1.Introduction(Tan K H, NUS)
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Transcript of 1.Introduction(Tan K H, NUS)
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Lectures! Design philosophy ! Action Effects: Bending and axial load! Action Effects: Shear and Torsion! Serviceability: Cracking and deflections! Strut-and-tie method for design! Design and detailing of openings
! Slender column design! Flat slab system! Collapse load methods for slab design! Design of structural systems
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Reinforced Concrete: Mechanics & Design.3 ed.
MacGregor, J.G.Prentice Hall, 1997
Recommended text
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Reinforced Concrete Structures.
Park, R. & Paulay, T. John Wiley & Sons, 199X
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
STRUCTRUALCONCRETE Plain Concrete
Reinforced Concrete
Partially PrestressedConcrete
Prestressed Concrete
INTRODUCTION
Matrix + Reinforcement
Concrete +Steel bars
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Brief History of Structural Concrete
1824 Patent on Portland Cement (Aspdin)1854 Reinforced Concrete (Wilkinson)1886 First prestressing system using tie-rods
(PH Jackson, USA)1910 Various concrete institutes established1920s RC buildings, bridges & liquid containers
constructed; circular prestressing; practical PC; external prestressing
1930s Partial prestressing (Abeles, England)1938 Ultimate strength theories in USSR1940s Bridge design & construction with PC
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
1956 Ultimate strength theories in England/USA
1960s Working stress design1970s Limit state design1980s Durability issues1990s “Structural concrete” coined;
Unification of codes & theories;Performance-based design;New materials.
1998 Formation of International Federationfor Structural Concrete (fib)
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Design Objectives
!Functionability!Safety!Economy!Restorability
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
" Working stress design (WSD)!Focus on working load level!Check induced stress against allowable values
" Ultimate strength design (USD)!Focus on ultimate load level!Check factored actions against resistance
" Limit state design (LSD)!Considers both serviceability and ultimate limit
states" Performance-based design (PBD)
DESIGN APPROACHES
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
γγγγfP
MuUltimate strength design (USD)
" Mu ≤≤≤≤ φφφφMn for e.g.
P
fs"Working stress design (WSD)
" fs ≤≤≤≤ fs,allow = fy/1.5 for e.g.!Limit state design (LSD)!∆∆∆∆s ≤≤≤≤ ∆∆∆∆max ; ws ≤≤≤≤ wmax
!Mu ≤≤≤≤ φφφφMnPerformace-based design (PBD)Bridge’s deformation should not affect rail alignmentBridge is able to take a train load of xxx-xx
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Higher loads
Serviceability
Restorability
Safety
WSD
USD
LSD
PBD
Damage Control
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
PIS ≤≤≤≤ PIRe.g.
S(γγγγfFk) ≤≤≤≤ φφφφR(fk/γγγγm)Action effect Resistance
w(γγγγfFk, fk/γγγγm) ≤≤≤≤ w*Crack width Allowable value
Design criteria
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Specifications /Codes of Practice
! BS 8110 Structural Use of Concrete. Parts 1,2,3.British Standards Institution, 1985, 1997 (Part 1)
! CP65 Singapore Standard on Code of Practice for Structural Use of Concrete, 1999
! ACI 318 Building Code Requirements for Structural Concrete and Commentary.American Concrete Institute, 1999, 2002
! Eurocode 2
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Structural Concrete
Matrix ReinforcementConcrete Steel bars
High-strength concrete
Polymer concrete
Light-weight concrete
Self-compacting concrete
Fibrous concrete
Galvanised steel bars
Epoxy-coated bars
Fibre-reinforced polymer bars
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Materials
f y( M
P a)
fc’ (MPa)
1200
800
400
0 30 60 90 120
New RC
conventional
High strengthconcrete
Ultra-high strengthconcrete
Ultra-high strengthsteel
High strengthsteel
highrise RC
Concrete strength
Ste
el s
treng
th
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Characteristic Strength of Materials, fk
fk = fm - ksfrequency
strengthfm
5%e.g. for concrete
fk = fm - 1.64s
depends on reliability/quality
control
fk
k x s (std. dev.)
