UKSSSC- Steel Structure

 INTRODUCTION

Study about all the components in which steel is used as structural member. Structure member like beam, column, slab etc and their method of connections also explained under the steel structure engineering. Steel structure also a broad field but here I will discuss only that point who is important in the purpose of UKSSSC JE Only.

Important Topics 👇

1- Connection and their types

2- Strength of all type connection

3- Beam and necessary criteria

4- Column and necessary criteria

📝 CHAPTER-1: RIVET CONNECTION

"The joint process of any two member by the mean of rivet, called rivet connection." Rivet made by mild steel generally. Rivet formed by following three are-

◆- shop rivet

◆- field rivet

◆- hand driven rivet 

On the behalf of these three types, find the strength of joint by given specification. Rivet provides either chain or zig-zag (stuggerd)

How to wind the diameter of a rivet:- 

Dia of rivet (Φ) = 6.05√t, t= thickness of member

This is called Unwin's formula and calculate the diameter in mm.

◆Gross dia of rivet -

● if thickness of member is less than 25mm- Ag = ¢+1.5

● if thickness of member is greater than 25mm- Ag = ¢+2

◆ Gross dia of bolt-

● if thickness of member less than 14mm- Ag = ¢+1

● if thickness of member 14mm to 24mm- Ag = ¢+2

● if thickness of member grater than 24mm- Ag = ¢+3

Permissible stresses on mild steel rivet- 

Rivet Joints- rivet joint provide in the following two manners:-

1- Lap joint

2- Butt joint

1- Lap joint- Lap joint also classified into two categories-

I)- Single Rivet Lap Joint- use only one rivet to joint two members

Single rivet lap joint

II)- Double Rivet Lap Joint- two rivet use joint two members.

Double rivet lap joint

2-Butt joint- Butt joint also classified into two categories-

I)- Single Plate Butt Rivet Joint- use a single plate member to made the connection b/w two members through rivet.

Single plate butt joint

Thickness of using plate is 20% more from thickness of main plates.

II)- Double Plate Butt Rivet Joint- two plate member are use in opposite direction of each other while connection is made through rivets.

Double plate butt joint

Thickness of using plate is equal to 3/5 to 5/8 time of thickness of main plate.

Criteria for providing rivet holes-

Arrangement or review hole in chain pattern

◆pitch- the horizontal distance b/w two adjacent rivet hole.

◆ gauge- the vertical distance b/w two adjacent rivet hole.

● minimum pitch distance- 2.5 time of rohit dia

● minimum edge distance for a rivet hole- 1.5Φ

●maximum pitch distance- 32t or 300mm whichever less

● in case of zig zag riveting the  gauge distance should not exceed 75mm

● pitch for tension member- 16t or 200mm whichever less

● pitch for compression member- 12t or 200 whichever less

Strength of various rivets joints-

A-shearing strength - π/4d^2×τab

B- Bearing strength - t×dn×fab

dn-gross dia of rivet

fab- bearing strength of rivet

C- Tensile strength - fst×(b-dn)×t

Rivet value(Rv) is equal to least value from shear,bear and tensile strength.

Number of rivet = Load/Rv

Efficiency of joint (η) = Rv / strength of solid plate ×100

Strength of solid plate = l×t×Fst

Fst = permissible stress

Fst for axial stress= 0.6fy

Fst for bending stress= 0.66fy

Fst for Bearing stress= 0.75fy

📝 CHAPTER-2: WELDED CONNECTION

Welded connection is classified under the following two categories are-

◆ Butt weld

◆ Fillet weld

A- Butt weld- Type of butt weld in various form like single v, double v, single u, double u, single j, double j etc..

♂ Throat thickness (tn) = 5/8 time of thickness of thinner member

♂ strength of butt weld = L×tn×Fst

Here tn= throat thickness and Fst = permissible stress

● maximum bending stress = 165 N/mm2

B-Fillet weld- fillet weld depend on the thickness of member and provide by connecting member in various angles.

♂ minimum thickness criteria-

Up to 10mm member - 3mm weld size

10 mm to 20 mm - 5 mm weld size

20 mm to 32 mm - 6 mm weld size

32 mm to 50 mm - 8 to 10 mm weld size.

♂ maximum size of weld = 3/4 × thickness of member

Throat thickness(tn) =k×size of weld

Where k depend on the facing angle of connection made.

