Pushkar singh new steel structure

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CONTENT
1. STEEL STUCTURE.
 Introduction
 Properties of steel.
 Technical terms of design of structure.
2. STEEL STRUCTURAL JOINTS.
 Method of connecting structuralsteel.
 Technical terms of relating joints.
 Design formulae of riveted joints.
3. DETAILS OF STEEL COLUMN
 Typical structuresection for column.
 Details of laced and battened column.
 Beam end connection to column.
 Column splice and gusted base.
4. PLATE GIRDER.
 Introduction
 Definition of plate girder.
 Components of plate girder.
 Deck type plate Girder Bridge.
 Plate Girder Bridge – half through type.
 Multi span plate Girder Bridge.
5. PURPOSEOF STEEL.
6. USES OF STEEL.
7. ADVANTAGES OF STEEL STRUCTURE.
8. DISADVANTAGES OF STEEL STRUCTURE.
9. STEEL STRUCTURE DRAWING.
 Technical terms used in structuredrawing.
10.WORKING DRAWING.
 Element of weld symbols.
 Steel structurefor structuraluses.
11.STEEL STRUCTURE FEBRICATION.
12.ROOF SYSTEM OF STEEL TRUSSESS.

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PREFACE
These course materials have been
prepared especially to meet the requirements of
engineering students, structural draughtsmen, and
apprentices in structural drafting. It corresponds in scope to
the duties of the structural steel draughtsmen, and it
therefore covers, not only the preparation of the detailed
working drawings for steel structures, but also the design of
the details of construction. It is a text-book in structural
Drafting, and it may be used as a text-book in elementary
structural Design. As a reference book for structural
draughtsmen, it gives practical points as well as theory.
Knowledge of the use of drawing instruments is
presupposed, but the fundamentals of structural drafting
are fully presented. The application of these fundamentals
is illustrated by the drawings of many different types of
members of steel structure. Exceptionally exhaustive are
the chapters on the design of beams and the component
parts of plate girders. The tables at the end of the book are
sufficiently complete for most student courses, so that no
steel manufacturers' handbook need be used. Many of the
tables are arranged more conveniently for both students
and draftsmen than the tables in the usual handbooks,
particularly the tables for I-beams, channels, and angles.

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STEEL STRUCTRUES
INTRODUCTION:
Steel is an alloy made by combining iron and other
elements, the most common of these being carbon. When carbon
is used, its content in the steel is between 0.2% and 2.1% by
weight, depending on the grade. Other alloying elements
sometimes used are manganese, chromium, vanadium and
tungsten.[1]
Carbon and other elements act as a hardening agent,
preventing dislocations in the iron atom crystal lattice from sliding
past one another. Varying the amount of alloying elements and the
form of their presence in the steel (solute elements, precipitated
phase) controls qualities such as the hardness, ductility, and tensile
strength of the resulting steel. Steel with increased carbon content
can be made harder and stronger than iron, but such steel is also
less ductile than iron.
PROPERTIES OF STEEL: -
STEEL
PHYSICAL MAGNETIC
DUCTILITY
ELASTICITY
STRENGTH
TECHNICAL TERMS OF DESIGN OF STRUCTURES: -
1. DEAD LOAD: -
The self weight of the structure along with all
the super-imposed loads permanently attached to the
structure, is called dead load the dead loads do not change
their position or magnitude with time.

