Structural Design Of The Super-Long Construction Trestle For Hangzhou Bay Bridge Project

This paper is dedicated to solving typical issues encountered in the severe marine environmental conditions, motivated by the practical demands for the structural design of the super-long construction trestle for Hangzhou Bay Bridge Project. The research addresses the identification of the trestle design criterion, selection of appropriate methods for calculating the wind, wave and tide actions at the estuary site, analysis of the vertical bearing capacity of the open-end steel-pipe piles, and evaluation of the ultimate lateral bearing capacity of the trestle bridge.(1)The design criterion of trestle bridgeThe design of trestle structures should follow the fundamental principles of safety, serviceability and economy. In order to carry out the principles, a concept of"three design states"is proposed for design. According to the probability of operation-event occurrence, the three protection levels are defined during its lifetime, which are "operation state","non-operation state" and"disaster state". Accordingly a protection standards for the three states is proposed, i.e., "no damage in operation state","repairable in non-operation state" and"no collapse in disaster state". With different design states and protection standards, the trestle bridge can economically resist disasters at a high level.The"risk analysis"is introduced into the design of the trestle bridge. Based on the basic project data and assumed economic losses for each items, the appropriate return period of the design environment effect is worked out.(2)The characteristic of the wind, wave and tide in Hangzhou Bay and calculating methods of their forcesHow to calculate the loads of wind, wave and tide in marine is a special problem in the bay bridge's construction. The wind, wave, tide are randomly and they have their statistical characteristics. The mechanisms that they act on the structures are complex. These above conditions make accurate calculating rather difficult. Therefore, in this paper, the mechanisms of the wind, wave, tide, the calculating methods of the loads and the parameters'determination are introduced and discussed.(3)The analysis of the vertical bearing capacity of the open-end steel-pipe pilesAccording to the current specifications for piles, the calculating results of the vertical bearing capacity of the open-end steel pipe pile are generally larger than the field test results. So, based on previous researches, this paper does a further study on the vertical bearing capacity of the open-end steel-pipe piles. The physical characteristics of the soil column are discussed. The concept of"effective plug length"is proposed. The impact of plugging effect to the pile end resistance is studied. Finally, an applicable formula that has clear physical concepts is proposed.(4)The analysis of the ultimate lateral bearing capacity of the trestle bridgeThe calculating methods for the large displacement pile are compared and investigated; the physical boundary conditions of the tubular steel piles of the trestle are also studied. The finite element model that considers the non-linear interaction between the piles and the soil is established. The criterion for the ultimate lateral bearing capacity is set. By step loading at the top of the piles and observing the displacement, the ultimate lateral bearing capacity of the piles is analyzed and the safety margin for the trestle structure is evaluated.(5) The application of the results to design the Trestle for Hangzhou Bay Bridge projectThe results of this paper have been successfully applied in the design of the super-long trestle structure protruding from the south-bank for erection of Hangzhou Bay Bridge. The conclusions made in this paper are instrumental in structural design of modern construction trestles.