Constructability considerations in long span bridge design

As the spans of cable stayed bridges and suspension bridges increase in length, erection methods have progressively evolved to meet the demands of the design. One of the critical considerations in the design of long span bridges is structural adequacy and stability in the temporary conditions that exist during construction. Selection of the most appropriate erection method is consequently a key issue for the engineer during the design stage and subsequently should be agreed with the contractor during implementation. This paper reviews the construction methods on a number of recently completed long span bridges, including Stonecutters Bridge in Hong Kong, where a span of 1,018m has been erected using advanced erection techniques while subject to potentially severe typhoon wind loading. The method of deck erection needs to remain structurally robust, while practicality and safety are also fundamental factors in determining how best to erect the bridge deck. Options are also considered for construction of the substructure, where maximizing the use of precast concrete elements can lead to considerable savings in both programme and cost. In a marine environment, casting pier bases in a dry dock not only ensures an improved level of quality, it also drives cost effectiveness and enhances safe working practices.