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2. LIVE LOAD: -
The load on a structure other than the dead load
is called live load. The live loads change their position and
magnitude with time, such as weight of the furniture. It is
expressed as uniformly distributed static load.
3. WORKING STRESS OR PERMISSIBLE STRESS: -
The allowable stress, to
which a structural member can be subjected, is called working
stress or permissible stress. It may be developed in the
member without causing structural damage to it.
4. BEARING STRESS: -
When a load is exerted or transferred from one
surface to another in contact, the stress is known as baring
stress. It is located on the net projected area of contact.
5. FACTOR OF SAFETY: -
The ratio of yield stress of the material to the
working stress is called factor of safety.
6. MODULUS OF ELASTICITY: -
The ratio of long longitudinal stress to the
longitudinal strain within the elastic region is known as
modulus of elasticity.
7. SHEAR MODULUS OF ELASTICITY OR MODULUS
OF RIGIDITY:
The ratio of shear stress to shear strain within the
elastic region is known as shear modulus of elasticity or
modulus of rigidity.
8. BULK MODULUS OF ELASTICITY: -
The ratio of hydrostatic
stress (or volumetric stress) to the volumetric strain within the
elastic region, is called bulk modulus of elasticity.

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9. POISSON’S RATIO: -
The ratio of transverse strain (or lateral
strain), to the longitudinal strain under an axial load, is known as
Poisson’s ratio. Its value for steel, within the elastic region,
varies from 0.25 to 0.33.
10.FATIGUE STRENGTH: -
The strength, at which steel fails
under repeated applications of load, is known’s as fatigue
strength.
11.IMPACT STRENGTH: -
The impact strength of steel is the
measure of its ability to absorb energy at height rates of
loading.
STEEL STRUCTURE JOINTS: -
Design of buildings and other
structures have two main aspects, viz. functional requirements
and safe to the loads coming over it.
METHODS OF CONNECTING STRUCTRURALSTEEL: -
The structural steel sections can be jointed
together by the following methods:
1. RIVETING: -
Rivets are manufactured from mild steel
bars by riveting machines. The members which are too jointed
are held securely together and holes are drilled to size in them.
The diameter of the hole is kept 15 mm larger than the nominal
diameter of the rivet up to 25 mm. for rivets more than 25 mm
diameter; the hole is kept 2.0 mm larger than the diameter of
the rivets.

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2. BOLTING: -
This is temporary fastening for jointing. The
structuralcomponents not subjected to vibrations can be joined
by means of bolts. Unfinished bolts whose shanks are not
uniform are called black bolts and are allowed lower
permissible stress. The turned and fitted bolts are allowed
higher stresses as per i.s.800 code. While doing riveting, the
bolts are also used in keeping the structural parts together as
temporary measure which is removed after riveting.

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3. WELDING: -
In this process the ends of the structural
part of be jointed are held in the position and are heated to
such an extent that the melts and on cooling becomes
homogeneous and joints the ends. The two most common
methods of welding are arc welding and oxyacetylene gas
welding. For satisfactory welding the addition metal is provided
with the help of metallic rod during heating the ends. Now-a-
days the welding has proved with the help of metallic rod during
heating the ends. Now a day the welding has proved to be most
effective and has replaced the riveting to a great extent.
TECHNICAL TERMS RELATING TO JOINTS: -
(a). NOMINAL DIAMETER OF RIVET: -
It is the actual diameter
of the rivet measured in cold condition before driving.
(b). GROSS DIAMETER OF RIVET: -
It is the diameter of the
rivet measured after driving. Actually it is equal to diameter of
the hole drilled for riveting. In all calculations of rivet joints this
diameter is taken into account for all calculation purposes.
(c).PITCH OF RIVET OF (p): -
It is centre to centre distance
between two rows of rivets measured the direction of the force.

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(d). GAUGE DISTANCE OF RIVET (g): -
It is the distance
between two rows of rivets measured between centre to centre
and measured at right angle to the force.
(e). EDGE DISTANCE: -
It is the distance of the edge of the member
from the centre of the rivet. It should not be less than 1.5
d.where “d” is the gross diameter of the rivet.
(f). NET DIAMETER OF THE BOLT: -
It is the diameter of the bolt
measured at the root of the thread.
(g). SIZE OF WELD: -
Itis the thickness of the fillet weld
measured along the plane of the member.
(h).THORAT THICKNESS: -
The minimum width of the weld measured at
angle 90 to the diagonal as calculating effective area of the weld
taking force, the throat thickness multiplied with the length of
the weld.
(i). BEARING STRENGTH: -
It is maximum strength of the rivet against bearing of
the plate.
(j). SHEAR STRENGTH: -
Itis a maximum strength of rivet or
bolt in shearing.
(k). TEARING STRENGTH: -
Itis maximum strength of the joint plate in
tension with rivet/bolt holes in it.

