strain hardening at high strains and
the absence of clearly defined yield point. Moreover, residual stresses locked-in during
the process of rolling also provide an added complexity.
Thus the three components, which contribute to a reduction in the actual strength of
columns (compared with the predictions from the ideal column curve) are:
(i) Initial imperfection or initial bow.(ii) Eccentricity of application of loads.
(iii) Residual stresses locked into the cross section.
2.5 Connections
2.5.1 Introduction
Steel sections are manufactured and shipped to some standard lengths, as governed by
rolling, transportation and handling restrictions. However, most of the steel structural
members used in structures have to span great lengths and enclose large three-
dimensional spaces. Hence connections are necessary to synthesize such spatial
structures from one- and two-dimensional elements and also to bring about stability of
structures under different loads. Thus, connections are essential to create an integral
steel structure using discrete linear and two-dimensional (plate) elements.
A structure is only as strong as its weakest link. Unless properly designed, the
connections joining the members may be weaker than the members being joined.However, it is desirable to avoid connection failure before member failure for the
following reasons:
To achieve an economical design, usually it is important that the
connections develop the full strength of the members.
Usually connection failure is not as ductile as that of steel member failure.
Hence it is desirable to avoid connection failure before the member failure.
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Therefore, design of connections is an integral and important part of design of steel
structures. They are also critical components of steel structures, since
They have the potential for greater variability in behaviour and strength,
They are more complex to design than members, and
They are usually the most vulnerable components, failure of which may lead
to the failure of the whole structure.
Thus designing for adequacy in strength, stiffness and ductility of connections will
ensure deflection control during service load and larger deflection and ductile failure
under over-load. Hence, a good understanding of the behaviour and design of joints
and connections in steel structures is an important pre-requisite for any good design
engineer.
2.5.2 Types of Connections
Connections are normally made either by bolting or welding. Bolting is common in
field connections, since it is simple and economical to make. Bolting is also
regarded as being more appropriate in field connections from considerations of
safety. However, welded connections, which are easier to make and are more
efficient, are usually resorted to in shop fabrications.
Two types of bolts are used in bolted connection. The most common type is bearing
bolts in clearance holes, often referred to as ordinary bolts or black bolts. They are
popular since they are economical, both in terms of material and installation costs.
(a) Bearing Connection
(b) Friction Connection
Clamping
Force, P0
XBearing
Stress
Contact
Force, P0
T
T
Frictional
Force T
Fig. 2.12: Bolt Shear Transfer Mechanism
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The main disadvantage of bearing type of bolted connections is that the elements
undergo some slip even under a small shear, before being able to transfer force by
bearing. This is due to clearance between the bolts and the holes. Such a slip causes
increased flexibility in the lower ranges of load and unexpected joint behaviour in somesituations. In such cases high strength friction grip (HSFG) bolts are used.
2.5.3 High Strength Bolts (IS 3757:1985 & IS 4000:1992)
In HSFG bolted joints, high strength bolts (8G or 10K grade) are pre-tensioned against
the plates to be bolted together, and so that contact pressure is developed between the
plates being joined [Fig. 2(b)]. When external shear force is applied, the frictional
resistance to slip between the plates prevents their relative slip. These bolted joints
achieve higher stiffness in shear because of frictional resistance between the contact
surfaces. Only when the externally applied force exceeds the frictional resistance
between the plates, the plates slip and the bolts bear against the bolt holes. Thus even
after slip, there is a reserve strength due to bearing.
The HSFG bolts are expensive both from material and installation points of view. They
require skilled labour and effective supervision. Due to their efficient force transfer
mechanism they have become very popular recently. Moreover, their performance is
superior under cyclic loading compared to other forms of jointing.
High strength bolts are made from bars of medium carbon steel. The bolt of propertyclass 8.8 and 10.9 are commonly used in steel construction. These bolts should confirm
to IS 3757. These bolts are often used with two washers. These washers serve two
purposes:
1. To distribute the clamping pressure to a larger area of softer metal of
fastened parts, and to prevent the nut or bolt head from damaging the
component member.
2. To prevent the threaded portion of the bolt from bearing on connected
member.The strength of high strength bolts are achieved through quenching and tempering
process or low alloying steel. They are less ductile. The materials of bolts do not have a
well defined yield point. Instead of using yield stress, so called proof load is used. The
proof load is obtained by multiplying tensile stress area (may be taken as Area
corresponding to root diameter at thread and in approximately equal to 0.8 times the
shank area of bolt) with proof stress. In IS800, the proof stress is taken as 0.7 times the
ultimate stress of bolt.
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Special techniques are used for tightening the nuts to induce a specified initial tension
in the bolt, which causes the sufficient friction between faying faces. These bolts with
induced initial tension are called High Strength Friction Grip(HSFG) bolts. Due to this
friction, the slip in the joint is eliminated and hence the joints with HSFG bolts are
called non-slip connection or friction type connections. The induced initial tension in
the bolt is called proof-load of the bolt and the coefficient of friction between bolt head
and faying surfaces is called the slip factor.
The sizes of bolt m16 to M36 are available, bolt of sizes M16, M20, M24 & M30 are
commonly used in practice. These bolts are identified by manufacturers identification
symbol and the property class.
Though the material cost of HSFG bolts are about 50% higher than the black bolts andrequire special workmanship for installation, they provided the following advantages:
(a) HSFG bolts do not provide any slip between the elements connected,
especially in close tolerance holes, thus providing the rigid connection.
(b) Due to clamping action, load is transmitted by friction only and bolts are not
subjected to shear and bearing.
(c) Due to smaller number of bolts gusset plate size are reduced.
(d) Deformation is minimized.(e) Since HSFG bolts under working loads do not rely on resistance from
bearing, holes larger than the usual can be provided to ease erection and to
take care of lack of fit. Thus the holes may be standard, extra large, or
short / long slotted. However, the type of holes governs the strength of
connection.
