Hvordan oppnås ønsket pålitelighet for
konstruksjoner
Steinar Leivestad,
Standard Norge
2015-12-09
In the Deck mating situation for the Statfjord C concrete
(back ground picture, concrete Condeep structure is submerged to 6m
platform
freeboard, having full characteristic loads governing design of all wall thicknesses of cells and domes
etc. with, γF = 1,2, γC = 1,25, γS = 1,15 )
adequate safety was obtained by
Adequately precise prediction models for:
•Loads
•Load effects
•Resistance models
•This was achieved by use of best practice and up to date standard
And
Adequate confidence that design is actually correct
•Achieved by extensive control by designer and client
Adequate confidence that execution is actually correct
•Achieved by extensive control by contractor and client
And
•Achieved by having personnel with adequate qualifications and
experience in all positions
In the Deck mating situation for the Statfjord C concrete
platform
(back ground picture, concrete Condeep structure is submerged to 6m
freeboard, having full characteristic loads governing design of all wall thicknesses of cells and domes
etc. with, γF = 1,2, γC = 1,25, γS = 1,15 )
adequate safety was obtained by
Adequately precise prediction models for:
•Loads
•Load effects
•Resistance models
•This was achieved by use of best practice and up to date standards
And
Adequate confidence that design is actually correct
•Achieved by extensive control by designer and client
Adequate confidence that execution is actually correct
•Achieved by extensive control by contractor and client
And
•Achieved by having personnel with adequate qualifications and
experience in all positions
IN FUTURE PROJECTS THE SAME IS ACHIEVED BY
Adequately precise prediction models in design standards
for: - Loads
- Load effects
- Resistance models
Adequate methods for the execution in execution
standards
and
Adequate confidence that design is actually correct
Adequate confidence that execution is actually correct
•This is achieved by a Quality Scheme for control
(scheme to be developed in EN 1990)
• Control of design (EN 1990 + design standards)
• Control of execution (Design + Execution standards)
• Qualifications and experience of personnel
ISO 2394 Levels of design “sophistication”
4.4.2.1 Risk-informed decisions concerning design and assessment
In a risk-informed design and/or assessment, the decisions shall be optimized with due
consideration of the total risks, considering loss of lives and injuries, damages to the qualities of
the environment, and monetary losses. The time horizon to be considered in the assessment of the
total risks shall be determined on the basis of the duration of the functionality which the structure
shall provide.
4.4.2.2 Reliability-based design and assessment
As an alternative to risk-based design and assessment of structures, a reliability-based approach
can be chosen. This approach shall utilize an assessment and minimization of costs and/or
minimization of committed resource usage subject to given reliability requirements for the structure.
The reliability requirements shall be assessed on the basis of a full risk-informed assessment as
described in 4.4.2.1and will thus facilitate reliability differentiation in dependency of consequences
of failure and costs of reliability improvements.
4.4.3 Semi-probabilistic approaches
For structures for which the consequences of failure and damage are well understood and the
failure modes can be categorized and modelled in a standardized manner, semi-probabilistic codes
are appropriate as basis for design and assessment. Standards shall serve to ensure the quality of
analysis, design, materials, production, construction, operation and maintenance, and
documentation, and thereby explicitly or implicitly account for the uncertainties which influence the
performance of the structures. The specifications given in standards should be developed such that
they quantify all known
uncertainties.
8.4 Target failure probabilities
The target failure probabilities, i.e. pft, should be chosen taking into account the
consequence and the nature of failure, the economic losses, the social
inconvenience, effects to the environment, sustainable use of natural resources, and
the amount of expense and effort required to reduce the probability of
failure.
- What is acceptable failure probability;
Is a probability of 1% of the fatality risk of a 16 years old boy ok today?
- What is the actual failure probability for normal “on-land” structures in Norway and
Europa today.
Would the public accept a larger risk than today??
- How do you convert failure into consequence if it is not total collapse???
- What would the annual number of fatalities per million be if the actual reliability
index was 3,8????
- How to enter the effect of flaws and errors in design and execution into the
estimated reliability?????
ISO 2394 Annex G Informative
This is the only place in ISO 2394 where numerical values
are indicated, it could be questioned if these values would
be accepted by society today?