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(l). SOILD PLATE STRENGTH: -
The maximum strength of the
plate without any holes in tension.
(m). RIVTE – VALUE: -
It is the maximum strength of the rivet out of the
shearing and bearing strength for a particular joint. In case of
double cover place the shear strength is taken in double of that
of single cover butt joint or lap joint.
(n). EFFICIENCY OF JOINT: -
It is the strength of the joint divided by the
solid plate strength multiplied with 100. Mathematically –
DESIGN FORMULAE FOR RIVETED JOINTS: -
(a) . the diameter of the rivet is decided by using the following
unwin’s formula:
d = 1.91 t
Where d – normal diameter of the rivet in cm.
t – Thickness of the plate to be jointed in cm.
(b). the maximum bearing strength of the rivets is determined by
the following formula:
Pь = pь.dt
Where pь – maximum bearing strength.
pь – permissiblebearing stress.
d’ – gross diameter of the rivet or whole diameter.
t – Thickness of the plate.
EFFICIENCY OF JOINT = STRENGTH OF JOINTX 100 %
SOILD PLATESTRENGTH OF JOINT

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(c). the maximum tearing strength of the plate per pitch length of
the plates determined by the following formula:
Pᵼ=( p-d’)pᵼ
Where Pᵼ - maximum tearing strength.
p – Pitch of rivets.
d’ – gross diameter of rivets.
t – Thickness of the plate.
Pᵼ - permissible tensile strength in the plate.
(d). the shearing strength of the rivet is determined by
the following formula:
MAX.STRENGTH INSINGLESHEARPs = ps(π/4)(d’)²
MAX.STRENGTH INDOUBLESHEAR = 2 X ps(π/4)(d’)²
Where ps – permissiblestresses in shearing.
d’ – gross diameter of the rivet.
DETAILS OF STEEL COLUMNS: -
a) TYPICAL STRUCTURAL SECTIONS FOR COLUMNS :
Columns are
members carrying axial compression. Ideally their cross
sections should be so proportioned to have large radii of
gyration in both axes. Among I - sections ISHB with width
equal to depth are, hence, most suitable for columns.
Built up columns are made of double joists or double
channels. The compound sections are to be properly laced
or battened.
b) DETAILS OF LACED AND BATTENED CLOUMNS :
Lacing and
battens connect the channels together so that they act as a
single column. Lacing is preferred for columns with eccentric
loads, and battens for columns with axial loads.

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There are two types of lacing system –
i. Single lacing.
ii. Double lacing.

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(C) BEAM END CONNECTIONS TO CLOUMNS: -
Steel beams are connected to columns by –
 Framed connections.
 Seated connections.
FRAMED CONNECTIONS: -
Framed connection is two angle placed
on either side of the web of the beam and connected to column.
The connection should be able to resist the shear at the beam
end and the moment at the joints. A shelf angle provides as
temporary support for the beam at the erection time the
number of rivets are only indicative of the arrangement of
connection.

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SEATED CONNECTIONS: -
The seated connections of the beam to the column are of two
types:
i. Stiffened.
ii. Unstiffened.
The beam is connected to the column as it rests between a seat
angle at the lower end and a flange angle at the upper end of
the beam. A pair the seat angle. The stiffened seat connection is
when the beam load is heavy. The connection with only seat and
flange is called unstiffened seated connection.

