Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The South African National Standard for the structural use of cold-formed steel (SANS 10162-2)
provides capacity prediction models for screwed connections. Screwed connections are
designed against shear failure of the screw(s), section tear-out, net section failure and tilt-andbearing
failure. Previous studies (Rogers & Hancock, 1997) showed that the capacity is typically
determined by the tilt-and-bearing type failure mode. The aim of this document is to report on
the reliability of single screwed connections in cold-formed steel against this critical failure
mode.
Predicted nominal capacities depend on the ultimate tensile strength of the steel, the thickness
of the connected plates and the diameter of the screw. Design capacities are obtained by
multiplying the nominal capacities by a capacity reduction factor of 0.5, according to
SANS 10162-2. Reliability is assessed by means of FORM analyses, taking uncertainty in the
prediction model and variability of input parameters into account.
Laboratory testing of 222 single screwed connections allowed to statistically describe the model
factor, i.e. the ratio of actual tested- over unbiased predicted capacity. For each connection, the
steel strength, plate thickness and screw diameter were measured, with the measured values
used to predict capacity. This implies that the model factor accounts for uncertainty in the
prediction model and experimental setup, while the variability of input parameters is separately
accounted for through appropriate statistical modelling.
Variability in the input parameters was described using appropriate statistical distributions
from expert literature (Holicky, 2009:199; JCSS, 2000). For steel strength, the mean value and
standard deviation were obtained from tensile tests, while mean values and standard deviations
of the plate thickness and screw diameter were obtained from the above mentioned
measurements. The experimental work and numerical analysis resulted in a model factor with a mean just
exceeding unity and a small standard deviation. This suggests that the design code under
consideration is able to accurately predict the nominal capacity of screwed connections. The
FORM analysis resulted in computed reliability indexes significantly higher than the
corresponding target values which suggest conservative and reliable design formulations. Die eksperimentele werk en numeriese analise het gelei tot 'n model faktor met 'n gemiddeld
hoër as een en 'n klein standaardafwyking. Dit dui daarop aan dat die ontwerp-kode onder
oorweging in staat is om die nominale kapasitiet van skroef verbindings akkuraat te voorspel.
Die betroubaarheid analise het gelei tot betroubaarheidsindekse aansienlik hoër as die
ooreenstemmende teiken waardes wat daarop dui dat die ontwerp formulerings betroubaar en
hoogs konserwatief is. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse Nasionale Standaard vir die strukturele gebruik van koud gevormde staal
(SANS 10162-2) bied voorspellingsmodelle vir die kapasitiet van skroef verbindings. Skroef
verbindings word ontwerp teen skroef faling, staal profiel faling, die uitskeer van skroewe en
ook faling weens skroef kanteling. Vorige studies (Rogers & Hancock, 1997) het getoon dat die
kapasiteit gewoonlik bepaal word deur die skroef-kantel falingsmodus. Die doel van hierdie
navorsing is om verslag te doen oor die betroubaarheid van tipiese enkel skroef verbindings in
koud gevormde staal strukture teen hierdie kritiese falingsmodus.
Voorspelde nominale kapasiteite hang af van die treksterkte van die staal, die dikte van die
verbonde profiele en die diameter van die skroef. Volgens die SANS 10162-2 word die ontwerp
kapasiteit verkry deur die nominale kapasiteit met 'n kapasiteitsverminderingsfaktor van 0.5 te
vermenigvuldig. Betroubaarheid word ontleed deur middel van ʼn eerste orde betroubaarheidsmetode
analise, met die in ag neming van onsekerheid in die voorspellingsmodel en wisselvalligheid
van die parameters.
Laboratoriumtoetse van 222 enkel skroef verbindings het ʼn statistiese beskrywing van die
model faktor toegelaat. Die model faktor is bereken as die verhouding tussen die getoetste
kapasitiet en die voorspelde kapasitiet. Die staal sterkte, profiel dikte en skroef diameter is
gemeet vir elke verbinding met die gemete waardes wat gebruik is om die kapasiteit te
voorspel. Dit beteken dat die model faktor slegs onsekerhede in die voorspellingsmodel en van
die eksperimentele opstelling in ag neem, terwyl die wisselvalligheid van die parameters
afsonderlik in ag geneem word deur toepaslike statistiese modellering.
Variasie in die parameters is beskryf met gepaste statistiese verdelings voorgestel deur verskeie
literatuur (Holicky, 2009:199; JCSS, 2000). Aangaande die staal sterkte, is die gemiddelde
waardes en standaardafwykings verkry deur standaard trek toetse terwyl die gemiddelde
waardes en standaardafwykings van die plaat dikte en skroef diameter verkry is deur die
bogenoemde metings.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95891 |
| Date | 12 1900 |
| Creators | Van Wyk, Rudolf |
| Contributors | Viljoen, Celeste, Stellenbosch University. Faculty of Engineering. Department of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xvi, 157 p. : ill. |
| Rights | Stellenbosch University |
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