ce 313-lecture-2(concepts in structural steel design )

8/18/2019 CE 313-Lecture-2(Concepts in Structural Steel Design )

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LECTURE 2

Concepts in Structural Steel Design

ALGHRAFY 2016CE 313 STEEL STRUCTURES (I)

1

STEEL STRUCTURES (I)

(CE 313)

سم ا لرحن لرحيم

By


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Introduction

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STRUCTURAL DESIGN

Structural design may be defined as a mixture of art andscience, combining the experienced engineer’s intuitivefeeling for the behavior of a structure with a sound knowledge

of principles of statics, dynamics, strength of materials andstructural analysis, produce a safe economical structure which will serve its intended purpose. At the same time it isnecessary to be sensitive to preserve environment and naturalmaterials in structural design. So structural design should besafe, economic, aesthetic and sustainable.


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Introduction

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Design concept & rationaleensure strength, stability and stiffness


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Introduction

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Design concept & rationale


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Type of Structural Steel Sections

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SteelStructuralSections

• Hot-Rolled Sections.

• Cold Formed Sections.

• Built-Up Sections.


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• Hot-Rolled Sections.

W(a) Wide-flange

Shape

S(b) American

Standard

Beam

C(c) American

Standard

Channel

L(d) Angle

WT or ST(e) Structural

Tee

(f) Pipe

Section(g) Structural

Tubing

(h) Bars (i) Plates

a – Wide-flange : W 18 97

b – Standard (I) : S 12 35

c – Channel : C 9 20

d – Angles : L 6 4 ½

e – Structural Tee : WT, MT or ST e.g. ST 8 76

f & g – Hollow Structural Sections HSS : 9 or 8 8


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• Cold Formed Sections

(a) Channels (b) Zees (c) I-shaped double channels

(d) Angles (e) Hat sections


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• Built-Up Sections.

Built-up (W) shapes.

Built-up (C) Channels.

Built-up (L) Angles.


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• Tension Members.

(a) Round and rectangular bars, including eye bars

and upset bars.

(b) Cables composed

of many small wires.(c) Single and double

angles.

(d) Rolled W – and S –

sections.

(e) Structural

tee.(f) Build-up box

sections.

Perforated

plates


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• Compression Members.

(a) Rolled W-and S-

sections.

(c) Structural

tee.

(b) Double

angles.(e) Pipe

section

(d) Structural

tubing

(f) Built-up section


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(a) Rolled W-and

other I-shaped

sections.

(c) open web joist.(b) Build-up

Sections.

(f) Built-up members

• Bending Members.

(d)

Angle(e)

Channel(g) Composite steel-Concrete


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Tables of Structural Shapes


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L O A D S

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Dead Loads: Also known as gravity loads, includes the weight of the structure and all fixed and permanent attachments.

Live Loads: Also belong to gravity loads, but their intensity and location may vary (non- permanent loads).

Highways / Rail Live Loads: AASHTO, AREA

Impact Loads: Associated with Live Loads.

Snow Load20 to 40 psf ( 1000 to 2000 Pa )

Wind Loads:

Exerts pressure or suction on the exterior surfacesand it has a transient nature.

Earthquake Load:Latitude Load on structure.

Thermal Loads:For Indeterminate Structures.

9 – Other Loads:e.g. - Rain Loads -Ponding-Hydrostatic Loads- Blast Loads.


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Philosophies of Design:

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Adequate safety no matter what design philosophy is used.

Provision must be made for both overload and understrength.

The fundamental requirement is:

Required strength ≤ Available strength

A. Working Stress Design (Allowable Stress Design), widely known as (ASD) –used for over 100 years.

Maximum applied stress ≤ Allowable stressRequired strength ≤ Allowable strength

Allowable strength = Nominal strength / Safety factor A. Limited States Design (Load & Resistance Factor Design), also known as

(LRFD) – first introduced in 1986.

Load factors are applied to service loads and theoretical strength of the member isreduced by a resistance factor.

Σ(Loads x Load factors) ≤ Resistance x Resistance factor


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Safety factors and load combinations for ASD

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Safety factorsR a ≤ R n/ Ω=R d

R a= Required strengthR n= Nominal strength (Calculated theoretical strength with no safety factors or

resistance factors.)Ω = Safety factor (>1)

R d= R n/ Ω = Allowable strength

Yielding, flexure or buckling Ω=1.67Rupture Ω=2.00Fillet and Weld Ω=2.00


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Safety factors and load combinations for ASD

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load combinations

DD+LD+(Lr or S or R)

D+0.75(L)+0.75(Lr or S or R)D+(0.6Wor0.7E)D+0.75(0.6W)+0.75L+0.75(Lr or S or R)D+0.75(0.7E)+0.75L+0.75(S)0.6D±(0.6W or 0.7E)

D=Dead load

E=Earthquake loadL=Live load

Lr=Roof live loadR=Rain loadS=Snow load

W=Wind load


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Safety factors and load combinations for LRFD21


Safety factorsΣγiQi ≤ ΦR n

Qi = A load effect γi =A load factorR n =Nominal resistance or strength

Φ= Resistance factor (


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Type of Steel Used

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Thank You

2016

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CE 313 STEEL STRUCTURES (I)

ce 313-lecture-2(concepts in structural steel design )

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