Lecture Note 1 (Steel)

7/23/2019 Lecture Note 1 (Steel)

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Materials and Structures

CVEN2302

Lecturer-1: General Principles

Dr Hamid Valipour



Unit conversion

Length 1 m = 100 cm = 1000 mm

Load (Action)- Concentrated force 1 kN = 1000 N

- Concentrated Moment & Torque 1 kN.m = 1000 N.m = 10

6

N.mm- Force per unit length 1 kN/m = 1000 N/m = 1 N/mm

- Force per unit area 1 kN/m2

= 1000 N/m2= 10

-3 N/mm

2

1 Pa = 1 N/m2

1 kN/m2

= 1 kPa

Internal force (Action effect)- Axial & Shear force 1 kN = 1000 N

- Bending Moment & Torque 1 kN.m = 1000 N.m = 106 N.mm

Stress and Material Strength1 MPa = 1 N/mm

2= 10

6 N/m

2

1 GPa = 1000 MPa = 109

Pa



Material properties

• Young modulus: E = 200000 MPa= 200 GPa

• Shear modulus: G= 80000 MPa= 80 GPa

• Yield stress: f y= (MPa)

Shall not exceed that given inTable 2.1 ( AS4100- 1998)

• Ultimate tensile strength: f u= (MPa)

Yield strain:

5102

)MPa(

y y y

f

E

f

y

y u

u f

f yruptureLong plastic

plateau

(Stress)

(Strain)



Table 2.1 ( AS4100- 1998)



Table 2.1 (continue) ( AS4100- 1998)

S e e p r e v i o u s

s l i d e f o r N o t e s .







Steel members (Sections)

Classification of sections:

• Hot rolled (plates, taper flange beam, equal leg angle, unequal

leg angle, universal beam, universal column, parallel flange

channel)

• Standard welded sections (welded beam, welded column)

• Cold-formed and welded hollow sections (circular, rectangular

and square hollow sections)

• Fabricated sections (Top hat-UB+PFC)



Outline of steel sections

x x

y

y

TFB UB

y

y

x x x x

y

y

UC

r

PFC

y

y

x x

98o

EA

x

x

y

y y

y

x

x

UA

WC

y

y

x x x x

y

y

WB

r r r

weld

weld

Universal Beam Universal Column Paralell Flange Channel

Equal Angle Unequal Angle

Welded Beam Welded Column

Taper Flange Beam

Circular HollowSection

CHS RHSRectangular HollowSection

Square HollowSection

SHS

r r

Plate

PLTSQ Square (Square bar) Round (Round bar)

RND

x x

y

y

x x

y

y

x x

y

y

Tophat-UB+PFC

Hot Rolled

Hollow section Fabricated

x

y

x

y

Welded section



Structure performance

Structures must have reliable performance

under all expected actions such as permanent actions and

imposed actions.

withstand extreme or frequent actions such as wind action and

earthquake action.

Clients have an expectation of satisfactory performance to fulfill

design function under short-term actions such as vibration and foot-fall.

under long-term actions such as element deflections due to creep

in RC structures.



Design philosophy

Allowable stress designStrength:

Design stress < Allowable stress = (reduction factor) x ( f y or f u )

Serviceability:Limiting the deflection or element size for serviceability

Limit state design (LRFD)

What is limit state?

A condition beyond which a structural component or the entire

structure ceases to fulfil the function for which it is designed. Two

major limits are, ultimate limit state and serviceability limit state.



Design at different levels

StructureMember

Section

Element

Member Structure

Section and Elements

Element

Element Element

Element

Element

Element



Applicability of AS4100- 1998 (clause 1.1)

This standard sets out minimum requirements for the design, fabrication,erection & modification of steelwork in structures in accordance with the

limit states design concept.

This Standard applies to steel buildings, structures & cranes.

This standard does not apply to:

- Steel elements less than 3 mm thick, with the exception of sections

complying with AS/NZS 1163 and packers.

- Steel members for which the value of the yield stress ( f y ) used indesign exceeds 690 MPa.

- Cold-formed members, other than those complying with AS/NZS 1163,

shall be designed in accordance with AS/NZS 4600.

- Composite steel-concrete members, which shall be designed in

accordance with AS2327.

• Road, railway and pedestrian bridges (AS 5100.1, 2 & 6 apply).



Definitions

• Action (load): the cause of stress or deformations in a structure

which could be

— dead load or permanent action (G), live load or imposed action (Q),

wind action (W u), earthquake action ( E u), snow (F sn), liquid pressure

(F lp

), rainwater ponding (F pnd

) and ground water (F gw

) in accordance

with (Section 1 AS/NZS 1170[1].0)

• Action effect (load effect): the internal force (i.e. axial force and

shear ) or bending moment due to actions or loads.

• Design action (design load): the combination of the nominal actions

or loads and the load factors as specified in AS1170.

