DESIGN OF RC STRUCTURES.pdf

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1. WELLCOME
1

2. Limit state method of Design
PRESENTED BY
Name : Avik Ghorai
Roll No : 18201321019
Paper Name : DESIGN OF RC STRUCTURES
Paper Code : CE(PC)501
Semester : 5th
Department : Civil engineering
CA1 Examination For Odd Semester-2022
Institute of Science &
Technology
2

3. Limit state method of Design
3

4. INTRODUCTION
Designerhastoensurethestructures,he
designsare:
Fitfortheirpurpose
Safe
Economicalanddurable
4

5. INTRODUCTION
FollowingUncertaintiesaffectthesafetyofa
structure
aboutloading
aboutmaterialstrengthand
about structural dimensions
about behaviour under load
5

6. LIMIT STATE DESIGN
Limit State:State at which one of the conditions pertaining
to the structure has reached a limiting value
Limit States
Limit States of Strength Limit States of Serviceability
Strength as governed by material Deflection
Buckling strength Vibration
Stability against overturning, sway Fatigue cracks (reparable damage)
Fatigue Fracture Corrosion
Brittle Fracture Fire resistance
6

7. RANDOM VARIATIONS
7
Resistance, S
Load effect, Q
f(S)
f(Q)
Q
m
Frequency
Probability density functions for strength and load effect
S
m

8. LIMIT STATES DESIGN
Basis of Limit States Design2
Q
2
s
mmQS





8
Fig. 1 Probability distribution of the safety margin R-Q
R-Q
R-Q<0 R-Q>0
(R-Q)
m
f(R-Q)

(R-Q)

9. PROBABILITY OF FAILURE 























2
Q
2
R
mm
QR
m
f
QR
QR
P




9

10. SAFETY INDEX2
Q
2
S
mmQS





 2.32 3.09 3.72 4.27 4.75 5.2 5.61
P
f
= (-)10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
10
-8
10
P
f=[-]

11. PARTIAL SAFETY FACTOR)V1(S)V1(Q
2
ssqm
2
qqsm  
1
1mukfk SQ  /
11

12. ALLOWABLE STRESS DESIGN (ASD)
Stressescausedbythecharacteristicloadsmustbelessthan
an“allowablestress”,whichisafractionoftheyieldstrength
Allowablestressmaybedefinedintermsofa“factorof
safety"whichrepresentsamarginforoverloadandother
unknownfactorswhichcouldbetoleratedbythestructure
12
Characteristic
Load Effects
Characteristic Strength
Factor of Safety


13. Allowablestress=(Yieldstress)/(Factorofsafety)
Limitations
Materialnon-linearity
Non-linearbehaviourinthepostbuckledstateand
thepropertyofsteeltotoleratehighstressesby
yieldinglocallyandredistributingtheloadsnot
accountedfor.
Noallowanceforredistributionofloadsinstatically
indeterminatemembers
13
ALLOWABLE SRESS DESIGN (ASD)

14. LIMIT STATES DESIGN
“LimitStates"arevariousconditionsinwhicha
structurewouldbeconsideredtohavefailedto
fulfilthepurposeforwhichitwasbuilt.
“UltimateLimitStates”arethosecatastrophic
states,whichrequirealargerreliabilityinorderto
reducetheprobabilityofitsoccurrencetoavery
lowlevel.
“ServiceabilityLimitState"referstothelimitson
acceptableperformanceofthestructureduring
service.
14

15. General Principles of
Limit States Design
StructuretobedesignedfortheLimitStatesatwhich
theywouldbecomeunfitfortheirintendedpurpose
bychoosing,appropriatepartialsafetyfactors,
basedonprobabilisticmethods.
Twopartialsafetyfactors,oneappliedtoloading(
f)
andanothertothematerialstrength(
m)shallbe
employed.
15

16. 
fallows for;
Possible deviation of the actual behaviour of the
structure from the analysis model
Deviation of loads from specified values and
Reduced probability that the various loads acting
together will simultaneously reach the
characteristic value.
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17. LIMIT STATES DESIGN
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(Load * Load Factor)
(Resistance )
(Resistance Factor)
•
m takes account;
–Possible deviation of the material in the structure from that
assumed in design
–Possible reduction in the strength of the material from its
characteristic value
–Manufacturing tolerances.
–Mode of failure (ductile or brittle)

