Research On The Robustness Of A Suspension Bridge With Single Tower

The robustness of the structure means that the destruction of the structural components does not cause progressive collapse of the structure.The bridge structure is the lifeline of the country’s transportation,and it has a huge investment and plays an important role in the national economy.If a large bridge collapses progressively,it will cause huge loss of life and property.In order to ensure the safety of bridge structure,the robustness of the structure must be considered in the design.The hanger of the suspension bridge suffers from the coupling effect of fatigue and corrosion,and there is a risk of explosion,car impact,artificial damage,etc.So there is a certain possibility of hanger fracture.In the present thesis,a earthanchored suspension bridge with single tower is taken as the background.The importance evaluation method which is suitable for slings is put forward.Also,the robustness of the structure under the condition of suspension cable fracture is studyed.The main research contents are as follows:1)The typical progressive collapse accidents of structures occurring in recent years at home and abroad is analyzed.The general definitions of structural robustness and progressive collapse are gived.The research status of quantitative evaluation of structural robustness and the design code of structural progressive collapse prevention at home and abroad are summarized.The shortcomings of existing studies are pointed out.2)The meaning of the components importance evaluation index is given,and the the necessity of evaluating the importance of suspension bridge slings is pointed out.The evaluation method of sling importance based on internal force,strain energy and sling safety factor is proposed.The calculations of importance coefficient under dead load and live load are respectively carried out.The results show that the importance evaluation method based on the sling safety factor is superior to the other two methods in reflecting the difference in the importance of each sling and identifying key components;3)The robustness of a earth-anchored suspension bridge with single tower after hanger failure is studied.The critical slings are determined based on the importance evaluation method of the sling safety factor.The influence of key slins failure on the remaining hangers,the main cables,the stiffening beams,and the pylon are analyzed.The importance coefficients of two adjacent sling combinations are calculated.The influence of different failure modes of two adjacent hangers on the structure is explored The results show that the failure of a single hanger has a great influence on the same side hangers and has little effect on the other side hangers.The breakage of a single hanger does not cause progressive breakage of the remaining hangers.The effect of hanger breakage on the remaining hangers has the characteristics of “proximity” and the hanger adjacent to the broken hanger is significantly affected.It is shown that after the single hanger breaks,the stiffening beam stress is in a safe range and the main cable stress changes little.It is also shown that after the single hanger breaks the pylon units are always under pressure,and the stress of the pylon units is much smaller than the design value of concrete compressive strength.When two adjacent hangers fail simultaneously or gradually,the remaining hangers will be damaged,but the stress of the remaining hangers does not reach the breaking strength,and the structure is generally safe.