Design Of Steel Structure - 3350601

Dr. Subhash Technical Campus Faculty of Diploma Studies

Design Of Steel Structure - 3350601

1 Prepared By : Prof. Vandit Bhatt Diploma Civil Engineering

Concept of steel structure

The steel structure is a metal structure that is made of structural steel components

connect with each other to carry loads and provide stability to structure.

Structural steel is a category of steel which is made up of use of iron, carbon, and

manganese.

Most of structural element is available in various shape and it is create form of

Skelton by joining them with each other with the help of bolt connection or weld

connection.

Various types of structural components are made by two method either it is made by

hot rolled process or it is made by cold rolled process.

Based on carbon content , the steel is classified as

I. Low carbon steel ( 0.10 % to 0.25%)

II. Medium carbon steel ( 0.25% to 0.60%)

III. High carbon steel ( 0.60% to 1.5%)

Advantage of steel structure

Steel offers much better compressive and tensile strength as compare to concrete.

Lighter construction.

Erection is faster.

Connection using bolting, welding, riveting can be done easily.

Unlike masonry or RCC, steel structure can be easily recycled.

Life of steel structure is more as compare to other structure.

Disadvantage of steel structure

It requires corrosion protection.

Strength reduce at higher temperature.

It requires skilled workers to construct the structure.

Cost of steel structure is more than concrete structure.

Design philosophy of steel structure

Structural steel design consist mainly three design philosophy

I. Working stress method (WSM)

II. Ultimate strength method (USM)

III. Limit state method (LSM)

The course deals with design of steel structures using “limit state design Method”.

The design methodology is based on the latest Indian standard code of practice for

general construction. ( IS -800: 2007)




Introduction of bolted connection

Various structural components such as beam, column, strut, tension member etc. are

connected with each other and its make a form of steel structure.

Many components are made by angle, plates, channels, I section etc.

This component is connected by bolt, weld or rivet.

Bolt are most common fasteners which is used to connect this component and make it

safe and serviceable structure.

Types of connection

Based on rigidity we can classify the connection in three types

I. Rigid Connection

II. Pinned or simple connection

III. Semi rigid connection.

In rigid connection structural member can resist axial force, shear force, and bending

force.

In rigid connection position of ends or joints does not change.

In simple or pined connection there is only axial force and shear force can be

transferred but moment cannot be transferred, it create some amount of moment in

member.

In semi rigid connection axial force and shear force transfers completely in member

but moment transfers partially in member.

In actual field there is all connection is semi rigid connection.




Types of bolt

For the connection of structural member various types of bolt is used.

I. Black bolt or C grade bolt or unfinished bolt

II. Turned bolt

i. Precision bolt ( A grade bolt)

ii. Semi precision bolt ( B grade bolt)

III. Ribbed bolt

IV. High strength friction grip bolt ( HSFG Bolt)

For 4.6 class bolt,

Fu = 400 N/mm2

Fy = 240 N/mm2

Advantage of bolted connection

No need to hammering so it is sound proof work.

Accident of fire not to be done in steel structure.

No need to expensive equipment.

This can be done by unskilled workers.

Small changes can be possible during work process.

All components can be easily unbolted so it can be use in other places.

It is not time consuming work.

Bolt holes

For the connecting two structural member to each other by bolt we need to make a

hole in member.

Generally holes are made by drilling process.

Other method is punching sometimes used but it reduce ductility and toughness of

member.

As per IS-800 : 2007 ( cl. 17.2.4.2) we should use material whose yield strength is

more than 360 Mpa for punching othewise it is advisable to use drilling to make hole

in structure.

Standard clearance of bolt holes

Bolt hole diameter is made larger than diameter of bolt.

Extra larger portion of holes is called clearance.

Here diameter of bolt is denoted by d and hole diameter is denoted by dh.

Nominal size of bolt ,d ( in mm)

Standard clearance (In mm)

12 to 14 mm 1 mm

16 to 24 mm 2 mm

> 24 mm 3 mm

If d = 16 mm diameter , the hole dia. is = 16 + 2 = 18 mm




Minimum and Maximum spacing ( pitch)

A centre to centre distance between two adjacent bolt is called pitch distance.

As per IS-800, cl. 10.2.3 , page 74 , maximum distance between two bolt should not

exceed 32 t or 300 mm

Where t is thickness of thinner plate or angle.

As per IS-800: 2007, cl. 10.2.2, page 73, minimum pitch distance should be 2.5 d,

where d is dia. Of bolt.

