1

Basic principles of steel structures

Dr. Xianzhong ZHAO

x.zhao@mail.tongji.edu.cn

Lecture Questionnaire (1)Language preferred ( C = in Chinese, E = in English)

ECEC6

otherECCC7

EECC5ECEE4EEEC3EEEC & E2EEEE1

Tick the oneyou prefer

Coursework &written exam

Handout &textbook

Writing on theblackboard

OralPresentationNO.

From this course you prefer to:Learn steel struc. 1 2 3 4 5 6 7 Practisein English format English

SyllabusAimsTo introduce procedures for designing steel members and connections.

Syllabus (total 41 courses)Introduction =>2Steel properties =>6Tension members =>3Compression members (Columns) =>7Bending Members (Beams) =>8Beam-columns =>7

Connections =>8

Coursework & AssessmentAssignment 1 Attendance, activities & Coursework 30%Assignment 2 Experiments EPUT 10%Assignment 3 Final written examination 60%

IntroductionOutlines

what is steel structure?

why choose steel structures?

where & when use steel structures?

main structural types

state-of-the-art and prospective market

design concept & rationale of steel structures

What’s steel structure?architecture → structure →steel structure

Architecture

Structure

Steel structure

What’s steel structure?definition & scope

STEEL STRUCTURE: a structure which is made from organised combination of structural STEEL members designed to carry loads and provide adequate rigidity

Steel structure RC structurePK

steel structure, reinforced concrete (RC) structure, concrete-filled-steel tubular (CFT) structure, steel-RC composite structure?

steel shelfsteel furniture

……Steel structure? Yes, but

steelwork of buildings, bridges and civil eng. works in this course

2

What’s steel structure?definition & scope

steel structures involve sub-structure or members in a buildingmade from structural steel

SHANGHAI STADIUMSteel roof + concrete stand

SHANGHAI GRAND THEATERSteel roof + concrete columns

What’s steel structure?definition & scope

structural member（构件） is physically distinguishable part of structure with independent structural function, e.g. member (杆件)、element(板件)、cable(索) and their combination

cable

Why use steel structure?advantages

High strengthThe high ratio of strength to weight (the strength per unit weight)

Excellent ductility and seismic resistanceWithstand extensive deformation without failure even under high tensile stress

Elasticity, uniformity of materialPredictability of properties, close to design assumption

Ease of fabrication and speed of erection

high ratio of strength to weight

By M.F.Ashby

Elasticity, ductility and uniformity of material Ease of fabrication and speed of erection

3

Why use steel structure?disadvantages

Susceptibility to corrosionMaintenance costs / thin-walled structure

Loss of strength at elevated temperatureFireproofing costs

Susceptibility to bucklingSlender member in compression

Fatigue and brittle fracture

Long-span structuresMulti-storey & high-rise buildingsBuildings of heavy duty plantsTower & mast structuresPortal framesBridgesInfrastructuresDeployable structuresGeneralized structures: mechanical

Where & when use steel structures?