(f) Noiseless fabrication, as bolts are tightened with wrenches.
(g) The possibility of failure at the net section under the working load iseliminated.
(h) Since the loads causing fatigue will be within proof load, the nuts are
prevented from loosening and fatigue strength of joint greater and better
than the welded and riveted joints.
(i) Since the load is transferred by the friction, there is no stress concentration
in holes.
(j) Unlike riveted joints few person are requires for connections.
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(k) No heating is required and no danger of tossing of bolt. Thus the safety of
worker is enhanced.
(l) Alteration, if any (e.g. replacement of the defective bolt) are done easily
than in welded or riveted connections.
2.5.4 Bolt Holes
Bolt holes are usually drilled. Punching can reduce the toughness and ductility and may
lead to brittle fracture. Punched holes should not be used where plastic tensile straining
can occur. IS800 allows punched holes only in materials whose yield stress Fy does not
exceed 360 MPa and where thickness does not exceed (5600/Fy) mm.
Bolt holes are made larger than the bolt diameter to facilitate erection and to allow for
inaccuracies in fabrication. The clearance is 1.0mm for bolts less than 14mm and 2mmfor bolts between 16mm and 24mm and 3mm for bolts exceeding 24mm.
Over size holes and slotted holes are allowable and should not be used often.
A oversize hole should not exceed 1.25d or (d+8) mm in diameter, where d is nominal
bolt diameter in mm. A slotted hole should exceed the appropriate hole size in width
and 1.33d in length, for short slotted hole and 2.5d in length, for long slotted hole.
2.5.5 Spacing and Edge Distance of Bolt Holes
The center- to-center distance between individual fasteners in a line, in the direction ofload or stress is called the Pitch. The distance between any two consecutive fasteners in
a zigzag pattern of bolts measured parallel to the direction of loads/stress is called the
staggered pitch. A minimum spacing of 2.5 times the nominal diameter of fasteners is
specified in the code to ensure that there is sufficient space to tighten the bolts, prevent
the overlapping of the washers and provide adequate resistance to tear-out of bolt.
The distance from the center of fasteners hole to the edge of an element (measured at
right angles to the direction of load) is called the end or edge distance. The edgedistance should be sufficient for bearing capacity and to provide space for bolt head,
washers and nut.
Maximum edge distance = 12t where = (250/y)0.5
Pitch (min.) 2.5 X nominal diameter of bolt
Pitch (max.) 32 t or 300 mm
(a) Parts in tension 16t or 200mm whichever is less
(b) Parts in compression 12t or 200mm whichever is less
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(c) Tacking fasteners 32t or 300mm whichever is less
16t 0r 200mm whichever is less for plates
exposed to weather.
Where t is the thickness of thinner outside plate or angle.
2.5.6 Connection Design Philosophies
Traditional methods of analysis of connection stresses were based on the following
assumptions:
Connected parts are rigid compared to connectors themselves and hence
their deformations may be ignored
Connectors behave in a linear-elastic manner until failure.
Connectors have unlimited ductility.
However, in reality, connected parts such as end plates, angles etc. are flexible and
deform even at low load levels. Further, their behaviour is highly non-linear due to
slip, lack of fit, material non-linearity and residual stresses. Ductility of welds in some
orientation with respect to direction of loads may be very limited, (e.g., Transverse fillet
welds).
Even though truss joints are assumed to be hinged the detailing using gusset plates and
multiple fastener and welding does not represent hinged condition. However, in practicethe secondary moment associated with such a rigid joint is disregarded unless the
loading is cyclic.
The complexity and variability in strength of connections require a rational design
philosophy to account for their behaviour. Keeping in view the large number of joints
to be normally designed in a structure and the considerable variability in the design
strength, any sophisticated analysis is neither desirable nor warranted. The design
should ensure that equilibrium is satisfied, slenderness of the elements is consistentwith the ductility demand and the deleterious effect of stress concentration on fatigue
strength is considered in cyclically loaded structures. The following approach is
consistent with connection design requirements in most general cases encountered in
practice in statically loaded systems.
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The steps to be followed in the proposed rational design approach are enumerated
initially. These are illustrated using a simple framing angle connection between a beam
and a column of a framed building designed to transfer a shear force ofV, as shown in
Fig. 6.
V V
(a) Connection (b) Freebody Diagram
Critical section
for block shear
Fig. 2.13: Simple Framed Angle Shear Connection
2.6 Analysis of Structures
In structural design process term analysis refers to the determination of axial forces
bending moments shear, torsional moments etc acting on different members of astructure due to applied loads and their combination (static or dynamic). In general
design may involve the development of structural layout & system or the arrangement
of different members but for the design engineers, design involves the selection of size
of members to resist the forces and moments determined in analysis phase safely &
economically. In design phase we not only design the members but also their
connections and the foundations. So that the loads are transmitted to the soil.
For statically determinate structures (simply supported beams, cantilevers, trusses
etc.)The analysis is relatively simple & the laws of statistics can be used to determine
the forces & moments on each member. The relative stiffness of intersecting members
does not affect analysis. After analysis is completed and critical moments and forces in
different members are tabulated the design of members are straight forward process
using an appropriate method limit state method etc. For statistically determinate
structure. There is no need for reanalysis or redesign of members.
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However for statistically determinate analysis, the procedure is rather complex. A no. of
analytical methods have been developed which include slope
deflection method, moment distribution method, Kanis method, portal
method etc. In these methods assumptions are usually made regarding
the distribution of applied load among the members according to
relative stiffness of connecting members, the response and behaviour
of members and structures to applied loads, the rigidity of joints etc.