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(d) COLUMN SPLICE AND GUSSETED BASE: -
a. COLUMN SPLICE :
A column splice is a joint which is required when
the column length is to be extended. The column is a compound
section consisting of ISHB 250 and flange plates 300 mm wide,
16 mm thick. Two splice plates are placed on either side of the
flange and connected by rivet to the columns on the upper and
lower portions of the joints. Cleat angles are used for alignment
at the erection stage.
b. GUSSETED BASE: -
A gusseted base is commonly used for
transferring the column load to concrete block of the
foundation. It consists of a base plate connected to the
column through gusseted plates and base angles. Holes are
left in the base plate for anchor bolts from the concrete.

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PLATE GIRDER
INTRODUCTION
A plate girder bridge is a bridge supported by two
or more plate girders. The plate girders are typically I-
beams made up from separate structural steel plates (rather
than rolled as a single cross-section), which are welded or, in
older bridges, bolted or riveted together to form the vertical web
and horizontal flanges of the beam. In some cases, the plate
girders may be formed in a Z-shape rather than I-shape.
DEFINITION
A built- up beam fabricated with plates and angles is called
plate girder.
COMPONENT OF PLATE GIRDER
1. Web plate
2. Flange plate
3. Flange angles
4. Stiffeners
 Intermediate stiffeners
 Bearing stiffeners
 Longitudinal stiffeners

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DECK-TYPE PLATE GIRDER BRIDGE: -
In the deck-type bridge, a wood, steel
or reinforced concrete bridge deck is supported on top of two or more
plate girders, and may act compositely with them. In the case of
railroad bridges, the railroad ties themselves may form the bridge
deck, or the deck may support ballast on which the track is laid.
Additional beams may span across between the main girders, for
example in the form of bridge known as ladder-deck construction.
Also, further elements may be attached to provide cross-. Bracing and
prevent the girders from buckling.
PLATE GIRDER BRIDGE: HALF-THROUGH TYPE: -
In the half-through bridge, the bridge deck is supported
between two plate girders, often on top of the bottom flange.
The overall bridge then has a 'U'-shape in cross-section. As
cross-bracing cannot normally be added, vertical stiffeners on
the girders are normally used to prevent buckling (technically

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described as 'U-frame behaviour'). This form of bridge is most
often used on railroads as the construction depth (distance
between the underside of the vehicle, and the underside of the
bridge) is much less. This allows obstacles to be cleared with less
change in height.
.
MULTI-SPAN PLATE GIRDER BRIDGE: -
Multi span plate-girder bridges may be an economical way to
span gaps longer than can be spanned by a single
girder. Piers serve as intermediate abutments between the
end Abutments of bridge. Separate plate girder bridges span
between each pair of abutments in order to allow for expansion
joints between the spans. Concrete is commonly used for low
piers, while steel trestle work may be used for high bridges

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.PURPOSE OF STEEL: -
1. To alter the magnetic and electrical properties of steel.
2. To change the structureof steel.
3. To increase the resistanceto heat corrosion.
4. To increase the surfacehardness.
5. To make the steel easily workable.
6. To vary the strength and hardness.
USES OF STEEL: -
NAME OF STEEL CORBON CONTENT USES
Mild steel up to 0.10% Motor body, sheet metal,
tin plates, etc.
Medium carbon
steel
up to 0.25% Boiler plates, structural
steel, etc.
up to 0.45% Rail, tyres, etc.
up to 0.60% Hammers, large stamping
and pressing dies, etc.
High carbon steel
or hard steel
Up to 0.75% Sledge hammers, springs,
stamping dies etc.
ADVANTAGES OF STEEL STRUCTURE: -
A steel structure has the following advantages:

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1. It possesses high strength.
2. It has long service life.
3. It is gas and water tight.
4. It can be readily disassembled or replaced.
5. It can be readily transported from the place of
manufacture to the work site.
6. It can resist high loads with comparatively light
weight and smaller dimensions.
NOTE: -
(1). A structure may be One dimensional, Two dimensional, and
Three dimensional. If the width and thickness of the structure is
small in comparison to its length, it is known as one dimensional
structure. A two dimensional structure is also called a surface
structure. A three dimensional structure is also called a space
structure and may have any shape.
(2). A structure in which the member is represented by a line, is
called a skeleton structure
(3). A structure large in two dimensions and small in third
dimension, is called surface structure.
DISADVANTAGE OF STEEL STRUCTURE: -
1. Steel structure, when placed in exposed conditions is
subjected to corrosion. There they require frequent
painting.
2. Steel structure need, fire proof treatment which
increases cost.
STEEL STRUCTURE DRAWING

