Construction and Design of Post-Tensioned Pearl-Chain Bridges using SL-Technology

Pre‐fabricated closed‐spandrel concrete arch bridges have existed for more than 50 years. Pearl‐Chain (PC) Bridges are a new award‐winning state‐of‐the‐art segmental concrete arch bridge concept invented by professor Kristian Hertz. A PC‐Arch can consist of a number of pre‐tensioned low‐weight SL‐Decks. One SL‐Deck is a combination of light aggregate concrete, and regular concrete. Curved post‐tensioning ducts are cast into the elements, and several SL‐Decks are post‐tensioned together in an arch shape to become a PC‐Arch. A PC‐Bridge is built by erecting a number of adjacent PC‐Arches and applying a filling layer of lower stiffness above the arches to level the road surface. The present Ph.D. thesis is part of a larger development project about Pearl‐Chain Bridges funded by Innovationsfonden. The project also included another Ph.D. study about the developed materials used in Pearl‐Chain Bridges. A row of companies have cooperated with the DTU‐team in a consortium during the three year project period: Abeo, Perstrup Betonindustri, Skandinavisk Spændbeton og Sweco.
A method for calculation of the bending moment capacity was presented. The method was illustrated in a case study of a 30 m span PC‐Bridge. The case showed that the pre‐compression in the arch from pre‐stressing, rise/to span ratio, and layer thickness of the filling as expected had influence on the capacity and could be altered to meet the capacity demands of a specific project. For an unevenly loaded bridge, in general, the lowest capacity was found to be in the joint between SL‐Decks in the loaded side of the span, and in the SL‐Deck in the non‐loaded side. Arches under critical loading in the ¼ point of the span have a higher positive than negative bending moment, and advantageously the PC‐Arches are designed to have higher positive than negative bending moment capacities in the SL‐Decks. Concrete hinges were investigated for use in PC‐Bridges. The true behavior of such hinges was far from ideal, and therefore had an influence of the overall static system. The responses of two types of hinges were investigated by full‐scale testing, and numerical modelling. Despite of high levels of normal force in PC‐Bridges, the result showed that a Mesnager inspired hinge type had a response similar to what was predicted in the literature. A specially designed saddle bearing also had elastic and plastic rotational resistance, but this hinge type was more practical to implement in a PC‐Arch.
Two full‐scale 13 m span PC‐Arches were successfully assembled, post‐tensioned and lifted into position next to each other on a test‐foundation by use of a developed fast erection procedure. The same two arches were subsequently load‐tested in the ¼ point of the span in two tempi: 1) A test to 2/3 of the load carrying capacity, where the behavior of the arches during loading was recorded and evaluated. It showed that the arches deflected as expected for a regular concrete arch, and that stresses are transferred between arches via so called Hammerhead joints. 2) A test to fracture to observe the ductility in the system, and fracture type. The collapse occurred after two plastic hinges were formed in the 3/8, and 5/8 points of the span. Several warnings signs were observed when approaching the maximum loading.