Suitable Middle-Pylon Stiffness And Mechanical Transmission Effect In Kilometer Level Multi-pylon Continuous Suspension Bridge

Kilometer level multi-pylon continuous suspension bridges are one type of optimum bridges for continuous crossing broad water. The bridge has advantages of reducing anchorage size, shoreline and land occupation, passage narrowing,deepwater-foundation works, and ship-impact probability. Meanwhile, the bridge has remarkable economic and environmental benefits. Because of the middle pylons,kilometer level multi-pylon continuous suspension bridges have very different mechanical properties from tranditional suspension bridge with two pylons. The"multi-pylon effect" and "mechanical transimission effect" are critical to the engineering application of the bridges. Currently, for the two effects, their mechanical characteristics and rules are still unclear, analysis approach and calculation method need further study.The author carried on the research work by taking the Taizhou Yangtze Highway Bridge as the engineering background, and by relying on the 11th Five-Year National Key Project of Science and Technology Support Program "Multi-pylon continuous suspension bridge: theory study and engineering demonstration"(2009BAG15B00). In this thesis, several focuses were put on the suitable multi-pylon stiffness value,multi-pylon deflection calculation and mechanical transimission effect in bridges. The main research work covers the following aspects:(1) By means of numerical analyzing the consituous suspension bridges with 3, 4 and 5 pylons, the influence to middle-pylon effect was studied considering parameters of pylon-girder coupling and middle pylon stiffness. Based on this study, the selection principle to the middle pylon stiffness was proposed. The applicable of national code"Design specification for highway suspension bridge"(JTG/T D 65-05-2015),about deflection limit to pylons and anti-slide safety value to saddles, was disussed.(2) Based on the deflection theory, a simple mechanical model was developed for multi-pylon continuous suspension bridges. The equal stiffness for pylon was proposed in the span direction,and one simplified formula was proposed to calculate the deflection of pylons. By using the formula, the influence rules to mechanical properties of middle pylon were investigated, considering the parameters of span-sag ratio,side-middle span ratio, and stiffness of main calble, also pylon stiffness and dead load.(3) By means of influce line analysis, the influence to structural peformance were studed under considering the parameters of pylon stiffness, cable-girder couple and pylon-girder couple were. Futhermore, the characteristics of mechanical transimission effect were dicussed based on the analyses of multi-pylon continuous suspension brdiges with 4 to 6 pylons.(4) An experimental research was carried out by testing the model with 1:80 scale.The mechanical properties were experimental studied to a three-pylon continuous suspension bridge, under construction and complete stage. On this basis, a experimental model for five-pylon continuous suspension bridge was builded, and some relevant research works were carried on.Through above research works, the characteristics of middle-pylon effect and mechanical transimission effect were clarified, considering the parameters of middle pylon stiffness, pylon-girder coupling, and span-sag ratio, side-middle span ratio of main calble. The selection principle to the middle pylon stiffness was proposed, one simplified formula was proposed to calculate the deflection of pylons. The mechanical transimission effect was understood deeply. These results can be conductive to the analysis and design process and construction of kilometer level multi-pylon continuous suspension bridges.