Long-span structuresAirport terminals

Stadiums

Exhibition centres

TheatresTrain stations

High-rise buildings

Tai-bei 101

CCTV

World trade centre

Jinmao tower

Buildings of heavy duty plant Tower & Mast structures

TV Tower Eiffel Tower TV Tower

4

Portal frames Bridges

Infrastructures Agricultural buildings

Sight-seeingDeployable structures

Oh, he is coming…

5

Generalized structures Main structural typesbuildings and bridges

truss structuresBar or truss members

frame structuresBeams and columns

grids structureslatticed structure or dome

arch

prestressed structures

beam bridge

truss bridgetruss members

arch bridge

cable-stayed bridge

suspension bridge

Main structural typesbuildings: truss structures

Main structural typesbuildings: frame structures

Main structural typesbuildings: grid /domes Main structural types

buildings: prestressed structures

6

Main structural typesbuildings: prestressed structures

Main structural typesbridges: truss bridges

Main structural typesbridges: arch bridges

Main structural typesbridges: cable-stayed bridges

Main structural typesbridge: suspension structures

State-of-the-art & prospective markettechnology & economy

technologyAccurate and automatic fabrication

economyLess construction time and less structural weight

environmentLess wet workReuse, Reduce & Recycle / removable

7

State-of-the-art & prospectivemarket for steel structures

2007 y > overall output of the world before 1966

2008 y > 2nd-8th output

0

100

200

300

400

500

600

China Japan America Russia India Korea Germany Ukraine

Raw

stee

l ou

tput

, Mt

2007 2006 2005 2004 2003

8

7

6

5

4

3

2

42.8Ucran

48.5Germany

51.4Korea

53.1Italy

72.7Russia

97.2USA

120.2Japan

485.9Sum.2~8

Output/MtNationsNo.

489.2China1

State-of-the-art & prospectivemarket for steel structures

Crude steel consumed kg/head

Forecast average2017 = 550kg/head

2007-2017

750

450

360

Coastal

Central

Western

Regional Kg/head 2006

434

227

170

Coastal

Central

Western

Kg/head 2017

National average2007 = 340kg/head

Data: CRU, NBS, CISA

State-of-the-art & prospectivemarket for steel structures

中国建筑业房屋竣工面积

2004128163

200080715

0

20000

40000

60000

80000

100000

120000

140000

1985 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

万平米

Steel structure 2%→4%

0

50,000

100,000

1960 1970 1980 1990 2000

Ｋ㎡

Wooden

Steel

R.C

SteelR.COthers

year

steel structureR.C structure

M/ton

↑JAPAN↓CHINA steel used in buildings

Residential Housing

Design concept & rationaleensure strength, stability and stiffness

StiffStrengthstabilityLight

All OK !

Not stiff enough (need bigger E)

Not strong enough (need bigger σy )

Not stable enough

Too heavy (need lower ρ)

Design concept & rationale

metallurgySteel

fabrication

Member + connectionerection

structural system

Loads

action

Strength, stability , rigidityForce, deformation

S ≤ RPerformance required:Safety, serviceability, durability

Design concept & rationaleLoads

action

structuralmodel

elementmember

restraintconnection

loadingactions

?

?

?

8

Design concept & rationaleelementmember

restraintconnection

loadingactions

?

?

?

Analytical model

Design concept & rationaleLoads

action

force

deformation

Mechanics of materialsStructural analysisElastic mechanicsPlastic mechanics

Design concept & rationale

metallurgySteel

fabrication

Member + connectionerection

structural system

Loads

action

Strength, stability , rigidityForce, deformation

S ≤ RPerformance:Safety, serviceability, durability

Design concept & rationale

metallurgySteel

fabrication

Member + connection

Strength, stability , rigidity

Mechanics of materialsYou got a high level?

Tension memberCompression memberBeamBeam-columnconnection

Design concept & rationale

S≤R fR

R

fs

S

RaRnSa Sn

Sn Rn

objective

Rd-Sd0

Sn≤Rn

Sn RnSd≤Rd

subjective

Acceptable:point of view of safety

point of view of economy

fR-S

Design concept & rationale

RaSa Sn Rn

DESIGN METHOD

— ASD

— LRFD

∑ψSn≤Rn/K

∑γSψSn≤Rn/γR

fd

9

Design concept & rationale

brittle / ductile fracture of steel members or connectionsglobal buckling of structures/memberslocal bucklingexcessive development of plastic deformationloss of geometry stabilityfatigue failure

possible failure modes

brittle / ductile fracture of steel members or connections

possible failure modes

global buckling of structures/members

possible failure modes

local buckling

possible failure modes

excessive development of plastic deformation

possible failure modes

原试件 MCP-1 MPP-1

10

loss of geometry stabilityfatigue failure

possible failure modes

your task:Prevent all these failure modes

possible failure modes