Forex.For20 mm dia. Bolt minimum pitch= 2.5*d=2.5*20 =50mm

Edge distance, end distance & gauge distance

The distance between centre of bolt and edge of plate or angle element is called end

distance.

A perpendicular distance between centre of bolt and edge of element is called edge

distance.

The minimum edge / end distance,

= 1.7 *dh ….for hand flame cut edges.

= 1.5 * dh…. for machine flame cut edges.

For ex. 20mm dia bolt min edge distance = 1.7 * dh ( hand flame)

e= 1.7 * 22 = 37.4 mm = 40 mm

Types of bolted joints

Bolted joints can be classified into two groups

I. Lap joint

i. Single bolted lap joint

ii. Double bolted lap joint

iii. Chain bolted lap joint

iv. Zigzag bolted lap joint

II. Butt joint

i. Single cover butt joint.

i. single bolted

ii. double bolted

ii. Double cover butt joint




Failure of bolted joints

Shear failure of bolt

Bearing Failure of bolt

Tensile failure of bolt

Bending failure of bolt

Shear failure of plate

Bearing failure of plate

Tensile failure of plate.




EXAMPLES

Example: Two Plate 80 mm wide and 12 mm and 20 mm thick are connected by lap

joint to resist design tensile load of 70 kN. Design a lap joint using M 16 bolts of grade

4.6 and grade 410 plates.

Solution:

Nominal diameter of bolt, d = 16 mm

Hole diameter = do = 16 + 2 = 18 mm

The bolts are in single shear.

70kn

Shear capacity of bolt:

Vnsb=

(nn . Anb+ ns Asb)

Vnsb=

(1 x 157+ 0)

Vnsb= 36257.59 N

Vnsb= 36.26 kN

Design shear capacity of bolt,

Vdsb=

=

= 29.0 kN

IS : 800 – 2007 cl. 10.3.3, page 75

for 4.6 grade bolt,

fu = 400 N/mm2

nn = 1 ( single shear)

ns = 0

20 mm

12 mm

70 kN

70 kN




IS : 800 – 2007

cl. 10.3.4, page 75

IS : 800 – 2007

cl. 10.2.2

cl. 10.2.4.2, page 74

Minimum pitch

p = 2.5 d

= 2.5 x 16

= 40 mm

fu = 400 MPa (for bolt)

t = 12 mm ( thinner plate)




Introduction of welding process

Welding is a method of connecting two pieces of metal by heating to a plastic or fluid

state with or without pressure.

Two types of welding process is used (i.e. electric welding and gas welding) , in most

of structural element is connected by electric welding.

However gas welding is also used primarily for cutting pieces to shape.

It is slow and hence it is generally used for repair and maintenance work only.

Electrodes are heated at around 3300 Co to 5000 Co and filled liquid metal between

the gaps of two metal elements to make a bond between them.

Various process of welding are used in structural steel application are as under

1. Shielded metal arc welding (SMAW)

2. Submerged arc welding (SAW)

3. Gas – shielded metal arc welding (GMAW)

4. Electro slag welding (ESW)

5. Flux core arc welding (FCAW)

6. Stud welding (SW)

Advantages of welding

The structure has less weight as compare to bolted connection

Welding process is quick and save time of construction.

Welded structure is more rigid as compare to bolted connection.

Noise produce is very less, therefore suitable for residential areas.

Welded connection gives better appearance to the structure.

Welding is practicable even for complicated shapes of joints.

Welding can be done easily in narrow space.

Painting can be done easily.

Disadvantages of welding

Welding is requires highly skilled persons.

The inspection of welded joint is difficult and expensive.

Costly equipment is necessary to make welded connection.

Welded joints are brittle and have less fatigue strength.

Members jointed by welding may distort due to heating of members

Welding at the site may not be feasible due to lack of power supply.

Types of welds

1. Groove weld or Butt weld

2. Fillet weld

3. Slot weld

4. Plug weld




Fillet weld are used 80%

Groove weld are used 15%

Slot and plug weld are Used 5%

Properties of fillet weld

Properties of fillet weld

Size of weld (S)

Effective throat thickness (tt)

End returns




Overlap

Effective length or area of weld

Minimum Size of Weld (S)

The size of fillet weld should not be less than 3 mm nor more than thickness of

thinner part joined.

The minimum size of fillet weld shall be as per given table.

Maximum Size of Weld (S)

Maximum size of weld is equal to the thickness of plate.