Moreover to perform the analysis, the proportion of various structural
elements should be known in advance for this preliminary design is
generally required. Thus in these types of structure, analysis and
design are interactive process.After the first cycle of analysis has been completed. The members are designed as per
the codal rules-it is usually necessary to re analyze the structure to
check the validity of member sizes. For complex structures several
cycle of analysis and design may be required (many times three cycles
are found to be sufficient). Handbook often provides formulae and
coefficients to simplify the preliminary design of continuous beams or
simple rigid jointed frame such as portal frames.Various computer programs are available for analysis and design of different types of
structure. They include ABACUS, ADINA, ANSYS, ASKA, GT-
STRUDL, SAP and STRESS. The above list is not exhaustive. Many
of these packages were developed for use in mainframe computers.
Recently a number of packages have been developed for use with IBM
PC or compatible systems. Notable among them are SAP 2000,
STAAD III , and STAAD PRO , ETABS , DAST, LARSA, STRAP,RISA 3D, ROBOT Millennium, SPACEGASS, STRUCAD * 3D,GT-
STRUDL and STRUDDS. The windows versions of these packages
are also available. These program are quote general in terms of loading
geometric configuration and support conditions.
With these programs it is now possible to analyze any structure with any complicated
geometry subjected to any pattern of loading (static or dynamic) and
having any boundary conditions or discontinuity.
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However, a structural engineer is often guided in his effort by the code of practice. A
represents the consensus of opinion of experienced engineers and
professionals. The code serves following distinct functions:
1. They ensure adequate structural safety by specifying certain essential
minimum requirements of design.
2. They aid the designer in design process. Often the results of sophisticated
analysis are made available in form of simple formulae or chat.
3. They ensure consistency among different engineers.
4. They protect the structural engineer from disputes, though codes in many
cases do not provide legal protection.
5. In India, the Bureau of Indian standard issues the code and standardhandbooks. Committees, representing procedures, designers, educators,
fabricators, government bodies and other interested bodies write them. The
draft is circulated to a larger section of engineers, designers and
professionals. The committee considers their comments and finally Bureau
of Indian standards print the book.
6. The code depends upon design philosophies. Various design philosophy
have been evolved in different parts of world with regards to structural steeldesign.
7. The earliest codified design philosophy is working stress method of design
(WSM). This method of design is based on linear elastic theory. Now it has
been replaced by limit state design philosophy.
2.6.1 Allowable Stress Design (ASD)
With the development of linear elastic theories in the 19th century the stress-strain
behaviour of new materials like wrought iron & mild steel could be accuratelyrepresented. These theories enabled indeterminate structures to be analysed and the
distribution of bending and shear stresses to be computed correctly. The first attainment
of yield stress of steel was generally taken to be the onset of failure. The limitations due
to non-linearity and buckling were neglected.
The basic form of calculations took the form of verifying that the stresses caused by the
characteristic loads must be less than an allowable stress, which was a fraction of the
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yield stress. Thus the allowable stress may be defined in terms of a factor of safety"
which represented a margin for overload and other unknown factors which
Yield Stress
Allowable Stress Factor of Safety=could be tolerated by the structure. The allowable stress is thus directly related to yield
stress by the followingexpression:
In general, each member in a structure is checked for a number of different
combinations of loading. The value of factor of safety in most cases is taken to be
around 1.67. Many loads vary with time and these should be allowed for. It is
unnecessarily severe to consider the effects of all loads acting simultaneously with their
full design value, while maintaining the same factor of safety or safety factor. Usingthe same factor of safety or safety factor when loads act in combination would result in
uneconomic designs.
A typical example of a set of load combinations is given below, which accounts for the
fact that the dead load, live load and wind load are all unlikely to act on the structure
simultaneously at their maximum values:
(Stress due to dead load + live load) < allowable stress
(Stress due to dead load + wind load) < allowable stress(Stress due to dead load + live load + wind) < 1.33 times allowable stress.
In practice there are severe limitations to this approach. These are the consequences of
material non-linearity, non-linear behaviour of elements in the post-buckled state and
the ability of the steel components to tolerate high theoretical elastic stresses by
yielding locally and redistributing the loads. Moreover the elastic theory does not
readily allow for redistribution of loads from one member to another in statically
indeterminate structures.2.6.2 Limit State Design
Limit States" are the various conditions in which a structure would be considered to
have failed to fulfil the purpose for which it was built. In general two limit states are
considered at the design stage and these are listed in Table 1.
Table 2.7: Limit States
Ultimate Limit State Serviceability Limit State
Strength (yield, buckling) Deflection
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Stability against overturning andsway
Fracture due to fatigue
Brittle Fracture
Vibration
Fatigue checks (including reparable damage due tofatigue)
Corrosion
Ultimate Limit States are those catastrophic states, which require a larger reliability
in order to reduce the probability of its occurrence to a very low level. Serviceability
Limit State" refers to the limits on acceptable performance of the structure.
Not all these limits can be covered by structural calculations. For example, corrosion is
covered by specifying forms of protection (like painting) and brittle fracture is covered
by material specifications, which ensure that steel is sufficiently ductile.
Limit state may be defined as the acceptable limit for the safety and serviceability of
structure before failure occurs. Thus the concept of design with limit state is to achieve
acceptable probabilities so that the structure will not become unfit for use and will not
reach a limit state.
In limit state design are preferred to use the term limit states rather than failure. Thus
limit state is a state of impeding failure beyond which a structure ceases to perform its
intended function satisfactorily. The reliability design is ensured by requirement.
Design action Design strength
The limit states are classified as:
(a) Limit state of strength
(b) Limit state of serviceability
(c) Limit state of strength
The limit state of strength are those associated with failure (or imminent failure), under
the action of probable and most unfavorable combination of loads on structure using
appropriate partial safety factors which may endanger the safety of life and property.
