Risk Assessment Of Concrete Cracking In Negative Moment Zone Of Steel-concrete Composite Beam

In recent years,steel-concrete composite beams have been widely used in bridges due to their advantages such as reducing the weight of the structure.The cracking of concrete slabs in the negative bending moment region of steel-concrete composite continuous beams is one of the main problems faced in its field application,and it is also a hotspot of scientific research for researchers and professionals in the field of bridge engineering.Considering the multiple uncertainties faced in the manufacturing,construction and inservice operation of steel-concrete composite beams,concrete cracking risk in the negative bending moment area of steel-concrete composite beams has been quantitatively assessed.This will benefit further application of steel-concrete composite beam bridge as well as risk assessment and maintenance decision-making of in-service structures.In this paper,the risk probability prediction of whether the concrete in the negative bending moment region cracks under the design load and whether the crack width exceeds the limit after cracking was carried out.On the basis of static loading test,proposed a statistical inversion theory-based risk assessment method,which updated the distribution parameters of random variables and further improved the accuracy of calculation results.The main contents and conclusions of this paper are as follows:(1)A probability method based on ANSYS and MATLAB collaborative sampling is proposed for the risk calculation of concrete cracking in the negative bending moment region of the composite beam.This method not only realizes the probability calculation and sensitivity analysis functions in the PDS module of ANSYS,but also effectively avoids the problem that certain random variable distribution type is restricted in the module.This further improves the accuracy of probability calculation results,and can provide insights for risk assessment or relevant problems where restricted random variables distribution type is a concern.(2)Summarized and analyzed currently existing formulas for calculating the crack width of steel-concrete composite beams from the perspectives of theory formulation,influencing factors and its applicability.The calculation method stated in the "Code For Design of Steel-Concrete Composite Structures" was recommended.Provided a highly accurate calculation model for the risk calculation of whether the crack width of the steelconcrete composite beam exceeds its limit.(3)Considering the effects of concrete shrinkage and creep and the cyclic loading of traffic vehicle on crack width,a calculation formula is proposed for long-term concrete slab crack width in the negative bending moment region of steel-concrete composite beam.The proposed model provides theoretical support for prediction of crack width during inservice operation.Considered the randomness of influencing factors,a risk probability prediction is made on whether the long-term crack width can exceed its limit,and the time-variant crack width pattern was also predicted.(4)A dynamic update method for crack probability of composite beams in the negative bending moment area based on statistical inversion analysis and bridge monitoring data was proposed.According to static loading test data of the Approach Bridge of the South-to-North Water Transfer Bridge,statistical inversion analysis was conducted on concrete cracking risk factors in the negative bending moment region,and the existing probability distribution of the influencing factors was updated to make the probability distribution of the influencing factors more objective.The randomness of the calculation results was reduced.This solves the issue that large discrepancy exists between the experimental measurement data or incomplete statistical parameters and when they are applied to the actual project,making the probability estimation results more realistic and accurate.