When the thickness of thinner plate is more than 6 mm the size of weld should be at

least 1.5 mm less than the thickness of that plate.

When the fillet weld is applied to the round toe of the section the size of weld should

not be exceed ¾ of the thickness of thinner plate.

Effective throat thickness (tt)

The effective throat thickness of a fillet weld is the shortest distance from the root to

the face of the weld.

The effective throat thickness of fillet weld shall not be less than 3 mm an d shall not

be exceed 0.7 a , where a is a size of weld in mm.

If fillet weld is having equal and unequal legs, the effective throat thickness shall be

compute as




End returns

The fillet weld terminating at the ends or sides of parts should be returned

continuously around the corners for a distance of not less than twice the size of weld

end returns 2S, where S = Size of weld




Examples

Design suitable fillet weld to connect a tie plate 60 mm * 8 mm to a 12 mm thick

gusset plate. The plate is subjected to a load equal to the full strength of the

member; assume shop weld and Fe 410.

Solution:

Cross sectional area of the tie plate,

Ag = 60 * 8 = 480 mm2

For Fe 410, fy = 250 N/mm2.

Tension capacity of the member,

For 8mm thick plate, Is: 800-2007

Minimum size of weld = 3mm Table -21

Maximum size of weld = 8 – 1.5 = 6.5mm (cl. 10.5.8.1) Page -78

So , use size of weld between this two value

Take S = 4mm

Effective throat thickness tt =0.7 * S

= 0.7 * 4

tt = 2.8 mm

For fu = 410 N/mm2 and shop welding,

fwd = 189 N/mm2

P = lw. tt.fwd

109.09 * 103 = lw * 2.8 * 189

lw = 206.14 mm.... Total length of weld is required

Consider only side welds (no end weld)

Length of weld on each side = 206.14/ 2

= 103.07mm

End returns = 2S

= 2 * 4

= 8mm

Required length of weld on each side

= 103.07 + 8

= 111.07 mm




Introduction of Tension Member

A structural member which takes axial tensile load on it and the length of member is

increased is known as tension member.

It is also known as Tie member or Tie.

When tension members takes load on it the stress distribution is uniform on all over

structural member. So maximum stress can get by net area which is resist by cross

sectional area.

So tension member is economical and effective in industries.

In the tension member there is no local buckling so maximum yield strees value can

be applied on member.

Examples Of Tension Member

Components of roof truss

Sag rod in roof purlin system.

Bridge trusses.

Suspenders in suspension bridges.

Cables in cable stayed bridges

Transmission and communication line.

Wind bracing system in multi storied buildings.

Types Of Tension Member

Based on types of structure it can be classified into five groups.

Single structural member ( rolled section)

Compound section

Built up section

Rods and bars

Wires and cables

Design Strength Of Tension Member

Design strength should follow Below condition

T < Td.

Where Td is Design strength of the member in tension.

The design strength of member under axial tension Td is kept lowest of the three.

i. Design strength Due to yielding of gross section (Tdg)

ii. Design strength of rupture of critical section ( Tdn)

iii. Design Strength due to block Shear ( Tdb)




Design strength Due to yielding of gross section (Tdg)

In general tension member can resist ultimate load without failure.

This value can be find by bellows equation

Tdg = Ag .fy/ ymo IS- 800, Pg -32

Where

fy = yield stress of material

Ag= gross area of section

ymo = partial safety factor

Design strength of rupture of critical section ( Tdn)

When bolt hole area is deduct from member we get net area of member.

According to elasticity theory stress value near to the bolt hole is 2 to 3 times larger

than normal stress of member.

So it is advisable that the member should design with less bolt hole so member can

get maximum stress value on it by applied load.

For Plates

The design strength due to rupture of critical section of plate (Tdn) is given by

Tdn = 0.9 An fu/ ym1

Where

An = net area of the member

fu= ultimate stress of the material

ym1= Partial Safety factor

For Angle

Tdn = 0.9 Anc.fu/ym1 + β. Ago.fy / ymo

Where ,

Β= 0.7 >1.4 -0.076 (w/t)(fy/fu)( bs/Lc) < fu.ymo/fy.ym1

W= outstand lag width

Bs= shear lag width

Anc= net area of the connected leg

Ago= gross area of outstanding leg

Lc= c/c length of bolt hole

For Preliminary sizing the rupture strength of net section may be approximately taken as :

Tdn = α An.fu /ym1

α= 0.6 for one bolt, 0.7 for three bolt, 0.8 for four or equivalent weld length




Design Strength due to block Shear ( Tdb)

The block shear strength , Tdb of connection shall be taken of smaller of

Tdb1 = ( Avg. fy/3. ym1). + 0.9 Atn. fu. / ym1)

Tdb2 = ( 0.9 Avn. fu/ 3 ym1) +Atg. fy/ ymo)

Tdb is considered as smaller of the Tdb1 & Tdb2.

