semester ii (2018-2019)

University of Anbar Steel Structures (DWE4336)

College of Engineering Dr. Ahmed T. Noaman

Department of Dams & Water Resources Eng. Phase: 4

Semester II (2018-2019)

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Course Description:

Design of structural steel systems using AISC LRFD code, welded and bolted connections of

axial members, framed and seated shear connections, rigid and semi-rigid moment

connections, base plate connections, beam and column splices, steel concrete composite

construction, and use of software to design typical systems.

Recommended Textbook(s):

---------------------------

Prerequisites:

DWE3313 Strength of materials

DWE3321 Theory of Structures

Course Topics:

1 Structural Design Philosophy, an introduction to the LRFD method.

2 Properties and behavior of structural steel.

3 Strength of tension members, design by codes and specifications.

4 Strength of compression members, design by codes and specifications.

5 Strength of beams in bending, design by codes and specifications

6 Bending and axial forces in beam-columns, design by codes and specifications

7 Introduction to plastic hinges, collapse mechanism.

8 Steel member connections, design by codes and specifications.

9 Design of a complete steel structure (Design of Hydraulic steel structure).

10 Use of commercial software for the design of structural elements

Program and Course Outcomes:

1. Students should be able to design bolted and welded connections and composite (steel/concrete)

beams and columns.

2. Students will also be familiar with the use of plastic analysis to determine failure modes and

Corresponding ultimate capacity of steel structural systems.

3. Students will learn to use commercial software to analyze and design steel structural elements

Class Schedule: 50-minute session (Monday) + 100 -minute session (Thursday) per week





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Methods of Assessment:

Progress exams (P1 and P2) in March and May 2019 (20% marks)

Quizzes (min. two) (5% marks)

Attendance and Class activity (5% marks)

Student Project (5% marks)

Home work (5% marks)

Final exam (60% marks)

Selected References

1. J.C. McCormac and S. F. Csernak , Structural Steel Design, LRFD Method, Prentice Hall, 5th

edition, 2012.

2. Manual of Steel Construction, LRFD, Fourteenth Edition, American Institute for Steel

Construction, 2011

3. W. Segui, Steel Design, Global Engineering, 5th edition, 2013.

4. Design of hydraulic steel structures, ASCE Press, 1997.





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Chapter one

Introduction

1. Types of steel structures:

1 – Building: (1) public, (2) industrial, (3) residential

2 – Bridges: (1) pedestrian, (2) over ground, (3) railroads

3 – Others: (1) transmission towers , (2) vessels , (3) gates , (4) tanks (5) ships and air planes

2. Steel:

The basic constituent of structural steel is iron, an element widely and liberally available over the

world’s surface but with rare exceptions found only in combination with other elements. The main

deposits of iron are in the form of ores of various kinds which are distinguished by the amount of

metallic iron in the combination and the nature of the other elements present. The most common ores

are oxides of iron mixed with earthy materials and chemically adulterated with, for example, sulphur

and phosphorus. Iron products have three main commercial forms; wrought iron, steel and cast iron in

ascending order of carbon content.

Table 1.1, which gives some physical properties of these three compounds, shows that as the carbon

content of the metal increases the melting point is lowered; this fact has considerable importance in the

production process. Modern steelmaking depends for its raw material on iron produced by a blast

furnace. Iron ore is charged into the furnace with coke and limestone. A powerful air blast raises the

temperature sufficiently to melt the iron, which is run off. The iron at this stage has high carbon

content; steel is obtained from it by removing most of the carbon. In the most modern processes

decarburizing is done by blowing oxygen through the molten iron.





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3. Advantages of steel as a structural material

1. High strength

2. Uniformity

3. Elasticity





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4. Permanence

5. Ductility

6. Toughness

7. Addition to existing structures





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8. Miscellaneous

4. Disadvantages of steel:

1. Corrosion

Cavitation





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2. Fireproofing cost

3. Susceptibility to buckling

4. Fatigue





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5. What is Steel? " Steel Properties"

- It's an alloy of iron and the nonmetallic element carbon 0.3 – 0.2 % .

Carbon steels "structural"

High strength or low alloy

Tempered alloy

6. Stress - Strain diagram for steel





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Table (2-4) page 2 – 48 structural steel specifications AISC "

American Institute of Steel Construction" – LRFD " Allowable stress

Design " Manual

Example: A36 fy = 36 ksi (yield stress)

fu = 58 ksi (ultimate strength)

ε

0.002

Modulus of elasticity for aluminum is 10,000 ksi while for steel is ≈ 30000

ksi. Thus , the elastic deformation of an aluminum structure = 3 times that

of an identically loaded steel structure of the same dimensions

- yield of aluminum fy = 35 ksi

Strength = 38 - 42 ksi

- weight of alloy is about 36% as much as steel , besides

resistance to corrosion , reduced maintenance but higher initial

cost.

fy fu

σ

High strength steel





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7. Structural Steel sections

(5 – 1) standard rolled shapes:

They are formed from hot steel by passing through roll several times to

obtain the desired shape.

Standard Sections

1 – W section (wide – flange section)

W36*230 tables (p.p. 1 – 12 , 1 -29)

36. nominal depth

230 weight of sect. per foot

2 – S section (Standard beam section)

S18*70 table (p.p. 1 – 32 , 1 -33)

3 – M shapes (Special sections from W sections)

Tables (p.p. 1 – 30 , 1 -31)

4 – HP shapes

Tables (p.p. 1 – 34 , 1 -35)





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5 – Channel shape (C – shape)

Tables (p.p. 1 – 36 , 1 - 37)

C12*30

12. depth

30 weight

6 – MC shapes

Special type of C shapes

7 – Angles (L – shapes)

L1 * L2 * t

Tables (p.p. 1 – 42 , 1 - 49)

8 – T sections

Tables (p.p. 1 –50 , 1 - 69)





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9 – Pipes

1 – circular , 2 – square , 3 – rectangular

Tables (p.p. 1 –74 , 1 - 101)

10 – Bars and Plates

Bars: circular, square, rectangular , etc.