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The main aim in that section was
that student should attain considerable skill in understanding and
drawing the main views, viz. elevation, plan, and side views of
object. Student also studied about other types of projection,
section and development of surface etc.
TECHNICAL TERMS USED IN STRUCTURAL DRAWING
A. PRELIMINARY DRAWING: -
Drawing adequate to serve as a basis
for more definitive drawing and showing the designer’s general
intension.
B. WORKING DRAWING: -
Set of drawing for the construction of a
building including architectural structural and service drawings
which usually include site drawings, general location drawing
(plan, section, elevation) assembly drawings and notes required
for construction.
C. SITE PLAN:-
Plans used to locate the position of building in
relation to setting out point, means of access, and general
layout of site. These plans also sometimes contain information
on services, drainage network etc.
D. LAYOUT PLAN: -
The plans used to identify site in relation to town plan.
E. GENERAL LOCATION PLAN:-
The plan used to show the
position occupied by various space in a building. The general
construction and location of principal elements, components
and assembly details.
F. DETAILS: -

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The drawing used to show all the information
necessary for manufactured and application of structural
components.
G. RANGE: -
Drawing used to show the basic sizes system
of reference and performance.
H. ASSEMBLY DRAWING: -
The drawings used to show in detail the
construction of building junction in and b/w elements and
components and b/w components.
I. SHOP DRAWING: -
The drawings used to assist the workman in
the manufactured fabrication (or) assembly of various parts.
J. ELEVATION: -
A vertical front view of a building element (or) of a
building components see from above.
K. PLAN: -
A horizontal section of a building at a given height
seen from above plan is also a horizontal view of a site (or) of a
building, of building components, of installations etc.
L. REFELECTED PLAN: -
A horizontal section of a building, at a given
height seen from below.
M. SECTION: -
A view of the parts contained in an
intersecting surface, usually a plan surface. It is also a section,
completed by the view of the parts behind the intersecting
surface.
N. VIEWS: -

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Representation on a plan of how an observer,
situated at infinity and looking in a direction perpendicular to
the plane. Sees a building element of building component.
WORKING DRAWNG
Following are the main requirements of structural working
drawings-
1. Main purpose of working to show how the design is too
materialized. The working drawing should give the client/
contractor exactly the information he needs. To get this
purpose the drawing should be neatly arranged and
systematically numbered.
2. It should be clear, simple and clean.
3. It should have only relevant and necessary notes.
4. It should be accurately drawn so that scaled measurement
agrees with figures.
5. It should be free of repetitious details.
6. Drawing the preparation of the working drawings. Its
relationship with the specification should be kept in mind and
the decision regarding specification should be transmitted to
those engaged upon working drawings.
7. Information relative to design, location and dimensions of the
elements of a product is the provider of working drawing.
8. Details should be indicating the filling together of materials and
the precise shape of various parts.
9. It should have neatness, ability for correlelating details and
their arrangement in a logical sequence.
10. The preparation working drawing requires considerable skill. A
good draughtsman should havethrough knowledge of building

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materials; method of construction and the ability t
comprehend the designer’s intent.
E L E M E N T S O F W E L D S Y M B O L S

