Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Standards define target reliability levels that govern the safety of designed structures. These
target levels should be around an economic optimum for the class of structure under
consideration. However, society may have safety requirements in excess of that required to
achieve an economic optimum. The LQI criterion can be used to determine society’s willingness
to invest in safety, thereby defining a minimum acceptable safety- or reliability level. This thesis
determines economically optimised reliability levels for reliability class two concrete structures in
South Africa, over a range of typical input parameters.
Rackwitz’s (2000) approach is used here, adjusted for the South African context. The structure is
described using a simple limit state function, defined as the difference between load and
resistance, with resistance a function of a global safety parameter. South African construction
costs, costs of increasing safety, failure costs and discount rates are used in the objective function
for economic optimisation.
Life Quality Index (LQI) theory is used as a basis to derive society’s willingness to pay (SWTP) for
safety and the corresponding reliability level is found by applying the LQI criterion. In the South
African context the derivation of SWTP presents some challenges, which is discussed.
Situations where the minimum required reliability would exceed the economically optimum
reliability level are discussed.
Various reliability based cost optimization case studies are conducted covering a broad range of
typical concrete design situations. From these case studies a range of target reliability indices are
derived for typical concrete structural components and failure modes. Obtained values are
compared to current South African target levels of reliability provided by the South African
loading code and recommendations are made.
The approach used by Rackwitz (2000) is compared with results obtained from case studies and
used as basis to estimate optimum reliability levels for other types of buildings.
Functions are written in MATLAB to allow replication of the study for others seeking to derive
optimum reliability indices. / AFRIKAANSE OPSOMMING: Standaarde spesifiseer teiken betroubaarheidsvlakke wat die veiligheidsvlak van ontwerpte
strukture bepaal. Hierdie teikenvlak moet rondom die ekonomiese optimum wees vir die klas van
struktuur onder oorweging. Die samelewing verkies moontlik ‘n hoër veiligheidsvlak as wat deur
die ekonomiese optimum dikteer word. Die LKI (Lewens Kwaliteit Indeks) maatstaf kan gebuik
word om die samelewing se bereidwilligheid om in veiligheid te belê te bepaal en sodoende ‘n
minimum veiligheidsvlak bepaal. Hierdie tesis bepaal die ekonomiese optimum
betroubaarheidsvlak vir klas twee beton strukture in Suid-Afrika vir wisselende parameters.
Rackwitz (2000) se benadering word in hierdie studie gebruik en is aangepas vir Suid-Afrikaanse
omstandighede. Die struktuur word beskryf deur ‘n eenvoudige limiet staat funksie, gedefinieer
as die verskil tussen die las en weerstand, met die weerstand as die funksie van ‘n globale
veiligheidsparameter. Suid-Afrikaanse konstruksie koste, veiligheidsvermedering koste,
falingskoste en diskonteer koerse word gebruik vir optimering.
Die LKI teorie word gebruik om SBB (Samelewing Bereidheid om te Belê) vir veiligheid af te lei en
die ooreenkomstige betroubaarheidsvlak word bepaal deur die LKI maatstaf toe te pas. In die
afleiding hiervan vir Suid-Afrikaanse omstandighede is sekere uitdagings teegekom wat bespreek
word.
Situasies waar die minimum betroubaarheidsvlak hoer is as die ekonomiese optimum word
bespreek.
Verskillende betroubaarheids gebaseerde optimering gevalstudies word gedoen op tipiese beton
struktuur elemente. Van hierdie gevalstudies is optimum betroubaarheidsindekse vir die tipiese
beton elemente en galingsmodusie afgelei. Die betroubaarheidsindekse word vergelyk met
huidige betroubaarheidsindekse soos wat voorgeskryf is in die Suid-Afrikaanse laskode
(SANS10160-1(2011)).
Rackwitz (2000) se benadering word vergelyk met die resultate van die gevallestudies en word
gebruik as basis om optimum betroubaarheidsvlakke vir ander tipes geboue te voorspel.
MATLAB funksies is geprogrameer om minimum en optimum betroubaarheidsindekse af te lei.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86329 |
| Date | 04 1900 |
| Creators | Smit, Charl Francois |
| Contributors | Barnardo-Viljoen, C., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xiii, 173 p. : ill. |
| Rights | Stellenbosch University |
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