2.6.2.1 Partial Safety Factor
The major innovation in the new codes is the introduction of the partial safety factor
format. A typical format is described below:
In general calculations take the form of verifying that
S* R*
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where S* is the calculated factored load effect on the element (like bending moment,
shear force etc) and R* is the calculated factored resistance of the element being
checked, and is a function of the nominal value of the material yield strength.
S* is a function of the combined effects of factored dead, live and wind loads. (Other
loads if applicable, are also considered)
In accordance with the above concepts, the safety format used in Limit State Codes is
based on probable maximum load and probable minimum strengths, so that a consistent
level of safety is achieved. Thus, the design requirements are expressed as follows:
Sd Rd
where Sd = Design value of internal forces and moments caused by the design Loads,
Fd
Fd = f * Characteristic Loads.
f = a load factor which is determined on probabilistic basis
Rd = Characteristic Value of Resistance/m
Where m = a material factor, which is also determined on a probabilistic basis
It should be noted that f makes allowance for possible deviation of loads and the
reduced possibility of all loads acting together. On the other hand m allows for
uncertainties of element behaviour and possible strength reduction due to
manufacturing tolerances and imperfections in the material.
Collapse is not the only possible failure mode. Excessive deflection, excessive
vibration, fracture etc. also contribute to Limit States. Fatigue is an important design
criterion for bridges, crane girders etc. (These are generally assessed under
serviceability Limit States)
Thus the following limit states may be identified for design purposes:
Ultimate Limit State is related to the maximum design load capacity
under extreme conditions. The partial load factors are chosen to reflect the
probability of extreme conditions, when loads act alone or in combination.
Serviceability Limit State is related to the criteria governing normal use.
Unfactored loads are used to check the adequacy of the structure.
Fatigue Limit State is important where distress to the structure by
repeated loading is a possibility.
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The above limit states are provided in terms of partial factors reflects the severity of the
risks.
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The limit states of strength include:
(i) Loss of equilibrium of structure as a whole or any of its part or
component.
(ii) Loss of stability of structure (including the effect sway) or any of its part
including support & foundation.
(iii) Failures by excessive deformation rupture of structure or any of its parts
or components.
(iv) Fracture due to fatigue
(v) Brittle fracture.
The limit states of serviceability include:
(a) Deformation and deflection which may adversely affect the appearance oreffective use of structure or may cause improper functioning of
equipment or services or may cause damage to finishes & nonstructural
components.
(b) Vibration in structure or any of its components causing discomfort to people
damages to structure, its content or which may limit its functional
effectiveness. Special consideration shall be given to systems
susceptible to vibration such as large open floor area free of partition toensure that such vibrations are acceptable for the intended use and
occupancy.
(c) Repairable damage or crack due to fatigue
(d) Corrosion , durability
(e) Fire
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CHAPTER III
CHOICE OF SECTION
The design of steel sections is governed by the cross sectional area, section modulus,
and radius of gyration. Though IS 808 and IS handbook No.1 list the properties of
various sections, due to the limitations of rolling mills only a few sections are available
in the market. Therefore, design is governed by not only sectional properties but also
the availability of the section. Another factor governing choice is the ease with which
sections can be connected. In India ISMB beams are the most commonly produced? So
are limited numbers of ISHB sections. Also, only medium channels are available. Only
a limited number of unequal angels are available in the market. Also, not all the equal-angel sections are available readily in the market. Hence it will be a good idea to get a
list of the available sections from steel producers like SAIL and plan the design
accordingly.
Though IS 800: 2007 code has removed the minimum thickness requirements, it is
advisable to use a minimum thickness of 6mm for the main members and 5 mm for
secondary members exposed to the atmosphere, especially in coastal areas.
Structural steel is probably the most versatile commonly used structural material. Notonly its versatility apparent in great variety of structures for which it is used but also in
many different forms possible in a single building structure or a complex structure.
Many of the properties of structural steel of interest to the design can be described by
behaviors of steel during simple tension test.
Fig. 3.1: A Channel Section
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A channel section has only an axis of symmetry. Due to this it is subjected to twisting
or torsion along with bending when used as beam.
The various section properties of ISMC 400:
1. Weight = 49.4 Kg/m
2. Sectional Area = 62.93 cm2.
3. Depth of section (h) = 400mm.
4. Width of Flange (b) = 100mm.
5. Thickness of flange (tf) = 15.3mm.
6. Thickness of web (tw) = 8.6mm.
7. Center of gravity (cyy) = 2.42cm.
8. Moment of inertia Ixx = 15082.8cm4, Iyy = 504.8cm4.9. Radius of Gyration rxx = 15.48cm, ryy = 2.83cm.
10.Modulli of section zxx = 754.1cm3, Zyy = 66.6cm3.
11.Radius at root (r1) = 15mm
12.Radius at toe (r2) = 7.5mm.
13.Flange Slope= 60.
14.Section Modulus (Plastic) Zpz = 891.03cm3, Zpy= 127.69cm3.
15. Depth between Root Fillets d = 332.8mm16.Local Buckling Ratios: Flange = 6.5, Web = 38.7, Torsional Constant
Il = 35.33X104 mm4
17.Warping Constant Iw = 152.584 X 109 mm6
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CHAPTER IV
GENERAL STATEMENT FOR STAAD
STAAD.Pro V8i is the most popular structural engineering software product for 3D
model generation, analysis and multi-material design. It has an intuitive, user-friendly
GUI, visualization tools, powerful analysis and design facilities and seamless
integration to several other modeling and design software products. The software is
fully compatible with all Windows operating systems but is optimized for
Windows XP.
For static or dynamic analysis of bridges, containment structures, embedded structures
(tunnels and culverts), pipe racks, steel, concrete, aluminum or timber buildings,transmission towers, stadiums or any other simple or complex structure, STAAD.Pro
has been the choice of design professionals around the world for their specific analysis
needs.