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Following are the main elements which form a weld symbol.
1. REFERENCE LINE: -
Reference line is drawn first to represent a
particular weld (or) welds. The position of the weld basic symbol
with relation to the reference line indicates (or) represents the
location of the weld in relation to the arrow head. Weld on both
sides of the joints is represented by sketches on both side of the
reference line. If the weld is on the same side of the joint as the
arrow head, the weld sketch is drawn underneath the reference
line and vice versa.
2. ARROW: -
For providing complete indication of joint, in relation to
the part to be jointed, the head of an arrow is used in indicating
the reference side of the joint.
Care should be taken while drawing the basic
sketch symbol of the weld on the reference line. The
perpendicular portion of the basic symbolshould be always drawn
to the left he and side of the basic symbol, irrespective of the
orientation of weld metal.
3. BASIC SYMBOL: -
The basic symbols have been shown in following table.
DIMENSION AND OTHER DATA: -

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Following point is the carefully followed while
dimensioning and giving other data in structural weld
drawings.
(a) The length of the weld is denoted by letter ‘l’ when the
weld is continuous. It may be omitted.
(b) Letter ‘p’ denotes the unwelded length particulars of the
unwelded weld are described clearly.
(c) The included angle in case of grooves weld is denoted by
letter ‘a’.
(d) Root opening depth of filling for plug or slot welds are
denoted by the letter ‘r’.
(e) The size of the weld is denoted by the letter‘s’. In all
welding it is off the same size, one note indicating that unless
otherwise indicated, all fillet weld are mm size will be
sufficient and there is no need to write everywhere.
4. CONTOUR AND FINISH SYMBOLS: -

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Both the contour and finish symbols are used
together. The letter ‘f’ indicates the finish symbol. The finishing of
welds other then cleaning should be indicated by suitable contour
and finish symbol as given in table.
All the fillet welds, which are required to be welded approximately
flat faced without recourse to any method of finishing, are shown by
adding the flush contour to the weld symbol, observing the usual
location significance.
All the fillet welds, which are required to be made
flate faced by mechanical means, should be shown by adding both
the flush contour symbol and using standard finishing symbol to the
weld symbol.
When the fillet welds are required to be mechanically
finished to convex contour, they should be shown by adding both the
convex-contour symbol and user’s finish symbol.
4. SUPPLEMENTRY SYMBOLS: -
The supplementary symbolis located at
the point of changein direction of the reference line. Below the table
gives the interpretation of welding symbols commonly met in practice.
This table will give guidance to the students in drawing welding in
structuredrawings.

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STEEL SECTION FOR STRUCTURAL USES
Steel structure is built with rolled steel section. This
typical section and their properties are given below.
I- I - SECTION : -
There are five types of I-sections. I - section are used
for beams and columns.
 Indian Standard junior Beams (ISJB).
 Indian Standard Light Beams (ISLB).
 Indian Standard Medium Weight Beams (ISMB).
 Indian Standard Wide Flange Beams (ISWB).
 Indian Standard Column Section Beams (ISSC).
II- CHANNELS: -
There are three types of channel section-junior, light
and medium weight. Channels are used for columns, beams, and
purlins and for compound section.
 Indian Standard Gate Channel (ISGC).
 Indian Standard Junior Channel (ISJC).
 Indian Standard Light Channel (ISLC).
 Indian Standard Medium Weight Channel with sloping
flanges (ISMC).
 Indian Standard Medium Weight Channel with parallel
flange (ISMCP).

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III-EQUALS ANGLES: -
Equals angle is in four series with varying unit
weights under each designation. Equal angle is used as struts, ties
and gussets in compound sections.
 Indian Standard Equal angles.
IV-UNEQUALS ANGLES: -
They are also in four series according to
their unit weights. An unequal angle has more stiffness in the
direction of longer leg and hence finds use in purlins and
compound sections.
 Indian Standard Unequal angles.
V- TEE SECTION: -
They are either rolled or split from h - section.
They are in five series as shown.
 Indian Standard Rolled Normal Tee Bars (ISNT).
 Indian Standard Rolled Deep Legged Tee Bars (ISDT).
 Indian Standard Slit Light Weight Tee Bars (ISLT).
 Indian Standard Slit Medium Weight Tee Bars (ISMT).
 Indian Standard Slit Tee Bars from H - Sections (ISMCP).