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Concretefc’ (MPa) W/C ratio
Normal structuralconcrete
20 - 45 0.40 – 0.45
High strengthconcrete
45 - 70 0.35 – 0.40
70 - 85 0.30 – 0.35Ultra-highstrength concrete 85 - 140 0.22 – 0.30
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Normal structural concrete
" Compressive strength : fcu or fc’(≈ 0.8fcu)(28-day characteristic)
" Tensile strength: ft’ = 0.1~0.2 fc’
" Modulus of rupture: fr = 0.623√fc’> ft’ (ACI)
" Modulus of elasticity: Ec= 4730 √fc’ (MPa)
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
An ↑↑↑↑ in fc’ leads to:
↓↓↓↓ in εεεεcu↑↑↑↑ in linear portion↓↓↓↓ in ductility↑↑↑↑ in Ec
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Stress-strain relation of concrete
fc/fc’ = 2εεεεc/εεεεc’ - (εεεεc/εεεεc’)2 (fc’≤≤≤≤45 MPa)
fc
fc’
0.4fc’Ec
εcεo’ εcu
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
High strength concrete
" Tensile strength: ft’ = 0.615√fc’ (fc’≤85 MPa)
" Modulus of rupture: fr = (0.623~1)√fc’ (MPa)
" Modulus of elasticity: Ec= (3323√fc’ + 6895)(wk/2323) (MPa)where wk: weight in kg/m3
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Reinforcement
Es=200,000 MPa
f y(M
Pa)
strain
Steel
0.005 0.010 εεεεs
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
FRP Reinforcement
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
PC Strand
Rebar
Tens
ile s
treng
th (M
Pa)
Strain %
CFRPAFRP
GFRP
0
2000
4 6 8 10
1000
2
FRP
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Design stress-strain relations
Concrete
BS8110, EC2, JSCE, CEB-FIP …similar
0.67fcu/γγγγmst
ress
(MP a
)
strain0.0035
5.5√√√√(fcu/γγγγm) kN/mm2
2.4x10-4√√√√(fcu/γγγγm)
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Steel
BS8110, ACI, JSCE, AS, CEB-FIP …similar
fy/γγγγm
fy/γγγγm
strain
200 kN/mm2
compression
tension
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Partial safety factors
1.5 (BS 1997)Concrete
1.15 (BS 1985)1.05 (BS 1997)
Steel
γγγγm
Design strength = Characteristic strength / γγγγm
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Loads (Actions)
Characteristicsload Fk
• Dead loads• Imposed loads• Dynamic loads• Accidental loads• Construction loads
• Earth loads• Wind loads• Seismic loads• Snow loads
⇒⇒⇒⇒ BS6399, ASCE7-98, AS1170
load
freq
uenc
y
5%
Fm Fk
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Load Combinations
LC = ΣγΣγΣγΣγkFk
" Ultimate limit state:e.g. 1.4Gk+1.6Qk (BS8110)
1.4Gk+1.7Qk (ACI318-99)
" Serviceability limit state:!short term effects! long term effects
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Limit state Load Comb. BS8110 ACI318-99
Dead & Live 1.4DL+1.6LL orDL+LL
1.4DL+1.7LL
Ultimatelimit state
Dead & Wind 1.4(DL+WL) or DL + 1.4WL
0.75(1.4DL+1.7WL)
Dead & wind & live
1.2(DL+LL+WL) 0.75(1.4DL+1.7LL+1.7WL) or
0.9DL+ 1.3WL
Serviceability Dead & Live short-term effects,
limit state Dead & Wind long-term effects, etc.
(Deflection, Cracking, etc)
Dead & wind & Iive
to be considered
Load Combinations
DEPARTMENT OF CIVIL ENGINEERING
Tan K H, NUS
Summary
Designobjectives
ResistanceActioneffects
PIS≤≤≤≤PIR
ActionsMaterial
properties
•numerical•analytical*•simplified*
•analytical*•formulae*•tests