16.26: Design and construction of composite bridges

Abstract

ABSTRACTComposite bridges, where steel girders are used compositely with a concrete deck slab, can be preferred over steel or concrete bridges due several reasons. They are less expensive and require less maintenance than orthotropic steel decks and they are lighter than concrete girders. They often require less temporary structures for execution and by using prefabricated elements fast erection can be achieved. Composite bridges are often chosen for span ranges that are in between the typical span ranges of concrete and steel bridges.When designing a composite bridge deck it is important to carefully consider the different material characteristics of steel and concrete to achieve an optimum design both in respect of erection sequence and material quantities. The concrete slab has a high resistance to compression forces whereas steel is prone to buckling, but has a high tension capacity.The Constantine ramp bridges (Algeria, 2014) are open steel box girders with a filigran concrete slab. They are located on steep slopes in a congested urban area, which gave limitations to the construction methods. A composite deck solution was chosen so that steel segments could first be lifted into place by a medium size crane and secondly prefabricated concrete slab filigran members could be placed on the steel and used as formwork for the final in situ casting of the concrete slab. The construction sequence was planned so that the concrete slab would be mainly in compression in the dead load situation to optimize material quantities.Composite bridge decks are often applied in cable stayed bridges, since the concrete slab has good abilities to resist the high compression induced by the inclined cable stays particularly near the towers. Examples of recent composite cable stay bridges are Busan Bridges (Korea 2014, main span 475 m) and New NY Bridge (New York, under construction, main span 366 m) where bolted wide flange steel girders were used in combination with a concrete slab and Sungai Johor Bridge (Malaysia 2013, main span 500 m) where an open box section was applied.Composite bridge decks are often used in combination with all steel or all concrete decks to balance the weight when for example the main span is very large compared to the back spans such as for the Stonecutters bridge (Hong Kong, 2009, Main Span 1018m).