Page (1 – 138)

11 – Rails page (1 -112)

(5 – 2) Cold – formed steel shapes:

Made by bending thin sheets of carbon or low alloy steel into almost any

desired section.





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8. Loads

Structures have to carry different types of loading. These can be broadly

divided into two categories dead, and live loads.

(1) Dead Loads

They are loads due to self-weight (mass) of the structure. They are

includes structural frames' own weight and other loads that are

permanently attached to frame, like, pipes , electrical conducts, air

conditioning and heating ducts , lighting fixtures, roof covering,

suspended ceilings.

. (2) Live Loads

They're all loads other than dead load." Like : human, furniture, movable

equipments , vehicles , and snow or rain …. etc."

Floor loads

They're uniformly distributed static loads.

UBC1999 "Unified Building Code: "





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Snow loads

Density 5 – 6 pcf

Flat surfaces 30 – 40 psf

Inclined surfaces (horizontal projection) 10 psf

Wind Loads

Special considerations for wind are required for tall buildings.

The N.B.C. recommended the following wind pressure

For tanks and chimneys, tunnels, the above values should be multiplied by

shape factor.

Wind pressure can be approximately predicted as follows (Bernoulli's

equation):

q = 0.5 ρ v2 ----------- (1)

where:

q = pressure in psf

ρ = mass density of air

v = velocity in mph

ρ = 0.0765 pcf ----------- (2)

Height (ft) Wind pressure (psf)

Less than 30 15

30 – 49 20

50 – 99 25

100 – 499 30

Shape of Structure factor

Rectangular and square 1

Hexagonal and octagonal 0.8

Round or elliptical 0.6





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q = 0.00256 v2 ------------- (3)

Aerodynamic effects “sloping roofs"

+ suction -

Wind ward Wind leeward

α

When considering aerodynamic effects:

P = C q

P = static pressure

C = coefficient suggested by ASCE

α = slope of the roof

C = -0.7 (α ≤ 20◦)

C = 0.07 α – 2.1 (20◦ < α ≤ 30

◦)

C = 0.03 α – 0.9 (30◦ < α ≤ 60

◦)

C = 0.9 (α >60)

For leeward surface: C = -0.6

Impact and Dynamic loads

The term “impact" refers to extra static load applied to approximate the

dynamic effect of a suddenly applied load like cranes and various types of

machinery.

If = 25L

50

≤ 0.3

L = length of portion of span (ft)

If = impact factor





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Impact load (static) = dynamic load * (1 + If)

Or If = 1 for elevator

= 0.25 for machinery

Traffic loads

Highway traffic is made up for four principal kinds of vehicles – the truck

tractor, truck, bus, and passenger car.

Earthquake loads

W W

Cw = inertia reaction

Earth motion

(a) @ rest (b) under horizontal motion

from an earthquake

Water and Soil pressure

P = γ h

γ = density of soil or water

h = difference between the reference level and the surface of the liquid or soil

γ soil = 90 – 120 lb/ft3

γ water = 62.4 lb/ft3





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9. Methods of Design

In Steel Structures DWE4336, we consider AISC specifiications and methods:

1. Allowable Stress Design (ASD)

2. Load and Resistance factor Design (LRFD)

3. Plastic Analysis and Design

1 - Allowable Stress Design (ASD)

It's called also working stress method. The analysis in this method is based on the

use of:-

1. classical analytical formulae of stress and strain

2. actual working loads (service loads)

2 – Plastic analysis and design.

based on a consideration of failure conditions rather than working load

conditions. A member is selected by using the criterion that the structure will fail

at a load substantially higher than the working load. Failure in this context means

either collapse or extremely large deformations. The term plastic is used because,

at failure, parts of the member will be subjected to very large strains—large

enough to put the member into the plastic range.

3 – Load and Resistance Factor Design.

Design strength = Φ actual strength





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30 '

30 '

Ex1: For the gable frame shown in fig. below, if wind speed = 180 mph,

roof dead load = 15 lb/ft2. Determine:

1 – The magnitude and direction of the force applied at point O due to the

roof load.

2 – The uniform static load applied due to the wind and the load transmitted

by the purlin to the point O

Solution:

Length of rafter ab = √ 212 + 30

2 = 36.6 ft

Length between each purlin = 36.6/3 = 12.2'

6 @ 10ft = 60 ft

21 ft

Purlin beam

Frame

Rafter

20 ft





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1) Load on point O :

(15/1000) * 12.2 *30 = 5.5 kips

2) q = 0.00256 v2 , q = 0.00256 (180)

2 = 16.4 lb/ft

2

α = 35 , C = 0.03 α – 0.9 (30 < α ≤ 60)

C = +0.15 (comp.)

For the leeward surface C = - 0.6

Wind ward : P = 0.15 * 16.4 = 2.46 lb/ft2

U.S.L.(windward) = 2.46 * 30 = 73.8 lb/ft

U.S.L.(leeward) = 0.6*16.4 * 30 = 295.2 lb/ft

For point O : load = 73.8*12.2 = 900.36 lb

10. Introduction to LRFD:

The factored resistance ɸRn is called the design strength. The summation on

the left side of Equation above is over the total number of load effects

(including, but not limited to, dead load and live load), where each load

effect can be associated with a different load factor. Not only can each load

effect have a different load factor but also the value of the load factor for a

particular load effect will depend on the combination of loads under

consideration. Equation above can also be written in the form:





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semester ii (2018-2019)

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