Laser-welded corrugated core steel sandwich bridge decks

Doctoral thesis, 2020

Steel bridge decks are often used for applications when a lightweight structure is sought for. Conventional orthotropic steel decks suffers from drawbacks in several aspects, including high production costs and durability problems. Another possibility for the application of bridges is to use a sandwich panel as a deck. A sandwich panel consists of two outer face plates, separated by a core. Here, the stiff face plates yield the bending stiffness and the core provide the shear stiffness. As the core is often lightweight, it generally has a low stiffness. Thereby, a sandwich plate theory that accounts for shear deformations is needed. Laserwelded Corrugated Core Steel Sandwich Panels (CCSSPs) have shown a good potential to become the next generation lightweight bridge decks with enhanced structural properties compared to its predecessor. The work presented in this thesis aims at verifying CCSSPs for bridge applications and to gain an increased understanding of their structural behaviour. Even though considerable research effort related to all-steel sandwich panels has been made, focus in previous work has been on other types of core configurations. Very little work has been devoted to corrugated core panels, particularly with reference to bridge deck applications, which is topic of this thesis.      

In this work, a production process is presented for the novel CCSSP. Four demonstrator panels, of C-Mn and Duplex stainless steel are produced. Furthermore, the manufacturing process does never produce the ideal intended geometry. This influences the stresses in the fatigue-sensitive welds. In this thesis the effect of these geometric variations from the production are studied with respect to the weld stresses and the results show that one important factor is the width of the weld.       

Fatigue is a highly important factor for steel bridge decks and it has a strong relation to durability and strength requirements that are put on the deck. Here, the fatigue-strength of laser-welds in CCSSPs is assessed using experiments and computer simulations. The results from this study enables design of CCSSPs with respect to fatigue. In addition, the results also indicate very good fatigue performance for CCSSP bridge decks.     

To ensure that structural requirements concerning stiffness and strength are satisfied, reliable analysis methods are needed. To find an optimal bridge deck topology, and to run many load-cases, these analyses also needs to be time-efficient. In this thesis, two approaches with these targets are evaluated using numerical analyses. The results show that it is possible to accurately predict stresses using a deformation driven sub-modelling approach. Incorporation of the deformability of the weld region is shown to have a high impact on the state of stress in the welds, and a modelling technique is presented in this aspect. In addition, equivalent stiffness properties of CCSSPs are investigated and derived herein.