EN 1990 Capter 2 opens for reliability differentiation,
details in Annex B (informative) proposed rev.
B2.1 Consequences classes
(1) For the purpose of reliability differentiation, consequences classes (CC) may be established by considering the
consequences of failure or malfunction of the structure as given in Table B2.
Table B2 - Definition of consequences classes
Consequences
Class
CC3
Description
High consequence for loss of human life, or
economic, social or environmental
consequences very great
CC2
Medium consequence for loss of human life,
economic, social or environmental
consequences considerable
CC1
negligible consequence for loss of human
life, and economic, social or environmental
consequences small
Examples
of
buildings
and
civil
engineering works
Grandstands, public buildings where
consequences of failure are high (e.g. a
concert hall) and public buildings where the
function is critical (e.g. hospitals, firestations),
large bridges etc.
Residential and office buildings, public
buildings where consequences of failure are
medium (e.g. an office building), small and
medium size bridges etc.
Agricultural buildings, buildings where people
do not normally enter (e.g. storage buildings),
greenhouses etc.
(2) The criterion for classification of consequences is the importance, in terms of consequences of failure, of the
structure or structural member concerned. See B2.3
(3) Depending on the structural form and decisions made during design, particular members of the structure may
be designated in the same, higher or lower consequences class than for the entire structure.
NOTE The requirements for reliability are related to the structural members of the construction works, the system reliability
should for reasons of robustness be higher than for the individual members.
EN 1990 Annex B, proposed rev
B2.2 Differentiation by β values
(1) The reliability classes (RC) may be defined by the β reliability index concept.
(2) Three reliability classes RC1, RC2 and RC3 may be associated with the three consequences classes CC1, CC2
and CC3.
(3) Table B3 gives recommended target values for the reliability index β for new structures associated with reliability
classes (see also Annex C) using a 50-year reference period.
Table B3- Recommended target values for reliability index β for new structures (ultimate limit states)
Target values for β
Reliability Class
Annual value
Value for a
50 years reference period
RC3
5,2
4,3
RC2
4,7
3,8
RC1
4,2
3,3
Note 1: The corresponding failure probabilities for the reference period of 50 years are equal to 50 times the annual values,
which makes the two requirements in principle equivalent. The difference is that the 50 years requirement allows temporary
higher annual failure probabilities for some periods, if compensated by lower ones for others.
NOTE 2 A design using EN 1990 with the partial factors given in annex A1 and EN 1991 to EN 1999 is considered generally to lead
to a structure in RC2.
NOTE 3 Reliability classes for members of the structure above RC3 are not further considered in this Annex, since these
construction works and their members each require individual consideration.
Sikkerhetsnivå i dagens standarder
• I diskusjonene i EN 1990 Expert Group er det enighet om;
• Sikkerhetsnivået i dagens byggeri er nok betydelig høyere enn det
måltallene for sikkerhetsindeksen skulle tilsi
• Det er liten grunn til å tro at samfunnet ville være villig til å akseptere
vesentlig økning i faktisk konstruksjonssvikt.
• Dagens sikkerhetsnivå og partialfaktorer er basert på kalibrering mot
tidligere praksis IKKE de måltall som refereres
• Måltall for sikkerhetsindeks er primært egnet for å vurdere oppnådd
sikkerhet ved ulike alternative løsninger opp mot hverandre, ikke som
absolutte måltall.
• Bruk av “global sikkerhet” konsepter er en “pådriver” for absolutt verdier
for måltall.
Nye
bestemmelser
for eksisterende
konstruksjoner
introduserer nye
problemstillinger
Existing structures, indicative target values
Note the
significant
increase of target
reliability index
when the area
involved in the
collapse Acol
increases,
This could
correspond to a
- system failure
versus a
- member failure.
System of European standards for
Construction Products Directive (CPD)
WORKS
+
National legislation
Interface Society /
construction project
For a construction
project use of
Eurocodes with the
underlying standards
for execution and
materials provide
confirmation at the
interface to society
that structures are
safe, assuming
design and execution
are without flaws.