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VI-PLATES: -
Plates, strips and flats are in used in fabricating
compound sections.
VII-ROUND AND SQUARE BARS: -
They are used for structural
works and other engineering fabrication.

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STEEL STRUCTURE FABRICATION
The fabrication of steel
structureis very important. Firstthe fabrication of parts is done
in the workshops and then it is dismantled and finally enacted
at the site; according to the markings done by the workshop.
FABRICATION PROCEDURE: -
The main fabrication
procedures which are done inside the workshop.
(1). CUTTING. (2). STRAIGHTENING.
(3). CROPPING. (4). SHEARING.
(5). DRILLING. (6). PUNCHING.
(7). BENDING. (8). RIVETTING.
(9). WELDING. (10). PLANNING.
(11). EDGEGRINDING. (12). TEMPLATE MAKING.
(13). BORING. (14). ERECTION AND CHECKING AT
WORKSHOP.
(15). SHOP PAINTING. (16). ERECTION MARKING.
(17). DISMANTLING AND DESPATCH.

34
ADMN. NO……………………. SIGN. OF T.O…………………………….
ROOF SYSTEMS WITH STEEL TRUSSES: -
Factory building is provided with roof system
consisting of steel trusses and roofing of as besots cement,
galvanised iron or aluminium sheet. Roof trusses are
economical for span more than 6m. Commonly a rise to span
ratio between 15to 1/3 is provided for trusses in Indian
conditions –
1. The roof with equal slopes on both sides.
2. North light roof with slope on south side and vertical
glazing on the north side, which admits uniform glare
free light inside the factory. The roof load is transferred
to the purlins which act as beams between the trusses.
The reactions from the purlins come at the nodal points
of the truss. In the truss action, the members are in axial
compression (struts) or in axial tension (ties).
“Truss fabricated for roof with hot-rolled steel sections is
called steel roof truss”.
COMPONENT OF ROOF TRUSS: -
i. SPACING OF TRUSS: -
The economical spacing of roof trusses works out to
be 1/3 to 1/5 of span.
ii. PRINCIPAL RAFTERS: -
The top chord members of a roof truss are called
principal rafters. They support the roof covering
through purlins. They are mainly compression
members and may be subjected to shear and
bending moment if the purlins are not placed at
nodal points.
iii. MAIN TIE: -
The bottom chord member is known as main tie. It is
usually in tension and takes compression if reversal
of loads occurs due to wind load.

35
ADMN. NO……………………. SIGN. OF T.O…………………………….
iv. RIDGE LINES AND EVES: -
The top line of the roof truss is called the ridge line
and the bottom edge of roof surface is called eves.
v. ROOF COVERING: -
Corrugated sheets of galvanised iron or asbestos
cement are commonly used. Glass, fibre glass and
slates are also used for covering.
LOADS ON ROOFS: -
The following loads acts on roofs:
I. DEAD LOADS: -
This includes load of roof covering,
purlins and self – weight of roof truss. The self – weight
of the truss can be assumed to be 100 to 150 N/m².
II. IMPOSED LOAD OR LIVE LOAD: -
IS: 875 – 1964 (revised) recommended for roofs
sloping greater than 10 degrees.
(a) For roof membrane, sheets or purlin 750 N/m²
less 20 N/m² for every degree increase in slope
over 10 degree subjected to a minimum of
400kN/m².
(b)For members supporting the roof members
and roof purlins, such as trusses, beams,
girders, etc.2/3 of load in (a).
III. SNOW LOAD: -
IS: 875 – 1964 recommends snow load of 25 N/m² per
centimetre depth of snow. No snow load may be
considered if roof slopes more than 50°. The possibility
of total or partial snow load should be considered, i.e.
half of the roof fully loaded with design snow load and
the other half loaded with half the design snow load.