EXAMPLES

A single unequal angle 100 * 75 * 6 mm is connected to a 10 mm thick gusset plate at

the ends with six 16 mm diameter bolts to transfer tension. Determine the design

tensile strength of the angle assuming the yield and ultimate stress of steel used are

250 Mpa and 410 Mpa. Assume that the longer leg is connected to the gusset plate.

Also calculate the efficiency of the member.

Solution:

d = 16mm , 6 nos of bolt

do = 16 + 2 = 18 mm

fy= 250 Mpa

fu = 410 Mpa

g = 60mm

Area of gross section for ISA 100 * 75 * 6 mm

Ag = 1014 mm2

Minimum edge distance = 1.7 dh

= 1.7 * 18

= 30.6mm

e= 40mm

Minimum Pitch distance = 2.5d

= 2.5 * 16

p= 40mm

Strength govern by yielding of gross section Tdg




Tdg = Ag.fy / γmo

= 1014 * 250 / 1.10

= 230.45 KN.

Strength govern by rupture of critical section Tdn

Tdn = 0.9 Anc. fu/ γm1 + β Ago. fy/ γmo

where , β = 1.4 – 0.076 ( w/t) ( fy/fu) ( bs/Lc)

w = outstanding leg width = 75 mm

bs = shear leg width = 75 + 60 – 6 = 129 mm

Lc = c/c dist. bet. The out most bolt in the direction of load = 5 * 40 = 200mm

β = 1.4 – 0.076 ( w/t) ( fy/fu) ( bs/Lc)

β = 1.4 – 0.076 ( 75/6) ( 250/410) ( 129/200)

= 1.026 > 0.7

and, fu. γ mo/ ( fy. γm1) = 410 * 1.10 / ( 250 * 1.25)

= 1.44

1.026 < 1.44 … ok

β = 1.026.

Anc = net area of connecting leg = [( (100) – ( 6/2) – 18) * 6] = 474 mm2

Ago = gross area of out standing leg = [ ( 75 – ( 6/2) ) * 6] = 432 mm2

Tdn = 0.9 Anc. fu/ γm1 + β Ago. fy/ γmo

= (0.9 * 474 * 410 / 1.25 ) + (1.026 * 432 *250 / 1.10)

= 139924.8 + 100734.54

= 240659.3 N

Tdn = 240.66 KN.

Strength govern by block shear:

Avg = [(5 * 40 ) + 40] * 6 = 1440 mm2

Avn = [ ( 5 * 40) + 40 – (5.5 * 18 )] * 6 = 846 mm2

Atg = 40 * 6 = 240 mm2

Atn = [(40 –(0.5 *18) *6] = 186 mm2

Tdb1 = Avg.fy/( . γmo) + 0.9 Atn.fu/ γm1

= 1440 * 250/ ( * 1.10 ) + (0.9 *186 *410 ) / 1.25

= 188951 + 54907

= 243858 N

= 243.86 KN

Tdb2 = 0.9 Avn.fu/( . γm1) + Atg.fy/ γmo

= 0.9* 846* 410 / ( . 1.25) + 240 * 250 / 1.10

= 144187 + 54545

= 198.73 KN

Smaller of Tdb1 & Tdb2 is Tdb

Tdb = 198.73 KN

The design strength of angle is smallest of Tdg, Tdn, Tdb. is value of Td.

Td = 198.73.KN.




Efficiency of the member :

Tension capacity of the member ,

Tdg = Ag.fy/ γmo

= 230.45 KN

Tensile strength of the member ,

Td = 198.73 KN.

η = Td / Tdg

= 198.73 / 230.45

η = 86.23 %




Introduction of compression member

A structural member consist axial compressive load is called compression member.

Two types of compression member are:

1. Column

2. Strut.

When compression member is in vertical position is called column.

Strut can be use in horizontal, vertical, inclined direction but it is used for shorter span

and small loading.

Shape of compression member is depends on availability of section, connection

problems and types of structure.

Effective length of compression member

For compression member the distance between two points of bending part of column

where moment value is zero, this length is called effective length (kL).