Eurocode - 1990
Basis of structural design
TC250
 This figure is drawn to
illustrate the situation for
Concrete Works, similar
figures could be drawn for
Eurocode - 1991
Actions on structures
TC250/SC1
•
•
•
Steel structures
Composite
steel/concrete
Aluminum structures
While not for
Eurocode - 1992
Design of concrete structures
TC250/SC2
• Timber structures
• Masonry structures
As these are not having
satisfactory standards for
the Execution of the
Works.
EN 13670
Execution of concrete structures
TC104/SC2
EN 206-1
Concrete
TC104/SC1
ISO 6934 or ETA
Tendons & PT kits
EN 10080
reinforcement
EN 13369 - xx or ETA
Prefabricated elements
TC229
Product and testing standards
TC104/SCs and WGs
Product and testing standards
Product and testing standards
Product and testing standards
NS-EN 1990/NA
NA.A1.3.1 Design values of actions in persistent and
transient design situations
NA.A1.3.1(1) For structures in reliability classes 1, 2, 3 (see
Table NA.A1 (901)), the values ascribed to γF in tables
NA.A1.2(A), NA.A1.2(B) and NA.A.1.2(C) may be used.
This is on the condition that the requirements for a quality
system, design supervision and inspection during execution
specified in the following text and in tables NA.A1(902) and
NA.A1 (903) are complied with. For structures in reliability
class 1 (CC1/RC1), the partial factor γF for variable actions
may be reduced by the factor kFi = 0.9.
Note, we can not say anything about
reliability if we don’t have control over the
quality of design and execution!
We do not only need adequately precise design and construction
methods, we need design and execution without flaws, and
standards to provide for that.
Illustration of the effect of control on the β value from
reduced variability on load-effects and resistance.
Compared to use of load factors γFI = 0,9-1,0-1,1.
Diagrams from Milan Holicky.
6
5
4
3
2
0
0.2
6
Strict,
(illustratio
0.6 n)
0.8
0.4
β
5
Normal
A
B
β = 3,8
4
C
χ
3
0
6
5
5
RC3
β = 4,3
4
RC2
β = 3,8
RC1
3
β = 3,3
3
0
0.
4
0.
6
0.
8
6
β
4
0.
2
χ
0.2
0.4
0.6
.
0.8
2
Low,
(illustration)
6
Comparison of basic and increased
production quality keeping γc=1,5 and
γm=1,15. Figure 1 is taken from Milan
Holicky, Figure 2 shows new results by
Holicky assuming reduced variability as a
result of improved execution control.
6
β
5
A
B
4
β = 3,8
β
C
χ
3
5
A
β = 3,8
0.2
0.4
β
0
C
0.2
0.4
0.8
A
5
χ
3
0.6
6
B
4
0
0.6
B
0.8
Figure 1. Variation of the reliability index β
of the beam with the load ratio χ for
reinforcement ratio ρ = 1 %, basic
production quality, γc=1,5, γm=1,15 and
load combinations A, B and C.
.4
3
0
C
χ
0.2
0.4
0.6
0.8
Figure 2. Variation of the reliability index β of the beam with
the load ratio χ for reinforcement ratio ρ = 1 %, increased
production quality,
upper diagram
γc=1,35, γs=1,05
lower diagram
γc=1,5, γs=1,15
Structural failures are due to a set of
reasons:
• risk inherent in our design procedures (β’s)
• errors in design
• errors in execution
• errors in use
• acts of God
Society have no acceptance or forgiveness for
the first four, hardly even the last
Failures are normally due to a combination of
errors, hardly ever only the first
Target β -values are low, real values are ~ok!
When designing steel structures according to EN 1993-1-1 [10] for
buckling of slender compression members in combined compression
and bending you need the interaction factor kyy, for calculating expression (6.61)
M y , Ed + ∆M y , Ed
M z , Ed + ∆M z , Ed
N Ed
+ k yy
+ k yz
≤1
χ y N Rk
M y , Rk
M z , Rk
χ LT
γ M1
γ M1
γ M1
for buckling around the y-y axis, in the for a plastic design according to method 1 you
need to calculate the following expressions given in Annex A and shown in figure 5;
Calculate kyy=
and with
and with
C my C mLT
µy
1
N C
1 − Ed yy
N cr , y
with
N Ed
N cr , y
=
N Ed
1− χy
N cr , y
1−
µy
 Wel , y
 1,6 2
1,6 2 2 

C yy = 1 + (wy − 1)  2 −
Cmy λ max −
Cmy λ max n pl − bLT  ≥


w
w
 W pl , y

y
y

2
bLT = 0,5 aLT λ 0
M y , Ed
M z , Ed
χ LT M pl , y , Rd M pl , z , Rd
Figure 5 The interaction factor kyy for use in expression (6.61)
WHAT IS PROBABILITY OF AN ERROR AND
WHAT HAPPENS TO β (10-6) IF CALCULATION IS ERRONEOUS????