• Design action effect (design load effect): the action or load effectcomputed from the design actions (design loads).

— Axial force ( N * ), Shear force (V * ), Bending moment ( M * ), torsion (T * )

or combination of them



Structural Actions (loads)

• Origin: events apply actions to the structure during its lifetime (G, Q, W u, E u , F sn , F lp , F pnd & F gw ).

• Confidence: reflects how accurately the actions applied to the structure

over its lifetime can be predicted.

known: self-weight of structure, machinery, permanent equipments andcladding, permanent partitions .

estimated: environmental actions (wind, earthquake) or occupancy actions

such as imposed action ( live load ).

• Duration: it can be of short-term or long-term nature and it is moreimportant for concrete and timber.

• Distribution:

distributed: forces applied over large area

concentrated: forces applied over specific localised area

• Return period: return period, intensity and duration is important

frequent event

rare event



Design process (General)

Project!

Defini tion of project(Design brief)

Includes: specific use,

constraints, functional &

structural requirements

Information search

Includes: design data,

information from other

consultants, loads

Structural systems

(Conceptual design)

Includes:

type of structural system,Connections and

construction techniques

Preliminary designs

and selection

Detailed design

Drawings and technical

specificationsConstruction



Design process (Structure)

( D e a d &

L i v e L o

a d )

w i n d L o

a d

G,Q

W

Analysis

Load Combination or

Combination of Actions (AS 1170[1].0)

Design action effect

(Design axial force, shear, bending moment)

Design action effect (Capacity factor) (Nominal capacity)

* N M *V *

Idealised model

P e r m a n e

n t & I m p

o s e d L o a d



General modes of failure

Classification of failure modes

Local

Global

Combination of local and global

Steel yielding (ductile failure mode)

Steel fracture and fatigue (brittle failure mode)

Buckling related failure modes



Rigid (connection): the original angle between the members

remains unchanged.

Semi-rigid (connection)

Simple (connection): the connections at the ends of the member

shall be assumed not to develop bending moment.

Forms of Construction and Idealised model

90o

o90

90o

w

90o

90o

<

w

w

< 90o

Rigid

Semi-Rigid

Simple

(Hinge)



Flush end T-stubPlate connection

Single web Double web

angle angle

Top & Seat Extended

with Double end plate

web angle

Header Top and seat

plate angle

Common connections in steel frames



Elastic analysis (In accordance with clause 4.4, AS4100-1998)- First order

- Second order including P- and/or P- effects ( Appendix E, A4100-1998).

Plastic analysis (In accordance with clause 4.5, AS4100-1998)

Advanced analysis ( Appendix D, AS4100-1998)

Methods of determining action effects (clause 4.1,

AS4100- 1998)

P P

Sway Frame

Braced Frame

PP

The transverse displacement of one end

relative to the other is effectively prevented.

The transverse displacement of one end

relative to the other is not effectively prevented.

M = P P-

P- M = P

Second order

effect Second order

effect



Limit state design

- Stability limit state

The structure as a whole (and any part of it) shall be designed to

prevent instability due to overturning, uplift or sliding

- Strength limit state

The structure and its component members and connections shall bedesigned in such a way that

Design action effect < Design capacity= * Nominal capacity

or S * < Ru

– is capacity reduction factor given in Table 3.4 ( AS4100- 1998).

- Serviceability limit state

The structure and its components shall be designed for the

serviceability limit state by controlling or limiting deflection,vibration, bolt slip and corrosion, as appropriate, in accordance

- Fatigue, Fire, Earthquake and Britt le fracture limit state



Capacity (reduction) factor

depends on material- steel

- concrete

- timber

and further on

- origin and reliability of strength data

- accuracy of behavioural model

- structural role of member (primary or secondary)

- Effect of failure of a single element on whole structure



Table 3.4 Capacity factor ( ) for strength limit state

( AS4100- 1998)

Design capacity for Clauses Capacityfactor,

Member subject to bending

- full lateral support

- segment without full lateral support

- web in shear

- web in bearing

- stiffener

5.1, 5.2 & 5.3

5.1 & 5.6

5.11 & 5.12

5.13

5.14, 5.15 & 5.16

0.90

0.90

0.90

0.90

0.90

Member subject to axial compression

- Section capacity- Member capacity

6.1 & 6.26.1 & 6.3

0.900.90

Member subject to axial tension 7.1 & 7.2 0.90

Member subject to combined actions

- Section capacity- Member capacity

8.38.4

0.900.90

Connection components other than a bolt, pin or

weld

9.1.9(a), (b), (c) & (d)

9.1.9(e)

0.90

0.75



Table 3.4 Capacity factor ( ) for strength limit state

( AS4100- 1998) (continue)

