Study On Seismic Safety Of A Reinforced Concrete Lighthouse Structure On The Reef In Deep-sea Area

Large-scale dredging and island-building projects have been carried out in the South China Sea these years,creating many islands with large infrastructures on it.Some lighthouses have been built on these islands since then,which has greatly improved navigation safety in the water area.However,these islands in the South China Sea are all located on the west side of the Pacific Rim seismic belt,where earthquakes of magnitude 6 and above were recorded in the history.As the tallest building on the reefs,these lighthouses may be damaged and destroyed under earthquakes because of its towering shape.Based on numerical simulation analysis,this paper conducted a related study on the seismic safety of one actual lighthouse structure on these islands.The main contents and results of this study are as follows:(1)Based on shaking table tests of the lighthouse structure conducted by the project team,a detailed finite element model of the scaled lighthouse structure was established.Nonlinear dynamic time-history analysis was conducted to study the seismic performance and failure mode of the lighthouse structure.The test results are consistent with the finite element analysis,both of which indicate that the lighthouse structure test model exhibits horizontal swaying vibration under a horizontal earthquake,and a failure mode of tensile cracking under scaled severe earthquakes of 8 degrees.(2)The finite element model of the prototype lighthouse structure was established,with its seismic response analysis carried out.The results show that the lighthouse structure’s design is reasonable,its story drift under 8-degree frequent earthquakes and rare earthquakes meet the limit requirements with a big safety margin.Its seismic response is mainly dominated by the 1st or 3rd order mode of vibration.The main stress concentration part consists of two connection parts: the connection part between the lower half of the cylinder and the telescopic section,the connection part between the telescopic section and the upper surface of the second layer.The former part is likely to be damaged by tension.(3)Seismic response analysis of the lighthouse structure with the influence of soil layer and soil-lighthouse interaction was carried out.The influence of soil layer above the island bedrock and soil-structure interaction were studied separately.The results show that seismic responses of the lighthouse structure will be significantly amplified with the influence of soil layer;moreover,seismic responses of the lighthouse structure will be increased considering the soil-structure interaction in most cases.Therefore,the influence of soil layer and soil-structure interaction should be considered in the seismic response analysis and seismic design of lighthouse structures on the island.(4)A nonlinear dynamic constitutive model based on the improved Matasovic skeleton curve and the generalized Masing criterion is used to describe the mechanical behavior of the coral sand.The finite element model consisting of coral sand and lighthouse structure was established to carry out the seismic response analysis considering the nonlinear dynamic reaction.The results show that the nonlinearity of coral sand will enhance the seismic response of the structure,with less impact under frequent earthquakes and greater impact under severe earthquakes.