WHO USE WHAT TECHNICAL STANDARD
Standard etc.
Designer
Constructor
Concrete
producer
Material
producer.
Building law and regulations PU
Interface between society and construction project
PU*
EN 1990 Basis of design
PU*
EN 1991 Actions
PU*
EN 1992 Design of concrete
National Standards for quantity, cost
and bidding
PU*Interface
PU Interface
Design/Constructor
Design/Constructor
EN 13670 Execution of
concrete str., incl Execution spec
PU Interface
PU* Interface
Design/Constructor
Design/Constructor
SU
PU Interface
PU*Interface
Constructor/producer
Constructor/producer
SU
PU Interface
PU* Interface
Producer/material
Producer/materialpro
PU*
PU
SU
PU*
EN's for special tasks, bored piles, diaphragm walls etc.
EN 206-1+ NA Concrete
EN for concrete constituents
SU
EN 12620
EN 197, NS 3086
EN 1080
EN for testing concrete
SU
SU
EN 12350 Fresh concrete
EN 12390 Hardend concrete
EN for testing constituents
PU* = Primary user, who the standard is "written for"
PU = Primary user, one who needs to know the standard in detail
SU = Secondary user, one who needs to be aware of the standard
Interface standard are standards that are used for communication between the parties who are both primary users (PU)
There are three main pillars
• DESIGN
• Eurocodes provide potentially safe design, if only it is
without flaws…....
• EXECUTION
• EN 13670 and EN 1090 provide potentially safe
execution, if only it is without flaws ………
• QUALITY MANAGEMENT
• ISO 9000/9001 common for bakers, hairdressers,
designers and contractors provides adequate quality
management if only content is appropriate…….
 There must be adequate procedures relevant to the
work i.e. design, execution of concrete, steel etc.
This is a task for the EUROCODES to ensure.
We have in EN 1990 the building blocks for a reliability
management system, but we have nowhere established a
coherent system, or invited the member states to do so,
this is area of MS competence
FROM EN 1990 Annex B
EN 1090
EN 13670
CC1
RC1
DSL1
IL1
EXC1
CC2
RC2
DSL2
IL2
EXC2
CC3
RC3
DSL3
IL3
EXC3
Proposal in EN 1990 Annex B for a Quality
Management system and differentiation dependant
on Consequence of failure.
NA.A1.3.1(902) Kvalitetssystem
NA.A1(902.1) Ved prosjektering, utførelse og kontroll av konstruksjoner i pålitelighetsklasse 2, 3
og 4 skal et kvalitetssystem være tilgjengelig. For konstruksjoner i pålitelighetsklasse 4 skal
kvalitetssystemet tilfredsstille kravene i NS-EN ISO 9000-serien.
MERKNAD For marine konstruksjoner for petroleumsindustrien i pålitelighetsklasse 3 krever
myndighetene (Petroleumstilsynet) at kvalitetssystemet skal tilfredsstille NS-EN ISO 9000serien.
NA.A1(902.2) Kvalitetssystemet skal spesifisere krav for:
− organisasjon;
− personell;
− prosjektering, omfang og dokumentasjon av beregninger;
− programvare benyttet i prosjekteringen;
− prosjekteringskontroll;
− utførelse (arbeidsutførelse og arbeidsledelse);
− kontroll av materialer og komponenter;
− kontroll av utførelse;
− kontroll under bruk;
− system for håndtering av avvik;
dokumentasjon av: prosjekteringskontroll, kontroll av utførelse og kontroll under bruk
NA.A1.3.1(902) Kvalitetssystem
NA.A1(902.1) Ved prosjektering, utførelse og kontroll av konstruksjoner i pålitelighetsklasse 2, 3
og 4 skal et kvalitetssystem være tilgjengelig. For konstruksjoner i pålitelighetsklasse 4 skal
kvalitetssystemet tilfredsstille kravene i NS-EN ISO 9000-serien.