Effective length is depends on the end condition of column.

End condition can be classified into four group

I. Both ends pined (hinged)

II. Both ends are fixed

III. One end fix and other hinged

IV. One end fix and other free

Short, long and intermediate compression member

Length of column is less as compare to its cross sectional area is known as short

column.

L/r <= 88.85 and fy = 250 Mpa. for short column

This member is not used in practical field.

Length of column is more as compare to its cross sectional area is known as long

column.

Intermediate member is fail by buckling and yielding and it is behave like inelastic.

Failure modes

The possible failure mode of an axially loaded column can be classified into three

groups.

1. Local buckling

2. Overall flexural buckling

3. Squashing




Design Compressive Strength Of Compression Member

Axially Loaded Member

i. concentrically loaded

ii. Loaded Through One Leg

The design compressive strength Pd is given by

Pd = Ae * fcd

Where Pd = factored load on column

Ae = effective cross sectional area.

fcd = design compressive stress




Introduction

When column resist more load, internal connection should put to joint column so

column can be effective and effective.

Spacing of two component of column should be arranged such as that its slenderness

ratio will be same for both column.

When column is made by two or more column elements is called built up column.

Generally It is made of angles, channels, I-section and joint in the direction of length.

Two element can be joint by

1. Lacing

2. Battening

Function of lacing or battens is to held the column in its original position after loading

is applied. Other function is to distribute stresses equally in two column.

Lacing and battening is not design as load carrying member.

Lacing

Lacing system is two types.

1. Single lacing system

2. Double lacing system

Lacing should be uniform through out in the length of column.

Generally for the lacing member flats, angles or round bars is used.




Distinguish between single lacing and double lacing

Single lacing One member is used on one face of

column.

Used when load value is small.

Effective length Le = L

Min. width of lacing , b = 3d

where d = dia. Of bolt.

Thickness of lacing

t > Le/40

Axial force in lacing

F = Vt / 2 Sinθ

Double lacing Two member is used on one face of

column.

Used when load value is large.

Effective length Le =0.7 L

Min. width of lacing , b = 3d

where d = dia. Of bolt.

Thickness of lacing

t > Le/60

Axial force in lacing

F = Vt / 4 Sinθ

Design requirements for lacing

1. Angle Of Inclination (θ) cl. 7.6.4

2. Slenderness ratio (KL/r) cl. 7.6.5.1

3. Effective length of lacing (Le) cl. 7.6.6.3

4. Width of lacing bars (b) cl. 7.6.2

5. Thickness of lacing (t) cl. 7.6.3

6. Transverse shear (Vt) cl. 7.6.6.1

7. Check for compressive strength

8. Check for tensile strength

9. End condition

10. Overlap




Example : design a single lacing system for a column composed of 2ISMB 300 @35.8

Kg/m placed back to back at clear spacing of 200 mmAxial factored load on column is

1500 KN. Effective length of column is5m.

Solution :

Assume angle of lacing θ = 45˚

For ISMC 300

g = 50 mm

rmin = 26.1 mm

For 2- ISMC 300

rzz = 118.1 mm

ryy = 126.3 mm ( for spacing of 200mm)

Spacing of lacing = Lo

Lo = 2 ( 50 + 200 + 50)

= 600 mm

For each component of column

Lo/rmin = 600 / 26.1 = 22.98 < 50 …. OK

For built up column

KL/rmin = 5000/118.1 = 42.34

22.98 < 0.7 * ( 42.34 * 1.05)

< 31.12 …..OK

Single lacing is sufficient

Efective length of lacing (Le) :

Effective length of lacing,

Le =

= 424.26 mm

Width of lacing (b)

Assume 16 mm dia. Bolt

b = 3d

b = 3* 16

= 48 mm

Provide b = 50 mm

Thickness of lacing (t) :

For single lacing

t = Le / 40

t = 424.26/40

t = 10.6 mm

Size of lacing flat is 50 * 12 mm.