Face angle       value of k

60°- 90°                0.70

91° -100°              0.65

101°-106°             0.60

107°-113°             0.55

114°-120°             0.50

Strength of fillet weld =L×tn×τab

τab =shear stress (108 N/mm2- maximum)

📝 CHAPTER-3 : TENSION MEMBER

Strength of member = Anet×Fst

Here Fst = permissible tensile stress in N/mm2

Anet= Actual area that will be covered

How to calculate Anet ?

◆ for chain rivet; - Anet= t(b-nd)

t = thickness of member 

b= width of member 

n= no of rivet

d= gross dia of rivet hole

◆ for zig-zag rivet; - 

Anet = t {(b-nd) + m×s^2/4g}

m= no of inclind line in a zig zag rivet connection

s= pitch distance

g= gauge distance

◆ Angle connection;-

● single angle connection: Anet =A1+A2K

Where K = 3A1/ 3A1+A2

● Double angle connection

♂ Same side gusset angle- Anet = A1+A2K

Where K = 5A1/5A1+A2

♂ Opposite side gusset angle- 

Anet = 2(Ag-dn×t)

Ag= gross area of angle find from steel table

dn = gross dia of rivet

📝 CHAPTER-4: BEAMS

◆Joist Beam - Roof supporting small size beam called Joist beam.

◆Girder Beam - To support the small size beam (Joist) called Girder Beam.

◆Lintel Beam - To provide the opening of window and doors, called Lintel Beam.

◆Purlin - Roof beam supported by roof truss.

◆Rafter - Roof beam supported by purlin.

◆Spenderal Beam- Roof beam placed at outermost wall of a building.

◆Stringer Beam- Longitudinal beam used in bridge floor and supported by floor beam.

◆Built-up Beam- Additional plate provide in the flange side with the help of rivet or weld joints.  

Why use the built-up beam ?

When M.O.R < M.B, than need to provide additional plate in flange side.

Reflection criteria for Beam-

● for simply supported beam - Deflection not exceed - span/325

● for cantilever beam - Deflection not exceed - 2×span/325

Depth Criteria of beam- Span/12 to span/14

Criteria for thickness of web-

● non staffined - not exceed d/85

● staffined - d/130 to d/200

d = depth of web

📝 CHAPTER-5 COLUMNS

Slenderness ration = effective length / r (min)

Radius of gyration (r) =√I/A

Section modulus (Z) = I/y

Short column- fail under the crushing

L/d < 12 or slenderness ration less than 32

Long column- fail under the buckling

L/d > 12 or slenderness ratio greater than 120

Intermediate column- slenderness ration b/w 32 to 120. fails under crushing and buckling both.

◆End Conditions of steel column 

◆ strut - strut is a inclined compressive member. Angle struts are classified as;

● Continuous angle struts

● Discontinuous angle struts

A- Continuous angle struts- 

¡ _connected by single rivet

♂ effective length KL = L

♂ permissible compressive stress = 0.8fac

♂ slenderness ratio not more than 180

¡¡_connected by double rivet

♂ effective length KL = 0.85 L

♂ permissible compressive stress = fac

¡¡¡_ double angle back to back

♂ effective length KL = 0.7 to 0.85L

♂ permissible compressive stress = fac

iv_ double angle same side

♂ effective length KL = L

♂ permissible compressive stress = 0.8fac

◆Lacing of column-

● thickness of single lacing 

t not less than KL/40

● thickness of double lacing

t not less than KL/60

◆ Spacing b/w lacing

● minimum - KL/r (min) not greater than 0.50

● maximum - KL/r (min) not greater than 0.07 × whole slenderness ration of column.

◆ Angle of lacing- not less than 40° and more than 70°

Stiffener-

●vertical - 0.33d - 1.5d

● horizontal - 0.2d

◆Most economical steel section - tubular section

◆the effective length of battled column increased by- 10%

◆the effective length of lacing column increased by- 5%

◆ slenderness ratio of a steel column suported through out it's length by masonry wall is -10

◆ steel column permissible stress in axial compression- slenderness ratio

◆ when only superimposed load act on column the value of slenderness ratio is- 180

◆ when column in compression, slenderness ratio is- 250

◆ when column in tension, slenderness ratio is- 350

◆ slenderness ratio for lacing column- 145

◆ economic depth of web plate is- 1.1√(m/σbc× Tw)

◆ shape factor- f= Zp/Z

● Rectangular -1.5

● Circular - 1.7

● Square and diamond- 2

● Triangle - 2.343

● I- section - 1.15

◆Width of lacing -