NA.A1(902.2) Kvalitetssystemet skal spesifisere krav for:
− organisasjon;
− personell;
− prosjektering, omfang og dokumentasjon av beregninger;
− programvare benyttet i prosjekteringen;
− prosjekteringskontroll;
− utførelse (arbeidsutførelse og arbeidsledelse);
− kontroll av materialer og komponenter;
− kontroll av utførelse;
− kontroll under bruk;
− system for håndtering av avvik;
dokumentasjon av: prosjekteringskontroll, kontroll av utførelse og kontroll under bruk
Tabell NA.A1(903) – Krav til kontrollform ved prosjektering
og ved utførelse, avhengig av kontrollklasse
Kontrollform
Prosjektering
Utførelse
Egenkontroll
Intern
systematisk
kontroll
(DSL 1)1)
Utvidet
kontroll 2)
+
Uavhengig
kontroll 5)
(DSL 2)1)
PKK1 / UKK1
kreves
PKK2 / UKK23)
PKK3 / UKK3
Kontrollklasse
1)
Egenkontroll
Intern
systematisk
kontroll
Utvidet
kontroll 2)
+
Uavhengig
kontroll 5)
(DSL 3)1)
(IL 1)1)
(IL 2)1)
(IL 3)1)
kreves ikke
kreves ikke
kreves
kreves ikke
kreves ikke
kreves
kreves
enkel utvidet
kontroll
kreves
kreves
kreves
enkel utvidet
kontroll
kreves 3)
kreves
kreves
normal
utvidet
kontroll
kreves
kreves
kreves
normal
utvidet
kontroll
kreves 4)
Se punktene B4 og B5 (informativt tillegg B) for parallelle betegnelser og bestemmelser, DSL og IL.
Utvidet kontroll utføres i byggherrens regi enten av byggherrens egen organisasjon eller et annet foretak som er uavhengig av
foretaket som utførte arbeidene
3)
Der de løsningene som benyttes gjør at bæreevnen er særlig avhengig av utførelsen, for eksempel for: materialer med høy
fasthet (stålsort S460 eller høyere, betong trykkfasthetsklasse B55 eller høyere), sveisesoner i utmattingspåkjente
konstruksjoner, konstruksjonsdeler med etteroppspent armering, samt i eventuelle energiabsorberende soner i seismisk
påkjente konstruksjoner (se NS-EN 1998-1) utføres og kontrolleres arbeidene i overensstemmelse med kravene for
utførelseskontrollklasse UKK3 (utvidet kontroll).
4) Ved prefabrikkerte produkter som skal beregnes i overensstemmelse med Eurokodene, kan forutsetningen om uavhengig
kontroll av utførelsen ansees tilfredsstilt dersom produktet er produsert i henhold til en harmonisert standard og underlagt
samsvarskontroll under en sertifiseringsordning med sertifisert kontrollsystem, med et ekstra kontrollelement ivaretatt internt for
eksempel av egen prosjekteringsavdeling.
5) MERKNAD Denne standarden forutsetter at det, som et tillegg til utvidet kontroll, utføres uavhengig kontroll i henhold til
byggesaksforskriften SAK10 § 14-2 siste ledd, i form av bekreftelse av at utvidet kontroll er gjennomført og dokumentert.
2)
Control pyramid in a project, with interface to authorities
Basics open for national choice
Standards need a system to get things right
Authorities needs a system to confirm that things are right
Execution class 3 [CC3/RC3 + special technology]
Clients Quality System / Authorities
Authority control if req.
INDEPENDENT
DSL3 / IL3
Execution class 2 [CC2/RC2]
Constructors Quality System
INTERNAL
Execution class 1 [CC1/RC1]
DSL2
SYSTEMATIC
IL2
Interface between
”project” and
building authorities
•Documentation
•Audit
Constructors Quality System
SELF
DSL1
CHECKING
/ IL1
Quality in a project should come from below,
as “good quality work” from the very start. Not
as “corrections” from above.
Control shall help us manage our projects not give us the
catastrophe with the pyramid turned upside down
OUR AMBITION !!