STAAD.Pro is a general purpose program for performing the analysis and design of a
wide variety of types of structures. The basic three activities which are to be carried out
to achieve that goal:
(a) Model generation(b) The calculations to obtain the analytical results
(c) Result verification - are all facilitated by tools contained in the program's
graphical environment.
The design philosophy and procedural logistics for member selection and code
checking are based upon the principles of allowable stress design. Two major failure
modes are recognized: failure by overstressing, and failure by stability considerations.
The flowing sections describe the salient features of the allowable stresses beingcalculated and the stability criteria being used. Members are proportioned to resist the
design loads without exceeding the allowable stresses and the most economic section is
selected on the basis of least weight criteria. The code checking part of the program
checks stability and strength requirements and reports the critical loading condition and
the governing code criteria. It is generally assumed that the user will take care of the
detailing requirements like provision of stiffeners and check the local effects such as
flange buckling and web crippling.
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4.1 Technical Reference
Input Generation: The GUI (or user) communicates with the STAAD analysis engine
through the STD input file. That input file is a text file consisting of a series of
commands which are executed sequentially. The commands contain either instructions
or data pertaining to analysis and / or design.
Types of Structures: A STRUCTURE can be defined as an assemblage of elements.
STAAD is capable of analyzing and designing structures consisting of both frame,
plate/shell and solid elements. Almost any type of structure can be analyzed by
STAAD.
A SPACE structure, which is a three dimensional framed structure with loads applied
in any plane, is the most general.A PLANE structure is bound by a global X-Y coordinate system with loads in the same
plane.
A TRUSS structure consists of truss members who can have only axial member forces
and no bending in the members.
A FLOOR structure is a two or three dimensional structure having no horizontal
(global X or Z) movement of the structure [FX, FZ & MY are restrained at every joint].
The floor framing (in global X-Z plane) of a building is an ideal example of a FLOORstructure. Columns can also be modeled with the floor in a FLOOR structure as long as
the structure has no horizontal loading. If there is any horizontal load, it must be
analyzed as a SPACE structure.
Specification of the correct structure type reduces the number of equations to be solved
during the analysis. This results in a faster and more economic solution for the user.
Unit Systems: The user is allowed to input data and request output in almost all
commonly used engineering unit systems including MKS, SI and FPS. In the input file,the user may change units as many times as required. Mix and match between length
and force units from different unit systems is also allowed. The input-unit for angles (or
rotations) is degrees. However, in JOINT DISPLACEMENT output, the rotations are
provided in radians. For all output, the units are clearly specified by the program.
Structure Geometry and Coordinate Systems: A structure is an assembly of
individual components such as beams, columns, slabs, plates etc. In STAAD, frame
elements and plate elements may be used to model the structural components.
Typically, modeling of the structure geometry consists of two steps:
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Fig. 4.1: Cartesian (Rectangular) Coordinate System
Fig. 4.2: Cylindrical Coordinate System
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Fig. 4.3: Reverse Cylindrical Coordinate System
Local Coordinate System: A local coordinate system is associated with each member.
Each axis of the local orthogonal coordinate system is also based on the right hand rule.
Fig. 1.5 shows a beam member with start joint 'i' and end joint 'j'. The positive direction
of the local x-axis is determined by joining 'i' to 'j' and projecting it in the same
direction. The right hand rule may be applied to obtain the positive directions of the
local y and z axes. The local y and z-axes coincide with the axes of the two principal
moments of inertia. Note that the local coordinate system is always rectangular.
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Fig. 4.4: When Global-Y is vertical
Fig. 4.5: When Global-Z is vertical
A wide range of cross-sectional shapes may be specified for analysis. These include
rolled steel shapes, user specified prismatic shapes etc. Fig. 1.6 shows local axis
system(s) for these shapes.
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Relationship between Global & Local Coordinates: Since the input for member
loads can be provided in the local and global coordinate system and the output for
member-end-forces is printed in the local coordinate system, it is important to know the
relationship between the local and global coordinate systems. This relationship is
defined by an angle measured in the following specified way. This angle will be defined
as theBeta Angle.
Beta Angle: When the local x-axis is parallel to the global Vertical axis, as in the case
of a column in a structure, the beta angle is the angle through which the local z-axis (or
local Y for SET Z UP) has been rotated about the local x-axis from a position of being
parallel and in the same positive direction of the global Z-axis (global Y axis for SET Z
UP).
When the local x-axis is not parallel to the global Vertical axis, the beta angle is the
angle through which the local coordinate system has been rotated about the local
x-axis from a position of having the local z-axis (or local Y for SET Z UP) parallel to
the global X-Z plane (or global X-Y plane for SET Z UP)and the local y-axis (or local z
for SET Z UP) in the same positive direction as the global vertical axis. Figure 1.7
details the positions for beta equals 0 degrees or 90 degrees. When providing member
loads in the local member axis, it is helpful to refer to this figure for a quick
determination of the local axis system.Reference Point: An alternative to providing the member orientation is to input the
coordinates (or a joint number) which will be a reference point located in the member
x-y plane (x-z plane for SET Z UP) but not on the axis of the member. From the
location of the reference point, the program automatically calculates the orientation of
the member x-y plane (x-z plane for SET Z UP).
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Fig. 4.6: Relationship between Global and Local axes
Loads: Loads in a structure can be specified as joint load, member load, temperature
load and fixed-end member load. STAAD can also generate the self-weight of the
structure and use it as uniformly distributed member loads in analysis. Any fraction of
this self-weight can also be applied in any desired direction.
Joint Load: Joint loads, both forces and moments, may be applied to any free joint of a
structure. These loads act in the global coordinate system of the structure. Positive
forces act in the positive coordinate directions. Any number of loads may be applied ona single joint, in which case the loads will be additive on that joint.