18. IS800 SECTION 5 LIMIT STATE
DESIGN
5.1 Basis for Design
5.2 Limit State Design
5.3 Actions
5.4 Strength
5.5 Factors Governing the Ultimate Strength
5.5.1 Stability
5.5.2 Fatigue
5.5.3 Plastic Collapse
5.6 Limit State of Serviceability
5.6.1 Deflection
5.6.2 Vibration
5.6.3 Durability
5.6.4 Fire Resistance
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19. Basis for Design
the structure shall be designed to withstand safely all loads
likely to act on it throughout its life.
It shall also satisfy the serviceability requirements, such as
limitations of deflection and vibration.
It shall not suffer total collapse under accidental loads
such as from explosions or impact or due to consequences
of human error to an extent beyond the local damages.
The objective of design is to achieve a structure that will
remain fit for use during its life with an acceptable target
reliability.
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20. The potential for catastrophic damage shall be limited or avoided by
appropriate choice of one or more of the following:
i) avoiding, eliminating or reducing exposure to hazards, which the
structure is likely to sustain.
ii) choosing structural forms, layouts and details and designing such
that
the structure has low sensitivity to hazardous conditions.
the structure survives with only local damage even after serious
damage to any one individual element by the hazard.
20

21. Conditions to be satisfied to avoid
a disproportionate collapse
building should be effectively tied together at each principal floor
level and each column should be effectively held in position by
means of continuous ties (beams) nearly orthogonal
each storey of the building should be checked to ensure
disproportionate collapse would not precipitate by the notional
removal, one at a time, of each column.
check should be made at each storey by removing one lateral
support system at a time to ensure disproportionate collapse would
not occur.
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22. Actions
Classification of Actions
by their variation with time as given below:
a) Permanent Actions (Qp):Actions due to self-weight of structural and
non-structural components, fittings, ancillaries, and fixed equipment etc.
b)Variable Actions(Qv):Actions due to construction and service stage
loads such as imposed (live) loads (crane loads, snow loads etc.), wind
loads, and earthquake loads etc.
c)Accidental Actions (Qa): Actionsdue to explosions, impact of vehicles,
and fires etc.
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23. Partial Safety Factors (Actions)
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Combina
tion
Limit State of Strength Limit state of Serviceability
DL
LL
WL/
EL
AL DL
LL
WL/
ELLead
ing
Accompa
Nying
Leading
Accompanyin
g
DL+LL+CL 1.5 1.5 1.05   1.0 1.0 1.0 
DL+LL+CL+
WL/EL
1.2
1.2
1.2
1.2
1.05
0.53
0.6
1.2
 1.0 0.8 0.8 0.8
DL+WL/EL
1.5
(0.9)
*
  1.5  1.0   1.0
DL+ER
1.2
(0.9)
1.2       
DL+LL+AL 1.0 0.35 0.35  1.0    

24. PARTIAL SAFETY FACTORS (Strength)
Sl.
No
Definition Partial Safety Factor
1Resistance, governed by yielding 
mo
1.1
2Resistance of member to buckling 
mo
1.1
3Resistance, governed by ultimate stress

m1
1.25
4 Resistance of connection 
m1
Bolts-Friction Type
Bolts-Bearing Type
Rivets
Welds
Shop Fabrications Field
Fabrications
1.25
1.25
1.25
1.25
1.25
1.25
1.25
1.50
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25. Factors Governing the Ultimate
Strength
frame stability against overturning and sway
Fatigue design shall be as per Section 13 of this code. When
designing for fatigue, the load factor for action,f,equal to unity
shall be used for the load causing stress fluctuation and stress
range.
Plastic Collapse Plastic analysis and design may be used if the
requirement specified under the plastic method of analysis
(Section 4.5) are satisfied.
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26. Limit State of Serviceability
Deflections are to be checked for the most adverse but realistic
combination of service loads and their arrangement, by elastic analysis,
using a load factor of 1.0
Suitable provisions in the design shall be made for the dynamic effects
of live loads, impact loads and vibration/fatigue due to machinery
operating loads.
The durability of steel structures shall be ensured by following
recommendations of Section 15.
Design provisions to resist fire are briefly discussed in Section 16.
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27. LIMITING DEFLECTIONS under LL
Only
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Type of
building
Deflection Design Load Member Supporting
Maximum
Deflection
Indus
trial
building
Vertical
Live load/Wind
load
Purlins and Girts
Purlins and Girts
Elastic cladding
Brittle cladding
Span / 150
Span / 180
Live load Simple span Elastic cladding Span / 240
Live load Simple span Brittle cladding Span / 300
Live load Cantilever span Elastic cladding Span / 120
Live load Cantilever span Brittle cladding Span / 150
Live load or
Wind load
Rafter supporting
Profiled Metal Sheeting Span / 180
Plastered Sheeting Span / 240
Crane load
(Manual
operation)
Gantry Crane Span / 500
Crane load
(Electric
operation
over 50 t)
Gantry Crane Span / 1000

28. DEFLECTION LIMITS under LL Only
Deflection
Design Load Member Supporting Maximum Deflection
Lateral Crane+
wind
No cranes Column Elastic cladding Height / 150
No cranes Column
Masonry/brittle
cladding
Height / 240
Crane Gantry (lateral) Crane Span / 400
Vertical
Live load Floors & roofs
Not susceptible to
cracking
Span / 300
Live load Floor & Roof
Susceptible to
cracking
Span / 360
Lateral Wind Building --- Height / 500
Wind Inter storeydrift --- Storeyheight / 300
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