For lacing bar,

I =

= 7200 mm2

A = 50 * 12




= 600 mm2

rmin =√

=√

= 3.464 mm

Le/rmin of the lacing bar = 424.26/3.464

= 122.47 < 145….OK

Now, for Le/rmin = 122.47 and fy = 250 Mpa

10 9.4

2.47 ?(2.32)

fcd = 83.7 – 2.32

= 81.38 N/mm2

Compressive strength of lacing (Pd)

Pd = Ae * fcd

= (50 * 12 ) * 81.38

= 48.83 KN

Transverse shear force (Vt):

Vt = 2.5 % of axial load on column

= (2.5 / 100 ) * 1500

= 37.5 KN (for two sides of column)

Axial force in lacing = Vt / 2 sin θ

F = 37.5 / 2 sin 45

= 26.52 KN ( for one side column)

48.83 KN > 26.52 KN , hence lacing is safe in compression.

Check for tensile strength :

Td = 0.9 (b – d) t .fu / γm1

= 0.9 (50 – 18) * 12 * 410 / 1.25

= 113.35 KN

OR

Td = Ag.fy/γmo

= (50 *12)*250 / 1.10

= 136.36 KN

Td is taken smaller of this two value

Td = 113.35 KN > 26.52 KN

Hence, lacing flat is safe in tension.




Section used for purlin

Purlin provides support to the roofing material, various loads act on purlin are:

Weight of roof covering and fixtures

Self weight of purlin

Live load from sheeting

Snow load ( if exists)

Wind load from sheeting.

Self weight of purlin, live load and weight of roof covering acts vertically downward.

Various section used for purlins like

Angle purlin- it is used for small shops when spacing of roof truss is between 3 to 5 m.

Channel Section- It is used for medium shops when spacing of roof truss is between 4 to 6

m.

Beam purlin – It is used for heavy shops, when spacing of roof truss is between 6 to 8 m.

Distinguish between angle purlin and tubular purlin

Angle purlin

Generally used in every types of roof

truss.

For Same load and span weight of

angle section is more as compare to

pipe section.

For 1 m length c/s area and weight is

more as compare to tubular section.

surface area is more for angle

section

Maintenance is costly

Tubular purlin

Generally used for light weight

structure.

For Same load and span weight of

pipe section is more as compare to

angle section.

For 1 m length c/s area and weight is

less as compare to angle section.

Surface area is less for pipe section.

Maintenance is economical.

Design of angle purlins

Angle purlin is unsymmetrical on both axis.

Angle purlin is advisable to use when angle of roof truss is less than 30 degree.

As per BS 5950-1 : 2000 angle purlin should be design as below

i. In the design of purlin un factored load is used.

ii. Span of purlin should not be more than 6.5 m.

iii. Roof slope should not more than 30 degree.

iv. Load acts on purlin considered as uniformly distributed.

i. Minimum depth of purlin = L / 45 , where L = span of purlin.

ii. Minimum width of purlin = L / 60 , where L = span of purlin

iii. Maximum B.M. in purlin , Mz =

, where w = udl in KN/m (working load).




iv. section modulus required.

Zez =

, where Zez = elastic section modulus, bending about z-z axis.

v. Permissible deflection :

permissible deflection =

, IS-800 , pg. 31, Table -6

actual deflection =

, ….. For udl.




Advantages of steel roof truss over timber truss

Steel roof truss is more stronger and durable as compare to timber truss.

Steel truss can be made in any shape as per architectural need.

Steel truss is available in various size and less wastage of material.

Steel roof truss is fire proof and termite proof.

Steel roof truss can be prepared in a very less time.

For longer span steel roof truss can be use easily.

Repair and maintenance cost is less as compare to other structure.

Cross sectional area of the members is less.

Component of roof truss

Span : centre to centre distance between two support of roof truss is called span.

Spacing of roof truss : horizontal distance between two roof truss is called spacing of

roof truss. In general spacing of roof truss is kept as 1/3 to 1/5 of span.

Principal rafter : distance between support of roof truss to ridge point is called

principal rafter. It provide support to the purlin and roofing material.

Main tie : bottom chord member of roof truss is known as main tie. It provides

support to sag tie and ridge.

Sag tie: connecting line of ridge point and centre of main tie is known as sag tie.

Ridge line: connecting line of ridge point of one truss to ridge point of other truss is

known as ridge line.

Eaves line: connecting line of bottom point of one roof truss to other roof truss is

called eaves line.

Purlins: a member is placed on two adjacent point of panel point is called purlin. It

provides support to the roofing material. Purlin is placed on principal rafter.

Rise: vertical distance between main tie to ridge point is caaled rise.

Pitch: ratio between rise to span is called pitch. In general pitch kept as 1/3 to 1/5 of

span.

Roofing material: a material is used for cover purlin and truss is known as roofing

material. Generally roofing material is made up of G.I Sheet or A.C Sheet.

Documents

Design Of Steel Structure - 3350601