Member Load: Three types of member loads may be applied directly to a member of a
structure. These loads are uniformly distributed loads, concentrated loads, and linearly
varying loads (including trapezoidal). Uniform loads act on the full or partial length of a
member. Concentrated loads act at any intermediate, specified point. Linearly varying
loads act over the full length of a member. Trapezoidal linearly varying loads act over
the full or partial length of a member. Trapezoidal loads are converted into a uniform
load and several concentrated loads.
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Any number of loads may be specified to act upon a member in any independent
loading condition. Member loads can be specified in the member coordinate system or
the global coordinate system. Uniformly distributed member loads provided in the
global coordinate system may be specified to act along the full or projected member
length. Refer to Fig. 1.3 to find the relation of the member to the global coordinate
systems for specifying member loads. Positive forces act in the positive coordinate
directions, local or global, as the case may be.
Area / One-way Load / Floor Load: Often a floor is subjected to a uniform pressure.
It could require a lot of work to calculate the equivalent member load for individual
members in that floor. However, with the AREA, ONEWAY or FLOOR LOAD
facilities, the user can specify the pressure (load per unit square area). The program willcalculate the tributary area for these members and calculate the appropriate member
loads. The Area Load and One way load are used for one way distribution and the Floor
Load is used for two way distribution.
The following assumptions are made while transferring the area/floor load to member
load:
(a) The member load is assumed to be a linearly varying load for which the
start and the end values may be of different magnitude.(b) Tributary area of a member with an area load is calculated based on half the
spacing to the nearest approximately parallel members on both sides. If the
spacing is more than or equal to the length of the member, the area load will
be ignored.
(c) Area / Floor load should not be specified on members declared as
MEMBER CABLE, MEMBER TRUSS, MEMBER TENSION or
MEMBER COMPRESSION or CURVED.Fixed End Member Load: Load effects on a member may also be specified in terms of
its fixed end loads. These loads are given in terms of the member coordinate system and
the directions are opposite to the actual load on the member. Each end of a member can
have six forces: axial; shear y; shear z; torsion; moment y, and
moment z.
Prestress and Post stress Member Load: Members in a structure may be subjected to
prestress load for which the load distribution in the structure may be investigated. The
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prestressing load in a member may be applied axially or eccentrically. The
eccentricities can be provided at the start joint, at the middle, and at the end joint. These
eccentricities are only in the local y-axis. A positive eccentricity will be in the positive
local y-direction. Since eccentricities are only provided in the local y-axis, care should
be taken when providing prismatic properties or in specifying the correct BETA angle
when rotating the member coordinates, if necessary. Two types of prestress load
specification are available; PRESTRESS, where the effects of the load are transmitted
to the rest of the structure, and POSTSTRESS, where the effects of the load are
experienced exclusively by the members on which it is applied.
Temperature and Strain Load: Temperature difference through the length of a
member as well as differences of both faces of members and elements may also bespecified. The program calculates the axial strain (elongation and shrinkage) due to the
temperature difference. From this it calculates the induced forces in the member and the
analysis is done accordingly. The strain intervals of elongation and shrinkage can be
input directly.
Support Displacement Load: Static Loads can be applied to the structure in terms of
the displacement of the supports. Displacement can be translational or rotational.
Translational displacements are provided in the specified length while the rotationaldisplacements are always in degrees. Note that displacements can be specified only in
directions in which the support has an "enforced" specification in the Support
command.
Steel Design Consideration As Per IS800 in STAAD: In STAAD implementation of
IS:800, the user is allowed complete control of the design process through the use of
design parameters. Available design parameters to be used in conjunction with IS:800.
Stability Requirements: Slenderness ratios are calculated for all members and checkedagainst the appropriate maximum values. Section 3.7 of IS:800 summarizes the
maximum slenderness ratios for different types of members. In STAAD implementation
of IS:800, appropriate maximum slenderness ratio can be provided for each member. If
no maximum slenderness ratio is provided, compression members will be checked
against a maximum value of 180 and tension members will be checked against a
maximum value of 400.
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Truss Members: As mentioned earlier, a truss member is capable of carrying only
axial forces. So in design no time is wasted in calculating bending or shear stresses,
thus reducing design time considerably. Therefore, if there is any truss member in an
analysis (like bracing or strut, etc.), it is wise to declare it as a truss member rather than
as a regular frame member with both ends pinned.
Deflection Check: This facility allows the user to consider deflection as criteria in the
check code and member selection processes. Note that deflection is used in addition to
other strength and stability related criteria. The local deflection calculation is based on
the latest analysis results.
The purpose of code checking is to verify whether the specified section is capable ofsatisfying applicable design code requirements. The code checking is based on the
IS:800 (1984) requirements. Forces and moments at specified sections of the members
are utilized for the code checking calculations. Sections may be specified using the
BEAM parameter or the SECTION command. If no sections are specified, the code
checking is based on forces and moments at the member ends.
The code checking output labels the members as PASSed or FAILed. In addition, the
critical condition (applicable IS:800 clause no.), governing load case, location (distancefrom the start) and magnitudes of the governing forces and moments are also printed
out.
Code Checking: The purpose of code checking is to verify whether the specified
section is capable of satisfying applicable design code requirements. The code checking
is based on the IS:800 (1984) requirements. Forces and moments at specified sections
of the members are utilized for the code checking calculations. Sections may be
specified using the BEAM parameter or the SECTION command. If no sections are
specified, the code checking is based on forces and moments at the member ends.
The code checking output labels the members as PASSed or FAILed. In addition, the
critical condition (applicable IS: 800 clause no.), governing load case, location
(distance from the start) and magnitudes of the governing forces and moments are also
printed out.
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Member Selection: STAAD is capable of performing design operations on specified
members. Once an analysis has been performed, the program can select the most
economical section that is the lightest section, which satisfies the applicable code
requirements. The section selected will be of the same type (I-Section, Channel etc.) as
originally specified by the user. Member selection may be performed with all types of
steel sections listed in Section 7B.13 and user provided tables. Selection of members,
whose properties are originally provided from user specified table, will be limited to
sections in the user provided table. Member selection can not be performed on members
whose cross sectional properties are specified as PRISMATIC.
