Experimental Study On The Hydrodynamic Characteristics Of Frame-type Ecological Caisson Structure

With the increasing demand for deepwater wharf construction,the traditional gravity structure is increasingly unable to meet the engineering requirements due to the high cost and high ground requirements.The development of new hydraulic structures has become an inevi Tab trend.The frame-type ecological caisson structure has become the most promising new structure and has attracted wide attention from the port engineering community.This structure combines the advantages of traditional gravity structure and high pile structure-that is,it can use its own gravity to maintain stability and have good permeability,reducing the force of waves on the wharf.So far,due to lack of sufficient research(especially few studies on the dynamic response of structures under various loads),there are no engineering examples.It is gratifying that in 2020 Rizhao Port decided to try to adopt the frame ecological caisson structure at berth 17 # in Lanshan Port Area.The premise is that the dynamic response parameters of the structure under different combinations of wave load,horizontal load of forward and reverse gantry crane,tether load,impact load and other loads need to be accurately obtained.The physical model test method was used to study the dynamic response of the frametype ecological caisson structure under different loads.The test tested the fluctuation pressure of the submerged caisson and wave baffle of the structure,the strain on the pile group and the side wall of the caisson.The following main conclusions are obtained:(1)The frame-type ecological caisson structure has good wave permeability and good external load bearing capacity.It is a recommended hydraulic structure.The wave pressure on the wave-facing surface and bottom plate of the structure is much smaller than the wave pressure of the effluent caisson under the same wave conditions,and the wave pressure distribution is regular(less affected by the transmitted wave).(2)The natural frequency of the frame caisson structure varies within the range of 53.28 ~ 56.38 Hz.Under any possible load combination,the dynamic response of the frametype ecological caisson structure is within the elastic deformation range.When different load combinations act,the value of the strain at each position can be obtained by linear superposition of single load strain.(3)Under static and quasi-static forces and waves,there is little difference in pile strain at any position in the pile group,but when the ship’s impact(impact)force acts,the strain of the pile gradually decreases from the front to the pile.This is related to the impact time.(4)The combination of wave + ship impact + door crane load is a structural strain control combination.When this load is combined,the strain of the lower node of different piles varies within the range of 110~250με;the strain of the upper node varies within the range of 56~79με.Under the condition of strain control load combination,the strain of the outer contour wall of the frame-type ecological caisson structure is ≯30με;the maximum strain of the inner bulkhead changes within the range of 27~46με.(5)The fluctuating pressure under the roof of the frame-type ecological caisson structure is closely related to the water level.Between the average water level and the designed high water level,the impact of wave impact is often under the roof.For the bearing surface,the most unfavorable water level exists,and the most unfavorable water level measured by the test is about + 3.8m.The envelope strength of the wave impact of the caisson structure roof at the most unfavorable water level varies within the range of 53-93 Kpa.The height of the front wave barrier of the caisson structure is increased from 1.4m to 3.9m,which can reduce the fluctuation pressure intensity of the wave surface and roof of the caisson under relatively unfavorable water level conditions(the reduction ratio is about 10% to 15%).Another additional effect of increasing the height of the wave shield at the front of the structure is to move the position of the top plate subjected to wave impact backwards.