36
ADMN. NO……………………. SIGN. OF T.O…………………………….
IV. WIND LOAD: -
IS: 875 – 1994 gives wind load in terms of basic wind
pressure p.
The design wind pressure on a roof is determined by
combination of external wind pressure and air pressure.
DESIGN DATAS: -
The steel roof truss is designed in such a way that it contains
either compression or tension member and does not having any
bending stress. In a truss the compressive members should be
short in length so as to reduce the buckling effect of the
members. The number of panels in a truss is determined by the
thumb rule.
n = (2/3) S n = number of panels s = effective span of
truss in meters.
1) Spacing of trusses
Common spacing ---- 3 to 5 m. Economical spacing ----
1/3 to 1/5 of span.
2) Pitch
 Corrugated Iron sheet ---- 26.50
 Asbestos sheet ---- 200
 Slates ---- 350
 Tiles --- 400
K 1.0 1.5 1.67 2.0 2.5
Increase in
permissible
stresses
33% 39% 41% 44% 50%

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ADMN. NO……………………. SIGN. OF T.O…………………………….
3) Spacing of purlins
Purlins are spaced such that they are at each
node of truss to avoid bending in the main rafter of the truss.
The spacing of the purlins also depends on the safe span of
sheeting material.
 Depth of purlin ≥ L / 45.
 Width of purlin ≥ L / 60. L is the spacing of trusses or
span of purlin.
4) Tension members.
 Double angle sections shall be used for main tie and single angle
sections for other members.
 Minimum size of the angle for main tie is ISA50x50x6mm.
 Minimum size of all other members is ISA50x50x5mm.
5) Compression members.
 Double angle sections are for main rafter.
 Single angle for other sections.
 When double angle are used for a member, they shall be
unequal angles with longer legs outstanding and when
single angles are used they shall be equal angles.
 Minimum size of the angle is 50x50x6mm for main rafter
and 50x50x6mm for other compression members.
6) Gusset plates.
 Minimum thickness –6mm
 Minimum size of rivets – 16mm.
 Minimum number of rivets – 2Nos.

38
ADMN. NO……………………. SIGN. OF T.O…………………………….
7) Bearing plate.
Bearing plate should be designed for total reaction at the
support considering the bearing pressure of supporting material.
Attach necessary anchor bolts also.
Minimumthickness of bearing plate shouldbe 6mm.

39
ADMN. NO……………………. SIGN. OF T.O…………………………….

40
ADMN. NO……………………. SIGN. OF T.O…………………………….
INDIAN STANDARDS
 IS 432 – 1982: Specification for mild steel and medium tensile
steel bars and hard drawn steel wire for concrete reinforcement
part – 1 Mild steel and medium tensile bar. Part – 2, Hard drawn
steel wire.
 IS 1786 -1985: Specification for high strength deformed steel
bars and wires for concrete reinforcement. [This has been
revised as 1786-2008(fourth revision)]
 IS 808 – 1989: Dimension of hot-rolled steel beam column,
channel and angle sections.
 IS 811 – 1987: Specification for cold-formed light gauge
structuralsteel construction.
 IS 1599 – 1985: Method for bend tests.
 IS 1608 – 1972: Method of tensile testing of steel products.
 IS 226 – 1975: Structuralsteel specification.

41
ADMN. NO……………………. SIGN. OF T.O…………………………….
REFERENCE
 DESIGN OF STEEL STRUCTURES. BY L. S. NEGI
Page no. 195 to 197
 CIVIL DRAUGHTSMANSHIP. BY G.S.BIRDIE
Page no. 659 to 678
Page no. 688
 BUILDING AND CIVIL ENGINEERING DRAWING.
BY DR.BALAGOPAL T.S. PRABHU
DR. K. VINCENT PAUL
DR. C. VIJAYAN
Page no. Part – VI
 INTERNET.
 TT – I NOTES
BY P.K. MADAVI SIR
Page no.
S

42
ADMN. NO……………………. SIGN. OF T.O…………………………….

43
ADMN. NO……………………. SIGN. OF T.O…………………………….

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ADMN. NO……………………. SIGN. OF T.O…………………………….

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