Member Selection by Optimization: Steel section selection of the entire structure may
be optimized. The optimization method utilizes a state-of-the -art numerical techniquewhich requires automatic multiple analysis. The user may start without a specifically
designated section. However, the section profile type (BEAM, COLUMN, CHANNEL,
ANGLE etc.) must be specified using the ASSIGN command (see Chapter 6). The
optimization is based on member stiffness contributions and corresponding force
distributions. An optimum member size is determined through successive
analysis/design iterations. This method requires substantial computer time and hence
should be used with cautionCombined Stress: Members subjected to both axial and bending stresses are
proportioned accordingly to section 7 of IS: 800. All members subject to bending and
axial compression are required to satisfy the equation of Section 7.1.1 (a) for
intermediate points, and equation of Section 7.1.1 (b) for support points.
For combined axial tension and bending the equation of Section 7.1.2 is required to be
satisfied.
Cm coefficients are calculated according to the specifications of Section 7.1.3information regarding occurrence of sides way can be provided through the use of
parameters SSY and SSZ. In the absence of any user provided information, sides way
will be assumed.
Shear Stress: Allowable shear stress calculations are based on Section 6.4 of IS: 800.
For shear on the web, the gross sections taken into consideration consist of the product
of the total depth and the web thickness. For shear parallel to the flanges, the gross
section is taken as 2/3 times the total flange area.
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Column with Lacings and Battens: For columns with large loads it is desirable tobuild rolled sections at a distance and inter-connect them. The joining of elementsections is done by two ways:
(a) Lacing and(b) Batten
Double channel sections (back-to-back and face-to-face) can be joined either by lacingor by batten plates having riveted or welded connection.
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CHAPTER V
RESULTS AND CALCULATIONS
5.1 Analysis for 5.0m span with load acting at center
Fig. 5.1: 5.0m span with load acting at center
Table 5.1: Steel Design Table from STAAD (All Units are - KN METER)
Member Table Result / FXCriticalCond./
MY
Ratio/ MZLoading /
Location
1 ST ISMC400 (Indian Sections)
PASS IS-7.1.1(A) 0.790 3
74.59 C 0.00 -71.66 0.00
2 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.790 3
74.59 C 0.00 -71.66 0.00
3 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.651 3
41.16 C 0.00 71.66 0.00
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4 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.996 3
41.16 C 0.00 -112.74 1.25
5 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.996 3
41.16 C 0.00 -112.74 1.25
6 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.651 341.16 C 0.00 71.66 1.25
7 ST ISMC400 (INDIAN SECTIONS)
PASS SHEAR-Y 0.000 1
0.00 T 0.00 0.00 0.00
8 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.790 3
74.59 C 0.00 71.66 0.00
9 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.790 3
74.59 C 0.00 71.66 0.00
10 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.651 3
41.16 C 0.00 71.66 0.00
11 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.996 3
41.16 C 0.00 -112.74 1.25
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12 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.996 3
41.16 C 0.00 -112.74 0.00
13 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.651 3
41.16 C 0.00 71.66 1.25
14 ST ISMC400 (INDIAN SECTIONS)
PASS SHEAR-Y 0.000 1
0.00 T 0.00 0.00 0.00
15 ST ISMC400 (INDIAN SECTIONS)
PASS SHEAR-Y 0.000 1
0.00 T 0.00 0.00 0.00
16 ST ISMC400 (INDIAN SECTIONS)
PASS SHEAR-Y 0.000 10.00 T 0.00 0.00 0.00
17 ST ISMC400 (INDIAN SECTIONS)
PASS SHEAR-Y 0.000 1
0.00 T 0.00 0.00 0.00
18 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.207 3
77.08 C 0.00 15.42 0.50
19 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.207 3
77.08 C 0.00 15.42 0.50
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20 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.207 3
77.08 C 0.00 -15.42 0.50
21 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.1(A) 0.207 3
77.08 C 0.00 -15.42 0.50
22 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.2 0.068 3
35.55 T 0.00 3.81 0.00
23 ST ISMC400 (INDIAN SECTIONS)
PASS IS-7.1.2 0.068 3
35.55 T 0.00 3.81 0.00
5.2 For load acting at center
Fig. 5.2: Variation of Maximum load with respect to different span
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Table 5.2: Following Listed Below Table Shows the values of Fx, Fy and Mz at nodes 1,4,6&8 when
load is acting at center
Table 5.2.1: Analysis for 4.0m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 2.309 94.094 0 0 0 -13.359
4 3 Combination Load Case 3 -2.309 94.093 0 0 0 13.359
6 3 Combination Load Case 3 2.309 94.094 0 0 0 -13.359
8 3 Combination Load Case 3 -2.309 94.093 0 0 0 13.359
Table 5.2.2: Analysis for 4.1m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 2.646 92.142 0 0 0 -13.603