Design capacity for Clauses Capacity factor,

Bolted connection

- bolt in shear

- bolt in tension

- bolt subject to combined shear and tension- ply in bearing

- bolt group

9.3.2.1

9.3.2.2

9.3.2.39.3.2.4

9.4

0.80

0.80

0.800.90

0.80

Pin connection

- pin in shear

- pin in bearing- pin in bending

- ply in bearing

9.5.1

9.5.29.5.3

9.5.4

0.80

0.800.80

0.90

Welded connection

- complete penetration butt weld- longitudinal fillet weld in RHS (t < 3mm)

- other fillet weld & incomplete penetration butt weld

- plug or slot weld

- weld group capacity

9.7.2.79.7.3.10

9.7.3.10

9.7.4

9.8

SP category GP category

0.90

0.70

0.80

0.80

0.80

0.60

---

0.60

0.600.60



- Stability limit state:

o {0.9G} (for combination that produce net stabilising)

o {1.35G}

o {1.2G,1.5Q}

o {G, E u, c Q}, where c is the combination factor (Table 4.1, AS1170)

o {1.2G, S u, c Q}, where S u can be {W u , F sn , 1.2 or 1.5F lp, 1.2F pnd , 1.2F gw}(clause 4.2.2 and 4.2.3, AS1170[1].0)

- Strength limit state:

o {1.35G}

o {1.2G,1.5Q}

o {0.9G, W u}

o {G, E u, c Q}

o {1.2G, S u, c Q}

- Serviceabil ity limit state: combinations may include one or a number

of the loads {G, s Q, l Q, W s , E s} using the short-term ( s ) and long-

term ( l ) factors given in Table 4.1.

Combinations of actions (Section 4, AS/NZS1170[1]. 0)



Table 4.1 Short-term, long-term & combination factors

for distributed imposed action ( AS1170 [1].0)

Character of imposed actionShort-term

factor, s

Long-term

factor, l

Combination

factor, c

Earthquake

factor, E

Floors

- Residential & domestic- Offices

- Parking

- Retail

- Storage

- Other

0.70.7

0.7

0.7

1.0

1.0

0.40.4

0.4

0.4

0.6

0.6

0.40.4

0.4

0.4

0.6

0.6

0.30.3

0.3

0.3

0.6

0.6

Roofs

- Roofs used for floor type

activities (see AS/NZS 1170.1)

- All other roofs

0.7

0.7

0.4

0.0

0.4

0.0

0.3

0.0

T bl 4 1 Sh l & bi i f



Table 4.1 Short-term, long-term & combination factors

for concentrated imposed action ( AS1170 [1].0)

Character of imposed actionShort-term

factor, s

Long-term

factor, l

Combination

factor, c

Earthquake

factor, E

- Floors

- Floors of domestic housing- Roofs used for floor type

activities

- All other roofs

- Balustrades

1.0

1.01.0

1.0

1.0

0.6

0.40.6

0.0

0.0

as for

distributed floor actions

0.0

0.0

0.3

0.30.3

0.0

0.0

- Long-term installedmachinery, tare weight

1.0 1.0 1.2 1.0



Design bending moment M

* for

strength limit state at mid-span of

the beam for parking use:

o {1.35G} 20.25 kN/m

o

{1.2G,1.5Q}

31.50 kN/mo {0.9G, W u} 13.50 kN/m

o {G, E u, c Q} 18.60 kN/m

o {1.2G, S u, c Q} 21.60 kN/m

Example -1:

G =15 kN/m & Q =9 kN/m

3 . 5 m

8.0 m

W

= 3 k N / m

u

mid-span

M = w l 2/8

o {1.35G} M *= 162.0 kN.m

o {1.2G,1.5Q} M *= 252.0 kN.m

o {0.9G, W u} M *= 108.0 kN.m

o {G, E u, c Q} M *= 148.8 kN.m

o {1.2G, S u, c Q} M *= 172.8 kN.m



The gravity loads act in the direction of gravity, including Dead, Live, etc.

The gravity loads typically are load per unit area (in kPa), however, the load

on the beams should be load per unit length (in kN/m).

To distribute the gravity loads among the beams, the load carrying

mechanism in the floor diaphragm should be identified in the first step.

The load carrying mechanism of the floor can be

- One-way (mainly transfer the load in one direction)

• Beams only in one direction or

• The aspect ratio is greater than 2 < l x / l y .

- Two-way (transfer the load in two directions)

Distributing the gravity loads:

Plan view of a floor bay

xl

yl

Edge

beam

E d g e

b e a m

45o

45o

Distributed load per unit length of the edge beams



Type of floor diaphragm:

Steel w ire

meshConcreteslab

Concrete slab

JoistSteelsheet

Steel w iremesh

Steelbeam

Stud

connectors

Steel beam

Concrete slab

Steelsheet

Concrete slab

One-way load transfer

T f fl di h ( ti )



Type of floor diaphragm (continue):

One-way load transfer

Documents

Lecture Note 1 (Steel)