Composite bridge design optimisation using HFMI-treatment: Design and optimisation of composite bridges using high frequency mechanical impact (HFMI) treatment
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Structural engineering and building technology (MPSEB), MSc
Publicerad
Författare
Englund , Cecilia
Dagduk, Saffa
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Bridges are structures that are usually subjected to repetitive loading which can
cause fatigue damage. Welds are specifically sensitive when considering fatigue
problems. Thus, a post-weld treatment called High Frequency Mechanical Impact
treatment (HFMI-treatment) is one solution that has the potential to increase fatigue
resistance. It can lead to reduced stress concentrations by improving the
geometry and introducing counteracting stresses by the weld. Further, it can be
useful to use high strength steel to increase the improvement even more.
The effect of using HFMI-treatment on new bridge design is still not thoroughly
studied. Therefore, HFMI-treatment is investigated by optimising a steel bridge
design using higher strength steel and also reducing material usage. A structural
design of a road bridge is performed considering the effect of HFMI-treatment of the
different welded joints. Additionally, the effect of implementing HFMI-treatment on
site when the bridge already has been erected is studied and compared to when
treatment is implemented in a workshop.
The study indicates that there is a significant decrease in utilisation ratios for fatigue
limit states when HFMI-treatment is implemented. The effect of HFMI-treatment
together with the use of higher steel grades resulted in enhanced fatigue performance
and also remarkable material savings. The most economical option appears to be to
use steel strength S460. On the other hand, S690 can help obtain a slender beam for
nearly the same cost if the beam height is limited. However, high stress ranges can
limit the improvement of HFMI which restricts the possibility of enhancing fatigue
strength.
The thesis concludes that implementing HFMI-treatment and increasing steel strength,
in new bridge designs, can be significantly beneficial. The cost of performing the
treatment is insignificant, and there is good potential for material and cost savings.
Furthermore, the best outcomes are obtained when the treatment is implemented
after erection.
Beskrivning
Ämne/nyckelord
Bridges, Fatigue, Welds, Post-weld treatment, High frequency mechanical impact treatment (HFMI-treatment), High strength steels, Optimisation.