4 3 Combination Load Case 3 -2.646 92.142 0 0 0 13.603
6 3 Combination Load Case 3 2.646 92.142 0 0 0 -13.603
8 3 Combination Load Case 3 -2.646 92.142 0 0 0 13.603
Table 5.2.3: Analysis for 4.2m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 2.98 90.191 0 0 0 -13.828
4 3 Combination Load Case 3 -2.98 90.19 0 0 0 13.829
6 3 Combination Load Case 3 2.98 90.191 0 0 0 -13.828
8 3 Combination Load Case 3 -2.98 90.19 0 0 0 13.829
Table 5.2.4: Analysis for 4.3m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 3.311 88.239 0 0 0 -14.034
4 3 Combination Load Case 3 -3.311 88.238 0 0 0 14.034
6 3 Combination Load Case 3 3.311 88.239 0 0 0 -14.034
8 3 Combination Load Case 3 -3.311 88.238 0 0 0 14.034
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Table 5.2.5: Analysis for 4.4m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 3.638 86.287 0 0 0 -14.22
4 3 Combination Load Case 3 -3.638 86.287 0 0 0 14.22
6 3 Combination Load Case 3 3.638 86.287 0 0 0 -14.22
8 3 Combination Load Case 3 -3.638 86.287 0 0 0 14.22
Table 5.2.6: Analysis for 4.5m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 3.981 84.836 0 0 0 -14.475
4 3 Combination Load Case 3 -3.981 84.835 0 0 0 14.475
6 3 Combination Load Case 3 3.981 84.836 0 0 0 -14.475
8 3 Combination Load Case 3 -3.981 84.835 0 0 0 14.475
Table 5.2.7: Analysis for 4.6m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 4.297 82.884 0 0 0 -14.622
4 3 Combination Load Case 3 -4.297 82.884 0 0 0 14.622
6 3 Combination Load Case 3 4.297 82.884 0 0 0 -14.6228 3 Combination Load Case 3 -4.297 82.884 0 0 0 14.622
Table 5.2.8: Analysis for 4.7m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 4.606 80.934 0 0 0 -14.747
4 3 Combination Load Case 3 -4.606 80.93 0 0 0 14.747
6 3 Combination Load Case 3 4.606 80.934 0 0 0 -14.747
8 3 Combination Load Case 3 -4.606 80.93 0 0 0 14.747
Table 5.2.9: Analysis for 4.8m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 4.964 79.981 0 0 0 -15.05
4 3 Combination Load Case 3 -4.964 79.98 0 0 0 15.05
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6 3 Combination Load Case 3 4.964 79.981 0 0 0 -15.05
8 3 Combination Load Case 3 -4.964 79.98 0 0 0 15.05
Table 5.2.10: Analysis for 4.9m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 5.29 78.529 0 0 0 -15.241
4 3 Combination Load Case 3 -5.29 78.529 0 0 0 15.241
6 3 Combination Load Case 3 5.29 78.529 0 0 0 -15.241
8 3 Combination Load Case 3 -5.29 78.529 0 0 0 15.241
Table 5.2.11: Analysis for 5.0m span with load acting at center
Node L/C Fx kN Fy kN Fz kN Mx kN-m My kN-m Mz kN-m
1 3 Combination Load Case 3 5.611 77.077 0 0 0 -15.415
4 3 Combination Load Case 3 -5.61177.07
7 0 0 0 15.415
6 3 Combination Load Case 3 5.611 77.077 0 0 0 -15.415
8 3 Combination Load Case 3 -5.611 77.077 0 0 0 15.415
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Fig. 5.3: Variation of fxwith respect to different span
Fig. 5.4: Variation of fy with respect to different span
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Fig. 5.5: Variation of MZwith respect to different span
In order to check the adequacy of the actual existing frame we are designing this section
with the help of STAAD-Pro.V8i and this results are checked manually by analyzing
this frame section with moment distribution method further it is checked by IS Code
method.
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For 5 m span: load acting at center :
Table 5.3: Distribution Factors
Joint Member k Sum DF
B BA I / 0.5 1 / 1.33
BC I / 2.14 2.667 I 1 / 5.71
BE I / 5 1 / 13.33
C CD I / 5 0.667 I 1 / 1.33
CB I / 2.14 1 / 1.43
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Table 5.4: Moment Distribution table For load acting at center
57
A B C D E F
AB BA BE BC CB CD DC DE ED EB EF FE
1
1.33
1
13.33
1
5.71
1
1.43
1
3.33
1
3.33
1
1.43
1
5.71
1
13.33
1
1.33
-91.25 +91.25 FEM
+63.81 +27.40 -27.40 -63.81 Bal
+31.91 -13.7 +13.7 -31.91 Co
-24.00 -2.39 -5.59 +9.58 +4.11 -4.11 -9.58 +5.59 +2.39 +0.24 Bal
-12 +1.19 +4.79 -2.79 -2.05 +2.05 +2.79 -4.79 -1.19 +12 Co
-4.50 -0.448 -1.05 +3.38 +1.45 -1.45 -3.38 +1.05 +0.448 +4.50 Bal
-0.72 +0.072 +0.07 -0.168 -0.03 +0.03 +0.168 -0.07 -0.072 +0.72 Co
-0.053 -0.107 -0.011 -0.025 +0.138 +0.059 -0.059 -0.138 +0.025 +0.011 +0.107 +0.053 Bal Co
-15.023 -30.047 -1.507 +31.46 +73.565 -74.676 +74.676 -73.565 -31.46 +1.507 +30.047 +15.023
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Fixed End Moments:
145 591.25 kN
8 8
FCD
wlM
= = =
146 591.25 kN
8 8FDC
wlM
+ = + = = +
15.023ABM = 73.565CBM = +
30.047BAM = 74.66CDM =
1.507BEM = 74.676DCM =
31.46BCM=
73.56DEM=
31.46EDM =
1.567EBM = +
30.047EFM =
15.023FEM = +
l = 2.14 m
For Load acting at centre: Taking the section ISMC400 @ 49.4 kg / m,
A = 6293 mm2; h = 400 mm; b = 100 mm
tf= 15.3 mm; tw = 8.6 mm; rx = 154.8 mm
ry = 28.3 mm; 3 3754.1 10 mmxxZ =
1 2 400 2 15.3 369.4 mmfd h t= = =
1. Determination of ac
214075.62
28.3y
l
r = = = N/mm2
From Table 5.1 of IS 800 : 1984 2105.82 mmac =
2. Determination of bc
15.31.78 2
8.6f
w
tT
t t= = =
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