Adaptability Analysis Of Bridge Load Limit Value Under Normal Service Limit State

In recent years,with the rapid development of the automobile industry,the carrying capacity of vehicles has gradually improved.However,due to the fact that most medium and small span bridges in our country are designed and built in accordance with the early specifications,the actual bridge operation is far higher than the design load,resulting in the phenomenon of bridge overload operation is more common.At the same time,due to the rapid growth of highway freight volume in our country,the use of large single trucks and semi-trailer trucks is increasing day by day,and the phenomenon of overweight is becoming more and more prominent.As a result,bridge collapses occur frequently in our country,bringing great economic losses and casualties to the society.Therefore,it is urgent to construct a complete set of highway bridge load limit standards.However,up to now,our country has not formulated the national highway bridge load limit standard.Only according to the existing measures to control the overload,the load limit values in different regions vary greatly,which cannot fundamentally solve the overload operation of bridges.Based on this background,this paper,based on the simplified analysis model of limited load value,combined with practical engineering,systematically analyzes the adaptability of bridge limited load value under the normal use limit state.The main research work is as follows:1)According to the car load models in different time codes in China,the variation law of design car load effect in each code under medium and small span is analyzed.2)Based on the existing analysis model of highway bridge load limit value,the highway load limit analysis program is compiled,and the bridge load limit coefficients corresponding to different resistance correction coefficients are calculated,providing the basis for the calculation of typical bridge load limit value.3)The simply-supported T-beam bridge and simply-supported hollow slab beam bridge in different periods are selected as the research objects,and the bearing capacity of the selected bridge is checked and calculated according to the current code,so as to check whether the selected bridge meets the code requirements and provide reliable engineering basis for subsequent load limit value analysis.According to the theory of load limit value analysis,the selected bridges are respectively subjected to load limit calculation according to level I and level ii of load limit safety level,and the adaptability of the lower limit values of different load limit safety levels is analyzed from the aspects of normal use and bearing capacity limit state.4)The model of simply supported beam bridge is established by MIDAS software.Typical load-limiting vehicles considering impact coefficient are used as test vehicles,which are arranged in the most unfavorable loading mode.The adaptability of load-limiting values of simply supported beam bridge is further verified from the aspect of normal use limit state.The structural response index under the limit state of existing bridges is given,and the early warning threshold of bridges is established.