| Cable-stayed bridges have the advantages of strong spanning ability,beautiful appearance,and low cost,and are widely used in large-span highways and urban road bridges.After the bridge is put into use for a period of time,the durability of the bridge’s sling structure will gradually show damage over time,for example,the protection of the cable body is cracked or damaged;the steel wire of the cable body is corroded and part of the steel wire is broken;the catheter,anchorage and protection of the anchorage area are corroded and damaged,etc.Therefore,a comprehensive and accurate durability evaluation of the sling structure of the bridge in use is of great significance to the safe operation and daily maintenance and repair of the sling bridge.Based on the investigation and testing of a large number of cable-stayed bridges,this paper has conducted a systematic study on the evaluation method of the durability of the cable-stayed bridges in use.The main research results are as follows:(1)Based on the investigation of bridge sling structure defects and cable sling accidents,the cause and mechanism of the durability damage of the bridge sling structure in use are systematically analyzed,including the effects on the PE sheath,cable steel wire and anchorage area damage cause and injury incentives.The analysis results show that the decrease in the durability level of the cable sling structure is mainly due to the damage and destruction of protective measures such as PE sheath,which causes the damage or corrosion of the steel wire of the cable body,which in turn leads to the corrosion and damage of the anchorage area;The main influencing factors of the decline in mechanical properties directly affect the safety and normal use of the sling structure.(2)According to the investigation and analysis results of bridge sling structure defects and their causes,a durability evaluation system for the cable sling structure was constructed,and the grading standards and assignment methods of specific indicators were discussed;the analytic hierarchy process,fuzzy mathematics theory and gray system theory combined organically,the grey fuzzy evaluation model of the durability of the sling structure was established,and the feasibility,rationality and reliability of the method were verified by examples.(3)Based on the principle of set pair analysis,the set pair model of the durability evaluation of the cable sling structure was established from the perspective of connection number;based on the extension theory,the matter-element matrix of the durability evaluation system was constructed to determine the classic domain of the system and the joint field,calculate the correlation function,and determine the durability evaluation level.The example analysis shows that the evaluation results of these two methods can better reflect the actual status of the durability of the sling.(4)As an important supplement to the comprehensive evaluation of the durability of cable slings in use,based on the basic principles of engineering structural reliability,the cable force limit state equations for the unit cable length mass?and natural frequencyf_n are established,and the reliability index?is calculated using the JC method.The failure probabilityP_f of the cable force of the sling is obtained as an important criterion for the damage degree of the sling.(5)With reference to the Durability Design Guide for Concrete Structures,a durability evaluation model for cable sling structures based on the durability index and environmental index has been established.Among them,the durability index includes the design,structural form,material properties,mechanical indicators,construction and installation of the cable sling structure etc.By comparing the calculated durability index with the environmental index,the durability evaluation of the sling structure can be achieved.(6)According to the durability damage mechanism of the sling sheath,the experimental study on the mechanical properties of the PE sheath material of the sling was carried out,and the preliminary development and exploratory experimental research of the new cold repair material were carried out.Including the thermal aging test of PE sheath material and cold repair material and the tensile test of the material after the PE sheath material,cold repair material,PE and cold repair material are bonded(the two materials are bonded at a 45°slope),etc,the construction has laid a certain foundation for further optimization of repair materials and the construction technology and process of cold repair materials. |
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