Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Structural design standards based on the principles of structural reliability are gaining worldwide
acceptance and are fast becoming the new basis for structural safety verification. The application
of these principles to establish a standardised basis for structural design using partial factor limit
states design procedures is done in the European Standard for the Basis of Structural Design EN
1990 from which it is adapted to the South African Standard Basis of Design for Building and
Industrial Structures SANS 10160-1. South Africa (SA) is on the advent of adopting the
European Concrete Design Standard EN 1992-1-1 (EC2) as the equivalent standard for local use.
This investigation seeks to provide a transparent quantitative reliability basis for the SA’s
adoption of EC2, as well as provide for its subsequent implementation under local conditions and
practice.
The investigation kicks-off with a critical review of the reliability framework for structural
resistance. The review establishes the relationships between the key elements of the framework,
shedding light on issues SA needs to consider as it adopts EC2. Important issues for SA to
consider include (1) target levels of structural performance ( -values), (2) partial factors,
(3) model uncertainties, and (4) quality control.
Design for shear resistance was investigated in greater detail by comparison of EC2’s Variable
Strut Inclination Method (VSIM) for stirrup design against alternative approaches, namely, (1)
South Africa’s currently operational SANS 10100-1 procedure, and (2) the fib Model Code 2010
first Level of Approximation (LoA I) and fib LoA III, which are based on the Modified
Compression Field Theory (MCFT). Unbiased capacity predictions from the MCFT-based
sectional analysis Program Response-2000 (R2k) served as LoA IV best-estimate results during
this assessment. Results of this investigation showed that EC2 offers higher capacity predictions
in excess of 1 MPa of stirrup reinforcement, with significantly higher predictions in the range of
1 to 2 MPa. A reliability performance assessment was therefore commissioned to assess safety
regimes in terms of achieved reliability across a parametric range of the amount of stirrup
reinforcement (from 0.45 to 2.0 MPa). The First Order Reliability Method (FORM) was implemented as part of the reliability
performance assessment of the EC2’s VSIM design procedure. The model uncertainty for shear resistance (stirrup failures) was characterised according to a database of published stirrupreinforced
concrete beam shear tests. Three cases of the Model Factor for shear resistance were
derived from the experimental database for alternative shear resistance prediction models; two of
which formed part of basic investigations conducted using the conventionally formulated
performance function, and the other was integrated as part of an independent validation
procedure using R2k predictions to obtain the reliability model.
Results obtained from the basic reliability model ( -values) generally indicated lower levels
of reliability with an increase in stirrup reinforcement and concrete strength, compared to those
estimated from the R2k-based reliability model ( -values). The disparity between and
-values revealed that systematic effects affect each model’s ability to predict the expected
value of true shear resistance
. There is reasonable evidence to suggest that the predictions
of
can be improved by accounting for each model’s peculiar sensitivity to concrete strength,
consequently providing more representative estimates of . However, in the interim, and
-values, respectively, represent reasonable lower and upper bound estimates of the
performance of EC2’s VSIM design procedure. / AFRIKAANSE OPSOMMING: Die beginsels van struktuur betroubaarheid word wêreldwyd aanvaar as basis vir struktuur
ontwerp standaarde en die versekering van voldoende struktuur veiligheid. Hierdie beginsels
word in die Europese Standaard Basis of Structural Design EN 1990 toegepas om
gestandaardiseerde partiële faktor gebaseerde limietstaat ontwerp prosedures daar te stel, van
waar dit aangepas is vir die Suid-Afrikaanse Standaard Basis of Design for Building and
Industrial Structures SANS 10160-1. Suid-Afrika (SA) staan op die punt om die Europese beton
ontwerp standaard EN 1992-1-1 (EC2) aan te neem as die ekwivalente standaard vir plaaslike
gebruik. Hierdie ondersoek het as doel om ‘n deursigtige kwantitatiewe betroubaarheidsbasis
daar te stel vir die aanneming van EC2 as SA standaard en om voorsiening te maak vir die
implementering daarvan onder plaaslike toestande en –praktyk.
Die ondersoek begin met ‘n kritiese oorsig van die betroubaarheidsraamwerk vir strukturele
weerstand. Die oorsig stel die verhouding vas tussen sleutel elemente van die raamwerk en werp
lig op aspekte wat SA moet oorweeg in die aanneming van EC2. Belangrike aspekte vir
oorweging sluit (1) teiken betroubaarheidsvlakke vir struktuur gedrag ( -waardes), (2) partiele
faktore, (3) model onsekerhede en (4) kwaliteitsbeheer in.
Skuif weerstandsontwerp is in groter detail ondersoek deur die EC2 se Veranderbare Stut Hoek
Metode (VSHM) vir skuifbeuel ontwerp te vergelyk met alternatiewe benaderings, naamlik, (1)
Suid Afrika se huidig operasionele SANS 10100-1 prosedure, (2) fib Model Code 2010 se
sogenaamde eerste Vlak van Benadering (VvB I) en fib VvB III, gebaseer op die Aangepaste
Drukveld Teorie (ADT). Onbevooroordeelde kapasiteit voorspellings van die ADT-gebaseerde
snit analise program “Response-2000 (R2k)” is in die evaluering gebruik as VvB IV bes
benaderde resultate. Die ondersoek toon dat EC2 hoër kapasiteit voorspel vir skuifbeuel
bewapening tot 1 MPa en beduidend hoër kapasiteite voorspel vir skuifbeuel bewapening tussen
1 en 2 MPa. ‘n Betroubaarheidsprestasie studie is vervolgens geloots om die veiligheid in terme
van behaalde betroubaarheid te bepaal oor ‘n parametriese bereik van 0.45 tot 2.0 MPa skuifbeuel
bewapening.
Die Eerste Orde Betroubaarheids Metode (EOBM) is implementeer as deel van die betroubaarheidsprestasie beoordeling van die EC2 VSHM ontwerp prosedure. ‘n Databasis van gepubliseerde skuifbeuel-bewapende betonbalk skuiftoetse is gebruik om die model onsekerheid
vir die verskillende skuifweerstandsmodelle statisties te beskryf. Drie Model Faktore is uit die
eksperimentele databasis afgelei, twee waarvan gebruik is in basiese ondersoeke met die
konvensioneel geformuleerde prestasie funksie en die derde as deel van ‘n onafhanklike
bevestigingsprosedure gebaseer op R2k voorspellings.
Resultate wat verkry is uit die basiese betroubaarheidsmodel ( -waardes) was laer (meer
konserwatief), en het ook vinniger afgeneem met ‘n toename in skuifbeuel bewapening as die
waardes wat uit die R2k-gebaseerde betroubaarheidsmodel ( -waardes) verkry is. Die verskil
tussen β en β -waardes toon dat sistematiese effekte die vermoë van elk van die modelle
beïnvloed om die verwagte waarde van die werklike skuifweerstand V te voorspel. Daar is
redelike bewyse om aan te voer dat die voorspellings van V verbeter sal kan word deur elke
model se unieke sensitiwiteit teenoor betonsterkte in ag te neem, om sodoende meer
verteenwoordigende β waardes te verkry. Intussen verteenwoodig die β en β -waardes
onderskeidelik redelike onder- en bogrens skattings vir die prestasie van EC2 se VSHM ontwerp
prosedure.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96913 |
| Date | 03 1900 |
| Creators | Mensah, Kenneth Kwesi |
| Contributors | Viljoen, C., Retief, J. V., 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 | Unknown |
| Type | Thesis |
| Format | 261 pages : illustrations |
| Rights | Stellenbosch University |
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